Manganese alloying improved electron transfer in dye-sensitized solar cells with Cu2Cu1-xMnxSnS4 counter electrodes

It is interesting to find that the irregular Cu3SnS4 (CTS) nanosheets auto-assembled into flower-like morphology accompanied with phase transformation from orthorhombic petrukite to tetragonal kuramite during a annealing at 550 °C for 15 min. On the contrary, a small amount of Mn alloying in orthorhombic CTS can suppress the transformation effectively. The contact between orthorhombic Cu2Cu1-xMnxSnS4 (CCMTS) and fluorine-doped tin oxide (FTO) glass and among the CCMTS grains was improved compared with that of the tetragonal CTS film and FTO glass. As a consequence, electron transfer was improved by Mn alloying in dye-sensitized solar cells (DSSCs) with CCMTS counter electrodes (CEs). In addition, the orthorhombic CCMTS CEs show better catalytic activity in reduction of I3− to I− in the electrolyte than that of CTS CEs. By replacing tetragonal CTS CEs by orhorhombic CCMTS CEs, the photovoltaic efficiency of the DSSCs was improved by more than 20%.