Improvement of Photovoltaic Performance of Cu₂ZnSn(S,Se)₄ Solar Cells by Modification of Back Electrode Interface with Amorphous Boron Nitride

Abstract An amorphous boron nitride (aBN) layer is inserted between Cu₂ZnSn(S,Se)₄ (CZTSSe) films and Mo back electrode of CZTSSe solar cell by magnetron sputtering to mitigate the carrier recombination at back interface by tuning energy band alignment and suppressing formation of secondary phases and Mo(S,Se)₂. The effect of the aBN layer on power conversion efficiency (PCE) of CZTSSe solar cell is investigated by numerical simulation and experiment. It is found that PCE is greatly improved via the insertion of suitable thick aBN layer, which is attributed to increased open‐circuit voltage (V_OC) and fill factor (FF). By quantitative analysis, it is deduced that the increased V_OC originates mainly from decrease in reverse saturation current density (J₀), followed by increase in shunt resistance (R_Sh), and the increased FF is mainly due to the decreased J₀, followed by increased R_Sh and decreased photogenerated current density (J_L). By optimizing aBN thickness through tuning sputtering time, the PCE increases from 8.68% of CZTSSe solar cell without the aBN layer to 9.51% of the CZTSSe solar cell with aBN layer. The influence mechanism of the aBN layer on the PCE is suggested by analyzing quantitatively the effect of the aBN layer on J_L and electrical parameters.