Enhanced Electrocatalytic Activity of the Annealed Cu2-xS Counter Electrode for Quantum Dot-Sensitized Solar Cells

Cu 2-x S films in situ formed on brass substrates were annealed at different temperatures (100, 200, 300, and 400°C) in flowing Ar gas, and introduced as the counter electrodes (CEs) for CdSe quantum dot-sensitized solar cells (QD-SSCs). The QD-SSC with the bare Cu 2-x S CE exhibited higher cell performance than that with the Pt CE. The QD-SSC with the 300°C-annealed Cu 2-x S CE achieved the best energy conversion efficiency of 4.25%, showing a 34% increase compared to the cell performance of that with the bare Cu 2-x S CE. This is because the Cu 2-x S film annealed at 300°C provided rapid charge transport and the increased electrochemical active sites due to the improved crystallinity and surface roughening, leading to significantly enhanced electrocatalytic activity. On the other hand, when the Cu 2-x S film was annealed at 400°C, secondary phases, such as CuO, Cu 2 O, CuSO 4 and ZnO, formed, which reduced the cell performance of the QD-SSC with the 400°C-annealed Cu 2-x S CE due to the poor electrocatalytic activity.