Bi-layer photoanodes with superior charge collection ability and diffusion length of sub-layer nanostructures for the fabrication of high efficiency dye-sensitized solar cells

Abstract

Simple, strategic design approach for the construction of various bi-layer photoanodes of same film thickness (∼15 μm) comprised of common TiO2 nanoparticles underlayer and dissimilar light-scattering one/three dimensional (1D/3D) TiO2 nanostructures as upper layers towards achieving high efficiency dye sensitized solar cells (DSSCs) are reported. Among the four different bi-layer DSSC photoanodes constructed in this work, typical ∼25 nm sized TiO2 nanoparticles underlayer and 1D nanowires upper layer (TNP + TNW) based photoanode has showed a maximum power conversion efficiency (PCE) of 9.90 ± 0.38% after TiCl4 post-treatment, higher than the PCE of photoanodes containing 3D TiO2 nanostructures such as hierarchical nanorods (THNR), core-shell microspheres and large nanocrystalline polygons + rods as upper layers. The maximum photovoltaic performance has been observed in the DSSC of TNP + TNW bi-layer photoanode owing to its sub-layer nanostructures with synergistic interfaces demonstrated superior light-scattering ability and efficient charge transport across sub-layers, thereby improved the charge collection yield and carrier lifetime. The TNP + THNR bi-layer photoanode has showed lower PCE due to the THNR upper layer comprised of rutile phase hierarchical nanorods chemisorbed much less dyes and increased charge recombination, while it has higher surface area, superior chemical capacitance and improved charge collection capacity in its sub-layers.