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Plasmon Enhanced Solar Cells, Jan-Henrik Smått

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Fotoniikka - valaiseva iltapäivä seminaarin esitys 24.9.2013. …

Fotoniikka - valaiseva iltapäivä seminaarin esitys 24.9.2013.
Center for Functional Materials, Physics, Åbo Akademi University, Turku, Finland.

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  • 1. Plasmon Enhanced Solar Cells Björn Törngren,1 Simon Sandén,2 Kenta Akitsu,3 Takaya Kubo,3 Hiroshi Segawa,3 Ronald Österbacka,2 Jan-Henrik Smått1 1 Center for Functional Materials, Physical Chemistry, Åbo Akademi University,Turku, Finland. 2 Center for Functional Materials, Physics, Åbo Akademi University,Turku, Finland. 3 Research Center for Advanced Science and Technology (RCAST), The University of Tokyo,Tokyo, Japan Fotoniikka – valaiseva iltapäivä – Turku 24.09.2013
  • 2. Joint project with RCAST  Plasmon Enhanced Organic Hybrid Solar Cells (POHSC) – 3 yr  Physical Chemistry (Smått) and Physics (Österbacka)  Research Center for Advanced Science and Technology (RCAST),The University of Tokyo, Japan (Prof. Segawa)  Several research visits between Finland and Japan
  • 3. POHSC – general outline PhysChem (ÅAU): Synthesis and modification of core- shell nanoparticles RCAST (UT): Development of novel dyes (NIR) – porphyrin-based Solar cell applications: Assembly into DSSC and organic SC Physics (ÅAU): Modeling of plasmonic core-shell particles Plasmon enhanced NPs NPs with tunable absorption properties 300 400 500 600 700 800 900 Absorbance(a.u.) Wavelength (nm)
  • 4.  Surface plasmons (SPs) are coherent oscillations of conduction electrons on a metal surface excited by electromagnetic radiation at a metal-dielectric interface  Resonance at a specific wavelength (Au NPs: ~530 nm) Willets, K.A.;Van Duyne, R. P. Ann. Rev. Phys. Chem. 2006, 58, 267. The surface plasmon effect
  • 5. Elongated nanoparticles (nanorods)  Elongated NPs show two surface plasmon peaks  By controlling the aspect ratio of gold nanorods, the position of the longitudinal peak can be tuned Murphy, et al. J. Phys. Chem. B 2005, 109, 13857. Transverse mode (T) Longitudinal mode (L) T L
  • 6. Synthesis of Au nanoparticles/rods  Au NPs with varying size by controlling the amount and strength of the reducing agent (Ø 15–30 nm)  Seed-mediated growth can be used to synthesize elongated Au nanorods with varying aspect ratios  Shifting the surface plasmon resonance from 520 nm up to 1000 nm Smith,D; and Korgel, B; Langmuir 2008, 24, 644.
  • 7. 10 nm Glass ITO P3HT PCBM Gold P3HT PCBM Organic or hybrid solar cellsDye-sensitized solar cells Surface plasmons in solar cells
  • 8. Current topics of the project  Stability issues of core/shell nanoparticles in DSSCs  Plasmon-enhanced polymer-sensitized solar cells (PSSC)  Charge generation and charge transport studies  Gold nanorods to modify the light absorption range  Plasmonic particles in organic bulk hetero-junction solar cells
  • 9. Core-shell Au@SiO2 nanoparticles Why is a thin silica shell needed? 1) It acts as an insulator to avoid charge recombination within the metal 2) It adjusts the plasmon-dye separation distance to minimize quenching 3) It protects the metal core from corrosion when the particles are subjected to electrolyte solution 4) It gives a better thermal stability that prevents sintering of the gold cores. Sheehan et al. J. Phys. Chem. C, 2013, 117, 927−934
  • 10. Silica coating approaches Turkevich approach:  ~15 nm gold cores Na2SiO3
  • 11. Coating thickness and completeness APS APS + Stöber MPTMS Direct Stöber Gold core diameter: 16 nm
