銅銦鎵硒CuIn1-XGaXSe2薄膜太陽能電池被認為是未來在太陽能產業上最具有潛力的材料之一，將CIGS薄膜太陽能電池鍍在可撓式基板開創了太陽能電池新的應用。本研究在軟性不銹鋼基板上藉由四元靶與鎵硒靶的共濺鍍開發一階濺鍍製程而不用任何額外的硒供應。在將來可搭配大面積的Roll-to-roll製程將能夠大幅的降低製程成本。

為了在可撓式不銹鋼基板上達到高效率的太陽能電池，需要鍍製擴散阻擋層去抑制來鐵元素從基板擴散至CIGS吸收層內，鐵元素若擴散至CIGS吸收層裡面，將會在CIGS吸收層內產生深層的缺陷並對效率造成影響。我們鍍製1um的鉻當擴散阻擋層，阻擋了來自不銹鋼基板的鐵元素並改善了不銹鋼基板的粗糙度。接著在鍍製CIGS吸收層之前，為了解決不銹鋼基板沒有來自基板的鈉來源，我們濺鍍氟化納靶材提供鈉來源。CIGS的薄膜製作是以一階段共濺鍍四元靶和鎵硒二元靶的方式而成，利用共濺鍍鎵硒二元靶可以在製程中創造出鎵的正向梯度，將幫助載子的收集。我們將探討鈉元素含量對於CIGS薄膜的電性、鎵的梯度、結構特性、元件表現上的影響。

在製程溫度600℃下，得到最好的元件轉換效率為9.15%。然而過高的工作溫度將會導致薄膜內的硒元素不足，因此限制了元件表現.從PL分析發現藉由在後退火中濺鍍硒靶補充硒元素，可有效的消除硒不足造成的缺陷以及提升薄膜品質，藉由調控適合的製程溫度以減少硒損失，在製程溫度550℃下元件轉換效率可從9.15%提升至11.25%，無須額外的硒供給。

uIn1-XGaXSe2 (CIGS) thin-film solar cell is considered to be one of the most promising material in the future of the solar industry due to its high performance and low-cost commercial production. The CIGS thin film solar cells deposited on the flexible substrate to offer a new type of solar cell applications. In this study, we developed a one-step sputtering process by co-sputtering quaternary target and Ga2Se3 binary target without extra selenium supply on the stainless steel flexible substrate. This kind of process will be scaled up by roll-to-roll deposition process to reduce the production cost significantly.

To reach highly efficient solar cells on the stainless steel flexible substrate，deposition of diffusion barrier is needed to suppress iron diffusion form substrate into CIGS absorber layer . If iron diffuses into the CIGS absorber layer, it will create a deep-defect in the CIGS absorber layer and detriment to efficiency. We deposited 1um Chromium (Cr) acts as a diffusion barrier to block iron from stainless steel substrate and improve the roughness of stainless steel substrate. In order to solve stainless steel substrate without extra sodium form substrate, we sputter sodium fluoride target to supply sodium source before depositing CIGS absorber layer.
The fabrication of CIGS thin film is made by co-sputtering quaternary target and Ga2Se3 binary target in one-step sputtering process. Usage of Ga2Se3 binary target will create normal Ga-grading profile during the deposition which help carriers be collected. We will discuss the impact of sodium content of the CIGS thin film for the electrical property, Ga-grading profile, structural characteristics and device performance.

The conversion efficiency can achieve 9.15% at 600℃.However, higher working temperature will make Se element loss in the CIGS thin films, which limit the device performance. From PL analysis, with Se supply in annealing process can remove Se-like defect transition and enhance film quality. By adjusting the temperature to reduce selenium deficiency, the conversion efficiency can be improved from 9.15% to 11.25% at 550℃without extra Se supply.

