A study on Cr incorporation to enhance performance of CZTSSe solar cells via optimizing selenization condition

•A new method to improve Voc and PCE of CZTSSe solar cell by Cr doping is put forward.•This is the first report on the effect of post-selenization on CCZTSSe solar cell.•The effect of selenization condition on PCE is ascribed to change of VOC and FF.•CuZn and 2CuZn + SnZn defects were inhibited by optimizing selenization condition.•This study shows hopeful character of Cr in increasing the PCE of CZTSSe solar cell.