Graphene nanoparticles-decorated silicon nanowires with tungsten oxide counter electrode for quasi-solid state hybrid solar cells

Abstract

Anchoring ionic liquid-functionalized graphene nanoparticles (IL-GNP) to silicon nanowires (SiNW) improves the solar spectral utilization from the visible to the near-infrared (NIR). Due to the bandgap of IL-GNP in the visible region, their p-type semiconducting nature and favorably aligned energy levels of SiNW and IL-GNP, the IL-GNP not only inject the intrinsically photogenerated electrons into SiNW upon photoexcitation but more importantly they efficiently channelize the hole transfer from SiNW to the liquid or gel hole transport layer (HTL). The HTL, which is an iodide-based ionic liquid gel electrolyte with SiO₂ nanoparticles as the gelatinizing agent, also restricts the light or chemical-induced degradation of the photoanode. Tungsten oxide (WO₃) film is employed as an optically transparent promising electrocatalytic counter electrode (CE) that is chemically compatible with the gel electrolyte. The quasi-solid solar cell with the following architecture: IL-GNP@SiNW/I₂,I⁻ gel/WO₃ delivers the best power conversion efficiency (PCE) of 7.93%, with an average value of 7.26%. This high-performance, low-cost solar cell shows good reproducibility and excellent stability. The reason for the improved solar cell performance in the presence of IL-GNP and replacing the liquid electrolyte by gel is furnished in detail through meticulous characterization.