Band offsets engineering at Cd_xZn_1-xS/Cu₂ZnSnS₄ heterointerface

Cd_1-xZn_xS/Cu₂ZnSnS₄ (CZTS)-based thin film solar cells usually use CdS as a buffer layer, but due to its smaller band gap (2.4 eV), CdS film has been replaced with higher band gap materials. The cadmium zinc sulfide (CdZnS) ternary compound has a higher band gap than other compounds, which leads to a decrease in window absorption loss. In this paper, the band offsets at Cd_1-xZn_xS/Cu₂ZnSnS₄ (CZTS) heterointerface are calculated by the first-principles, density-functional and pseudopotential method. The band offsets at Cd_1-xZn_xS/CZTS heterointerface are tuned by controlling the composition of Zn in Cd_1-xZn_xS alloy, the calculated valence band offsets are small, which is consistent with the common-anion rule. The favorable heterointerface of type-I with a moderate barrier height (<0.3 eV) can be obtained by controlling the composition of Zn in Cd_1-xZn_xS alloy between 0.25 and 0.375.