A Flexible High Performance Sandwich Structured Transparent Conductor Cu(In,Ga)Se2 Solar Cell Applications
Stuart R. Thomas1*, Wen-Chi Tsai1, Cheng-Hung Hsu1, Yu-Cheng Huang1, Jiun-Yi Tseng1, Tsung-Ta Wu1,2, Chia-ho Chang2, Jia-Min Shieh2, Chang-Hong Shen2, Yu-Lun Chueh1
1Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu, Taiwan
2National Nano Device Laboratories, Hsinchu, Taiwan
* presenting author:Stuart Thomas, email:srthomas@my.nthu.edu.tw
Tin-doped indium oxide (ITO) is currently the most commonly chosen transparent conducting oxide (TCO) for use in non-flexible applications; however, its brittleness limits its application on flexible substrates, whilst the scarcity of indium maintains an undesirably high cost for use in solar cell applications. As such, it is important that ITO alternatives are developed with suitably flexible mechanical and electronic properties at reasonable costs. The chalcopyrite absorber, copper indium gallium selenide, Cu(In,Ga)Se2, has a very high absorption coefficient (~104 cm-1), requiring only thin-films (~1 μm) for efficient solar cell fabrication, making it thin enough for flexible applications. However the lack of a high quality flexible TCO has, to date, limited its use in such applications. In this work, we present a new approach for the fabrication of high performance transparent electrodes suitable for flexible CIGS solar cell applications, using a stacked Al-doped ZnO/Ag-nanowire/Al-doped ZnO (AAA) sandwich structure.1 In our AAA electrode the Al-doped ZnO (AZO) layers act as a broad area charge carrier collector and protective encapsulant for the Ag-nanowire network. Concurrently, the Ag-nanowires provide low-resistance, long-range pathways that aid the extraction of charge carriers, but more importantly, they aid in maintaining a low resistivity for our total electrode structure, by maintaining charge transport pathways across cracks that develop in the AZO during repeated strenuous bending. These combined benefits enable us to fabricate CIGS solar cells that are able to maintain 95% of their initial power conversion efficiency, following 1000 bending cycles. In comparison, devices fabricated using equivalent thickness AZO and ITO electrodes are only able to maintain 57 and 5%, respectively, due to crack formation and delamination of the films.

1. W.-C. Tsai, S. R. Thomas, C.-H. Hsu, Y.-C. Huang, J.-Y. Tseng, T.-T. Wu, C.-h. Chang, Z. M. Wang, J.-M. Shieh, C.-H. Shen and Y.-L. Chueh, Journal of Materials Chemistry A, 2016.

Keywords: Solar Cell, CIGSe, Flexible Electrode, Low Cost, Transparent electrode