CIGS Synthesis by Reactive Transfer      Processing of Compound Precursors      B.J. Stanbery      Chief Scientist, Founde...
Outline  • Thermochemistry of Cu–In–Ga–Se    material system  • Motivation for alternative CIGS    processing approach  • ...
2010 MRS Workshop on Thin Film Photovoltaics      7 October 2010; Denver, CO      THERMOCHEMISTRY OF      CU–IN–GA–SE MATE...
Cu–(In,Ga)–Se Ternary Alloys  Molecularity (M) and Stoichiometry (S)  • M= [Cu]/([In]+[Ga])         M-axis                ...
CIGS Complex Non-Stoichiometric  Thermochemical Phase Structure               high quality          Metal sub-lattice     ...
CIGS Non-Stoichiometry and  Atypical Device Behavior         • Peculiar semiconductor behavior:           CIGS PV devices ...
Role of Nanostructuring in  CIGS PV Device Physics  • Intra-Absorber Junction (IAJ) model        – Device-quality CIGS is ...
2010 MRS Workshop on Thin Film Photovoltaics      7 October 2010; Denver, CO      MOTIVATION FOR ALTERNATIVE      CIGS PRO...
Characteristics of an Ideal CIGS  Manufacturing Method  • High device-quality material        – Ability to create intrinsi...
Synopsis of Prior Art for CIGS Synthesis:  Co-evaporation  • First method to achieve 10% efficiency and research    approa...
Synopsis of Prior Art for CIGS Synthesis:  Metal Precursor Selenization  • Most well-developed, widely used approach for  ...
Synopsis of Prior Art for CIGS Synthesis:  Oxide Precursor Selenization  • High-speed printing of copper indium gallium   ...
Synopsis of Prior Art for CIGS Synthesis:  Stacked Elemental Layers (SEL)  • Differs from the metal selenization approache...
2010 MRS Workshop on Thin Film Photovoltaics      7 October 2010; Denver, CO      REACTIVE TRANSFER PROCESSING2010 MRS Wor...
Reactive Transfer Processing of  Compound Precursors• Two-stage process                        Se, S                      ...
Reactive Transfer Processing  Compound Precursor Deposition  • Two methods have been developed for    deposition of compou...
Reactive Transfer Processing  Contact Transfer Synthesis (FASST®)                                                         ...
Field-Assisted Simultaneous  Synthesis and Transfer (FASST®)  • Combines features of        – Rapid Thermal Processing and...
Recrystallization of Nanoscale Precursor  Films Forming Large Grain CIGS         Precursor Film                   FASST® C...
CIGS Film by FASST® in 6 minutes  with Vacuum-based Precursors                                               XRD          ...
Metal-Organic Decomposition  (MOD) Precursor Film Deposition  • Inorganic compound reaction CIGS synthesis provides    pat...
MOD Comparison with Vacuum   Precursor Deposition MethodCo-evaporated        Top View        Top View            SprayCIGS...
NREL CRADA – Hybrid CIGS by FASST®                                              XRD                                SEM    ...
Reactive Transfer Processing  Non-Contact Transfer Synthesis (NCT™)                                                       ...
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MRS_Oct_7_2010_Workshop

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MRS_Oct_7_2010_Workshop

  1. 1. CIGS Synthesis by Reactive Transfer Processing of Compound Precursors B.J. Stanbery Chief Scientist, Founder, and Chairman HelioVolt Confidential2010 MRS Workshop and Proprietary Thin Film PV
  2. 2. Outline • Thermochemistry of Cu–In–Ga–Se material system • Motivation for alternative CIGS processing approach • Reactive Transfer Processing and variants for Rigid vs. Flexible substrates • Current status2010 MRS Workshop Thin Film PV 2
  3. 3. 2010 MRS Workshop on Thin Film Photovoltaics 7 October 2010; Denver, CO THERMOCHEMISTRY OF CU–IN–GA–SE MATERIAL SYSTEM2010 MRS Workshop Thin Film PV 3
  4. 4. Cu–(In,Ga)–Se Ternary Alloys Molecularity (M) and Stoichiometry (S) • M= [Cu]/([In]+[Ga]) M-axis 112 = CuInSe2 Se 247 = Cu2In4Se7 • S = 2[Se]/[Cu]+3([In]+[Ga]) 135 = CuIn3Se5 • ∆M= M-1; ∆S= S-1 • ALL high-efficiency ∆S>0 CIGS devices have Cu2Se3. 135 .(In,Ga)2Se3 ∆M<0 and ∆S>0 CuSe. 112 .(In,Ga)Se 247 247 Cu2Se. .(In,Ga)4Se3 • Formation reaction: ∆M<0 y Cu2Se + (1-y) (In,Ga)2Se3 + ∆Se → Cu In, Ga (Cuy(In,Ga)1-y)2Se3-2y+∆Se Intermetallic Plethora2010 MRS Workshop Thin Film PV 4
