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The document discusses photovoltaic solar energy conversion, focusing on advancements in solar cell technologies from first-generation silicon cells to third-generation solutions seeking to enhance efficiency and reduce costs. It highlights significant milestones in silicon production, manufacturing techniques, and research developments aimed at improving solar power efficiency through various innovative approaches. The content also reviews the impact of material science and quantum mechanics on photovoltaic technology and future directions in solar energy research.

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Photovoltaic Solar Energy Conversion (PVSEC) ‫إﻧﺘﺎج اﻟﻜﻬﺮﺑﺎء ﻣﻦ اﻟﻄﺎﻗﺔ اﻟﺸﻤﺴﻴﺔ‬ Courses on photovoltaic for Moroccan academic staff; 23-27 April, ENIM / Rabat Organic Q-Dots ZnO NRs PVSEC-Part III Fundamental and application of Photovoltaic solar DSSC cells and system Ahmed Ennaoui Helmholtz-Zentrum Berlin für Materialien und Energie ennaoui@helmholtz-berlin.de i@h l h lt b li d
Highlight First Fi t generation: Silicon ti Sili Silicon PV technology Shockley-Queisser limit y Route to high efficiency solar cells Second Generation: Thin Films • Substrate Chalcopyrite CIGS vs. Superstrate CdTe solar cells vs • Technology: CIGS module processing. • Thin layer silicon process: a-Si: H / Si • T d S l cell Tandem Solar ll New Concepts for Photovoltaic Energy Conversion Photoelectrochemical and Dye-sensitized solar cells Organic solar cells: donor-acceptor hetero-junction Nanostructures for solar cells: photon management and quantum dots p g q Ahmed Ennaoui / Helmholtz-Zentrum Berlin für Materialien und Energie
Silicon the first generation Copyrighted Material, from internet Silicon is first choice for solar cells because for good knowledge of Si processing in micro electronics industry. Jack Kilby (Texas Instrument) • Nobel Prize for Physics, 2000 obe e o ys cs, 000 • Co-inventor of the monolithic integrated circuit (1958) – became the Si microchip. Moore's law describes a long-term trend in the history of computing hardware: the number of transistors that th t can b placed iinexpensively on an iintegrated circuit d bl approximately every t years. N th be l d i l t t d i it doubles i t l two Now the Pentium 4 has around 55 million components per chip (2003). The history of computing hardware is the record of the ongoing effort to make computer hardware faster, cheaper, and capable of storing more data 1941, 1941 first silicon solar cell was reported Electronics 38 (8), 114-117 (1965) Efficiency less than 1% ( (US Patent 240252, filed 27 March 1941) , ) Lateral Thinking: Solar cells are optoelectronic devices, they depend on the interaction of electrons, holes, and photons We need an understanding of semiconductors at the quantum mechanical level.
Brief Business Scenario Copyrighted Material, from internet Top 10 PV Cell Producers Price learn cu e o c ysta e S PV-modules (by ce ea curve of crystalline Si odu es Cumulative installed PV by 2007 y doubling the number of total installed PV power drop 1st Germany 3.8 GW prices by the same factor. 2nd Japan 1.9 GW 3rd US 814 MW 4th Spain 632 MW Aktuelle Fakten zur Photovoltaik in Deutschland, Fraunhofer ISE / Fassung vom 8.12.2011 Report from Photon International, / http://www.renewableenergyworld.com
First generation: Silicon Solar Cells Copyrighted Material, from internet SILICON SOLAR PV TECHNOLOGY Production of Si Metallurgical Grade Silicon (MG) and Electronic grade (EG-Si), Metallurgical Grade Silicon (MG) is material with 98-99% purity Typical impurities (Fe), Al, Ca, Mg) Produced in about 1 Million tons per year, average price is 2 to 4 $/kg MG-Si: The sand is heated in a furnace containing a source of carbon Reduction of SiO2 with C in arc furnace at 1800 oC Heat MG to Si EG-Si distillation process with HCl to form SiHCl3) Fractional distillation (impurity segregation) extremely pure SiHCl3 CVD in a hydrogen atmosphere SiHCl3 into EG-Si Quartz Crucible Wafer based Si solar cells Czochralski (CZ) process. Float Zone (FZ) Record efficiency solar cells. FZ is more expensive than Cz material. Si is not the best: 90% absorption requires >100 µm of Si. Single Crystals: highest efficiency, slow process, high costs. Poly (multi) crystalline: low cost, fast process, lower efficiency . Source: Eicke R. Weber, Fraunhofer-Institute for Solar Energy Systems ISE
First generation: Silicon Solar Cells Copyrighted Material, from internet Purifying the silicon: I STEP 1: Metallurgical Grade Silicon (MG-Silicon is produced from SiO2 melted and taken through a complex series of reactions in a furnaceV T = 1500 to Seebeck voltage at Microelectronic 2000 C. STEP 2: Trichlorosilane (TCS) is created by heating powdered MG-Si at around 300 C in the reactor Imp rities s ch as Fe Al and B are remo ed reactor, Impurities such Fe, removed. Electronic t S Grade Chunks Cold Si + 3HCl SiHCl3 + H2 Hot STEP 3: TCS is distilled to obtain hyper-pure TCS (<1ppba)d then vaporized, and e- diluted with high-purity hydrogen, and introduced into a deposition reactor to form l ili n-type wafer yp polysilicon: SiHCl3 + H2→Si + 3HCl Si ρ = 2 π s V/I Impurities Electronic d (EG-Si), El t i grade (EG Si) 1 ppb I b iti Making single crucible crystal silicon STEP 1 Czochralski (CZ) process Seed crystal slowly grows STEPE 2 and 3 Device fabrication 1. Surface etch, Texturing Cells 2. Doping: p-n junction formation Ingot sliced 3. Edge etch: removes the junction at the edge to create wafers 4. Oxide Etch: removes oxides formed during diffusion 5. Antireflection coating: Silicon nitride layer reduces reflection Source: Wacker Chemie AG, Energieverbrauch: etwa 250kWh/kg im TCS-Process, Herstellungspreis von etwa 40-60 €/kg Reinstsilizium
First generation: Silicon Solar Cells Copyrighted Material, from internet Anti-Reflection Coating g Si3N4 layer reduces reflection of sunlight and passivates the cell . plasma enhanced chemical vapor deposition (PECVD))
First generation: Silicon Solar Cells Copyrighted Material, from internet Firing: The metal contacts are heat treated (“fired”) to make contact to the silicon. Screen Printer with automatic loading and unloading of cells
First generation: Silicon Solar Cells Copyrighted Material, from internet Firing: The metal contacts are heat treated (“fired”) to make contact to the silicon. . Firing furnace to sinter metal contacts
Shockley-Queisser limit Copyrighted Material, from internet Not all the energy in each absorbed photon can be captured for productive use. Under AM1 5 U d AM1.5 spectral di t ib ti Single-junction solar cell has a maximal conversion efficiency of ~32% t l distribution: Si l j ti l ll h i l i ffi i f 32% Solar Energy Materials & Solar Cells 90, 2329-2337 (2006) Reflection Loss 1.8% I2R Loss 0.4% 0.4% % 0.3% Recombination 1.54% 3.8% Losses 2.0% 1.4% Back Light Absorption 2.6% (1) Lattice thermalisation loss (> 50%) L tti th li ti l (2) Transparency to photons loss < Band gap (3) Recombination Loss (4) Current flow Source: University of Delaware, USA (5) Contact voltage loss
Shockley-Queisser limit Copyrighted Material, from internet
Technology approach to high efficiency solar cells Copyrighted Material, from internet Low reflection Low recombination, High carrier absorption Thinner emitter, closed spaced metal fingers Back surface field (p+-p ) Anisotropic texturing (current collection) Surface Passivation (SiO2 ca 0 01 μm) Key to obtain Voc: ca. 0,01 m) Photolithography to have small contact area and high aspect ratio Laser grooving and electroplating of metal. TiO2, SiO2, Z S M F2 ZnS, MgF Technological loss 2N + 1 d ARC = Texturing nARC 4n ARC Resistive loss ARC n2 Top contact Reflection loss High doping Recombination loss ‐ ‐ EBSF High doping Traditional cell design
Route to high efficiency solar cells Copyrighted Material, from internet Traditional cell design MINP PESC IBC PERC PERL (1) PERL developed at UNSW (EFF. 25%) Passivated Emitter and Rear Locally diffused1 (2) Localized Emitter Cell Using Semiconducting Fingers. (EFF. 18.6%, CZ n-type) (3) Laser-grooved, buried front contact (LGBC; EFF. 21.1%) n+ n++ P Buried contact (2) (1) 1 MartinGreen, PIP 2009; 17:183–189, University of New South Wales, Australia http://www.unsw.edu.au/ (3) Back contact
Route to high efficiency solar cells Copyrighted Material, from internet Thickness of the c-Si absorber without reflectivity and recombination losses y ⎛ 1 ⎞ η = (1 − R) ⎜1 − e −αW ⎟ ⎜ 1 + αL ⎟ ⎝ p ⎠ ⎡ ⎤ I sc = A . q . ∫ ⎢ η(λ) { { . Φ 0 (λ ) . (1 − R λ ) . exp - α λ .d ⎥dλ 123 144 2444 ⎥ 4 3 E G ⎢Collection light Cell area ⎣ Photon flux Absorbed Light ⎦
Route to high efficiency solar cells Copyrighted Material, from internet The space charge region and tunneling at metals/highly doped semiconductor junction Highly doped semiconductor (n++ , p++ = 1020...1021 carriers/cm3) Quantum Mechanics Tunneling
Route to high efficiency solar cells Copyrighted Material, from internet 1. 1 Rsurff Δns ,Δps Δp 2. Rsurf vns ,vps Nts 1. Reduction of the minority carrier concentration at the Ohmic y contact (realized with the back surface field - BSF). 2. Reduction of the Ohmic contact area and reduction of the surface recombination velocity at the non Ohmic contact Si – surfaces (realized with contact grids and surface passivation)
Route to high efficiency solar cells Copyrighted Material, from internet What is exactly a p y passivation? Most important interface in the world passivating properties observed in 1960 applied in the world record Si solar cell
Route to high efficiency solar cells Copyrighted Material, from internet BSF: Back Surface Field: The electric field back is to create a potential barrier (e.g. p+-p junction) on the rear of the cell to ensure passivation. The potential barrier induced by the difference in doping level between the base and the BSF tends to confine minority carriers in the base. These are therefore required to away from the rear face which is characterized by a very high rate of recombination. Fabrication tools: Diffusion furnace, PECVD, RTP, Screen-printer, Belt furnace, FZ wafers, boron BSF boron-BSF sample, and screen-printing pastes screen printing Ag gridlines SiN/SiO2 n+ emitter Al-Si p-Si eutectic BSF Al/Ag rear SiN/SiO2 contact Source: University of Delaware SunPower’s Backside Contact Cell http://www.sunpowercorp.de/about/ Record efficiency=26.8% at 25W/cm2 Irradiance
Route to high efficiency solar cells Copyrighted Material, from internet Metal Wrap Through Metal-Wrap-Through Solar Cell Photovoltech is commercializing the MWT solar cell; efficiencies ~ 15% Source: University of Delaware
Route to high efficiency solar cells Copyrighted Material, from internet The Sliver® Solar Cell Origin Energy (Australia) is commercializing the Sliver® Solar Cell (cell efficiencies 20%) Source: University of Delaware
