Band Tail Engineering in Kesterite Cu2ZnSn(S,Se)4 Thin-Film Solar Cells with 11.8% Efficiency

Myeng Gil Gang; Seung Wook Shin; Mahesh P Suryawanshi; Uma V Ghorpade; Zhaoning Song; Jun Sung Jang; Jae Ho Yun; Hyeonsik Cheong; Yanfa Yan; Jin Hyeok Kim

doi:10.1021/acs.jpclett.8b01433

Band Tail Engineering in Kesterite Cu₂ZnSn(S,Se)₄ Thin-Film Solar Cells with 11.8% Efficiency

J Phys Chem Lett. 2018 Aug 16;9(16):4555-4561. doi: 10.1021/acs.jpclett.8b01433. Epub 2018 Jul 31.

Authors

Affiliations

¹ Optoelectronics Convergence Research Center and Department of Materials Science and Engineering , Chonnam National University , 300, Yongbong-Dong , Buk-Gu, Gwangju 61186 , South Korea.
² Department of Physics and Astronomy and Wright Center for Photovoltaic Innovation and Commercialization , University of Toledo , Toledo , Ohio 43606 , United States.
³ Photovoltaic Laboratory , Korea Institute of Energy Research , 71-2, Jang-Dong , Yuesong-Gu, Daejeon 34129 , South Korea.
⁴ Department of Physics , Sogang University , Seoul 121-742 , South Korea.

PMID: 30048140
DOI: 10.1021/acs.jpclett.8b01433

Abstract

Herein, we report a facile process, i.e., controlling the initial chamber pressure during the postdeposition annealing, to effectively lower the band tail states in the synthesized CZTSSe thin films. Through detailed analysis of the external quantum efficiency derivative ( dEQE/ dλ) and low-temperature photoluminescence (LTPL) data, we find that the band tail states are significantly influenced by the initial annealing pressure. After carefully optimizing the deposition processes and device design, we are able to synthesize kesterite CZTSSe thin films with energy differences between inflection of d(EQE)/dλ and LTPL as small as 10 meV. These kesterite CZTSSe thin films enable the fabrication of solar cells with a champion efficiency of 11.8% with a low V_oc deficit of 582 mV. The results suggest that controlling the annealing process is an effective approach to reduce the band tail in kesterite CZTSSe thin films.