Compared
with the traditional Mo back electrode of Cu2ZnSn(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 MoO3 as the interface layer to modify the interface of FTO/(Cu,Ag)2ZnSn(S,Se)4 (CAZTSSe), and systematically investigate
the effects of the thickness of MoO3 interface layer on
the performance of FTO/MoO3/CAZTSSe solar cells. It is
found that the optimal thickness of the solution-deposited MoO3 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%.