Element substitution of kesterite Cu(2)ZnSnS(4) 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 Cu(2)ZnSnS(4) (CZTS) has been recognized as a potential CE material, but its electrocatalytic activity is still insufficient for the recovery of I(−)/I(3)(−) electrolyte in dye-sensitized solar cells (DSSCs). Herein, we attempt to enhance the electrocatalytic activity of kesterite CZTS through element substitution of Zn(2+) by Co(2+) and Ni(2+) cations, considering their high catalytic activity, as well as their similar atomic radius and electron configuration with Zn(2+). The Cu(2)CoSnS(4) (CCTS) and Cu(2)NiSnS(4) (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(2+) and Ni(2+). 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.