Facile control of intra- and inter-particle porosity in template-free synthesis of size-controlled nanoporous titanium dioxides beads for efficient organic–inorganic heterojunction solar cells

Abstract

In thin film solid-state heterojunction solar cells (HSCs), titanium-dioxide (TiO2) electrodes need to be optimized to have large specific surface area, controllable pore sizes, and superior light scattering properties. In this study, we synthesize hierarchical nanoporous TiO2 beads with sub-micron diameters by a template-free, fast, and low-temperature synthetic scheme to satisfy the aforementioned requirements for HSCs. These nanoporous TiO2 beads are composed of numerous TiO2 nano crystallites that provide mesopores, and the inter-particle distances of size-controlled TiO2 beads can provide additional controllable macropores. We report the first successful application of TiO2 bead films (SP250, SP450) with controllable hierarchical nanostructure to be sensitized with Sb2S3 for all-solid-state heterojunction solar cells (Sb-HSCs). The Sb-HSCs made using the controlled TiO2 beads as photoanodes exhibit a superior light-to electricity conversion efficiency of 4.8%, yielding more than 15% enhancement in comparison with that (3.6%) of commercial TiO2 nanoparticle (NP40) electrodes. The well-tailored photoanode with high surface area, fewer grain boundaries, multi-scale pore structure, and enhanced optical scattering results in much better infiltration of hole-conducting materials, decreased recombination with increased electron lifetime, and enhanced light scattering, which result in the enhanced photovoltaic properties.