Defect engineering enabling p-type Mo(S,Se)2:TM (TM = V, Nb, Ta) towards high-efficiency kesterite solar cells

[Display omitted] •A back surface field enhancement architecture is established in kesterite solar cells.•The hole doping of Mo(S,Se)2 is realized by in-situ dopant with group VB elements.•Group VB elements doping further increase the work function and hole concentration.•The ohmic contact accelerates the holes extraction and minimizes recombination loss. One important issue limiting the development of Cu2ZnSn(S,Se)4 (CZTSSe) solar cells is the severe recombination loss at CZTSSe/Mo(S,Se)2/Mo back contact, primarily arising from the non-matched potential barrier and inferior electric contact between absorber and weak n-type Mo(S,Se)2 interfacial layer. It is expected that a p-type Mo(S,Se)2 can effectively improve the hole extraction and enhance the device performance. In this work, we propose a plausible direction to build up an electrically benign back surface field by in-situ doping Mo(S,Se)2 with group VB elements (TM = V, Nb and Ta). It is turned out that the generated VMo, NbMo, or TaMo shallow acceptors could convert Mo(S,Se)2 from weak n-type to p-type conductivity and increase its work function (WF) and hole concentration. With the contact of p-type absorber (WF,absorber