Boost Open-Circuit Voltage of Cu2znsn(S,Se)4 Solar Cell by Cd/Nh3 Soaking

In this paper, we reported the boost of open-circuit voltages (VOC) of Cu2ZnSn(S,Se)4 (CZTSSe) solar cells by soaking the CZTSSe films in Cd/NH3 solutions before the deposition of buffer layers. The effects of the Cd/NH3 soaking on the properties of CZTSSe solar cells were investigated in depth. We found the Cd/NH3 soaking can promote the downward band bending of CZTSSe in the surface region of the film. Except that, the Cd/NH3 soaking can eliminate the deep level acceptor in CZTSSe which may cause the Fermi-level pinning at the absorber/buffer interface. Besides, the Cd/NH3 soaking can decrease the density of the defects at the absorber/buffer interface. The combination of these effects can significantly reduce the carrier recombination in the depletion region of CZTSSe solar cells. As the results, the VOC of CZTSSe solar cells were increased from ~460mV to ~480mV, the efficiency of the best CZTSSe solar cell was increased from 10.2% to 11.6% by the Cd/NH3 soaking process.