Route to high efficiency solar cells Copyrighted Material, from internet Rear Interdigitated Single Evaporation-Emitter W Th R I t di it t d Si l E ti E itt Wrap Through h • Both contacts on the rear • No h d i N shadowing on the front th f t • Carrier collection on two sides • Rear-side SiO2 passivation • Laser processing for ISFH lab result on 10x10 cm2 grooves, holes and η = 21% contact openings • Single Al evaporation Source: Institute for Solid State Physics , Leibniz University of Hanover/22nd EU-PVSEC (2007)
Roadmap: Different Generation of Solar cells and PV Power Costs First generation First-generation - based on expensive silicon wafers; 85% of the current commercial market. Ultimate Second-generation - based on thin films of materials Thermodynamic limit such as amorphous silicon, nanocrystalline silicon, at 1 sun cadmium telluride, or copper indium selenide. The materials are less expensive, but research is needed Shockley- to raise the cells' efficiency. Queisser limit Third-generation - the research goal: a dramatic increase in efficiency that maintains the cost advantage of second-generation materials. Their design may make use of carrier multiplication, hot electron extraction, multiple junctions, sunlight concentration, concentration or new materials. materials Efficiency and cost projections for first-, second- and third- generation photovoltaic technology (wafers, thin-films and advanced thin-film respectively. The horizontal axis represents the cost of the solar module only; it must be approximately doubled to include the costs of packaging and mounting. Dotted lines indicate the cost per watt of peak power. Advanced Research f achieving high efficiency f for ff from inexpensive materials with so-called third-generation Concentrating sunlight allows for a greater contribution from multi-photon processes Stacked cells with different bandgaps capture a greater fraction of the solar spectrum Carrier multiplication is a quantum-dot phenomenon that results in multiple electron–hole pairs for a single incident photon Hot electron Hot-electron extraction provides way to increase the efficiency of nanocrystal-based solar cells by tapping off energetic electrons and nanocrystal based holes before they have time to thermally relax. various thin-film technologies currently being developed reduce the amount (or mass) of light absorbing material required in creating a solar cell. This can lead to reduced processing costs Martin Green , Prog. Photovolt: Res. Appl. 9, (2001) pp 123-135
Basic: different ways to make a solar cells / Low cost processing Thin layer techniques Copyrighted Material, from internet Physical techniques Chemical techniques Solvent based techniques Electrochemical techniques Vacuum evaporation Reactive deposition Self-assembling Electroplating Gel processing Spray methods Epitaxial deposition Electrophoresis Chemical vapour deposition Doctor blading Laser deposition Langmuir-Blodgett Spin coating Sputtering Flow coating Ionization Dip coating Ion-assisted deposition Ionized cluster beam Printing Flexo printing Fl i ti Gravure printing G i ti Ink jet printing Offset printing Microcontact printing Relief printing Screen printing Kesterite Ink Electrophoresis Spin coating
How do NPs form? R. Schurr et al. Thin Solid Films 517 (2009) 2465–2468 Projekttreffen NanoPV A. Ennaoui et al. Thin Solid Films 517 (2009) 2511–251 Kesterite Vertraulich/Patent pending A. Ennaoui, Lin, Lux-Steiner PVSEC 2011 Ink Chemical reaction Critical concentrantion, Aggregation happens takes place nucleation begins due to its lowering the free energy Particles grow and consume all the solute Hot injection Best time to synthesize synthesis nanoparticles Subsequent growth of the nuclei lowers the solute concentration http://www.authorstream.com/Presentation/rahulpupu-976297-nanoparticles/
Nanostructured ZnO From microstructure to nanorodes and fuctionalization Ennaoui ´Group: Jaison Kavalakkatt, PhD/FU Berlin Confidential /IP, Patent Pending Non Vacuum processing / Low Cost Equipments next generation solar cells Changing electrochemical condition TE HRTE M M 5  nm 100 nm See Concept of Inorganic solid-state nanostructured solar cells Special issue Ahmed Ennaoui Solar Energy Materials and Solar Cells, Volume 95, Issue 6, June 2011, Pages 1527-1536 Ahmed Ennaoui / head of a research group: Thin Film and nanostructured solar cells /Solar Energy Division / Helmholtz-Zentrum Berlin für Materialien und Energie
Thin layer silicon process: (a-Si: H / Si) Copyrighted Material, from internet Heterojunction amorphous silicon / crystalline silicon (a-Si: H / Si) Si), say HIT with intrinsic Thin Layer Two heterojunctions a-Si: H / Si: The "front heterojunction is the" transmitter, while the second, the rear panel, acts as a field of repulsion or BSF. , p , p Intrinsic zone allows "better" surface quality at the junction layer . transparent conductive oxide (TCO) is deposited to ensure good contact between the amorphous layer and the metal. The heterojunction is obtained by depositing technologically "a layer a few “nm” hydrogenated amorphous silicon, a-Si: H.
Basic: Tandem Cell) Copyrighted Material, from internet EFF Lab 12 13% / Module 10% EFF. 12-13% Back Reflector Thin film mc Si mc-Si Bottom cell a-Si Top cell Textured TCO Glass substrate Sun-Light S Li h Practical Handbook of Photovoltaics: From Fundamentals to Applications, edited by T. Markvart and L. Castaner. Oxford: Elsevier, 2003
Basic: Efficiencies beyond the Shockley-Queisser limit Copyrighted Material, from internet Multijunction cells use multiple materials to match the spectrum spectrum. The cells are in series; current is passed through device The current is limited by the layers that produces the least current. The voltages of the cells add The higher band gap must see the light first. By making alloys, all band gaps can be achieved. Challenge: Lattice matched limited in material combinations GaInP/GaInAs/Ge Cells have powered Mars Exploration Rovers (MER) GaInP/GaInAs/Ge Cells record 38.8% @ 240 suns (2005) New? (R. King, et al, 20th PVSEC European Conference)
Basic: Efficiencies beyond the Shockley-Queisser limit Copyrighted Material, from internet Structure of Triple-Junction (3J) Cell Front Contact AR Coating n+ (In)GaAs n+ AlInP [Si] • Efficiencies up to 41% n+ I G P [Si] InGaP InGaP I G P p InGaP [Zn] Top Cell p AlInP [Zn] • Six different elements p++ AlGaAs [C] n++ InGaP [Si] Tunnel Junction n+ AlInP [Si] • Three different dopants n+ (In)GaAs [Si] InGaAs p (In)GaAs [Zn] Middle Cell p+ InGaP [Zn] p [ ] ++ AlGaAs [C] • Practically used: n++ InGaP [Si] Tunnel Junction 3-junction cells n+ (In)GaAs [Si] Buffer Layer n+ GaAs : 0.1µm n Ge G • Research: p Ge Substrate Bottom Cell 4 to 5 junctions Back Contact Yamaguchi et. al., 2003 Space Power Workshop
2nd. Generation: Cu(In,Ga)(S,Se2) Chalcopyrite solar cell The chalcopyrite structure can be deduced from the Diamond IV diamond structure according to the Grimm-Sommerfeld-rule, structure Si which states that a tetragonal structure is formed, if the average number of valence electrons per atom equals four nq N + mqM zincblende structure =4 III-V II-VI n + m + ... Epitaxial fil E i i l film: P l lli Polycrystalline N M elements N,M n,m atoms/unit cell GaAs , InP… thin film: qN, qM valence electrons CdTe, ZnS II-IV-V2 I-III-VI2 Epitaxial film: Polycrystalline thin film: y y ZnGeAs, Z G A … Cu(In,Ga)(Se,S)2 (Chalcopyrite and related compounds) I-III-VI2 Alloy: Group I= Cu, I III VI Cu Group III= In and Ga, Group VI = Se and S
Possible combinations of (I, III, VI) elements ⎛Sn⎞ ⎛ Cu ⎞ ⎛ Ga ⎞ (In) ⎜ ⎟ ⎜Zn⎟ ⎜ ⎟ ⎜ Ag ⎟ ⎜ ⎟ ⎜ In ⎟ ⎛S ⎞ ⎜ ⎟ ⎝ ⎠ ⎜ Au ⎟ ⎜ Al ⎟ ⎜ Se⎟ 26 Zn Z Element ⎝ ⎠ ⎝ ⎠ ⎜Te⎟ 1.225 Tetrahedral coordination radius ⎝ ⎠2 Cu(In,Ga)Se2 1.5 Electronegativity IIIa VIa 3 Li 4 Be 5 B 6 C 7 N 8 O 9 F 2s 0.975 0.853 0.774 0.719 0.678 0.672 2s 2p 0.95 1.5 2.0 2.5 3.0 3.5 3.9 2p 11 Na 12Mg 13 Al 14 Si 15 P 16 S 17 Cl 3s 1.301 1.230 1.173 1.128 1.127 1.127 3s 3p 3 3p 0.9 1.2 Ib IIb 1.5 1.8 2.1 2.5 3.0 3d 19 K 20 Ca 29 Cu 30 Zn 31 Ga 32 Ge 33 As 34 Se 35 Br 3d 4s 1.333 1.225 1.225 1.225 1.225 1.225 1.225 1.225 4s 4p 0.8 1.0 1.8 1.5 1.5 1.8 2.0 2.4 2.8 4p 4d 37 Rb 38 Sr 47Ag 48 Cd 49 In 50 Sn 51 Sb 52 Te 53 I 4d 5s 1.689 1.405 1.405 1.405 1.405 1.405 1.405 1.405 5s 5p 0.8 1.0 1.8 1.5 1.5 1.7 1.8 2.1 2.5 5p 5d 55 Cs 56 Ba 79 Au 80 Hg 81 Tl 82 Pb 83 Bi 84 Po 85 At 5d 6s 1.392 6s 6p 0.75 0.9 2.3 1.8 1.5 1.8 1.8 2.0 2.2 6p
Second Generation: Thin-film Technologies Copyrighted Material, from internet • Advantage: Low material cost, Reduced mass • Di d t Disadvantages: T i materiall (Cd), S Toxic t i (Cd) Scarce materiall (In, T ) t i (I Te) • CdTe – 8 – 11% efficiency (18% demonstrated) • CIGS – 7-11% efficiency (20% demonstrated) *CIGS based device CdTe based device Source: Rommel Noufi, NREL, Colorado, USA, http://www.nrel.gov/learning/re_photovoltaics.html
Potentials of thin film Cu-chalcopyrite technologies 1. S tt i 1 Sputtering of Cu and In fC d I 2. Rapid Thermal processing (RTP) • low material consumtions • low energy consumption • hi h productivity l high d i i large area • „monolithic“ interconnects - Laser • new products (e.g. flexible cells) wafer f substrate Wafer based technology Quelle: EI3 Thin film cell structure thickness 1.5-2 µm Source: HZB / Technology department
Potentials of thin film Cu-chalcopyrite technologies S Cu In 1 kWp : Comparison of c-Si and CuInS2 Source: HZB / Technology department
Module processing 1. KCN etching 2. CBD-Buffer Source: HZB / Technology department
Technology: Module processing Monolithic integration for series connection of individual cells P1: Series of periodic scribes that defines the width of the cells P2: After the absorber and buffer layer deposition Pulsed Laser P1 P3: After the window deposition +Ga +Se ZnO Front ZnO of one cell Buffer connected to the CIGS back Mo contact of Mo the next Glass 1. Deposition of Cu, In,Ga 2. RTP/Reaction with S/Se Source: HZB / EI2 department
Technology: Module processing Monolithic integration for series connection of individual cells Loads - + Zn:Al i-ZnO CdS CIGS + + + + Mo Glass P1 P2 P3 RSC Laser scribing and mechanical scribing pulse repetition rate i-ZnO/ZnO:Al i Z O/Z O Al pulse power CdS wavelength and spot diameter + Electrical isolation for front and CIGS contact scribes back Low series resistance for the interconnect scribe Mo Interconnect resistivity as low Glass as possible Source: ZSW
Best efficiency from annealing of stacked metal layers Substrate: soda lime glass coated with Mo Temperature/ C Temperature/°C Deposition of Cu and In, Ga layers by sputtering 500-550 Deposition of Se layer by evaporation Rapid thermal process (RTP) RTP Advantage: Design of production facilities Time/min Large-area Large area deposition Avoidance of toxic H2Se The most essential factor that decides if the absorber is going to result in a high- efficiency device, is its Cu content, or the Cu/(Ga+In) ratio Cu(In.Ga)(S,Se)2 CIGS film should be slightly Cu deficient with a thin even more Cu deficient surface Cu-deficient, thin, Cu-deficient layer. This surface layer corresponds to the stable ordered vacancy (OVC) Cu(In,Ga)3Se5.