  • 12. Modeling of plasmonic core-shell particles  Another aspect of the project is to model the plasmonic behavior of these materials using Mie theory  Optimal particle structure can be found λ = 550 nm Qext SiO2shellthickness(nm) Au core radius (nm) X nm Water n = 1.333
  • 13. Modeling of silica thickness (Mie theory) APS: 0.5 nm APS + Stöber: 5 nm MPTMS: 1.3 nm Direct Stöber: ~20 nm
  • 14. Chemical stability in iodide electrolyte Coating methods: A: APS B: APS + Stöber C: Direct Stöber D: MPTMS
  • 15. Temperature stability of Au@SiO2 NPs Au@SiO2 NPs (MPTMS method) RT 500 ºC  Heating required for sintering of TiO2 NPs in a DSSC could potentially damage the silica shell  No detectable difference!
  • 16. Assembly of (plasmon-enhanced) DSSC TiO2 nanoparticle paste (w/ or w/o Au@SiO2 NPs) screen-printed on the substrate, and sintered at 500 °C Electrolyte injectionPlacing two electrodes FTO/Glass substrate TiO2 nanoporous layer Pt coated-FTO TheTiO2 substrate was immersed in the solution overnight Solar cell structure Dye solution Photoanode Spacer Injection hole Electrolyte (30 µm) Pt-coated FTO Photoanode Solar cell fabrication (I3 –/I– redox couple in acetonitrile) Slide courtesy of Kenta Akitsu
  • 17. Plasmon-enhanced DSSC performance Sample Au@SiO2 Thickness [µm] VOC [V] JSC [mA/cm2] FF PCE [%] A1 1 wt% 1.726 0.85 4.0 0.68 2.3 A2 1 wt% 1.899 0.85 3.9 0.68 2.3 T1 – 1.844 0.85 3.7 0.68 2.2 T2 – 1.868 0.85 3.4 0.69 2.0 B.Törngren et al. J. Colloid Interface Sci., submitted
  • 18. Polymer-sensitized solar cell (PSSC)  Polythiophene derivative polymers where COOH units are attached to the polymer backbone to facilitate sensitization to TiO2  Uses a low molecular weight polymer as dye (here: PT-C 85, i.e. HR 85%) Electrolyte solution Pt/FTO TiO2/Polymer FTO R=H, Me PT derivative with carboxylic acid groups MW: 1100, 2700 Hydrolysis ratio (H:Me ratio) can be varied 0%-95% Akitsu et al. Jpn. J.Appl. Phys. 51 (2012) 10NE04
  • 19. Plasmon-enhanced PSSCs  TiO2 paste incorporating 1 wt% Au@SiO2 NPs was manufactured  Photoanode was made by screen-printing on FTO  PT-C 85 was adsorbed onto the TiO2 layer overnight Akitsu et al., in preparation.
  • 20. I-V and IPCE of Plasmon Enhanced PSSCs 7 6 5 4 3 2 1 0 Currentdensiy,mA/cm 2 0.60.50.40.30.20.10 Voltage, V 70 60 50 40 30 20 10 0 IPCE,% 700600500400300 Voltage, V 3 layers 2 layers 1 layer Sample Voc Jsc FF  Au 1 0.52 2.2 0.55 0.6 Ref 1 0.52 1.1 0.52 0.3 Au 2 0.53 4.6 0.55 1.3 Ref 2 0.50 3.7 0.55 1.0 Au 3 0.53 5.9 0.51 1.6 Ref 3 0.50 5.0 0.54 1.4 Dashed: with Au@SiO2 NPs Solid: without Au@SiO2 NPs
  • 21. IPCE enhancement factor: IPCE(Au)/IPCE(Ref)  IPCE enhancement over 400-650 nm  Peak slightly red-shifted compared to absorption of Au@SiO2 NPs in EtOH  larger dielectric constant of TiO2 3.0 2.5 2.0 1.5 1.0 0.5 Au/Ref.,- 650600550500450400350300 Wavelength, nm 1.4 1.2 1.0 0.8 0.6 Au/Ref.,- 650600550500450400350300 Wavelength, nm 0.14 0.12 0.10 0.08 0.06 0.04 0.02 0.00 Absorbance,- Au@SiO2 NPs in EtOH
  • 22. Outlook of other possibilities Au nanorods to enhance absorption in NIR region Plasmonic particles in organic BHJ solar cells 0 0.2 0.4 0.6 0.8 1 1.2 1.4 300 400 500 600 700 800 900 Absorbance(a.u.) Wavelength (nm) Gold nanoparticles Gold nanorods Longitudinal mode Aspect ratio ~3 Transverse mode 10 nm Glass ITO P3HT PCBM Gold Au NPs
  • 23. Summary  Plasmonic particles (e.g. gold nanoparticles) have proven useful for improving the efficiency of photovoltaic devices  A thin but complete silica shell is needed to protect the Au NPs in the harsh electrolyte solutions used in DSSCs  Plasmon-enhanced polymer-senisitized solar cells (PSSCs) have been manufactured using novel polythiophene derivative polymers  In both DSSCs and PSSCs the efficiency can be improved by incorporating Au@SiO2 nanoparticles

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