In situ synthesis of two-dimensional leaf-like Cu2ZnSnS4 plate arrays as a Pt-free counter electrode for efficient dye-sensitized solar cells

Kesterite-structure Cu2ZnSnS4 (CZTS) has been proved to be a high-performance Pt-free counter electrode (CE) material for dye-sensitized solar cells (DSSCs). Herein, a green but powerful two-step method based on solvothermal treatment was proposed to synthesize semi-transparent two-dimensional (2D) leaf-like CZTS plate arrays (PLAr) in situ on a FTO glass substrate, without any post-treatments, such as annealing, toxic sulfurization, or coating with other ancillary materials. The growth mechanism of the 2D leaf-like CZTS PLAr based on solvothermal treatment was illustrated. A power conversion efficiency (PCE) of 7.09% was obtained by utilizing leaf-like CZTS PLAr as the CE. Surprisingly, the PCE increased to 8.67% assisted by a mirror reflection. The excellent performance of DSSCs could be attributed to the high catalytic surface area, fast photo-generated electron transport at the counter electrode/redox electrolyte interface, remarkable electrocatalytic activity for I-3(-) reduction, low charge transfer resistance toward the reduction of I-3(-) ions, and high diffusion coefficient of the I-3(-). This work provides a green and feasible approach to construct high-quality metal sulfide nanoarrays on arbitrary conductive substrates under mild conditions (i.e. low temperature, no annealing, green, speediness) and promotes the development of Pt-free sulfide materials for sustainable photovoltaic applications.