Electroplating Cuprous Sulfide Counter Electrode for High-Efficiency Long-Term Stability Quantum Dot Sensitized Solar Cells

Currently, Cu2S based on brass foil is the most commonly used counter electrode (CE) in high efficiency quantum dot sensitized solar cells (QDSCs) because of its superior catalytic activity to the polysulfide electrolyte redox couple. Regretfully, the brass substrate is limited by the shortcomings of corrosion by polysulfide electrolyte and lack of long-term stability. In order to combine the high catalytic activity of Cu2S and superior tolerance of fluorine doped tin oxide (FTO) glass to polysulfide electrolyte, Cu2S film on the FTO glass substrate (Cu2S/FTO) CE was prepared by electrodeposition of the copper film via a multipotential step technique followed by dipping into polysulfide methanol solution. The Cu2S film was proven to be composed by the interconnected nanoflakes, which ensures the highly catalytic activity to the polysulfide redox couple electrolyte in QDSCs. The CdSe quantum dot (QD) sensitized solar cells with the optimized Cu2S/FTO CE exhibit a power conversion efficiency (PCE) of 5.21%, which is very close to that with the commonly used Cu2S/brass CE (5.41%) and much higher than that of Pt CE (1.68%). Furthermore, the cell device based on the Cu2S/FTO CE shows superior stability at a working state for over 10 h without decrease in PCE, which is a serious challenge for the Cu2S/brass CE.