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

• Published in: The journal of physical chemistry letters Vol. 9; no. 16; pp. 4555 - 4561
• Main Authors: Gang, Myeng Gil, Shin, Seung Wook, Suryawanshi, Mahesh P, Ghorpade, Uma V, Song, Zhaoning, Jang, Jun Sung, Yun, Jae Ho, Cheong, Hyeonsik, Yan, Yanfa, Kim, Jin Hyeok
• Format: Journal Article
• Language: English
• Published: American Chemical Society 16.08.2018
• ISSN: 1948-7185; 1948-7185
• DOI: 10.1021/acs.jpclett.8b01433

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.