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CIGS solar cell by selenization : Toward low-cost and high-efficiency device

CIGS solar cell by selenization : Toward low-cost and high-efficiency device. Prog . Photovolt : Res. Appl. 2009; 17:320–326. CIGS – high efficiency thin-film solar cell. Solar Energy Materials and Solar Cells Article in Press. Processing area – CIGS vs. CdTe. CIGS – Co-evaporation

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CIGS solar cell by selenization : Toward low-cost and high-efficiency device

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  1. CIGS solar cell by selenization: Toward low-cost and high-efficiency device

  2. Prog. Photovolt: Res. Appl. 2009; 17:320–326 CIGS – high efficiency thin-film solar cell

  3. Solar Energy Materials and Solar CellsArticle in Press Processing area – CIGS vs. CdTe CIGS – Co-evaporation → Small area CdTe – Close-spaced sublimation → Large area

  4. Solar EnergyVolume 77, Issue 6, December 2004, Pages 757-765 Prog. Photovolt: Res. Appl. 2009; 17:320–326 Large area process – Selenization (Shell Solar GmbH)

  5. Solar EnergyVolume 77, Issue 6, December 2004, Pages 757-765 Solar Energy Materials and Solar CellsVolume 93, Issue 8, August 2009, Pages 1318-1320 CIGS solar cell by Selenization - Low efficiency (CIGSS cell, Showa Shell Sekiyu K.K.) (Shell Solar GmbH)

  6. Prog. Photovolt: Res. Appl. 2008; 16:235–239 Gallium concentration in co-evaporated CIGS

  7. JOURNAL OF MATERIALS SCIENCE 7 (1972) 14-18 Precursor stacking and Ga concentration Se In Cu0.78Ga0.22 Mo Glass Using of CuGa precursor layer – prevents eutectic reaction of In and Ga ※ Gallium in CIGS/Mo interface – Improve adhesion and increase grain size

  8. Appl. Phys. A 88, 653–656 (2007) Precursor stacking and Ga concentration (a) CuGa-rich surface precursor stack Cu0.25Ga0.75 (high Ga) In Cu0.67Ga0.33 (low Ga) Cu0.25Ga0.75 (high Ga) Glass (b) In-rich surface precursor stack In Cu0.67Ga0.33 (low Ga) Cu0.25Ga0.75 (high Ga) Glass

  9. Thin Solid FilmsVolumes 451-452, 22 March 2004, Pages 544-551 Precursor stacking and Ga concentration Alternating precursor stack In Cu0.85Ga0.15 In Cu0.85Ga0.15 In Cu0.85Ga0.15 In Cu0.85Ga0.15 In Cu0.85Ga0.15 Mo Glass

  10. Photovoltaic Specialists Conference, 1993., Conference Record of the Twenty Third IEEE521-526 Precursor stacking and Ga concentration (a) Cu/In/Ga precursor stack Ga In Cu Mo Glass (b) Ga/Cu/In precursor stack In Cu Ga Mo Glass ※ Larger grain size: Ga/Cu/In stack

  11. CIGSS solar cell Se S In Cu(In,Ga)Se Cu(In,Ga)(S,Se) Cu0.78Ga0.22 Mo Mo Mo Glass Glass Glass • Increased bandgap and VOC

  12. Ga diffusion to bottom Ga diffusion by : Residual stress in Mo Residual stress in Mo Residual stress and small size of the Gaatom Residual stress by volume expansion Preferential reaction of In-Se Reference 1) 2) 3) 4) 5) References 1) MATERIALS RESEARCH SOCIETY SYMPOSIUM PROCEEDINGS, 2005 2) Photovoltaic Specialists Conference, 1996., Conference Record of the Twenty Fifth IEEE, 897-900 3) Solar Energy Materials and Solar Cells, Volume 90, Issue 15, 2181-2190 4) Solar Energy Materials and Solar Cells 41/42 (1996) 271-279 5) Thin Solid FilmsVolume 474, Issues 1-2, 1 March 2005, Pages 70-76 Stress can be induced by: Residual stress in Mo Difference in thermal expansion coefficient Volume expansion during selenization

