Ag, Ti dual-cation substitution in Cu2ZnSn(S,Se)4 induced growth promotion and defect suppression for high-efficiency solar cells

Abstract

The existence of various detrimental defects inside the absorber layer is a major obstacle limiting the performance of kesterite Cu₂ZnSn(S,Se)₄ (CZTSSe) thin-film solar cells. Cationic substitution is a viable strategy for overcoming this challenge and has drawn tremendous research attention. In this work, a dual-cation substituted CZTSSe involving Ag and Ti to separately occupy partial Cu and Sn lattice sites is proposed. Under 6% Ag and 1% Ti dual-cation substitution, the champion CZTSSe device delivers a highly interesting efficiency of 12.73%, accompanied by an outstanding V_OC of 530 mV. Further investigation demonstrates that Ag introduction can improve the density and crystallinity of CZTSSe thin films while decreasing the concentration of Cu_Zn acceptor defects. Further Ti substitution can effectively eliminate fine grains and reduce the defect density of Cu_Sn and [2Cu_Zn + Sn_Zn] defects, as well as the core level defects. This work explores the synergistic effect of Ag, Ti dual-cation substitution in CZTSSe solar cells for the first time, and the clarified device performance improvement mechanism opens up promising possibilities for the bright development of CZTSSe thin-film photovoltaic technology.