Fundamental understanding ZnO Absorber
Fundamental understanding buffer CIS EC ZnO EC < EC ? ZnS at EV Absorber The GBs Zn CIS, CIGS AO l Buffer Barrier for recombination: Absorber
Material Properties: Phases Diagram Copyrighted Material, from internet Simplified version of the ternary phase diagram Reduced to pseudo-binary phase diagram along the red dashed line Bold blue line: photovoltaic-quality material Relevant phases: α-, β-, γ- , δ-phase and Cu2Se α β γ δ phase,and CuIn3S5 Not found α: chalcopyrite CuInSe2 β: defect chalcopyrite Cu(In,Ga)3Se5 γ: Cu(In,Ga)5Se8
Material Properties: Phases Diagram Copyrighted Material, from internet α phase α-phase (CuInSe2): • Optimal range for efficient thin film solar cells: 22-24 at % • α-phase highly narrowed @RT • Possible at growth temp.: 500-550°C, @RT: phase separation into α+β 500 550 C, α β β phase β-phase (CuIn3Se5) • built by ordered arrays of defect pairs • anti sites (VCu, InCu) δ-phase (high-temperature phase) • built by disordering Cu & In sub-lattice Cu2Se • built from chalcopyrite structure by • Cu interstitials Cui & CuIn anti sites Hamakawa, Yoshihiro: Thin Film Solar Cells, Springer, 2004.
Material Properties: Impurities & Defects Partial replacement of In with Ga; 20-30% of In replaced: Ga/(Ga+In) ~ 0.3 20 30% Ga/(Ga In) Band gap adjustment: 1.03eV-1.7 eV - Widening of bandgap at the surface of the Incorporation of 0.1 at % Na film Na (Se) (stability d N 2(S )1+n ( t bilit decrease with n↑) ith ↑) - The surface composition of Cu-poor CIGS Cu poor Better film morphology films Passivation of grain-boundaries (Ga+In)/(Ga +In+Cu) ca. 0.75 Higher p yp conductivity g p-type y - The bulk compositions Reduce defect concentration 0.5< (Ga+In)= (Ga+In+Cu) < 0.75. The are many defect - 3 vacancies: VCu, VGa, VSe. - 3 i t titi l Cui, G i, S i. interstitials: C Ga Se Phase segregation of Cu(In,Ga)3Se5 - 6 antisites: occurs at the surface of the films. CuGa, CuSe, GaCu, GaSe, SeCu, SeGa Ordered-Vacancy/ Defect Compounds (OVC/ODC) Ordered or disordered arrays of vacancies are occupying the cation sites They can exceed the local range of the unit cell, we called vacancy compounds Superlattice structures of the ideal chalcopyrite, reported as stable phases: OVC/ODC OVC/ODC are observed in slightly Cu-deficient: Cu(In,Ga)3Se5 Schock, Rommel Noufi, , Prog. Photovolt. Res. Appl. 8, (2000) pp. 151-160
Roll-to-Roll deposition (R2R) Ion beam supported low temperature Source: Fahoum Mounir/Habilitation deposition of Cu, In, Ga, Se fC G S Substrate: Mo coated polyimide/ stainless steel foil (F f Fe from th substrate?) the b t t ?) Alternative Electrochemistry Advantages: • Low cost production • Flexible modules • High power per weight ratio Voltag e - + In,Ga,Cu -ions , , Annealing Buffer TCO G C In, Se Ga,Cu, I S
Recombination mechanism issue Ea nkT ⎛ j00 ⎞ VOC = − ln⎜ ⎜ j ⎟ ⎟ q q ⎝ SC ⎠ A: Diode quality factor EA: Activation energy J00 : Prefactor, weakly temperature-dependent Cu(In,Ga)Se2 EC Buffer B ff (1): interface recombination Eg 2 EF Ea = Φ b 1 EV Φb (2): bulk recombination E a = Eg
Important Remarks Conversion efficiencies achieved by CuInS2 (EG y ( = 1.53 eV) or CuGaSe2 (EG = 1.7 eV) absorbers are considerably lower than those achieved by Burried pn-junction low band gap Cu(In,Ga)Se2 or even CuInSe2. OVC Cu(In Ga)Se p p-Cu(In,Ga)Se2 ( , ) Why? OVC In l b d I low band gap Cu(In,Ga)Se2 C (I G )S •Formation of weakly n-type OVC layer •The bulk is p-type p yp •Buried p-n junction n ΔEV n-Cu(In,Ga)3Se5 OVC minimizes the recombination at the CIGS/buffer interface. OVC surface layer has direct and wider band gap than the bulk Φ OVC increases further the barrier ,Φ, for recombination at CIGS/CdS That is the key to high-efficiency solar cells.
Third Generation: Multi-junction Cells Multi- Copyrighted Material, HZB
Technology: CIGS module processing N. Naghavi, D. Abou-Ras, N. Allsop, N. Barreau, S. Bu¨ cheler, A. Ennaoui, C.-H. Fischer, C. Guillen, D. Hariskos, J. Herrero, R. Klenk, K. Kushiya, D. Lincot, R. Menner, T. Nakada, C. Platzer-Björkman, S. Spiering, A.N. Tiwari and T. Törndahl. Prog. Photovolt: Res. Appl. ( g pp (2010). Published online in Wiley InterScience, Vol. 18, issue 6 (2011) pp. 411- ) y , , ( ) pp 433
The world record chalcopyrite solar cell Cu(In,Ga)Se2
New Concepts for Photovoltaic Energy Conversion (Photo)electrochemical and Dye-sensitized solar cells Organic solar cells: donor-acceptor hetero-junction Nanostructures for solar cells
Semiconductor/Liquid versus Semiconductor/Metal Junction Vacuum level 0 Φ χ qχ CB qΦΜ CB EF,SC EF,SC qVB H+/H2 qVBB Metal EC 0 EC CE Back EF,SC EF,Metal EF,SC EF,redox contact Back H2O/H2 contact VB - 4.5 eV VB 1.23V Semiconductor (WE) Redox SCE EV Electrolyte EV e.g. I-/I2 Metal +0.243V Semiconductor Semiconductor e.g. Si e.g. Au V vs. NHE e.g. TiO2 Electrochemical scale Solid state scale Summer Semester Osaka University-Japan for graduate student in Research Center for Solar Energy Chemistry/Courses: Photovoltaic and hydrogen Research and development R&D
Semiconductor/Liquid versus Semiconductor/Metal Junction Summer Semester Osaka University-Japan for graduate student in Research Center for Solar Energy Chemistry/Courses: Photovoltaic and hydrogen Research and development R&D
Semiconductor/Liquid versus Semiconductor/Metal Junction Summer Semester Osaka University-Japan for graduate student in Research Center for Solar Energy Chemistry/Courses: Photovoltaic and hydrogen Research and development R&D
Photoelectrochemical Solar Cell (PECs): Photovoltaic mode Copyrighted Material, from internet ‐ Reduction Sc ‐M Back  contact I2 + e‐ + Countre I‐ + h+ Electrode (CE) Oxidation I‐ ‐+ h+ +  I2 + e‐ ‐ I + h I2 + e Electron and holes are photogenerated Holes are moved to the surface of the WE -- current react with I I‐ + h+ Electron are moved to the back contact V reacts with I2 i th other side (CE) t ith in the th id Voltage vs. redox I2 + e‐ Source: A.J. Nozik, National Renewable Energy Laboratory
Solar cells that mimic plants p y Chlorophyll Light absorption Dye y Charge transfer protein e- transfer Semiconductor oxide (TiO2) Proton pump Hole transfer Electrolyte Copyrighted Material, from internet
Solar cells that mimic plants: DSSC Copyrighted Material, from internet HOMO LUMO CO2 Sugar H2O O2 Photosynthesis The most widely used sensitizer abbreviated as N3. y “cis-Ru(SCN)2L2 (L = 2,2'-bipyridyl-4,4'-dicarboxylate)” source: partly http://en.wikipedia.org/wiki/Dye-sensitized_solar_cell Grätzel, M., Journal of Photochemistry and Photobiology C: Photochemistry Reviews 2003, 4, 145
Solar cells that mimic plants: DSSC Copyrighted Material, from internet HOMO: highest occupied molecular orbital LUMO: lowest unoccupied molecular orbital HOMO LUMO CO2 Sugar H2O O2 Photosynthesis The most widely used sensitizer abbreviated as N3. y “cis-Ru(SCN)2L2 (L = 2,2'-bipyridyl-4,4'-dicarboxylate)” source: partly http://en.wikipedia.org/wiki/Dye-sensitized_solar_cell Grätzel, M., Journal of Photochemistry and Photobiology C: Photochemistry Reviews 2003, 4, 145
Solar cells that mimic plants Copyrighted Material, from internet Few simple materials and you can create your own Grätzel Cell The most widely used sensitizer abbreviated as N3. “cis-Ru(SCN)2L2 (L = 2,2'-bipyridyl-4,4'-dicarboxylate)” Ru(II) + hν → Ru(II)* Ru(II)* → Ru(III) + e- I3- + 2e-→ 3I- 3I- + Ru(III)→ I3- + Ru (II) I‐ + h+ DSSC Module I2 + e‐
Solar cells that mimic plants Copyrighted Material, from internet Generation Transport Back B k reaction ( ) with I3- ti (c) ith ∂n ∂n 2 ( n − n0 ) τn = 1/kcb [I3-] = α Ie −α x + Dn 2 − Ru(III)/Ru*(II)) ∂t ∂x τn ( ) (b) (c) (a) Ru*(II)/Ru(II))
Solar cells that mimic plants: DSSC Copyrighted Material, from internet http://www.solaronix.com/ Mesoporous TiO2 anatase Efficiency of 10 % was obtained by the solar cells assembled at the EPFL in Lausanne (simulated sunlight AM 1.5, 1000 W/m2) Eff. = 10 %, AM 1.5, VOC = 823 mV, ISC = 16.9 mA/cm2, FF = 72.5 %) Download Dye Solar Cells Assembly Instructions @ : http://www.solaronix.com/technology/assembly/
Nanocrystalline based Solar cells Copyrighted Material, from internet Electron holes photogenerated Immediately injected in mesoporous TiO2 (or ZnO NRs) ZnO nanorodes T. Dittrich, A. Belaidi, A. Ennaoui J B Sambur et al. Science 2010;330:63-66 Extremely Thin Absorber Band energy diagram indicating the relevant energy levels and kinetic processes that describe PbS QD ET and HT into Concept of Inorganic solid-state nanostructured solar cells the TiO2 conduction band and the sulfide/polysulfide Solar Energy Materials and Solar Cells, Volume 95, Issue 6, June electrolyte, respectively. 2011, Pages 1527-1536
