We reveal a new approach for forming a Ag-graded absorber to overcome the large open-circuit voltage deficit in (Cu,Ag)2ZnSn(S,Se)4 solar cells.

Homogeneous molecular precursor solutions are excellent choices for obtaining smooth absorber layers, and they offer the potential to significantly lower the manufacturing cost of solar cells. Here, we present a thermally degradable metal butyldithiocarbamate-based solution approach to fabricate Cu2ZnSn(S,Se)4 solar cells. Low-cost Cu2O, ZnO, and SnO were used as the starting materials and were dissolved in the ethanol solution of butyldithiocarbamic acid. By tuning the composition of the Cu2ZnSn(S,Se)4 thin film, a power conversion efficiency of 6.03% on the basis of the active area has been achieved.

The partial substitution of Cu with Ag into the host lattice of CuZnSn(S,Se) thin films can reduce the open-circuit voltage deficit (V) of CuZnSn(S,Se) (CZTSSe) solar cells. In this paper, elemental Cu, Ag, Zn, Sn, S, and Se powders were dissolved in solvent mixture of 1,2-ethanedithiol (edtH) and 1,2-ethylenediamine (en) and used for the formation of (CuAg)ZnSn(S,Se) (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 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.

Additional elements in the Cu 2 ZnSn(S,Se) 4 (CZTSSe) absorber layers can play a crucial role in improving the performance of thin film solar cells. In this paper, a significant performance enhancement of CZTSSe thin film solar cells was achieved by the partial substitution of the Zn 2+ cation with Cd 2+ . A small amount of Cd 2+ can be successfully incorporated into the host lattice of CZTSSe to form a homogeneous Cu 2 Zn 1−x Cd x Sn(S,Se) 4 (CZCTSSe) alloy material. We demonstrated that the crystal growth and the band gap of CZCTSSe thin films are affected by the Cd doping level. Additionally, the impact of Cd content on the space-charge density (N c-v ) and the depletion width (W d ) of CZCTSSe solar cells was systematically investigated. By this cation substitution approach, the power conversion efficiency of the solar cells based on the CZCTSSe absorber was successfully increased from 5.41 to 8.11% for the optimal composition (x = 5%).