Boosting the open-circuit voltage of Cu₂ZnSn(S,Se)₄ solar cell by Cd/NH₃ soaking

Abstract

In this paper, the open-circuit voltages (VOC) of Cu2ZnSn(S,Se)4 (CZTSSe) solar cells were improved 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 films and solar cells were investigated in depth. We found the Cd/NH3 soaking can promote the downward band bending of the CZTSSe layer at the surface region. Except that, the Cd/NH3 soaking can eliminate the deep level acceptor in CZTSSe and decrease the density of the defects at the absorber/buffer interface. 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.