參考文獻
1. Philip Jackson*, D.H., Roland Wuerz, Oliver Kiowski, Andreas Bauer, Theresa Magorian Friedlmeier andMichael Powalla, Properties of Cu(In,Ga)Se2 solar cells with new record efficiencies up to 21.7%. Phys. Status Solidi RRL 2015. 9(1): p. 28-31.
2. Chirilă, A., et al., Potassium-induced surface modification of Cu(In,Ga)Se2 thin films for high-efficiency solar cells. Nat Mater, 2013. 12(12): p. 1107-1111.
3. Goetzberger, A., C. Hebling, and H.-W. Schock, Photovoltaic materials, history, status and outlook. Materials Science and Engineering: R: Reports, 2003. 40(1): p. 1-46.
4. Wei, S.-H., S.B. Zhang, and A. Zunger, Effects of Ga addition to CuInSe2 on its electronic, structural, and defect properties. Applied Physics Letters, 1998. 72(24): p. 3199-3201.
5. Paul Ramesh, P., et al., Photovoltaic performance of p-AgInSe2/n-CdS thin film heterojunctions. Materials Letters, 1998. 34(3–6): p. 217-221.
6. Zhou, L., S. Wu, and J. Yu, Study on the thin films of Cu(In1 − x,Alx) Se2 prepared by selenization process. Surface and Coatings Technology, 2013. 228, Supplement 1: p. S214-S218.
7. M. Bär, L.W., and C. Heske, Chemical structures of the Cu(In,Ga)Se2 ÕMo and Cu(In,Ga)(S,Se)2 ÕMo interfaces. PHYSICAL REVIEW B, 2008. 78(075404).
8. Hamda A. AI-Thani', F.S.H., Man Young, Sally Asher, Jeff L. Alleman,Mowafak M. Al-Jassim. and Don L. Williamson' The Effect of MO Back Contact on Na Out-Diffusion and Device Performance of MolCu(ln,Ga)WCdSRnO Solar Cells Photovoltaic Specialists Conference, 2002. Conference Record of the Twenty-Ninth IEEE, 2002: p. 720-723.
9. V. Albertsa, J.T., R.W. Birkmireb, Material and device properties of single-phase Cu(In,Ga)(Se,S)2 alloys prepared by selenization/sulfurization of metallic alloys. Thin Solid Films, 2004. 451-452: p. 207-211.
10. B.M. Basol, M.P., S. Aksu, J. Wang, Y. Matus, T. Johnson, Y. Han, M. Narasimhan, B. Metin, Electroplating Based CIGS Technology for Roll-to-Roll Manufacturing European Photovoltaic Solar Energy Conference and Exhibition (EU PVSEC) 2008: p. 2137 - 2141.
11. Gregory Brown1+, P.S., Jacob Woodruff1, B.C. , and a.D. Jackrel1, Device Characteristics of a 17.1% Efficient Solar Cell Deposited by a Non-Vacuum Printing Method on Flexible Foil 38th IEEE Photovoltaic Specialists Conference (PVSC), IEEE, 2012: p. 003230–003233.
12. Teodor K. Todorov, et al., Solution-processed Cu(In,Ga)(S,Se)2 absorber yielding a 15.2% efficient solar cell. PROGRESS IN PHOTOVOLTAICS, 2012. 21(1): p. 82–87.
13. T. Klinkert, M.J., F. Donsanti, D. Lincot, and J.-F. Guillemoles, Ga gradients in Cu(In,Ga)Se2: Formation, characterization, and consequences. Journal of Renewable and Sustainable Energy, 2014.
14. Gabor, A.M., G. Nat. Renewable Energy Lab., CO, USA , and J.R.T.A.S.A.L.T.M.A.C.R. Noufi, Band-gap engineering in Cu(In,Ga)Se2 thin films grown from (In,Ga)2Se3 precursors. Photovoltaic Energy Conversion, 1994., Conference Record of the Twenty Fourth. IEEE Photovoltaic Specialists Conference - 1994, 1994 IEEE First World Conference on 1: p. 83 - 86.
15. Bülent M. Başol1, V.K.K., Arvind Halani1, Craig R. Leidholm1, Jon Sharp2, James R. Sites2, Amy Swartzlander3, Richard Matson3 and Harin Ullal3, Cu (In,Ga)Se2 thin films and solar cells prepared by selenization of metallic precursors. Journal of Vacuum Science & Technology A, 1996. 14.
16. N. Naghavi , D.A.-R., N. Allsop , N. Barreau , S. Bücheler ,, et al., Buffer layers and transparent conducting oxides for chalcopyrite Cu(In,Ga)(S,Se)2 based thin film photovoltaics: Present status and current developments. Progress in Photovoltaics Research and Applications, 2010: p. 411-433.
17. Patrick Reinhard, A.C.a., Patrick Bl¨osch, Fabian Pianezzi, Shiro Nishiwaki, Stephan Buecheler, and a.A.N. Tiwari, Review of Progress Toward 20% Efficiency Flexible CIGS Solar Cells and Manufacturing Issues of Solar Modules. IEEE JOURNAL OF PHOTOVOLTAICS, 2013. 3.
18. Tobias Eisenbarth1, R.C., 3, Christian A. Kaufmann1, Axel Eicke2 and and T. Unold1, Influence of iron on defect concentrations and device performance for Cu(In,Ga)Se2 solar cells on stainless steel substrates. PROGRESS IN PHOTOVOLTAICS, 2012: p. 568-574.
