Solution-Deposited MoO₃ Interface Layer for High-Performance Bifacial Kesterite Thin Film Solar Cell

Compared with the traditional Mo back electrode of Cu 2 ZnSn(S,Se) 4 (CZTSSe) solar cells, the transparent and conductive electrode of fluorine-doped tin oxide (FTO) has the advantages of low lattice mismatch with the CZTSSe absorber, earth-abundant composition, transparency, and advanced applications in building integrated photovoltaics. Hence, the research of bifacial FTO/CZTSSe thin film solar cells has attracted more and more attention. However, the poor interface contact between n-type FTO/p-type CZTSSe prevents the improvement of power conversion efficiency (PCE) of CZTSSe thin film solar cells deposited on the FTO substrate. Therefore, back contact interface modification is an effective strategy to promote the performance of the FTO/CZTSSe solar cells. Here, we choose the solution-processed MoO 3 as the interface layer to modify the interface of FTO/(Cu,Ag) 2 ZnSn(S,Se) 4 (CAZTSSe), and systematically investigate the effects of the thickness of MoO 3 interface layer on the performance of FTO/MoO 3 /CAZTSSe solar cells. It is found that the optimal thickness of the solution-deposited MoO 3 interface layer is 30 nm. As a result, kesterite solar cells on the FTO substrate achieve a front-side PCE of 9.49 % and a rear-side PCE of 1.04%.