  13. Journal of Physics and Chemistry of SolidsVolume 64, Issues 9-10, September 2003, Pages 1499-1504 Diffusion of In and Ga • Vacancy diffusion • Diffusion in the grain boundaries is not significantly higher than inside the grains • In has a similar diffusivity in CGS as Ga in CIS. • Diffusion is higher in sodium-free films, possibly due to increased vacancy concentration • Indium and gallium diffusion more favorable VGa and VIn in the Cu-rich films (b) CuInSe/CuGaSe stack (a) CuGaSe/CuInSe stack CuInSe CuInSe CuGaSe CuGaSe Mo Mo Glass Glass ※ Atomic/Ionic radius of In and Ga In : 167pm In3+ : 94pm ※ CIS and CIGS Deposition by Co-evaporation Substrate temperature 510℃ No post-annealing Ga: 135pm Ga3+ : 76pm

  14. Thin Solid FilmsVolume 260, Issue 1, 1 May 1995, Pages 26-31 Table 3. Room temperature thermal expansion coefficients α for the constituent materials in the cell Stress originates from… Material Cd(Zn)S CuInSe, average Mo Corning 7509 Soda-Lime α ( x 10-6℃-1) 3.6 8.2 5.1 4.6 9.2 Reference Thermophysical Properties of Matter, Vol. 13, IFI Plenum Sol. Cells, 16 (1986) 399 22 Metals ReJerence Book, Plenum Corning Bulletin. Lange's Handbook of Chemistry Residual stress in Mo? Then, why there is no Ga segregation in co-evaporated CIGS? Stress originates from… Thermal expansion coefficient difference?

  15. J. Appl. Phys., Vol. 55, No. 4, 909 (1984) Stress originates from… • Volume expansion by selenization? • Volume expansion >100% by selenization • In the direction perpendicular to the interface, the selenide being free • In-plane ~35% linear expansion will be difficult. The interface will be subjected to a plane stress. Selenide • In-plane compressive stress • Decreased cation vacancy concentration • Diffusion of Ga toward bottom Precursors Mo Glass

  16. Thin Solid FilmsVolume 474, Issues 1-2, 1 March 2005, Pages 70-76 Selenization without Mo In Cu Ga In Glass ※ Selenized by elemental Se in closed-space

  17. Solar Energy Materials and Solar CellsVolume 89, Issues 2-3, 15 November 2005, Pages 129-137 Thin Solid FilmsVolume 515, Issue 15, 31 May 2007, Pages 5848-5851 Selenization without Mo and with N2 gas Cu-In-Ga Alloy Glass ※ 2-stage Selenized in Se,S/N2 Cu-In-Ga Alloy Glass ※ 2-stage Selenized in Se/N2

  18. Thin Solid FilmsVolume 474, Issues 1-2, 1 March 2005, Pages 70-76 Selenization with compound precursor

  19. Solar Energy Materials and Solar CellsVolume 93, Issue 8, August 2009, Pages 1318-1320 Selenization followed by sulfurization • Gadiffusion toward surface is dependent on the “sulfurization degree” • Increased surface Ga concentration by higher “sulfurization degree” • Decreased thickness of a small grain region • Higher Gaconcentration tended to form thinner grain region

  20. Photovoltaic Energy Conversion, Conference Record of the 2006 IEEE 4th World Conference on(2006) 560-563 Selenization followed by sulfurization In Cu0.8Ga0.2 Mo Glass

  21. Selenization followed by sulfurization • No Gadiffusion toward bottom interface after 10 min. selenization • Can achieve uniform Ga concentration after post-sulfurization • Looks like In-Gainterdiffusion is dominated over stress-induced diffusion In Cu0.78Ga0.22 Mo Glass ※ 400℃, DESe, 10min.

  22. To elucidate mechanism of Ga diffusion… a) Additional selenium reservoir at bottom b) Transfer and back-side selenization Ex) Se Se In In Cu0.78Ga0.22 Cu0.78Ga0.22 Mo Flip & Transfer Se Mo Se Glass Cu0.78Ga0.22 In

  23. Final goal: Homogeneous composition by one-step selenization with simple precursor stack In CIGS Cu0.78Ga0.22 Mo Mo Glass Glass

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