Photoelectrochemical solar cells (PECs) Photoelectrolysis mode 1/C2 Band gap must V+v(t) be at least 1 8 2 0 eV 1.8-2.0 V V But small enough to absorb most sunlight Lock‐in Material requirements b Potentiostat v=vme edges must straddle Redox potentials Band iωt Fast charge transfer WE RE CE Determination of Flat Band PotentialStable in aqueous solution (Vfb) I hν>EG V EC Metal WE RE CE Back EF,SC EF,redox (CE) contact 1.23eV 1.23eV EV Electrolyte ( (WE) ) Anode: 2H20 4e- + 02 + 4H+ E Cathode: 4H20 + 4e- 4OH- + 2H2 A. Ennaoui and et al. Solar Energy materials and Solar Cells Volume 29 (1993), Pages 289-370 This lecture was presented @ Osaka University-Japan for graduate student in Research Center for Solar Energy Chemistry/Courses: Photovoltaic and hydrogen Research and development R&D
Determination of Flat Band Potential (Vfb) V+v(t) Lock‐in Potentiostat v=vmeiωt WE RE CE vacuum 0 H+/H2 Ref. A. Ennaoui and et al. Solar Energy materials and Solar Cells Volume 29 (1993), Pages 289-370 This lecture was presented @ Osaka University-Japan for graduate student in Research Center for Solar Energy Chemistry/Courses: Photovoltaic and hydrogen Research and development R&D
Materials suitable for solar PECs Copyrighted Material, from internet
Photoelectrochemical solar cells (PECs) Photoelectrolysis mode D D D D D D D H2O→2H2+O2 ∆V=1.23V, ∆G=238kJ/mol Source: Mildred Dresselhaus, Massachusetts Institute of Technology
d0 and d10 metal oxides Copyrighted Material, from internet GaN-ZnO (Ga1-xZnx)-(N1-xOx) d0 d10 Ti4+: TiO2, SrTiO3,  K2La2Ti3O10 : TiO SrTiO K Ga3+: ZnGa2O4 3 : ZnGa Zr4+: ZrO2 In3+: AInO2 (A=Li, Na) Nb5+: K4Nb6O17, Sr2Nb2O7 Ge4+: Zn2GeO4 Ta5+: ATaO3(A=Li, Na, K), BaTa2O6 Sn4+: Sr2SnO4 W6 : AMWO6 ( 6+ (A=Rb, Cs; M=Nb, Ta) b b ) Sb5+: NaSbO7 N replaces O in certain positions, providing a smaller band gap. Problems with getting the nitrogen there without too many defects. Oxygen free options: Ta3N5, G 3N4 O f ti T Ge Domen et al. New Non‐Oxide Photocatalysts Designed for Overall Water Splitting under Visible Light. J. Phys. Chem. 2007
Use of PV for H2 production Hydrogen and Oxygen are p y g yg produced using p g photovoltaic effect Test of security - No damage to hydrogen car - Gasoline car completely destroyed p n p n p n Solid state solar cells O2 H2 e- e- H2 H + O Dark electrolysis cell Source: Partly A.J. Nozik, National Renewable Energy Laboratory
Water splitting: Hydrogen production Copyrighted Material, from internet Challenge: Material requirement : Material/catalysts, nano-materials, membranes (need Brainstorming ) Understand and control the interaction of hydrogen with materials H2O→2H2+O2 ∆V=1.23V, ∆G=238kJ/mol Source: Mildred Dresselhaus, Massachusetts Institute of Technology millie@mgm.mit.edu
Fuel Cells Copyrighted Material, from internet Fuel Cell uses a constant flow of H2 to produce energy. Catalyst = Pt Very expensive Reactionthe Pt quantity between Minimize takes place q y H2 and Othe active layer structure Improve 2 electrical energy. The most common fuel cell uses Propose new materials Proton Exchange Membrane, o PEM oto c a ge e b a e, or Need of catalyst (e.g. platinum for a reaction that ionizes the gas O2 is ionized to O2- 2 H2 is ionized to 2H+ 2H+ + O2- = H2O O2- and H+ combine Energy is given off in The “waste products” are water and heat electron form and gives off power to run an engine
Advantages and Challenges Copyrighted Material, from internet Advantages Zero emission No dependence on foreign oil Ability to harvest solar and renewable energy Abilit t h t l d bl Not many moving part in a car Hydrogen weighs less than g y g g gasoline car would not need as much energy to move Challenges g Still expensive to equip a car with a hydrogen fuel cell. Hydrogen is expensive to make, store, and transport The center is a platinum plate which is very expensive National Program in USA since 2007: 1 billion dollars to date in hydrogen car research for the “develop hydrogen, fuel cell and infrastructure technologies to make fuel-cell vehicles practical and cost-effective by 2020.”
Basic: Brief Business Scenario Copyrighted Material, from internet 1999 FOUNDED, 2001 BEGAN WITH THE PRODUCTION OF SILICON SOLAR CELLS WITH 19 EMPLOYEES. BY 2009, 2,600 EMPLOYEES (2007, 1700 EMPLOYEES) NOW THE LARGEST SOLAR CELL MANUFACTURER IN THE WORLD. (SINCE 2007) WORLD CONTINUE TO EXPAND PRODUCTION IN BITTERFELD-WOLFEN, GERMANY AND START CONSTRUCTION OF NEW MALAYSIAN PRODUCTION FACILITY. ALONGSIDE THE MONO-CRYSTALLINE AND POLYCRYSTALLINE (90% OF BUSINESS) CORE BUSINESS, WE USE A WIDE RANGE OF TECHNOLOGIES TO DEVELOP AND PRODUCE THIN-FILM MODULES. (THIN-FILM - 25% SHARE OF SMALLER MARKET) Year over year, Q-Cells SE has been able to grow revenues from €790.4M to €1.4B. http://investing.businessweek.com
Basic: Brief Business Scenario Copyrighted Material, from internet SunTech Power (China) - THE COMPANY WAS FOUNDED IN 2001 BY ZHENGRONG SHI - SALES $1.9B 2008, 1.3B 2007 PROFITABLE - EMPLOYEES: 6784 - WORLDS LARGEST SILICON CELL MAKER - AVERAGE CONVERSION EFFICIENCY RATES OF THEIR - MONOCRYSTALLINE AND MULTICRYSTALLINE SILICON PV CELLS - 16.4% AND 14.9% RESPECTIVELY - 2009 ANNOUNCES PLAN TO BUILD MANUFACTURING PLANT IN US Zhengrong Shi Boen in 1963 in China, finished his Master in China then he went to University of New South Wales (Austria). He ( ) 130KW obtained his doctorate degree on 8MW China 43KW 0.092-0.3-3.8MW 3MW Nevada solar power technology and Spanien Germany China returned to China in 2001 to set 14MW 5.1MW 10 MW up his solar power company (Net Spanien Nevada Abu Dhabi worth US$2.9 Billion (2008) 48KW Australien 500KW Nevada http://eu.suntech-power.com
Copyrighted Material, from internet Capacity 130MW Expansion 70MW 55MW 30MW 20MW R&D 1980 1999 2006 2007 2008 2010 Kaneka has been specializing in thin-film silicon technology: 1980 Started study of a-Si technology 1987 Participated in NEDO project (Government funded R&D) 1999 Started 20MW/yr commercial production 2006 Announced capacity expansion: - up to 30MW in 2006, 55MW in 2007, 70MW in 2008 2007 Introduction of new Hybrid PV Announced capacity expansion: up to 130MW in 2010
Copyrighted Material, from internet
Excitonic solar cells Copyrighted Material, from internet Exciton LUMO electrons holes Interface HOMO • all organic: polymer and/or molecular • hybrid organic/inorganic •ddye-sensitized cell iti d ll
Donor acceptor concept Copyrighted Material, from internet
Donor acceptor concept Copyrighted Material, from internet Interpenetrating Nanostructured Networks η record = 4,8% η FMF, ISE = 3,7% Aluminum Absorber Akzeptor Polymer Anode ITO Substrate Donor The light falls on the polymer Electron/hole is El t /h l i generated t d The electron is captured C60
The biggest Challenge Copyrighted Material, from internet Reducing the cost/watt of delivered solar electricity Find a concepts for a more efficient PV systems More efficiency, More abundant materials, Non-toxic material, Durability First Generation Fi t G ti Crystalline Si will remain the dominant PV technology for a long time, the current shortage will be overcome by increased production of pure Si and the introduction of purified metallurgical-grade Si. p g g Second Generation Thin film modules out of a-Si, CIS, or CdTe have an interesting market opportunity today, their long-term success will depend on efficiency improvements and cost reduction reduction. Third Generation TANDEM CELLS: Because sunlight is made up of many colours of different energy, from the high energy ultraviolet to the low energy infrared, a combination of solar cells of different materials can convert sunlight more efficiently than any single cell Multiple Exciton Generation: The objective is fighting termalization: In quantum dots, the rate of energy dots dissipation is significantly reduced and one photon creates more than one exciton via impact ionization Higher photocurrent via impact ionization (inverse Auger process)
Thank you so much Questions or comments? PVSEC 23th – 27th. 2012 / Rabat - Morocco Prof. Dr. Ahmed Ennaoui Helmholtz-Zentrum Berlin für Materialien und Energie
Parking: produce electricity and have the shadow

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Ennaoui cours rabat part III

  • 1.
    Photovoltaic Solar EnergyConversion (PVSEC) ‫إﻧﺘﺎج اﻟﻜﻬﺮﺑﺎء ﻣﻦ اﻟﻄﺎﻗﺔ اﻟﺸﻤﺴﻴﺔ‬ Courses on photovoltaic for Moroccan academic staff; 23-27 April, ENIM / Rabat Organic Q-Dots ZnO NRs PVSEC-Part III Fundamental and application of Photovoltaic solar DSSC cells and system Ahmed Ennaoui Helmholtz-Zentrum Berlin für Materialien und Energie ennaoui@helmholtz-berlin.de i@h l h lt b li d
  • 2.
