The effect of band offsets of buffer layers on CZTS for improvement of thin film solar cell performance

The development of kesterite CZTS-based solar cells is limited due to low open-circuit voltage and efficiency. The Conduction Band Offset between the p-type CZTS absorber layer and the n-type buffer layer is an influential factor in the performance of these devices. A wide range of n-type materials including CdS, ZnO, ZnS, Zn(O,S), (Mg,Zn)O, SnS2 and TiO2 were investigated as buffer layers in order to attain a better performance in CZTS thin-film solar cells. Some of these materials are identified as negative conduction band offset and some are categorized as positive conduction band offset. The simulations showed that the optimal conduction band offset for the proper performance of CZTS solar cells would be +/- 0.4 eV. Moreover, using SnS2, Mg0.2Zn0.8O, ZnO0.80S0.20, and ZnO0.55S0.45 semiconductors led to an efficiency of over 13 percent and applying Mg0.1Zn0.9O and ZnO(0.4)0S(0.60) led to an open-circuit voltage of over 0.7 V.