Cu2ZnSn(S, Se)4 solar cell with slight band tailing states achieves 11.83% efficiency by selenizing sputtered Cu–Zn–Sn–S precursor

The large band tailing states are believed to be a key challenge resulting in large deficit of open-circuit voltage and limit the performances of promising Cu2ZnSn(S,Se)4 (CZTSSe) solar cells. In the study, an effective process is proposed to alleviate the harmful effects of band tailing states and fabricate high performance CZTSSe devices. Cu2ZnSnS4 (CZTS) precursors are sputtered by a CZTS quaternary target and then annealed under a H2Se-containing atmosphere at different temperatures. The phase transformation and grain growth of CZTSSe absorbers in selenization process is illustrated. At the annealing temperature of 500 °C, the best performance device with the efficiency of 11.83% is achieved. The excellent back contact interface and the slight band tailing effect of the champion device are demonstrated by the temperature-dependent J-V and external quantum efficiency (EQE) measurement. The photoluminescence (PL) spectrum illustrates that the donor–acceptor pair formed by charged defects is the dominant reason of band tailing effect.