Highly electrocatalytic carbon black/copper sulfide composite counter electrodes fabricated by a facile method for quantum-dot-sensitized solar cells

Abstract

A facile and cost-effective method is proposed herein to fabricate highly electrocatalytic carbon black/copper sulfide (CB/Cu_XS) composite counter electrodes for quantum-dot-sensitized solar cells (QDSSCs). In brief, mesoporous CB thin films and copper salts are first deposited on FTO substrates by a spin-coating process; a sulfidation treatment is then conducted to facilitate accumulations of Cu_XS catalysts in the mesoporous structure. Experimental results illustrate that during the sulfidation, an ion exchange reaction and a reduction of Cu(II) to Cu(I) take place simultaneously, and that the obtained Cu_XS catalyst possesses a nonstoichiometric phase. The electrochemical properties of the resultant composite films are carefully investigated. The results show that the electrocatalytic activity of the CB/Cu_XS films related to the polysulfide redox reaction is much superior to that of common platinum. Compared to a solar cell equipped with a solution-processed CuS counter electrode, the QDSSC using a composite film prepared only by a single spin-coating displays similar photovoltaic performance. Furthermore, increasing the coating times can lead to improvements both in the electrocatalytic activity of the CB/Cu_XS films and in the cell performance of the relevant QDSSCs. When CdS/CdSe sensitizers are employed, the QDSSC using a CB/Cu_XS counter electrode fabricated with three coating times demonstrates a conversion efficiency of 5.62% under 1 sun irradiation.