Sputtering and sulfurization-combined synthesis of a transparent WS2 counter electrode and its application to dye-sensitized solar cells

Abstract

In this work, continuous and large-area tungsten sulfide (WS₂) films, deposited by radio frequency sputtering followed by a sulfurization process, were applied as a low-cost platinum (Pt)-free counter electrode (CE) for dye-sensitized solar cells (DSSCs). The composition and structure of WS₂ films were confirmed using X-ray diffraction, field-emission scanning electron microscopy, Raman spectroscopy and X-ray photoemission spectroscopy techniques. The WS₂ CE was phase pure and considerably transparent. The cyclic voltammetry, electrochemical impedance spectroscopy and Tafel curve showed that the WS₂ CE possesses high electrocatalytic activity and fast reaction kinetics for the reduction of tri-iodide to iodide, which can be attributed to its inherent catalytic property. Finally, TiO₂-based DSSC with an optimized WS₂ CE (sputtered for 10 min) showed as high as 6.3% power conversion efficiency, which was comparable to the performance of DSSC with a Pt-based CE (6.64%). Our study demonstrated the feasibility to develop low-cost, transparent, catalytically active, stable and abundant metal chalcogenide catalysts by an RF sputtering method to replace Pt CE for photovoltaic application.