    Highlight First Fi t generation:Silicon ti Sili Silicon PV technology Shockley-Queisser limit y Route to high efficiency solar cells Second Generation: Thin Films • Substrate Chalcopyrite CIGS vs. Superstrate CdTe solar cells vs • Technology: CIGS module processing. • Thin layer silicon process: a-Si: H / Si • T d S l cell Tandem Solar ll New Concepts for Photovoltaic Energy Conversion Photoelectrochemical and Dye-sensitized solar cells Organic solar cells: donor-acceptor hetero-junction Nanostructures for solar cells: photon management and quantum dots p g q Ahmed Ennaoui / Helmholtz-Zentrum Berlin für Materialien und Energie
  • 3.
    Silicon the firstgeneration Copyrighted Material, from internet Silicon is first choice for solar cells because for good knowledge of Si processing in micro electronics industry. Jack Kilby (Texas Instrument) • Nobel Prize for Physics, 2000 obe e o ys cs, 000 • Co-inventor of the monolithic integrated circuit (1958) – became the Si microchip. Moore's law describes a long-term trend in the history of computing hardware: the number of transistors that th t can b placed iinexpensively on an iintegrated circuit d bl approximately every t years. N th be l d i l t t d i it doubles i t l two Now the Pentium 4 has around 55 million components per chip (2003). The history of computing hardware is the record of the ongoing effort to make computer hardware faster, cheaper, and capable of storing more data 1941, 1941 first silicon solar cell was reported Electronics 38 (8), 114-117 (1965) Efficiency less than 1% ( (US Patent 240252, filed 27 March 1941) , ) Lateral Thinking: Solar cells are optoelectronic devices, they depend on the interaction of electrons, holes, and photons We need an understanding of semiconductors at the quantum mechanical level.
  • 4.
    Brief Business Scenario Copyrighted Material, from internet Top 10 PV Cell Producers Price learn cu e o c ysta e S PV-modules (by ce ea curve of crystalline Si odu es Cumulative installed PV by 2007 y doubling the number of total installed PV power drop 1st Germany 3.8 GW prices by the same factor. 2nd Japan 1.9 GW 3rd US 814 MW 4th Spain 632 MW Aktuelle Fakten zur Photovoltaik in Deutschland, Fraunhofer ISE / Fassung vom 8.12.2011 Report from Photon International, / http://www.renewableenergyworld.com
  • 5.
    First generation: SiliconSolar Cells Copyrighted Material, from internet SILICON SOLAR PV TECHNOLOGY Production of Si Metallurgical Grade Silicon (MG) and Electronic grade (EG-Si), Metallurgical Grade Silicon (MG) is material with 98-99% purity Typical impurities (Fe), Al, Ca, Mg) Produced in about 1 Million tons per year, average price is 2 to 4 $/kg MG-Si: The sand is heated in a furnace containing a source of carbon Reduction of SiO2 with C in arc furnace at 1800 oC Heat MG to Si EG-Si distillation process with HCl to form SiHCl3) Fractional distillation (impurity segregation) extremely pure SiHCl3 CVD in a hydrogen atmosphere SiHCl3 into EG-Si Quartz Crucible Wafer based Si solar cells Czochralski (CZ) process. Float Zone (FZ) Record efficiency solar cells. FZ is more expensive than Cz material. Si is not the best: 90% absorption requires >100 µm of Si. Single Crystals: highest efficiency, slow process, high costs. Poly (multi) crystalline: low cost, fast process, lower efficiency . Source: Eicke R. Weber, Fraunhofer-Institute for Solar Energy Systems ISE
  • 6.
    First generation: SiliconSolar Cells Copyrighted Material, from internet Purifying the silicon: I STEP 1: Metallurgical Grade Silicon (MG-Silicon is produced from SiO2 melted and taken through a complex series of reactions in a furnaceV T = 1500 to Seebeck voltage at Microelectronic 2000 C. STEP 2: Trichlorosilane (TCS) is created by heating powdered MG-Si at around 300 C in the reactor Imp rities s ch as Fe Al and B are remo ed reactor, Impurities such Fe, removed. Electronic t S Grade Chunks Cold Si + 3HCl SiHCl3 + H2 Hot STEP 3: TCS is distilled to obtain hyper-pure TCS (<1ppba)d then vaporized, and e- diluted with high-purity hydrogen, and introduced into a deposition reactor to form l ili n-type wafer yp polysilicon: SiHCl3 + H2→Si + 3HCl Si ρ = 2 π s V/I Impurities Electronic d (EG-Si), El t i grade (EG Si) 1 ppb I b iti Making single crucible crystal silicon STEP 1 Czochralski (CZ) process Seed crystal slowly grows STEPE 2 and 3 Device fabrication 1. Surface etch, Texturing Cells 2. Doping: p-n junction formation Ingot sliced 3. Edge etch: removes the junction at the edge to create wafers 4. Oxide Etch: removes oxides formed during diffusion 5. Antireflection coating: Silicon nitride layer reduces reflection Source: Wacker Chemie AG, Energieverbrauch: etwa 250kWh/kg im TCS-Process, Herstellungspreis von etwa 40-60 €/kg Reinstsilizium
  • 7.
    First generation: SiliconSolar Cells Copyrighted Material, from internet Anti-Reflection Coating g Si3N4 layer reduces reflection of sunlight and passivates the cell . plasma enhanced chemical vapor deposition (PECVD))
  • 8.
    First generation: SiliconSolar Cells Copyrighted Material, from internet Firing: The metal contacts are heat treated (“fired”) to make contact to the silicon. Screen Printer with automatic loading and unloading of cells
  • 9.
    First generation: SiliconSolar Cells Copyrighted Material, from internet Firing: The metal contacts are heat treated (“fired”) to make contact to the silicon. . Firing furnace to sinter metal contacts
  • 10.
    Shockley-Queisser limit Copyrighted Material, from internet Not all the energy in each absorbed photon can be captured for productive use. Under AM1 5 U d AM1.5 spectral di t ib ti Single-junction solar cell has a maximal conversion efficiency of ~32% t l distribution: Si l j ti l ll h i l i ffi i f 32% Solar Energy Materials & Solar Cells 90, 2329-2337 (2006) Reflection Loss 1.8% I2R Loss 0.4% 0.4% % 0.3% Recombination 1.54% 3.8% Losses 2.0% 1.4% Back Light Absorption 2.6% (1) Lattice thermalisation loss (> 50%) L tti th li ti l (2) Transparency to photons loss < Band gap (3) Recombination Loss (4) Current flow Source: University of Delaware, USA (5) Contact voltage loss
  • 11.
    Shockley-Queisser limit Copyrighted Material, from internet
  • 12.
    Technology approach tohigh efficiency solar cells Copyrighted Material, from internet Low reflection Low recombination, High carrier absorption Thinner emitter, closed spaced metal fingers Back surface field (p+-p ) Anisotropic texturing (current collection) Surface Passivation (SiO2 ca 0 01 μm) Key to obtain Voc: ca. 0,01 m) Photolithography to have small contact area and high aspect ratio Laser grooving and electroplating of metal. TiO2, SiO2, Z S M F2 ZnS, MgF Technological loss 2N + 1 d ARC = Texturing nARC 4n ARC Resistive loss ARC n2 Top contact Reflection loss High doping Recombination loss ‐ ‐ EBSF High doping Traditional cell design
  • 13.
    Route to highefficiency solar cells Copyrighted Material, from internet Traditional cell design MINP PESC IBC PERC PERL (1) PERL developed at UNSW (EFF. 25%) Passivated Emitter and Rear Locally diffused1 (2) Localized Emitter Cell Using Semiconducting Fingers. (EFF. 18.6%, CZ n-type) (3) Laser-grooved, buried front contact (LGBC; EFF. 21.1%) n+ n++ P Buried contact (2) (1) 1 MartinGreen, PIP 2009; 17:183–189, University of New South Wales, Australia http://www.unsw.edu.au/ (3) Back contact
  • 14.
    Route to highefficiency solar cells Copyrighted Material, from internet Thickness of the c-Si absorber without reflectivity and recombination losses y ⎛ 1 ⎞ η = (1 − R) ⎜1 − e −αW ⎟ ⎜ 1 + αL ⎟ ⎝ p ⎠ ⎡ ⎤ I sc = A . q . ∫ ⎢ η(λ) { { . Φ 0 (λ ) . (1 − R λ ) . exp - α λ .d ⎥dλ 123 144 2444 ⎥ 4 3 E G ⎢Collection light Cell area ⎣ Photon flux Absorbed Light ⎦
  • 15.
    Route to highefficiency solar cells Copyrighted Material, from internet The space charge region and tunneling at metals/highly doped semiconductor junction Highly doped semiconductor (n++ , p++ = 1020...1021 carriers/cm3) Quantum Mechanics Tunneling
  • 16.
    Route to highefficiency solar cells Copyrighted Material, from internet 1. 1 Rsurff Δns ,Δps Δp 2. Rsurf vns ,vps Nts 1. Reduction of the minority carrier concentration at the Ohmic y contact (realized with the back surface field - BSF). 2. Reduction of the Ohmic contact area and reduction of the surface recombination velocity at the non Ohmic contact Si – surfaces (realized with contact grids and surface passivation)
  • 17.
    Route to highefficiency solar cells Copyrighted Material, from internet What is exactly a p y passivation? Most important interface in the world passivating properties observed in 1960 applied in the world record Si solar cell
  • 18.
    Route to highefficiency solar cells Copyrighted Material, from internet BSF: Back Surface Field: The electric field back is to create a potential barrier (e.g. p+-p junction) on the rear of the cell to ensure passivation. The potential barrier induced by the difference in doping level between the base and the BSF tends to confine minority carriers in the base. These are therefore required to away from the rear face which is characterized by a very high rate of recombination. Fabrication tools: Diffusion furnace, PECVD, RTP, Screen-printer, Belt furnace, FZ wafers, boron BSF boron-BSF sample, and screen-printing pastes screen printing Ag gridlines SiN/SiO2 n+ emitter Al-Si p-Si eutectic BSF Al/Ag rear SiN/SiO2 contact Source: University of Delaware SunPower’s Backside Contact Cell http://www.sunpowercorp.de/about/ Record efficiency=26.8% at 25W/cm2 Irradiance
  • 19.
    Route to highefficiency solar cells Copyrighted Material, from internet Metal Wrap Through Metal-Wrap-Through Solar Cell Photovoltech is commercializing the MWT solar cell; efficiencies ~ 15% Source: University of Delaware
  • 20.
    Route to highefficiency solar cells Copyrighted Material, from internet The Sliver® Solar Cell Origin Energy (Australia) is commercializing the Sliver® Solar Cell (cell efficiencies 20%) Source: University of Delaware
  • 21.
