Phosphorus doped CuS as an advanced counter electrode for quantum dot-sensitized solar cells

Abstract

Developing an efficient material as a counter electrode (CE) with excellent catalytic activity and low cost is essential for the commercial application of quantum dot-sensitized solar cells (QDSSCs). Transition metal phosphides and sulfides have been demonstrated as outstanding multifunctional catalysts in a broad range of energy conversion technologies. Herein, we exploited an advanced phosphorus doped copper sulfide (P-doped CuS) as CEs in QDSSCs. P-doped CuS was synthesized by a hydrothermal process and subsequently a process for phosphatizing CuS in a tube furnace at 270 °C with NaH2PO2 as the phosphorus source. The morphology, composition and crystalline phase of P-doped CuS have been studied by X-ray and electron-based characterizations (XRD, SEM, TEM and XPS). The photovoltaic parameters of QDSSCs based on P-doped CuS CEs show an obvious dependence on the P-doping concentration, and QDSSCs based on the P-doped CuS CE with 1.9% P-doping yield a maximum power conversion efficiency of 3.45%, a 36% improvement over the QDSSCs based on the CuS CEs. Electrochemical impedance spectroscopy, Tafel polarization and cyclic voltammetry measurements showed that the electrocatalytic activity of P-doped CuS CEs in the S2−/Sn2− redox reaction was higher than that of CuS CEs, which supported the results of enhanced short-circuit current density, open circuit voltage and filling factor.