Differential effects of MoO3 and MoO2 sacrificial layers on the J–V performance of Cu2ZnSn(S,Se)4 solar cells

Abstract

An over-thick MoSe₂ layer and numerous voids at the absorbing layer inside and backside lead to a relatively low J_sc and PCE of CZTSSe solar cells. In previous studies, MoO₂ and MoO₃ sacrificial layers have been commonly used to eliminate those voids and reduce the thickness of MoSe₂ layers. However, there is still no clarity about which one is more effective. In this work, we prepared MoO₂ and MoO₃ sacrificial layers on the surface of Mo-coated SLG substrates by air annealing and ammonia (NH₃·H₂O) etching, respectively. J–V testing shows that both MoO₂ and MoO₃ can effectively improve the J_sc and PCE of CZTSSe solar cells, wherein MoO₃ is more effective. Comparative analysis shows that the electrical mechanism of J_sc and PCE improvement lies in the significant reduction of device series resistance (R_s). SEM images and XRD pattern results indicate that the reason for R_s decreasing is void elimination and MoSe₂ layer thickness reduction from 600 nm to 270 nm after applying MoO₃. With the aid of the MoO₃ sacrificial layer, the PCE of the CZTSSe device increases from 7.51% to 9.58% (total area 0.21 cm²) without the MgF₂ anti-reflection layer.