Efficient quantum-dot-sensitized solar cells with improved stability using thixotropic polymer/nanoparticles-based gel electrolyte

Abstract

In this article, the preparation of a gel electrolyte that consists of a polysulfide electrolyte with xanthan gum (XG) thixotropic gel and TiO2 nanoparticles (NPs) is reported for the development of improved performance of quantum-dot-sensitized solar cells (QDSSCs). Natural polysaccharide XG exhibited thixotropic sol−gel transitions, by which it can reversibly be converted from sols to high-viscosity gels under shear stress. XG is, for the first time, used to passivate the surface trap states or act as steric hindrance between TiO2/QDs/electrolyte interfaces. The incorporation of TiO2 NPs in the XG gel electrolyte improved the ionic conductivity of the gel electrolyte. For the Cu–In–Se QDSSC with gel electrolytes, the conversion efficiencies were 7.25% and 8.19% for XG and XG/NP gel electrolytes, respectively, whereas, the liquid electrolytes only delivered an efficiency of 6.86% under simulated sunlight (AM 1.5, 100 mW cm−2). Moreover, electrochemical analysis revealed that enhanced charge transfer and suppressed electron–hole recombination process occurred more frequently at the TiO2/QDs/electrolyte in QDSSCs with the XG/NP gel electrolyte compared with those with the liquid and XG gel electrolyte. Most importantly, the XG/NP gel electrolyte is also effective in various I-III-VI-based QDSSCs, including Cu–In–S and Ag–In–Se QDSSCs, for improving the cell power conversion efficiencies and stability because of the synergistic effect of XG and TiO2 NPs in polysulfide electrolytes. Notably, the best cell devices (Cu–In–S QDSSCs) constructed using XG/NP gel electrolytes have long-term stability under one-sun illumination, retaining 90% of the initial device's efficiency after 150 h.