    Route to highefficiency solar cells Copyrighted Material, from internet Rear Interdigitated Single Evaporation-Emitter W Th R I t di it t d Si l E ti E itt Wrap Through h • Both contacts on the rear • No h d i N shadowing on the front th f t • Carrier collection on two sides • Rear-side SiO2 passivation • Laser processing for ISFH lab result on 10x10 cm2 grooves, holes and η = 21% contact openings • Single Al evaporation Source: Institute for Solid State Physics , Leibniz University of Hanover/22nd EU-PVSEC (2007)
  • 22.
    Roadmap: Different Generationof Solar cells and PV Power Costs First generation First-generation - based on expensive silicon wafers; 85% of the current commercial market. Ultimate Second-generation - based on thin films of materials Thermodynamic limit such as amorphous silicon, nanocrystalline silicon, at 1 sun cadmium telluride, or copper indium selenide. The materials are less expensive, but research is needed Shockley- to raise the cells' efficiency. Queisser limit Third-generation - the research goal: a dramatic increase in efficiency that maintains the cost advantage of second-generation materials. Their design may make use of carrier multiplication, hot electron extraction, multiple junctions, sunlight concentration, concentration or new materials. materials Efficiency and cost projections for first-, second- and third- generation photovoltaic technology (wafers, thin-films and advanced thin-film respectively. The horizontal axis represents the cost of the solar module only; it must be approximately doubled to include the costs of packaging and mounting. Dotted lines indicate the cost per watt of peak power. Advanced Research f achieving high efficiency f for ff from inexpensive materials with so-called third-generation Concentrating sunlight allows for a greater contribution from multi-photon processes Stacked cells with different bandgaps capture a greater fraction of the solar spectrum Carrier multiplication is a quantum-dot phenomenon that results in multiple electron–hole pairs for a single incident photon Hot electron Hot-electron extraction provides way to increase the efficiency of nanocrystal-based solar cells by tapping off energetic electrons and nanocrystal based holes before they have time to thermally relax. various thin-film technologies currently being developed reduce the amount (or mass) of light absorbing material required in creating a solar cell. This can lead to reduced processing costs Martin Green , Prog. Photovolt: Res. Appl. 9, (2001) pp 123-135
  • 23.
    Basic: different waysto make a solar cells / Low cost processing Thin layer techniques Copyrighted Material, from internet Physical techniques Chemical techniques Solvent based techniques Electrochemical techniques Vacuum evaporation Reactive deposition Self-assembling Electroplating Gel processing Spray methods Epitaxial deposition Electrophoresis Chemical vapour deposition Doctor blading Laser deposition Langmuir-Blodgett Spin coating Sputtering Flow coating Ionization Dip coating Ion-assisted deposition Ionized cluster beam Printing Flexo printing Fl i ti Gravure printing G i ti Ink jet printing Offset printing Microcontact printing Relief printing Screen printing Kesterite Ink Electrophoresis Spin coating
  • 24.
    How do NPsform? R. Schurr et al. Thin Solid Films 517 (2009) 2465–2468 Projekttreffen NanoPV A. Ennaoui et al. Thin Solid Films 517 (2009) 2511–251 Kesterite Vertraulich/Patent pending A. Ennaoui, Lin, Lux-Steiner PVSEC 2011 Ink Chemical reaction Critical concentrantion, Aggregation happens takes place nucleation begins due to its lowering the free energy Particles grow and consume all the solute Hot injection Best time to synthesize synthesis nanoparticles Subsequent growth of the nuclei lowers the solute concentration http://www.authorstream.com/Presentation/rahulpupu-976297-nanoparticles/
  • 25.
    Nanostructured ZnO Frommicrostructure to nanorodes and fuctionalization Ennaoui ´Group: Jaison Kavalakkatt, PhD/FU Berlin Confidential /IP, Patent Pending Non Vacuum processing / Low Cost Equipments next generation solar cells Changing electrochemical condition TE HRTE M M 5  nm 100 nm See Concept of Inorganic solid-state nanostructured solar cells Special issue Ahmed Ennaoui Solar Energy Materials and Solar Cells, Volume 95, Issue 6, June 2011, Pages 1527-1536 Ahmed Ennaoui / head of a research group: Thin Film and nanostructured solar cells /Solar Energy Division / Helmholtz-Zentrum Berlin für Materialien und Energie
  • 26.
    Thin layer siliconprocess: (a-Si: H / Si) Copyrighted Material, from internet Heterojunction amorphous silicon / crystalline silicon (a-Si: H / Si) Si), say HIT with intrinsic Thin Layer Two heterojunctions a-Si: H / Si: The "front heterojunction is the" transmitter, while the second, the rear panel, acts as a field of repulsion or BSF. , p , p Intrinsic zone allows "better" surface quality at the junction layer . transparent conductive oxide (TCO) is deposited to ensure good contact between the amorphous layer and the metal. The heterojunction is obtained by depositing technologically "a layer a few “nm” hydrogenated amorphous silicon, a-Si: H.
  • 27.
    Basic: Tandem Cell) Copyrighted Material, from internet EFF Lab 12 13% / Module 10% EFF. 12-13% Back Reflector Thin film mc Si mc-Si Bottom cell a-Si Top cell Textured TCO Glass substrate Sun-Light S Li h Practical Handbook of Photovoltaics: From Fundamentals to Applications, edited by T. Markvart and L. Castaner. Oxford: Elsevier, 2003
  • 28.
    Basic: Efficiencies beyondthe Shockley-Queisser limit Copyrighted Material, from internet Multijunction cells use multiple materials to match the spectrum spectrum. The cells are in series; current is passed through device The current is limited by the layers that produces the least current. The voltages of the cells add The higher band gap must see the light first. By making alloys, all band gaps can be achieved. Challenge: Lattice matched limited in material combinations GaInP/GaInAs/Ge Cells have powered Mars Exploration Rovers (MER) GaInP/GaInAs/Ge Cells record 38.8% @ 240 suns (2005) New? (R. King, et al, 20th PVSEC European Conference)
  • 29.
    Basic: Efficiencies beyondthe Shockley-Queisser limit Copyrighted Material, from internet Structure of Triple-Junction (3J) Cell Front Contact AR Coating n+ (In)GaAs n+ AlInP [Si] • Efficiencies up to 41% n+ I G P [Si] InGaP InGaP I G P p InGaP [Zn] Top Cell p AlInP [Zn] • Six different elements p++ AlGaAs [C] n++ InGaP [Si] Tunnel Junction n+ AlInP [Si] • Three different dopants n+ (In)GaAs [Si] InGaAs p (In)GaAs [Zn] Middle Cell p+ InGaP [Zn] p [ ] ++ AlGaAs [C] • Practically used: n++ InGaP [Si] Tunnel Junction 3-junction cells n+ (In)GaAs [Si] Buffer Layer n+ GaAs : 0.1µm n Ge G • Research: p Ge Substrate Bottom Cell 4 to 5 junctions Back Contact Yamaguchi et. al., 2003 Space Power Workshop
  • 30.
    2nd. Generation: Cu(In,Ga)(S,Se2)Chalcopyrite solar cell The chalcopyrite structure can be deduced from the Diamond IV diamond structure according to the Grimm-Sommerfeld-rule, structure Si which states that a tetragonal structure is formed, if the average number of valence electrons per atom equals four nq N + mqM zincblende structure =4 III-V II-VI n + m + ... Epitaxial fil E i i l film: P l lli Polycrystalline N M elements N,M n,m atoms/unit cell GaAs , InP… thin film: qN, qM valence electrons CdTe, ZnS II-IV-V2 I-III-VI2 Epitaxial film: Polycrystalline thin film: y y ZnGeAs, Z G A … Cu(In,Ga)(Se,S)2 (Chalcopyrite and related compounds) I-III-VI2 Alloy: Group I= Cu, I III VI Cu Group III= In and Ga, Group VI = Se and S
  • 31.
    Possible combinations of(I, III, VI) elements ⎛Sn⎞ ⎛ Cu ⎞ ⎛ Ga ⎞ (In) ⎜ ⎟ ⎜Zn⎟ ⎜ ⎟ ⎜ Ag ⎟ ⎜ ⎟ ⎜ In ⎟ ⎛S ⎞ ⎜ ⎟ ⎝ ⎠ ⎜ Au ⎟ ⎜ Al ⎟ ⎜ Se⎟ 26 Zn Z Element ⎝ ⎠ ⎝ ⎠ ⎜Te⎟ 1.225 Tetrahedral coordination radius ⎝ ⎠2 Cu(In,Ga)Se2 1.5 Electronegativity IIIa VIa 3 Li 4 Be 5 B 6 C 7 N 8 O 9 F 2s 0.975 0.853 0.774 0.719 0.678 0.672 2s 2p 0.95 1.5 2.0 2.5 3.0 3.5 3.9 2p 11 Na 12Mg 13 Al 14 Si 15 P 16 S 17 Cl 3s 1.301 1.230 1.173 1.128 1.127 1.127 3s 3p 3 3p 0.9 1.2 Ib IIb 1.5 1.8 2.1 2.5 3.0 3d 19 K 20 Ca 29 Cu 30 Zn 31 Ga 32 Ge 33 As 34 Se 35 Br 3d 4s 1.333 1.225 1.225 1.225 1.225 1.225 1.225 1.225 4s 4p 0.8 1.0 1.8 1.5 1.5 1.8 2.0 2.4 2.8 4p 4d 37 Rb 38 Sr 47Ag 48 Cd 49 In 50 Sn 51 Sb 52 Te 53 I 4d 5s 1.689 1.405 1.405 1.405 1.405 1.405 1.405 1.405 5s 5p 0.8 1.0 1.8 1.5 1.5 1.7 1.8 2.1 2.5 5p 5d 55 Cs 56 Ba 79 Au 80 Hg 81 Tl 82 Pb 83 Bi 84 Po 85 At 5d 6s 1.392 6s 6p 0.75 0.9 2.3 1.8 1.5 1.8 1.8 2.0 2.2 6p
  • 32.
    Second Generation: Thin-filmTechnologies Copyrighted Material, from internet • Advantage: Low material cost, Reduced mass • Di d t Disadvantages: T i materiall (Cd), S Toxic t i (Cd) Scarce materiall (In, T ) t i (I Te) • CdTe – 8 – 11% efficiency (18% demonstrated) • CIGS – 7-11% efficiency (20% demonstrated) *CIGS based device CdTe based device Source: Rommel Noufi, NREL, Colorado, USA, http://www.nrel.gov/learning/re_photovoltaics.html
  • 33.
    Potentials of thinfilm Cu-chalcopyrite technologies 1. S tt i 1 Sputtering of Cu and In fC d I 2. Rapid Thermal processing (RTP) • low material consumtions • low energy consumption • hi h productivity l high d i i large area • „monolithic“ interconnects - Laser • new products (e.g. flexible cells) wafer f substrate Wafer based technology Quelle: EI3 Thin film cell structure thickness 1.5-2 µm Source: HZB / Technology department
  • 34.
    Potentials of thinfilm Cu-chalcopyrite technologies S Cu In 1 kWp : Comparison of c-Si and CuInS2 Source: HZB / Technology department
  • 35.
    Module processing 1. KCN etching 2. CBD-Buffer Source: HZB / Technology department
  • 36.
