Improvement of grain growth and composition distribution of Cu₂ZnSn(S,Se)₄ by using chloride-based precursor solution

Excellent crystallinity and uniform composition distribution of the Cu₂ZnSn(S,Se)₄ (CZTSSe) absorber are indispensable factors for the fabrication of photovoltaic device with excellent performance. Here, a facile and effective method is developed to improve the composition uniformity of CZTSSe absorber. It is inspiring that by replacing the acetates with chlorides as the solutes in the precursor solution, the issue of the composition non-uniformity especially for the distribution of Cu and Sn, which is ascribed to the rich-carbon in the acetate-based CZTSSe absorber, is able to be avoided. Due to less organic residues and composition uniformity, the grain size and the crystallinity of absorber could be significantly enhanced, and the photovoltaic performance of chloride-based CZTSSe solar cell is improved remarkably. Furthermore, substituting CuCl₂ with CuCl as the copper source in the precursor solution is able to obtain a stable solution, and the quality of CZTSSe absorber is further improved. As a consequence, 8.48% efficient CZTSSe solar cell has been yield.