Sheng-Kuei Chiu, Ya-Chiu Tsai2, Chia-Chun Wu2, Chien-Jen Tang2
1National University of Tainan, Taiwan, Taiwan
2Feng Chia University, Taichung City, Taiwan
CIGS solar cell is one of the most promising candidates for future photovoltaic applications because it is a material with a direct band gap, high absorption coefficient, tunable band gap, and high material stability. In this study, CIGS thin films were deposited by magnetron sputtering from two quaternary targets with the composition of Cu-poor and Cu-rich targets. As-deposited thin films were selenized by a rapid thermal annealing process to improve the quality of absorber layers. We investigated the influence of post-annealing temperature and post-annealing time on material composition, crystalline structure, raman spectrum, and microstructure. We observed when CIGS film was annealed at 500°C and for 30 minutes, it had better crystallization and less second phase. The study also used chemical bath deposition (CBD) and magnetron sputtering to produce buffer layers and analyzed optical properties and microstructure. Solar cell structures, from top to bottom, were stacked by Ag (Sputtering, 300 nm), AZO (Sputtering, 400 nm), i-ZnO (Sputtering, 50 nm), CdS (Sputtering or CBD, 50 nm), CIGS (Sputtering, 1500 nm~2000 nm), Mo (Sputtering, 1000 nm) and SLG. The measured highest conversion efficiency of the CIGS solar cell is 4.6 % with an open voltage of 412.5 mV, short circuit current density of 19.14 mA⁄cm2, and fill factor of 57.75 % by Cu-poor target. Solar cells fabricated by Cu-rich target showed a conversion efficiency of 0.7 % with an open voltage of 315 mV, short circuit current density of 6.09 mA/cm2, and fill factor of 34.86 %. Solar cell efficiency can be improved by adjusting the ratio of the quaternary-alloy target.