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

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 (NH3H2O) 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 cm(2)) without the MgF2 anti-reflection layer.