Elements co-alloying to improve electrocatalytic activity of nanocrystalline Cu2Cu1-x-yFexMnySnS4 counter electrodes

•Nanocrystalline Cu2Cu1-x-yFexMnySnS4 (CCMFTS) counter electrodes were prepared.•Electrocatalytic activity of the CEs was significantly improved by Fe and Mn co-alloying.•Photovoltaic conversion efficiency of 7.16% of the cell with CCMFTS CE was achieved. The most used counter electrodes (CEs) in dye-sensitized solar cells (DSCs) are made of platinum (Pt). However, the cost of Pt CEs is expensive. In addition, the poor corrosion resistance of Pt in liquid electrolytes hinders commercialization of DSCs. Sulfides are potential CE materials due to their excellent catalytic performance and low cost. Nanocrystalline Cu2Cu1-x-yFexMnySnS4 (CCFMTS) CEs were fabricated using Fe and Mn co-alloyed Cu3SnS4 (CTS) by an easy process of a spin-coating coupled with a post annealing. Electrochemical and photovoltaic properties of the DSCs assembled with the CCFMTS CEs were analyzed by EIS, Tafel and J-V tests. Electrochemical results show that series resistance (Rs) and charge transfer impedance (Rct) at the CE/electrolyte interface of the cells decreased by 21.68% compared with the cell with unalloyed CTS CE, while exchange current density (J0) and limiting diffusion current density (Jlim) were increased, which indicates conductivity and electrocatalytic activity of the CEs were improved after the co-alloying. As a consequence, the maximum actual output power (Pmax) of the cells was enhanced. In the optimal case, photovoltaic conversion efficiency (PCE) of 7.16% was achieved which is 84.83% of that of the cell with Pt CE.