3D Cu-doped CoS porous nanosheet films as superior counterelectrodes for quantum dot-sensitized solar cells

Quantum-dot sensitized solar cells (QDSCs), as a promising type of new generation photovoltaic devices, require an efficient and inexpensive counterelectrode (CE) for their commercial application. In this work, novel noble-metal-free Cu-doped CoS (Cu-CoS) CEs are designed for QDSCs. The hierarchical three-dimensional (3D) Cu-CoS porous nanosheet films on fluorine doped tin oxide (FTO) glass are prepared by a simple hydrothermal reaction followed by a cation exchange reaction process. As an alternative to Pt electrode, the 3D structure of porous Cu-CoS nanosheets with high reflectivity can provide a great large number of active catalytic sites and easy accessibility toward Sn2-/S2- electrolyte solution, leading to high electrocatalytic activity. Theoretical calculations are further performed to demonstrate the superior catalytic activity for the Cu-CoS CE. As a result, the QDSC with an optimized Cu-CoS CE exhibits a high photovoltaic conversion efficiency of 6.1% under 100mWcm^-2 irradiation, which is much higher than that of the references Pt and bare CoS CEs. Furthermore, this QDSC device shows long-term stability, which makes it as a very promising and low cost effective material for QDSCs.