Optimizing the Se/S atom ratio and suppressing Sb2O3 impurities in hydrothermal deposition of Sb2(S,Se)3 films via Na+ doping

Sb2(S,Se)3 is one of the most promising stibnite photovoltaic materials. At present, the reported highest power conversion efficiency (PCE) of Sb2(S,Se)3 solar cells is 10.7%; however, theoretically, the PCE can reach up to 32%. Unfavorable Se/S atom ratio and Sb2O3 recombination centers are important reasons for the large PCE gap. Herein, additional Na+ ions were deposited on Sb2(S,Se)3 films in a hydrothermal reaction. The Na+ doping increased the grain size and Se/S ratio of the Sb2(S,Se)3 films, and the corresponding band gap approached the ideal value of a single-junction solar cell. The presence of Na+ can effectively enhance the oriented growth of Sb2(S,Se)3 grains along (hk1). In addition, the Sb2O3 impurities on the surface of the Na+-doped Sb2(S,Se)3 films were significantly reduced. As a result, the best cell achieves a PCE of 8.58% and maintains more than 65% of its initial PCE after 2400 h aging test without encapsulation.