N-doped carbon@Cu nanocomposites as counter electrode catalysts in quantum dot-sensitized solar cells

Abstract

To improve the catalytic activity of carbons in counter electrodes (CEs), Cu nanoparticles (NPs) were introduced into mesoporous N-doped carbons (N-C) derived from metal-organic frameworks (MOFs) to prepare the composites of N-C and Cu NPs (N-C@Cu) via impregnation and subsequent reduction method in this work. The obtained N-C@Cu composites with 2–4 nm Cu NPs uniformly distributing in N-C were deposited onto fluorine doped tin oxide (FTO) substrates by screen-printing to fabricate CEs in quantum dot solar cells (QDSCs). The N-C@Cu CEs exhibit higher electrocatalytic activity than both pristine N-C/FTO and commonly used Cu2S/FTO CEs, which could be ascribed to the synergistic effect between CuxS NPs with the excellent electrocatalytic ability and MOF derived N-C with high graphitization, large hydrophilic surface as well as the abundant dopant active sites on the reduction of polysulfide. The superior performance of N-C@Cu composites results in an improved fill factor and a high short circuit current density. Based on optimized N-C@Cu CEs and Zn-Cu-In-Se quantum dot sensitizers, the QDSCs obtained present a promising power conversion efficiency of 9.23%, significantly superior to those of pristine N-C/FTO (7.20%) and Cu2S/FTO (8.89%) CEs based QDSCs.