Cd-Free Cu(In,Ga)(Se,S)2 Thin-Film Solar Cell With Record Efficiency of 23.35%

By Motoshi Nakamura, K. Yamaguchi, Y. Kimoto, Y. Yasaki, T. Kato, H. Sugimoto. IEEE Journal of Photovoltaics, 2019

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In this article, the excellent properties of state-of-the-art Cd-free Cu(In,Ga)(Se,S)₂ (CIGSSe) solar cells with Zn(O,S,OH)<italic>_x</italic>/Zn_0.8Mg_0.2O double buffer layers, deposited by a combination of chemical bath deposition and atomic layer deposition techniques, are presented. By the replacement of conventional CdS buffer layers with this double buffer layer, the open-circuit voltage (<italic>V</italic>_oc) deficit of the devices could be significantly reduced, and <italic>V</italic>_oc increased by approximately 15 mV. In addition, the fill factor and short-circuit current were also improved, increasing the device efficiency by approximately 0.5 absolute percent compared with devices with CdS buffers. The Cd-free double buffer layer improved the device efficiency regardless of the bandgap of the CIGSSe absorber. The minority carrier lifetime (<italic>τ</italic>) measured via time-resolved photoluminescence became longer, indicating that carrier recombination is mitigated using the double buffer layer. Based on the device parameters extracted by fitting the Suns–<italic>V</italic>_oc characteristics to the double-diode model, the longer <italic>τ</italic> could be attributed to the decreased recombination rate in the space-charge region, rather than in the bulk and at the interface. The best performing cell was evaluated by a reliable third party, the National Institute of Advanced Industrial Science and Technology; this cell achieved a new world record efficiency of 23.35% for 1-cm²-sized thin-film polycrystalline solar cells. The device parameters of this cell are also discussed in this article.

Subfields: Electrical and Electronic Engineering, Materials Chemistry

View Paper: https://www.semanticscholar.org/paper/3a44c2fd106b0e30499922b26e4c1ddbb18cb986