In Situ Vanadium Modification Induced a Back Interfacial Field Passivation Effect toward Efficient Kesterite Solar Cells beyond 11% Efficiency

Realization of a high-quality back electrode interface (BEI) with suppressed recombination is crucial for Cu₂ZnSn(S,Se)₄ (CZTSSe) solar cells. To achieve this goal, the construction of a traditional chemical passivation effect has been widely adopted and investigated. However, there is currently a lack of reports concerning the construction of a field passivation effect (FPE) for the BEI. Herein, considering the characteristic of the negligible difference in ionic radius between Mo (0.65 Å) and V (0.64 Å) as well as the presence of one less valence electron compared to Mo, vanadium (V) was employed and in situ incorporated into the MoSe₂ interfacial layer during the deposition of the Mo:V electrode and selenization process. This allowed for the establishment of a desirable in situ VI-FPE interface with p-MoSe₂:V/p-CZTSSe at the BEI. The p-type characteristic in MoSe₂:V is attributed to the presence of the V_Mo acceptor; notably, the Fermi energy level of MoSe₂:V has shifted downward by 0.62 eV compared to MoSe₂, thereby facilitating the formation of an optimized band alignment between MoSe₂:V and the absorber. Consequently, the photovoltaic parameters of the cell-FPE have experienced a significant increase due to the enhanced carrier transportation efficiency compared to cell-ref, resulting in a remarkable improvement in efficiency from 8.28 to 11.11%.