Elemental Precursor Solution Processed (Cu_1-xAg_x)₂ZnSn(S,Se)₄ Photovoltaic Devices with over 10% Efficiency

The partial substitution of Cu⁺ with Ag⁺ into the host lattice of Cu₂ZnSn(S,Se)₄ thin films can reduce the open-circuit voltage deficit (V_oc,deficit) of Cu₂ZnSn(S,Se)₄ (CZTSSe) solar cells. In this paper, elemental Cu, Ag, Zn, Sn, S, and Se powders were dissolved in solvent mixture of 1,2-ethanedithiol (edtH₂) and 1,2-ethylenediamine (en) and used for the formation of (Cu_1-xAg_x)₂ZnSn(S,Se)₄ (CAZTSSe) thin films with different Ag/(Ag + Cu) ratios. The key feature of this approach is that the impurity atoms can be absolutely excluded. Further results indicate that the variations of grain size, band gap, and depletion width of the CAZTSSe layer are generally determined by Ag substitution content. Benefiting from the V_oc enhancement (∼50 mV), the power conversion efficiency is successfully increased from 7.39% (x = 0) to 10.36% (x = 3%), which is the highest efficiency of Ag substituted devices so far.