One-dimensional SnO₂ nanotube solid-state electrolyte for fast electron transport and high light harvesting in solar energy conversion

We incorporated one-dimensional SnO₂ hollow nanotubes (1DTONT) into a quasi-solid-state nanogel polymer electrolyte to produce a highly efficient solid-state electrolyte for solid-state dye-sensitized solar cells (ssDSSCs). The concentration of 1DTONT in the solid-state electrolyte was systematically controlled to understand its effect on solar cell performance and stability. The addition of 1DTONT increases electrolyte viscosity, resulting in a solid-state electrolyte. Although the 1DTONT reduces ion mobility due to enhanced viscosity, its oriented structure with a high aspect ratio increases electron transport. Thus, ssDSSCs incorporated with solid-state 9 wt% 1DTONT electrolyte (ss-9 wt% 1DTONT) display lower charge-transfer resistance than those incorporated with quasi-solid-state nanogel polymer electrolyte. Additionally, 1DTONTs possess light scattering characteristics. Their large particle size distribution (from a few hundred nanometers to a few micrometers) and hollow structure result in multiple scattering opportunities. This feature allows 1DTONTs in solid-state electrolytes to form a thin light-scattering layer (~1 μm) on the TiO₂ photoanode. Therefore, ssDSSCs with ss-9 wt% 1DTONT electrolyte exhibit low transmittance and high light reflectance, producing high incident photon-to-current efficiency (IPCE) values over the wavelength range of interest. Overall, ssDSSCs with ss-9 wt% 1DTONT electrolyte exhibit a solar energy conversion efficiency of ~5.8% due to enhanced current density resulting from improved electron transport and light harvesting.