Metal–organic framework derived Co,N-bidoped carbons as superior electrode catalysts for quantum dot sensitized solar cells

Abstract

An efficient electrocatalyst for the reduction of polysulfide electrolytes is vital to the construction of quantum dot sensitized solar cells (QDSCs). Herein, Co,N-bidoped carbon nanomaterials, prepared simply via the pyrolysis of bimetallic (Zn and Co) zeolite-type-metal organic frameworks, were for the first time attempted as electrocatalysts to develop counter electrodes (CEs) for QDSCs. The CEs developed exhibit superior catalytic activity for polysulfide reduction in QDSCs, resulting in a low charge transfer resistance at the interface of the CE/electrolyte, an improved fill factor (FF) and a high short circuit current density (J_sc). The outstanding performances of the CEs can be ascribed to the inherent characteristics of Co,N-bidoped carbons with homogeneously dispersed active dopants of Co and N atoms, large hydrophilic surface area, and good conductivity. Moreover, density functional theory (DFT) indicated that the Co–N_x sites would be active sites for polysulfide reduction. When Co,N-bidoped carbons deposited on F-doped tin oxide glass were used as CEs, an impressive power conversion efficiency of 9.12% (V_oc = 0.635 V, J_sc = 26.15 mA cm⁻², FF = 0.549) under one sun illumination with 100 mW cm⁻² intensity was observed on QDSCs using Zn–Cu–In–Se QDs as sensitizers. Consequently, there is a good chance to fabricate QDSCs of high efficiency with the CEs derived from MOFs.