Mechanism for Improving Kesterite Solar Cells Performance via Filed Passivation Effect Induced by V-Doped MoSe₂ Interface Layer at Back Interface

One of the key issues impeding the enhancement of power conversion efficiency (PCE) of Cu2ZnSn(S,Se)(4) (CZTSSe) solar cells is the severe carrier recombination at CZTSSe/MoSe2 back interface, primarily arising from the reverse electric field formed between CZTSSe and n-type MoSe2 produced after selenization. To inhibit recombination at back interface, herein, the MoSe2 layer is converted from n-type to p-type by V doping in site through reaction of V-alloyed Mo (Mo:V) back electrode with Se during selenization, and CZTSSe solar cells with p(+)-type V-doped MoSe2 (MoSe2:V) interface layer are fabricated. It is found that the PCE of the device rises from 8.34% to 9.63% as back contact changes from soda lime glass (SLG)/Mo/n-MoSe2 to SLG/Mo:V/p(+)-MoSe2:V. The quantitative analysis demonstrates that the increased PCE predominantly originated from the decreased reverse saturated current density (J(0)), followed by the decreased series resistance (R-S), and lastly by the increased photogenerated current density (J(L)). The influence mechanism of the SLG/Mo:V/MoSe2:V back contact on device performance is suggested by studying the properties of Mo:V and MoSe2:V films and CZTSSe/MoSe2:V heterojunction. This work emphasizes the vital significance of the back surface passivation field induced by p(+)-MoSe2:V/p-CZTSSe heterojunction, which is enlightening for optimizing the back contact in kesterite photovoltaics.