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

Abstract

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-3Cu₂S) 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-3Cu₂S CEs have a photovoltaic conversion efficiency (PCE) of 4.59%. Moreover, the cells with GP-xCu₂S 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.