  5. 5. CIGS Complex Non-Stoichiometric Thermochemical Phase Structure high quality Metal sub-lattice Ga–In alloy device domain Order-Disorder maximum (2-phase ) Transition efficiency zone • All of the stable thermodynamic phases in the CIGS material system are crystalline but can vary in composition2010 MRS Workshop Thin Film PV 5
  6. 6. CIGS Non-Stoichiometry and Atypical Device Behavior • Peculiar semiconductor behavior: CIGS PV devices insensitive to % atomic composition variations & extended defects >19% efficiencies recently reported† over range: • 0.69 ≤ [Cu]/([In]+[Ga]) ≤ 0.98 (Group I/III ratio) • 0.21 ≤ [Ga]/([Ga]+[In]) ≤ 0.38 (Group III alloy ratio: Eg) • Empirical Observations – CIGS PV devices are always copper deficient compared to α-CuInSe2 – Compositions lie in the equilibrium α+β 2-phase domain †Jackson et al., Prog. PV, Wiley & Sons, 2007.2010 MRS Workshop Thin Film PV
  7. 7. Role of Nanostructuring in CIGS PV Device Physics • Intra-Absorber Junction (IAJ) model – Device-quality CIGS is a two-phase mixture of p-type α-CIGS and n-type β-CIGS phases, forming a nanoscale bulk heterojunction – These internal junctions form an interpenetrating percolation network, allowing positive and negative charges to travel to the contacts in physically separated paths, reducing recombination.2010 MRS Workshop Thin Film PV
  8. 8. 2010 MRS Workshop on Thin Film Photovoltaics 7 October 2010; Denver, CO MOTIVATION FOR ALTERNATIVE CIGS PROCESSING APPROACH2010 MRS Workshop Thin Film PV 8
  9. 9. Characteristics of an Ideal CIGS Manufacturing Method • High device-quality material – Ability to create intrinsic defect structures limiting recombination; role of the order-disorder transition? – Ability to control Group III and VI composition gradients – Control of extrinsic doping (e.g.: sodium) • High processing rate – Reduces capital cost for targeted throughput • Low thermal budget – Reduces operating cost and energy payback time • High materials utilization – Reduced materials consumption and recycling expenses2010 MRS Workshop Thin Film PV 9
  10. 10. Synopsis of Prior Art for CIGS Synthesis: Co-evaporation • First method to achieve 10% efficiency and research approach used to make all record cells since 1989 • Simultaneous evaporation of the constituent elements onto a high-temperature (450-700°C) substrate to directly synthesize CIGS in a single stage process • Competition between adsorption and desorption kinetics reduces (1) selenium utilization and (2) indium incorporation at temperatures near/above the order-disorder transition • Extended dwell at high temperatures generates high thermal budget and equipment costs2010 MRS Workshop Thin Film PV 10
  11. 11. Synopsis of Prior Art for CIGS Synthesis: Metal Precursor Selenization • Most well-developed, widely used approach for commercial manufacture of CIGS modules, providing good large-area uniformity • Deposition of multilayer metal films by PVD, plating, or particle suspensions followed by second-stage high-temperature annealing in Se or H2Se/H2S • Complex intermetallic alloying reactions and differential diffusion during selenization cause uncontrolled segregation • Selenium/Sulfur diffusion limits reaction rate and resulting extended dwell at high temperature generates high thermal budget; first stage deposition method determines materials utilization efficiency and capital intensity2010 MRS Workshop Thin Film PV 11
  12. 12. Synopsis of Prior Art for CIGS Synthesis: Oxide Precursor Selenization • High-speed printing of copper indium gallium oxide nanoparticle ink onto a metal foil substrate, subsequently annealed at high temperature in H2Se/H2S to convert the oxide into sulfo-selenide – Enables excellent materials utilization • Reduced diffusion lengths of chalcogens in nanoparticles speeds displacement reaction • Difficult recrystallization kinetics limit film densification and large grain growth • Composition gradient control challenging2010 MRS Workshop Thin Film PV 12
  13. 13. Synopsis of Prior Art for CIGS Synthesis: Stacked Elemental Layers (SEL) • Differs from the metal selenization approaches by incorporating layers of selenium, as well as the metals, into the precursor film itself – Circumvent the need to diffuse selenium through the entire thickness of the precursor stack – Enables intervention in intermetallic formation by stacking sequence control – Multi-step reaction kinetics shown to generate compound intermediates prior to CIGS formation • Rapid thermal processing used in second stage to minimize thermal budget and parasitic reactions2010 MRS Workshop Thin Film PV 13
