Iron alloying improved electrocatalytic activity of Cu2Cu1−xFexSnS4 counter electrodes in dye-sensitized solar cells.

Nanocrystalline Cu₂Cu_1−xFe_xSnS₄ (CCFTS) was prepared by a simple liquid-phase method. Physiochemical properties of the CCFTS powder as well as the CEs fabricated thereby were investigated using XRD, Raman spectroscopy, SEM, UV–Vis absorption, electrochemical impedance spectroscopy (EIS), etc. Conduction band shifts as well as the bandgap increases in the as-prepared CCFTS as a function of the Fe content were observed. For the dye-sensitized solar cells (DSSCs) with CCFTS counter electrodes (CEs), charge transfer impedance (R_ct1) and short-circuit current (J_sc) were reduced by 64.54% and improved by 14.64%, respectively, compared with that with Fe-free Cu₃SnS₄ (CTS) CE. The enhancement of electron transfer through the CE/electrolyte interfaces stems from the optimal energy level alignment and the surface morphology tuned by the Fe alloying and hence improve the electrocatalytic activity of the CEs for the reduction from I₃⁻ to I⁻. As a consequence, photovoltaic conversion efficiency (PCE) of 6.95% was obtained which is 1.25 times that of the cell with Fe-free CTS CE. This work confirmed that element alloying into nanocrystalline transition metal compounds is effective for catalytic activity improvement. Material preparation reported herein is feasible, has high efficiency and low cost, and believed beneficial to high DSSCs development. [ABSTRACT FROM AUTHOR]