Mechanism for Improving Kesterite Solar Cells Performance via Filed Passivation Effect Induced by V‐Doped MoSe2Interface Layer at Back Interface

One of the key issues impeding the enhancement of power conversion efficiency (PCE) of Cu 2 ZnSn(S,Se) 4 (CZTSSe) solar cells is the severe carrier recombination at CZTSSe/MoSe 2 back interface, primarily arising from the reverse electric field formed between CZTSSe and n‐type MoSe 2 produced after selenization. To inhibit recombination at back interface, herein, the MoSe 2 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 MoSe 2 (MoSe 2 :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‐MoSe 2 to SLG/Mo:V/p + ‐MoSe 2 :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/MoSe 2 :V back contact on device performance is suggested by studying the properties of Mo:V and MoSe 2 :V films and CZTSSe/MoSe 2 :V heterojunction. This work emphasizes the vital significance of the back surface passivation field induced by p + ‐MoSe 2 :V/p‐CZTSSe heterojunction, which is enlightening for optimizing the back contact in kesterite photovoltaics.