Synergy effect of carbon nanotube and graphene hydrogel on highly efficient quantum dot sensitized solar cells

Carbon based composite counter electrodes (CEs) containing metal sulfides have shown excellent catalytic activity in quantum dot sensitized solar cells (QDSCs), but the series resistance of the device is still greatly larger than that of brass based CEs of Cu x S/brass. In this work, carbon nanotubes (CNTs) are incorporated into the binary system of graphene hydrogel (GH) and copper sulfide (CuS) during gelation to form CNT-GH-CuS composite CEs. Results show that the ternary CEs exhibit greatly higher conductivity than that of binary CNT-CuS and GH-CuS CEs, and the series resistance dramatically drops from ∼3 to 0.79 Ω which is similar to that of Cu x S/brass CEs. Due to the improved conductivity, catalytic activity and intimate contact with substrate, the assembled Zn–Cu–In–Se QDSCs receive a record power conversion efficiency of 14.02%.