The effect of Rb doping on CZTSSe solar cells

Alkali metal doping is a promising method to enhance the performance of Cu2ZnSn(Se,S)4 (CZTSSe) solar cells due to its excellent effect on Cu(In,Ga)Se2 (CIGS) solar cells. In this work, rubidium (Rb) was doped in CZTSSe absorbers by sputtering Rb doped Cu2ZnSnS4 (CZTS) target with subsequent H2Se contained annealing. By this method, Na concentration in absorber was not decreased due to Rb doping. On the contrary, Na concentration was enhanced by 2.5 times in the absorber by Rb doping. Rb doping can also suppress the aggregation of Zn at CZTSSe/Mo interface and the formation of ZnSe, which result in the decrease of series resistance of solar cells. Eventually, the conversion efficiency of CZTSSe solar cells can be increased by Rb doping to 8.41%, which was accompanied by the increase of VOC, JSC and FF as well.