Aerogel based SiO2–TiO2 hybrid photoanodes for enhanced light harvesting in dye-sensitized solar cells

Abstract

It is intriguing and challenging to utilize aerogels with a very high surface area to enhance the light-harvesting capacity of a photoanode. Here we demonstrate highly efficient aerogel-modified photoanodes by modifying both the aerogel's microstructure and the photoanode's functions. A low-cost sol–gel and ambient-drying route is developed to fabricate high-quality SiO₂ and SiO₂–TiO₂ hybrid aerogels with tunable surface area (500–1170 m² g⁻¹) and packing density (0.03–0.27 g cm⁻³). Two series of hybrid photoanodes integrating SiO₂–TiO₂ aerogel microparticles and TiO₂ nanocrystallites are designed, to overcome the intrinsic weakness of the mesoporous structure in the electron-transporting property. The aerogel-modified photoanodes yield significantly higher photocurrent densities than the TiO₂ nanocrystallite photoanode due to their increased dye-loading capacity and the enhanced visible light scattering effect. A distinctive interaction enhancement of the cell efficiency between the dye-loading and the light-scattering effect induced by the aerogel microparticles is observed. At optimal conditions (aerogel: 0.202 g cm⁻³ packing density, 15 wt% incorporation), the primitive aerogel-modified photoanode exhibits a conversion efficiency of 7.57%, much higher than the pure TiO₂ counterpart (3.67%). When optimized with TiCl₄ treatment and a higher film thickness, it shows the highest efficiency of 9.41%, 16% higher than the TiCl₄-treated TiO₂ photoanode modified with a conventional scattering layer. The work affords a simple, powerful and versatile route towards highly efficient hybrid photoanodes utilizing mesoporous materials, and also shows great promise for extension to other applications such as supercapacitors or photocatalysis.