Bertrand FILLON CEA LITEN Grenoble

1. Nanostructures for High-Efficiency Solar Cells. Bertrand FILLON CEA LITEN Grenoble Arrhus, Denmark, June 2012

2. Content Introduce CEA/LITEN Nanotechnology for bulk silicon Nanotechnology for thin film PV cells Conclusion

3. One BU of Technological Research Division R & Dfor nuclear energy Defense programs Fundamental Research Technological Research for industry 15.000 researchers 4 Billions Euros annual 9 Instituts Getting ready for the New Economy

4. LITEN Key figures Chambéry: Solar Energies & Smart Building Grenoble: Green Transportation & Biomass Experimentalarea Manpower2012 Patents Budget 150 M€ 600 in portfolio 120 M€ turnover 1000 collaborators 150 new patents in 2011 30 M€ of CEA Funding

5. LITEN Electric Transports Electric Power Batteries Fuel Cells Hybridation Solar Energy & Buildings Nanomaterials µ-sources Energy recovery Organic electronics Large area electronics Solar Energy Solar PV, CPV, OPV Electrical systems Energetic efficiency Biomass & Hydrogen Solid Storage H2 Production H2 Storage Usages

6. Industrial partnerships Large companies Small companies Building/Solar Energy • Photovoltaic devices • Thermal devices • Positive energy building Transportation • Fuel cell • Energy storage • Hydrogen Nomad • Micro power sources • Energy scavenging • Organic Electronic

7. Content Introduce CEA/LITEN Nanotechnology for bulk silicon Nanotechnology for thin film PV cells Conclusion

8. Three main categories for solar cells New concepts 3rdgénération cells Thin film technologies a-Si/mc-Si, CIGS (CuInSe, CdTe) Crystalline Si cells

9. Improvements in silicon yield Diffusion of the transition metals • - Avoid contamination zones. • - Maintain the purity of the feed stock to the ingot and wafer. • - Improvement of feedstock yield. Etc…… Wafering zone High metallic impurities, High [Cs], SiC contamination > 20 mm Diffusion of the transition metals 4 Fe diffusion High content of [Oi] 3 To be gettered before processing 2 > 40 mm TIV 48 1 > 20 mm > 20 mm Lifetime pattern of an ingot cross section Pictures obtained with µwave Photon Conductivity Decay

10. Nanophenomena for the bulk silicon > 20 mm > 20 mm 4 > 20 mm 2 3 > 40 mm 1 • Taking in account 2 cm top, bottom and side crop we remove 22% ( 100 kg) of the total industrial weight (standard industrial G5 ingots is 450 Kg) • Zones 1, 2 and 3 can be recycled • Zone 4 (Carbon cut) is not recycled Improvement and better understanding of the trapping offer a higher free carrier life time thanks for the development of an advanced crucible and a well controlled gettering

11. Silica crucible with diffusion barrier Aluminum Iron High purity crucible Silicon High purity Si3N4 coating High purity diffusion barrier Fused silica crucible Silicon Si3N4 coating Standard fused silica crucible Fused silica crucible

12. Silica crucible with diffusion barrier Standard crucible+ Si HPC Crucible + Si Melted Si Si3N4 Coating High Purity Coating Silica crucible Pictures obtained with µwave Photon Conductivity Decay

13. Gettering effect on six inches mono like P type wafer Improvement of the free carrier life time Strong gettering on ingot bottom wafers Pictures obtained with µwave Photon Conductivity Decay

14. Content Introduce CEA/LITEN Nanotechnology for bulk silicon Nanotechnology for thin film PV cells Conclusion

15. Three main categories for solar cells New concepts 3rdgénération cells Thin film technologies a-Si/mc-Si, CIGS (CuInSe, CdTe) Crystalline Si cells

16. Electromagnetic field Absorption coefficient of material • Light absorption = f(ad, E2) • 3 routes to enhance coupling between solar light and cell • Longer path for light (scattering substrates): d↑ • Plasmonic structure: E↑ • New nanocomposite absorbers: a↑ Length of Light path

17. Scattering effect Conventional Plasmonic effect A A A Lost Lost Lost • Enhanced electric field E  • a ∞ E2 • A ∞ (1- R)(1-e-ad)  Longer Light path d  A ∞ (1- R)(1-e-ad) 