    Technology: Module processing Monolithic integration for series connection of individual cells P1: Series of periodic scribes that defines the width of the cells P2: After the absorber and buffer layer deposition Pulsed Laser P1 P3: After the window deposition +Ga +Se ZnO Front ZnO of one cell Buffer connected to the CIGS back Mo contact of Mo the next Glass 1. Deposition of Cu, In,Ga 2. RTP/Reaction with S/Se Source: HZB / EI2 department
  • 37.
    Technology: Module processing Monolithic integration for series connection of individual cells Loads - + Zn:Al i-ZnO CdS CIGS + + + + Mo Glass P1 P2 P3 RSC Laser scribing and mechanical scribing pulse repetition rate i-ZnO/ZnO:Al i Z O/Z O Al pulse power CdS wavelength and spot diameter + Electrical isolation for front and CIGS contact scribes back Low series resistance for the interconnect scribe Mo Interconnect resistivity as low Glass as possible Source: ZSW
  • 38.
    Best efficiency fromannealing of stacked metal layers Substrate: soda lime glass coated with Mo Temperature/ C Temperature/°C Deposition of Cu and In, Ga layers by sputtering 500-550 Deposition of Se layer by evaporation Rapid thermal process (RTP) RTP Advantage: Design of production facilities Time/min Large-area Large area deposition Avoidance of toxic H2Se The most essential factor that decides if the absorber is going to result in a high- efficiency device, is its Cu content, or the Cu/(Ga+In) ratio Cu(In.Ga)(S,Se)2 CIGS film should be slightly Cu deficient with a thin even more Cu deficient surface Cu-deficient, thin, Cu-deficient layer. This surface layer corresponds to the stable ordered vacancy (OVC) Cu(In,Ga)3Se5.
  • 39.
  • 40.
    Fundamental understanding buffer CIS EC ZnO EC < EC ? ZnS at EV Absorber The GBs Zn CIS, CIGS AO l Buffer Barrier for recombination: Absorber
  • 41.
    Material Properties: PhasesDiagram Copyrighted Material, from internet Simplified version of the ternary phase diagram Reduced to pseudo-binary phase diagram along the red dashed line Bold blue line: photovoltaic-quality material Relevant phases: α-, β-, γ- , δ-phase and Cu2Se α β γ δ phase,and CuIn3S5 Not found α: chalcopyrite CuInSe2 β: defect chalcopyrite Cu(In,Ga)3Se5 γ: Cu(In,Ga)5Se8
  • 42.
    Material Properties: PhasesDiagram Copyrighted Material, from internet α phase α-phase (CuInSe2): • Optimal range for efficient thin film solar cells: 22-24 at % • α-phase highly narrowed @RT • Possible at growth temp.: 500-550°C, @RT: phase separation into α+β 500 550 C, α β β phase β-phase (CuIn3Se5) • built by ordered arrays of defect pairs • anti sites (VCu, InCu) δ-phase (high-temperature phase) • built by disordering Cu & In sub-lattice Cu2Se • built from chalcopyrite structure by • Cu interstitials Cui & CuIn anti sites Hamakawa, Yoshihiro: Thin Film Solar Cells, Springer, 2004.
  • 43.
    Material Properties: Impurities& Defects Partial replacement of In with Ga; 20-30% of In replaced: Ga/(Ga+In) ~ 0.3 20 30% Ga/(Ga In) Band gap adjustment: 1.03eV-1.7 eV - Widening of bandgap at the surface of the Incorporation of 0.1 at % Na film Na (Se) (stability d N 2(S )1+n ( t bilit decrease with n↑) ith ↑) - The surface composition of Cu-poor CIGS Cu poor Better film morphology films Passivation of grain-boundaries (Ga+In)/(Ga +In+Cu) ca. 0.75 Higher p yp conductivity g p-type y - The bulk compositions Reduce defect concentration 0.5< (Ga+In)= (Ga+In+Cu) < 0.75. The are many defect - 3 vacancies: VCu, VGa, VSe. - 3 i t titi l Cui, G i, S i. interstitials: C Ga Se Phase segregation of Cu(In,Ga)3Se5 - 6 antisites: occurs at the surface of the films. CuGa, CuSe, GaCu, GaSe, SeCu, SeGa Ordered-Vacancy/ Defect Compounds (OVC/ODC) Ordered or disordered arrays of vacancies are occupying the cation sites They can exceed the local range of the unit cell, we called vacancy compounds Superlattice structures of the ideal chalcopyrite, reported as stable phases: OVC/ODC OVC/ODC are observed in slightly Cu-deficient: Cu(In,Ga)3Se5 Schock, Rommel Noufi, , Prog. Photovolt. Res. Appl. 8, (2000) pp. 151-160
  • 44.
    Roll-to-Roll deposition (R2R) Ionbeam supported low temperature Source: Fahoum Mounir/Habilitation deposition of Cu, In, Ga, Se fC G S Substrate: Mo coated polyimide/ stainless steel foil (F f Fe from th substrate?) the b t t ?) Alternative Electrochemistry Advantages: • Low cost production • Flexible modules • High power per weight ratio Voltag e - + In,Ga,Cu -ions , , Annealing Buffer TCO G C In, Se Ga,Cu, I S
  • 45.
    Recombination mechanism issue Ea nkT ⎛ j00 ⎞ VOC = − ln⎜ ⎜ j ⎟ ⎟ q q ⎝ SC ⎠ A: Diode quality factor EA: Activation energy J00 : Prefactor, weakly temperature-dependent Cu(In,Ga)Se2 EC Buffer B ff (1): interface recombination Eg 2 EF Ea = Φ b 1 EV Φb (2): bulk recombination E a = Eg
  • 46.
    Important Remarks Conversion efficienciesachieved by CuInS2 (EG y ( = 1.53 eV) or CuGaSe2 (EG = 1.7 eV) absorbers are considerably lower than those achieved by Burried pn-junction low band gap Cu(In,Ga)Se2 or even CuInSe2. OVC Cu(In Ga)Se p p-Cu(In,Ga)Se2 ( , ) Why? OVC In l b d I low band gap Cu(In,Ga)Se2 C (I G )S •Formation of weakly n-type OVC layer •The bulk is p-type p yp •Buried p-n junction n ΔEV n-Cu(In,Ga)3Se5 OVC minimizes the recombination at the CIGS/buffer interface. OVC surface layer has direct and wider band gap than the bulk Φ OVC increases further the barrier ,Φ, for recombination at CIGS/CdS That is the key to high-efficiency solar cells.
  • 47.
    Third Generation: Multi-junctionCells Multi- Copyrighted Material, HZB
  • 48.
    Technology: CIGS moduleprocessing N. Naghavi, D. Abou-Ras, N. Allsop, N. Barreau, S. Bu¨ cheler, A. Ennaoui, C.-H. Fischer, C. Guillen, D. Hariskos, J. Herrero, R. Klenk, K. Kushiya, D. Lincot, R. Menner, T. Nakada, C. Platzer-Björkman, S. Spiering, A.N. Tiwari and T. Törndahl. Prog. Photovolt: Res. Appl. ( g pp (2010). Published online in Wiley InterScience, Vol. 18, issue 6 (2011) pp. 411- ) y , , ( ) pp 433
  • 49.
    The world recordchalcopyrite solar cell Cu(In,Ga)Se2
  • 50.
    New Concepts forPhotovoltaic Energy Conversion (Photo)electrochemical and Dye-sensitized solar cells Organic solar cells: donor-acceptor hetero-junction Nanostructures for solar cells
  • 51.
    Semiconductor/Liquid versus Semiconductor/MetalJunction Vacuum level 0 Φ χ qχ CB qΦΜ CB EF,SC EF,SC qVB H+/H2 qVBB Metal EC 0 EC CE Back EF,SC EF,Metal EF,SC EF,redox contact Back H2O/H2 contact VB - 4.5 eV VB 1.23V Semiconductor (WE) Redox SCE EV Electrolyte EV e.g. I-/I2 Metal +0.243V Semiconductor Semiconductor e.g. Si e.g. Au V vs. NHE e.g. TiO2 Electrochemical scale Solid state scale Summer Semester Osaka University-Japan for graduate student in Research Center for Solar Energy Chemistry/Courses: Photovoltaic and hydrogen Research and development R&D
  • 52.
    Semiconductor/Liquid versus Semiconductor/MetalJunction Summer Semester Osaka University-Japan for graduate student in Research Center for Solar Energy Chemistry/Courses: Photovoltaic and hydrogen Research and development R&D
  • 53.
    Semiconductor/Liquid versus Semiconductor/MetalJunction Summer Semester Osaka University-Japan for graduate student in Research Center for Solar Energy Chemistry/Courses: Photovoltaic and hydrogen Research and development R&D
  • 54.
    Photoelectrochemical Solar Cell(PECs): Photovoltaic mode Copyrighted Material, from internet ‐ Reduction Sc ‐M Back  contact I2 + e‐ + Countre I‐ + h+ Electrode (CE) Oxidation I‐ ‐+ h+ +  I2 + e‐ ‐ I + h I2 + e Electron and holes are photogenerated Holes are moved to the surface of the WE -- current react with I I‐ + h+ Electron are moved to the back contact V reacts with I2 i th other side (CE) t ith in the th id Voltage vs. redox I2 + e‐ Source: A.J. Nozik, National Renewable Energy Laboratory
  • 55.
    Solar cells thatmimic plants p y Chlorophyll Light absorption Dye y Charge transfer protein e- transfer Semiconductor oxide (TiO2) Proton pump Hole transfer Electrolyte Copyrighted Material, from internet
  • 56.
    Solar cells thatmimic plants: DSSC Copyrighted Material, from internet HOMO LUMO CO2 Sugar H2O O2 Photosynthesis The most widely used sensitizer abbreviated as N3. y “cis-Ru(SCN)2L2 (L = 2,2'-bipyridyl-4,4'-dicarboxylate)” source: partly http://en.wikipedia.org/wiki/Dye-sensitized_solar_cell Grätzel, M., Journal of Photochemistry and Photobiology C: Photochemistry Reviews 2003, 4, 145
  • 57.
    Solar cells thatmimic plants: DSSC Copyrighted Material, from internet HOMO: highest occupied molecular orbital LUMO: lowest unoccupied molecular orbital HOMO LUMO CO2 Sugar H2O O2 Photosynthesis The most widely used sensitizer abbreviated as N3. y “cis-Ru(SCN)2L2 (L = 2,2'-bipyridyl-4,4'-dicarboxylate)” source: partly http://en.wikipedia.org/wiki/Dye-sensitized_solar_cell Grätzel, M., Journal of Photochemistry and Photobiology C: Photochemistry Reviews 2003, 4, 145
  • 58.
    Solar cells thatmimic plants Copyrighted Material, from internet Few simple materials and you can create your own Grätzel Cell The most widely used sensitizer abbreviated as N3. “cis-Ru(SCN)2L2 (L = 2,2'-bipyridyl-4,4'-dicarboxylate)” Ru(II) + hν → Ru(II)* Ru(II)* → Ru(III) + e- I3- + 2e-→ 3I- 3I- + Ru(III)→ I3- + Ru (II) I‐ + h+ DSSC Module I2 + e‐
  • 59.
