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Effect of Indium Doping on Surface Optoelectrical Properties of Cu2ZnSnS4 Photoabsorber and Interfacial/Photovoltaic Performance of Cadmium Free In2S3/Cu2ZnSnS4 Heterojunction Thin Film Solar Cell

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journal contribution
posted on 2016-04-27, 00:00 authored by Feng Jiang, Chigusa Ozaki, Gunawan, Takashi Harada, Zeguo Tang, Takashi Minemoto, Yoshitaro Nose, Shigeru Ikeda
Maximum conversion efficiency of 6.9% was obtained over an electrodeposited Cu2ZnSnS4-based thin film solar cell with a Cd-free In2S3 buffer layer by applying a rapid post-heat treatment to the In2S3/Cu2ZnSnS4 stacked layer. It was found that post-heating of the In2S3/Cu2ZnSnS4 stack promoted an increment of the acceptor density of the Cu2ZnSnS4 layer close to the In2S3–Cu2ZnSnS4 heterointerface of the In2S3/Cu2ZnSnS4 stack. Moreover, the diffusion of In also resulted in a red-shift of the band gap energy of Cu2ZnSnS4 from 1.47 to 1.40 eV. Due to extension of external quantum efficiency response of the solar cell to the long wavelength region, the solar cell based on the post-heated In2S3/Cu2ZnSnS4 stack reached appreciably large short circuit current density of more than 20 mA cm–2. The energy difference between the conduction band minimum of In2S3 and that of Cu2ZnSnS4 at the In2S3/Cu2ZnSnS4 heterointerface was determined to be a slightly positive value of 0.11 eV, indicating formation of a “notch-type” conduction band offset for efficient suppression of the interface recombination.