18. a) “Commercial” Texturing of TCO (ASAHI-U) b) ZnO-Al texturing : 10 s with HCl. c) Associated Haze measurement: H= scattering in transmission / total transmission Light management: scanning effect TCO texturation (a) (b) (c) Better control of the TCO nanostructure

19. Capability: 2D spatial control of thin film nano-structuration. Basic concept: Langmuir-blodget film of spheres deposited by capillarity mechanism => periodic array Potential interest: spectral tuning of the light scattering inside the solar absorber Scanning effect: substrate nano-structuring Bead self assembly : 2D nano-structuring High control of periodicity via the sphere size

20. Bead self assembly : 2D nano-structuring High control of periodicity via the sphere size

21. The texturing widens the spectral response Glass ZnO deposit Beads deposit ZnO deposit Example of light scattering enhancement (H=Tscat./Ttotal) Direct texturing Glass ZnO Direct texturing Reverse texturing ZnO Glass Periodicity range: =1000nm => Red-IR scattering

22. a-SiGe:H Texturing of a-SiGe:H cell Reverse texturing η=4.9% η=4.28% Solar cell:

23. a-SiGe:H Results predictable by optical simulation • Comsol multiphysics software • 2D Optical calculations TCO TCO Ag Glass TCO - a-SiGe:H TCO - Ag - E-field mapping => Simulation predictive approach and tunable texturing technology easily adaptable to various solar cell absorbers (Si, SiGe, CIGS, CdTe, ….)

24. Scattering effect Conventional Plasmonic effect A A A Lost Lost Lost • Enhanced electric field E  • a ∞ E2 • A ∞ (1- R)(1-e-ad)  Longer Light path d  A ∞ (1- R)(1-e-ad) 

25. Plasmonic effect in Solar Cells : principle Proposed solution: enhance the absorption of active layer by coupling it with a PGNM. resonance on metal nanoparticles (NPs) absorption inside the NP absorption in nanoparticle L L Electric field enhancement NPs in surrounding medium PGNM ð ð absorption inside the active layer absorption in active layer J J Active layer scattering scattering J J Challenge: Promote the light scatt./abs. (fNP↑) while limiting the NP absorption • Adapted nanotechnology for a fine tuning of NP size and density, • Adapted Optoelectronic (O/E) modelling to define the optimum PGNM localization inside the cell stack.

26. Plasmonic phenomena • Previous work : • - no fine control of nanoparticles • - localization of nanoparticles only on the surface EBPVD + 1h 200°C wet process [Yu et al., 2006, (USA)] [Pillai, 2007 (UNSW - Australia)] EU project: • Low T° deposition of nanoparticles with finely controlled properties (size distribution, shape, surface density, environment) • Optimal design of solar cells structures containing nanoparticles

27. Room temperature deposition The NPs can be manipulated NP Size/density not correlated NP synthesis: dedicated nanotechnology NP Source Deposition chamber Turbo pump ~10-3mbar Substrate Water cooling Mass spectrometer Grid +18V ФAr Ar Microbalance Pchamber ~10-5mbar Psource ~10-1mbar

28. NP source exit Nanotechnology facilities @ Cea The NP source has been installed in a commercial Sputtering deposition chamber Substrate holder The source faces the rotating substrate holder compatible with 200mm wafer.

29. + Ar flow - NP size control and density Nanoparticles size range: 2-10 nm • decahedral particle (7 nm) • icosahedral particle (8 nm)

30. Example: small NPs in contact with or inside the active layer NPs integration in real cells: Organic C +5% d2= 4.1010 cm-2 d1= 1.1011 cm-2 The global NP effect is positive

31. Content Introduce CEA/LITEN Nanotechnology for bulk silicon Nanotechnology for thin film PV cells Conclusion

32. Materials and technologies will offer great opportunities LITEN/INES LITEN/INES LITEN/INES LITEN/INES

33. (NL) (UK) (CH) University of Ljubjana (SL) www.eupvclusters.eu Optical modelling Nanotechnology Organic solar cell Nanotechnology a-Si:H solar cell Crucible technology Thank DSSC cell Numerical modelling of full cells DSSC cell Nanocrystal caracterization Expertise on plasmonic systems University of New South Wales (AUS)

34. A bientôt Thankyou www.eupvclusters.eu Thank you for your attention Bertrand FILLON Tel:0033685324833 bertrand.fillon@cea.fr