    Solar cells thatmimic plants Copyrighted Material, from internet Generation Transport Back B k reaction ( ) with I3- ti (c) ith ∂n ∂n 2 ( n − n0 ) τn = 1/kcb [I3-] = α Ie −α x + Dn 2 − Ru(III)/Ru*(II)) ∂t ∂x τn ( ) (b) (c) (a) Ru*(II)/Ru(II))
  • 60.
    Solar cells thatmimic plants: DSSC Copyrighted Material, from internet http://www.solaronix.com/ Mesoporous TiO2 anatase Efficiency of 10 % was obtained by the solar cells assembled at the EPFL in Lausanne (simulated sunlight AM 1.5, 1000 W/m2) Eff. = 10 %, AM 1.5, VOC = 823 mV, ISC = 16.9 mA/cm2, FF = 72.5 %) Download Dye Solar Cells Assembly Instructions @ : http://www.solaronix.com/technology/assembly/
  • 61.
    Nanocrystalline based Solarcells Copyrighted Material, from internet Electron holes photogenerated Immediately injected in mesoporous TiO2 (or ZnO NRs) ZnO nanorodes T. Dittrich, A. Belaidi, A. Ennaoui J B Sambur et al. Science 2010;330:63-66 Extremely Thin Absorber Band energy diagram indicating the relevant energy levels and kinetic processes that describe PbS QD ET and HT into Concept of Inorganic solid-state nanostructured solar cells the TiO2 conduction band and the sulfide/polysulfide Solar Energy Materials and Solar Cells, Volume 95, Issue 6, June electrolyte, respectively. 2011, Pages 1527-1536
  • 62.
    Photoelectrochemical solar cells(PECs) Photoelectrolysis mode 1/C2 Band gap must V+v(t) be at least 1 8 2 0 eV 1.8-2.0 V V But small enough to absorb most sunlight Lock‐in Material requirements b Potentiostat v=vme edges must straddle Redox potentials Band iωt Fast charge transfer WE RE CE Determination of Flat Band PotentialStable in aqueous solution (Vfb) I hν>EG V EC Metal WE RE CE Back EF,SC EF,redox (CE) contact 1.23eV 1.23eV EV Electrolyte ( (WE) ) Anode: 2H20 4e- + 02 + 4H+ E Cathode: 4H20 + 4e- 4OH- + 2H2 A. Ennaoui and et al. Solar Energy materials and Solar Cells Volume 29 (1993), Pages 289-370 This lecture was presented @ Osaka University-Japan for graduate student in Research Center for Solar Energy Chemistry/Courses: Photovoltaic and hydrogen Research and development R&D
  • 63.
    Determination of FlatBand Potential (Vfb) V+v(t) Lock‐in Potentiostat v=vmeiωt WE RE CE vacuum 0 H+/H2 Ref. A. Ennaoui and et al. Solar Energy materials and Solar Cells Volume 29 (1993), Pages 289-370 This lecture was presented @ Osaka University-Japan for graduate student in Research Center for Solar Energy Chemistry/Courses: Photovoltaic and hydrogen Research and development R&D
  • 64.
    Materials suitable forsolar PECs Copyrighted Material, from internet
  • 65.
    Photoelectrochemical solar cells(PECs) Photoelectrolysis mode D D D D D D D H2O→2H2+O2 ∆V=1.23V, ∆G=238kJ/mol Source: Mildred Dresselhaus, Massachusetts Institute of Technology
  • 66.
    d0 and d10metal oxides Copyrighted Material, from internet GaN-ZnO (Ga1-xZnx)-(N1-xOx) d0 d10 Ti4+: TiO2, SrTiO3,  K2La2Ti3O10 : TiO SrTiO K Ga3+: ZnGa2O4 3 : ZnGa Zr4+: ZrO2 In3+: AInO2 (A=Li, Na) Nb5+: K4Nb6O17, Sr2Nb2O7 Ge4+: Zn2GeO4 Ta5+: ATaO3(A=Li, Na, K), BaTa2O6 Sn4+: Sr2SnO4 W6 : AMWO6 ( 6+ (A=Rb, Cs; M=Nb, Ta) b b ) Sb5+: NaSbO7 N replaces O in certain positions, providing a smaller band gap. Problems with getting the nitrogen there without too many defects. Oxygen free options: Ta3N5, G 3N4 O f ti T Ge Domen et al. New Non‐Oxide Photocatalysts Designed for Overall Water Splitting under Visible Light. J. Phys. Chem. 2007
  • 67.
    Use of PVfor H2 production Hydrogen and Oxygen are p y g yg produced using p g photovoltaic effect Test of security - No damage to hydrogen car - Gasoline car completely destroyed p n p n p n Solid state solar cells O2 H2 e- e- H2 H + O Dark electrolysis cell Source: Partly A.J. Nozik, National Renewable Energy Laboratory
  • 68.
    Water splitting: Hydrogenproduction Copyrighted Material, from internet Challenge: Material requirement : Material/catalysts, nano-materials, membranes (need Brainstorming ) Understand and control the interaction of hydrogen with materials H2O→2H2+O2 ∆V=1.23V, ∆G=238kJ/mol Source: Mildred Dresselhaus, Massachusetts Institute of Technology millie@mgm.mit.edu
  • 69.
    Fuel Cells Copyrighted Material, from internet Fuel Cell uses a constant flow of H2 to produce energy. Catalyst = Pt Very expensive Reactionthe Pt quantity between Minimize takes place q y H2 and Othe active layer structure Improve 2 electrical energy. The most common fuel cell uses Propose new materials Proton Exchange Membrane, o PEM oto c a ge e b a e, or Need of catalyst (e.g. platinum for a reaction that ionizes the gas O2 is ionized to O2- 2 H2 is ionized to 2H+ 2H+ + O2- = H2O O2- and H+ combine Energy is given off in The “waste products” are water and heat electron form and gives off power to run an engine
  • 70.
    Advantages and Challenges Copyrighted Material, from internet Advantages Zero emission No dependence on foreign oil Ability to harvest solar and renewable energy Abilit t h t l d bl Not many moving part in a car Hydrogen weighs less than g y g g gasoline car would not need as much energy to move Challenges g Still expensive to equip a car with a hydrogen fuel cell. Hydrogen is expensive to make, store, and transport The center is a platinum plate which is very expensive National Program in USA since 2007: 1 billion dollars to date in hydrogen car research for the “develop hydrogen, fuel cell and infrastructure technologies to make fuel-cell vehicles practical and cost-effective by 2020.”
  • 71.
    Basic: Brief BusinessScenario Copyrighted Material, from internet 1999 FOUNDED, 2001 BEGAN WITH THE PRODUCTION OF SILICON SOLAR CELLS WITH 19 EMPLOYEES. BY 2009, 2,600 EMPLOYEES (2007, 1700 EMPLOYEES) NOW THE LARGEST SOLAR CELL MANUFACTURER IN THE WORLD. (SINCE 2007) WORLD CONTINUE TO EXPAND PRODUCTION IN BITTERFELD-WOLFEN, GERMANY AND START CONSTRUCTION OF NEW MALAYSIAN PRODUCTION FACILITY. ALONGSIDE THE MONO-CRYSTALLINE AND POLYCRYSTALLINE (90% OF BUSINESS) CORE BUSINESS, WE USE A WIDE RANGE OF TECHNOLOGIES TO DEVELOP AND PRODUCE THIN-FILM MODULES. (THIN-FILM - 25% SHARE OF SMALLER MARKET) Year over year, Q-Cells SE has been able to grow revenues from €790.4M to €1.4B. http://investing.businessweek.com
  • 72.
    Basic: Brief BusinessScenario Copyrighted Material, from internet SunTech Power (China) - THE COMPANY WAS FOUNDED IN 2001 BY ZHENGRONG SHI - SALES $1.9B 2008, 1.3B 2007 PROFITABLE - EMPLOYEES: 6784 - WORLDS LARGEST SILICON CELL MAKER - AVERAGE CONVERSION EFFICIENCY RATES OF THEIR - MONOCRYSTALLINE AND MULTICRYSTALLINE SILICON PV CELLS - 16.4% AND 14.9% RESPECTIVELY - 2009 ANNOUNCES PLAN TO BUILD MANUFACTURING PLANT IN US Zhengrong Shi Boen in 1963 in China, finished his Master in China then he went to University of New South Wales (Austria). He ( ) 130KW obtained his doctorate degree on 8MW China 43KW 0.092-0.3-3.8MW 3MW Nevada solar power technology and Spanien Germany China returned to China in 2001 to set 14MW 5.1MW 10 MW up his solar power company (Net Spanien Nevada Abu Dhabi worth US$2.9 Billion (2008) 48KW Australien 500KW Nevada http://eu.suntech-power.com
  • 73.
    Copyrighted Material, frominternet Capacity 130MW Expansion 70MW 55MW 30MW 20MW R&D 1980 1999 2006 2007 2008 2010 Kaneka has been specializing in thin-film silicon technology: 1980 Started study of a-Si technology 1987 Participated in NEDO project (Government funded R&D) 1999 Started 20MW/yr commercial production 2006 Announced capacity expansion: - up to 30MW in 2006, 55MW in 2007, 70MW in 2008 2007 Introduction of new Hybrid PV Announced capacity expansion: up to 130MW in 2010
  • 74.
  • 75.
    Excitonic solar cells Copyrighted Material, from internet Exciton LUMO electrons holes Interface HOMO • all organic: polymer and/or molecular • hybrid organic/inorganic •ddye-sensitized cell iti d ll
  • 76.
    Donor acceptor concept Copyrighted Material, from internet
  • 77.
    Donor acceptor concept Copyrighted Material, from internet Interpenetrating Nanostructured Networks η record = 4,8% η FMF, ISE = 3,7% Aluminum Absorber Akzeptor Polymer Anode ITO Substrate Donor The light falls on the polymer Electron/hole is El t /h l i generated t d The electron is captured C60
  • 78.
    The biggest Challenge Copyrighted Material, from internet Reducing the cost/watt of delivered solar electricity Find a concepts for a more efficient PV systems More efficiency, More abundant materials, Non-toxic material, Durability First Generation Fi t G ti Crystalline Si will remain the dominant PV technology for a long time, the current shortage will be overcome by increased production of pure Si and the introduction of purified metallurgical-grade Si. p g g Second Generation Thin film modules out of a-Si, CIS, or CdTe have an interesting market opportunity today, their long-term success will depend on efficiency improvements and cost reduction reduction. Third Generation TANDEM CELLS: Because sunlight is made up of many colours of different energy, from the high energy ultraviolet to the low energy infrared, a combination of solar cells of different materials can convert sunlight more efficiently than any single cell Multiple Exciton Generation: The objective is fighting termalization: In quantum dots, the rate of energy dots dissipation is significantly reduced and one photon creates more than one exciton via impact ionization Higher photocurrent via impact ionization (inverse Auger process)
  • 79.
    Thank you somuch Questions or comments? PVSEC 23th – 27th. 2012 / Rabat - Morocco Prof. Dr. Ahmed Ennaoui Helmholtz-Zentrum Berlin für Materialien und Energie
  • 80.
    Parking: produce electricityand have the shadow