A new probe into thin copper sulfide counter electrode with thickness below 100 nm for quantum dot-sensitized solar cells

Currently, most of CuS counter electrodes (CEs) used in quantum dot-sensitized solar cells (QDSSCs) are provided with a thickness of hundreds of nanometers or even several microns. Considering the CE with low thickness having many advantages, thin CuS films with thickness ranging from 47 nm below to 115 nm have been synthetized in this paper via chemical bath deposition (CBD) method with different bath concentrations. A power conversion efficiency (PCE) of 3.25% has been achieved utilizing CuS thin films a thickness of only 64 nm as CEs in QDSSCs without any structural optimization, which is higher than the value of the cell employing CuS CE with thickness of 2.8 μm. Electrochemical impedance spectroscopy, Tafel polarization, and two-point current-voltage measurements are used to investigate the electrocatalytic and conductive performance of CuS CEs with different thickness. Owing to the highest electrocatalytic capacity and good conductivity of the 64 nm-thick CuS CE, QDSSC assembled with this CE has reached relatively high PCE under one sun illumination (100 mW cm−2, AM 1.5). In addition, cyclic voltammetry measurements indicate that the thin CuS CE has a good stability against the polysulfide electrolyte.