Element substitution of kesterite CuZnSnS for efficient counter electrode of dye-sensitized solar cells.

Development of cost-effective counter electrode (CE) materials is a key issue for practical applications of photoelectrochemical solar energy conversion. Kesterite CuZnSnS (CZTS) has been recognized as a potential CE material, but its electrocatalytic activity is still insufficient for the recovery of I/I electrolyte in dye-sensitized solar cells (DSSCs). Herein, we attempt to enhance the electrocatalytic activity of kesterite CZTS through element substitution of Zn by Co and Ni cations, considering their high catalytic activity, as well as their similar atomic radius and electron configuration with Zn. The CuCoSnS (CCTS) and CuNiSnS (CNTS) CEs exhibit smaller charge-transfer resistance and reasonable power conversion efficiency (PCE) (CCTS, 8.3%; CNTS, 8.2%), comparable to that of Pt (8.3%). In contrast, the CZTS-based DSSCs only generate a PCE of 7.9%. Density functional theory calculation indicate that the enhanced catalytic performance is associated to the adsorption and desorption energy of iodine atom on the Co and Ni. In addition, the stability of CCTS and CNTS CEs toward electrolyte is also significantly improved as evidenced by X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy characterizations. These results thus suggest the effectiveness of the element substitution strategy for developing high-performance CE from the developed materials, particularly for multicomponent compounds.