Fabrication of High Efficiency Flexible CIGS Solar Cell with ZnO Diffusion Barrier on Stainless Steel Substrate
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Fabrication of High Efficiency Flexible CIGS Solar Cell with ZnO Diffusion Barrier on Stainless Steel Substrate Bae Dowon1ಳ, Kwon Sehan1, Oh Joonjae1, Lee Joowon1, Kim Wookyoung2 LG Innotek Components R&D Center, Solar Cell Lab, Ansan, Republic of Korea 2 Yeungnam Univ., School of Display and Chemical Engineering, Gyeongsan, Republic of Korea 1
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ABSTRACT i-ZnO layers were deposited as diffusion barriers fabricated by RF sputtering on stainless-steel substrates (SUS430, matches with AISI SUS24). It was found that the addition of ZnO layer between stainless-steel substrate and Mo back contact film deplete diffusion of metal ions from substrate and reduce recombination at CIGS layer, as identified by an SIMS depth profile, QE and C-V measurements. With such diffusion barriers, the efficiency, open-circuit voltage, short-circuit current and fill factor of CIGS solar cells all increased, compared to reference cells without diffusion barrier. For the better device performance, Na was supplied during Mo back-contact layer deposition by co-sputtering of the target, including Na-source. Efficiencies of cells were increased with increasing the quantity of Na source. Unlike barrier thickness effect, short circuit current was reduced and open circuit voltage, fill factor were increased with increasing Na-source, and achieved 12.6% efficiency without AR(anti-reflection) coating. The relationship and causality between these results and the Na-doping were analyzed using C-V measurements. INTRODUCTION The copper indium gallium diselenide (CIGS) thin-film solar cell recently reached 20.3 percent efficiency [1], setting a new world record for this type of cell. This record is almost same level to efficiency of multicrystalline silicon-based solar cells. CIGS cells use extremely thin layers of semiconductor material applied to a low-cost backing such as glass, flexible metallic foils, high-temperature polymers or stainless steel sheets. Not only efficiency and its flexibility due to the thin absorber, but also a variety of other benefits such as high specific power and aesthetic attractive design, provide a promising path for more affordable solar cells for residential and other uses. The concept of flexible CIGS based modules on the stainless steel is now accepted as a common idea in the flexible PV industry. Proven high efficiencies of up to Ș AM1.5=17.5% [2], very high stability against proton and electron radiation [3], potentially light weight, and high specific power as a result, high flexibility seem to fulfill even the desires of demanding customers such as space and transport industries. Moreover, in virtue of its outstanding application property without reference to flections of surface, the enlargement of the application area into BIPV(Building Integrated PV) is also expected. However, despite of these advantages, the most critical subjects are lack of sodium source and the diffusion of detrimental substrate elements, such as Fe, Ni and etc. into the CIGS layer due to the high temp
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