  14. 14. 2010 MRS Workshop on Thin Film Photovoltaics 7 October 2010; Denver, CO REACTIVE TRANSFER PROCESSING2010 MRS Workshop Thin Film PV 14
  15. 15. Reactive Transfer Processing of Compound Precursors• Two-stage process Se, S 112 = Cu(In,Ga)(Se,S)2 – Low-temperature 247 = Cu2(In,Ga)4(Se,S)7 deposition of multilayer compound precursor Cu2Se3. .(In,Ga)2(Se,S)3 films CuSe. 112 .(In,Ga) (Se,S) 247 247 – RTP reaction of Cu2Se. .(In,Ga)4(Se,S)3 compound precursors to form CIGS Cu In, Ga Intermetallic Plethora2010 MRS Workshop Thin Film PV 15
  16. 16. Reactive Transfer Processing Compound Precursor Deposition • Two methods have been developed for deposition of compound precursors – Low-temperature Co-evaporation • Equipment requirements similar to conventional single- stage co-evaporation but lower temperatures lead to higher throughput and reduced thermal budget – Liquid Metal-Organic molecular solutions • Proprietary inks developed under NREL CRADA • Decomposition of inks leads to formation of inorganic compound precursor films nearly indistinguishable from co-evaporated films (for some compounds)2010 MRS Workshop Thin Film PV 16
  17. 17. Reactive Transfer Processing Contact Transfer Synthesis (FASST®) Rapid Thermal Processor Electrostatic Chuck Print Plate Release Layer Precursor 2 Print Plate Release Layer Precursor 2 Precursor 1 Precursor 1 Metal Contact Layer Metal Contact Layer Substrate Substrate Flash Heating Print Plate Recoat Print Plate Release Layer emitter Device CIGS Processing CIGS Metal Contact Layer Metal Contact Layer Substrate Substrate Completed Device2010 MRS Workshop Thin Film PV 17
  18. 18. Field-Assisted Simultaneous Synthesis and Transfer (FASST®) • Combines features of – Rapid Thermal Processing and, – Anodic Wafer Bonding • Advantages – Rapid processing • Eliminates pre-reaction • Independent pre-heating of precursors – Confinement of volatile selenium – High electrostatic field provides intimate precursor film contact • Substrate compliance critical for uniform large-area contact so FASST® process variant most suitable for flexible substrate processing.2010 MRS Workshop Thin Film PV 18
  19. 19. Recrystallization of Nanoscale Precursor Films Forming Large Grain CIGS Precursor Film FASST® CIGS cross-section2010 MRS Workshop Thin Film PV © 2009 HelioVolt Corporation
  20. 20. CIGS Film by FASST® in 6 minutes with Vacuum-based Precursors XRD CIGS Mo SIMS Depth Profile  Chalcopyrite CIGS (& Mo)  (220/204) preferred orientation  Uniform elemental distribution ⇒ complete reaction of the two precursors achieved2010 MRS Workshop Thin Film PV
  21. 21. Metal-Organic Decomposition (MOD) Precursor Film Deposition • Inorganic compound reaction CIGS synthesis provides pathway for evolutionary adoption of MOD precursors • Key drivers – Low capital equipment cost – Low thermal budget – High throughput • Flexibility – Good compositional control by chemical synthesis – Variety of Cu-, In- and Ga-containing inks can be synthesized and densified to form multinary sulfo-selenide precursors • Efficient use of materials2010 MRS Workshop 21 Thin Film PV
  22. 22. MOD Comparison with Vacuum Precursor Deposition MethodCo-evaporated Top View Top View SprayCIGS Precursor Deposited Film CIGS Precursor Film Cross Section Cross Section 2010 MRS Workshop 22 Thin Film PV
  23. 23. NREL CRADA – Hybrid CIGS by FASST® XRD SEM  Chalcopyrite CIGS (& Mo)  (220/204) preferred orientation  Exceptionally large grains achieved  Columnar structure2010 MRS Workshop Thin Film PV
  24. 24. Reactive Transfer Processing Non-Contact Transfer Synthesis (NCT™) Process Step Cu, In, Ga, Se • Independent deposition of distinct compound precursor layers on Substrate substrate and source plate Source Plate with Transfer Film • Rapid non-contact reaction Pressure – Turns stack into CIGS with high efficiency grains Heat – Combines benefits of sequential selenization with Close-Spaced Vapor Transport (CSVT) for junction optimization Source Plate • CIGS adheres to the substrate and the source plate is reused Substrate CIGS Layer • More suitable for rigid substrates2010 MRS Workshop Thin Film PV 24

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