19. Reinhard, P., et al. High efficiency flexible Cu(In,Ga)Se<inf>2</inf> solar cells. in Active-Matrix Flatpanel Displays and Devices (AM-FPD), 2013 Twentieth International Workshop on. 2013.
20. Başol, B.M., et al., Copper indium diselenide thin film solar cells fabricated on flexible foil substrates. Solar Energy Materials and Solar Cells, 1993. 29(2): p. 163-173.
21. Hartmann, M., et al. Flexible and light weight substrates for Cu(In,Ga)Se₂ solar cells and modules. in Photovoltaic Specialists Conference, 2000. Conference Record of the Twenty-Eighth IEEE. 2000.
22. Kapur, V.K., et al. Non-vacuum processing of CIGS solar cells on flexible polymeric substrates. in Photovoltaic Energy Conversion, 2003. Proceedings of 3rd World Conference on. 2003.
23. Niki, S., et al., CIGS absorbers and processes. Progress in Photovoltaics: Research and Applications, 2010. 18(6): p. 453-466.
24. Nanosolar Achieves 17.1% Aperture Efficiency Through Printed CIGS Process. [cited 2011; Available from: http://www.marketwired.com/press-release/nanosolar-achieves-171-aperture-efficiency-through-printed-cigs-process-1569273.htm.
25. Pianezzi, F., et al., Electronic properties of Cu(In,Ga)Se2 solar cells on stainless steel foils without diffusion barrier. Progress in Photovoltaics: Research and Applications, 2012. 20(3): p. 253-259.
26. Ishizuka, S., et al., Alkali incorporation control in Cu(In,Ga)Se2 thin films using silicate thin layers and applications in enhancing flexible solar cell efficiency. Applied Physics Letters, 2008. 93(12): p. 124105.
27. Abou-Elfotouh, F., D.J. Dunlavy, and T.J. Coutts, Intrinsic defect states in CuInSe2 single crystals. Solar Cells, 1989. 27(1–4): p. 237-246.
28. Zhang, S.B., et al., Defect physics of the ${\mathrm{CuInSe}}_{2}$ chalcopyrite semiconductor. Physical Review B, 1998. 57(16): p. 9642-9656.
29. Schmid, D., et al., Chalcopyrite/defect chalcopyrite heterojunctions on the basis of CuInSe2. Journal of Applied Physics, 1993. 73(6): p. 2902-2909.
30. Persson, C., et al., $n$-type doping of $\mathrm{CuIn}{\mathrm{Se}}_{2}$ and $\mathrm{CuGa}{\mathrm{Se}}_{2}$. Physical Review B, 2005. 72(3): p. 035211.
31. Hashimoto, Y., et al., Solar cell. 2003, Google Patents.
32. Gloeckler, M. and J.R. Sites, Efficiency limitations for wide-band-gap chalcopyrite solar cells. Thin Solid Films, 2005. 480–481: p. 241-245.
33. Siebentritt, S., Wide gap chalcopyrites: material properties and solar cells. Thin Solid Films, 2002. 403–404: p. 1-8.
34. Wada, T., et al., Characterization of the Cu(In,Ga)Se2/Mo interface in CIGS solar cells. Thin Solid Films, 2001. 387(1–2): p. 118-122.
35. Granata, J.E., et al. Quantitative incorporation of sodium in CuInSe₂ and Cu(In,Ga)Se₂ photovoltaic devices. in Photovoltaic Specialists Conference, 1997., Conference Record of the Twenty-Sixth IEEE. 1997.
36. Wei, S.-H., S.B. Zhang, and A. Zunger, Effects of Na on the electrical and structural properties of CuInSe2. Journal of Applied Physics, 1999. 85(10): p. 7214-7218.
37. Kronik, L., D. Cahen, and H.W. Schock, Effects of Sodium on Polycrystalline Cu(In,Ga)Se2 and Its Solar Cell Performance. Advanced Materials, 1998. 10(1): p. 31-36.
38. Gloeckler, M., Device Physics of Cu(In, Ga)Se2 Thin-film Solar Cells. 2005: Colorado State University.
39. Blösch, P., et al., Diffusion barrier properties of molybdenum back contacts for Cu(In,Ga)Se2 solar cells on stainless steel foils. Journal of Applied Physics, 2013. 113(5): p. 054506.
40. Braunger, D., et al., Influence of sodium on the growth of polycrystalline Cu(In,Ga)Se2 thin films. Thin Solid Films, 2000. 361–362: p. 161-166.
41. Blösch, P., et al., Sodium-doped molybdenum back contacts for flexible Cu(In,Ga)Se2 solar cells. Thin Solid Films, 2013. 535: p. 214-219.
42. Jackson, P., et al., Properties of Cu(In,Ga)Se2 solar cells with new record efficiencies up to 21.7%. physica status solidi (RRL) – Rapid Research Letters, 2015. 9(1): p. 28-31.
43. Contreras, M.A., et al., Se activity and its effect on Cu(In,Ga)Se2 photovoltaic thin films. physica status solidi (a), 2009. 206(5): p. 1042-1048.