Graphite powder film-supported Cu2S counter electrodes for quantum dot-sensitized solar cells

A graphite powder (GP) film-supported Cu2S counter electrode (CE) has been prepared by an accessible and low-temperature method. GP film is prepared using a doctor-blading technique on an F-doped SnO2 conducting glass (FTO) substrate, while Cu2S is formed by immersion and heat treatment of a metal chalcogenide complex (N4H9Cu7S4) in an air atmosphere. GP films provide large areas for the loading of the flake-like catalytic active Cu2S particles. The lamellar structures of GP also provide an excellent electrical pathway for faster charge transportation from the external circuit to the catalyst, Cu2S. Electrochemical impedance spectroscopy and Tafel characterizations indicate that the GP film-supported Cu2S CE constructed using three Cu2S deposition cycles (GP-3Cu(2)S) exhibits a much smaller charge transfer resistance (R-ct) and higher catalytic activity than Pt or bare Cu2S. The quantum dot-sensitized solar cells (QDSSCs) with GP-3Cu(2)S CEs have a photovoltaic conversion efficiency (PCE) of 4.59%. Moreover, the cells with GP-xCu(2)S CE exhibit excellent stability under conventional working conditions for 12 h without any obvious decay in the PCE. In contrast, the PCE degrades severely for cells based on Pt or bare Cu2S.