Precursor solution chemistry via water additive enabling CZTSSe solar cells with over 12% efficiency

High-quality absorber films are imperative for highly efficient Cu2ZnSn(S,Se)4 (CZTSSe) thin-film solar cells. Precursor solution chemistry, interconnected with thin-film nucleation and the crystal growth process, should be studied insightfully. Thus, creative rationales and strategies could be proposed to improve the absorber quality, carrier characteristics, and hence device performance. However, the research on precursor solution chemistry in CZTSSe solar cells is still in its infancy. In this study, a facile eco-friendly additive strategy is reported to tailor the 2-methoxyethanol-based CZTS precursor solution chemistry. Incorporating water additives improves the homogeneity and thermogravimetric characteristics of a precursor solution by adjusting the particle sizes and coordination behavior inside the precursor solution. After the tailoring of the precursor solution chemistry, CZTSSe absorbers with high quality are fabricated. Hence, benefiting from the carrier dynamics enhancement, a CZTSSe device with a certified power conversion efficiency of 12.07% is achieved. The results open an avenue in precursor solution chemistry regulation through the use of eco-friendly additives to design highly efficient kesterite CZTSSe solar cells.