TiO₂ nanoparticulate-wire hybrids for highly efficient solid-state dye-sensitized solar cells using SSP-PEDOTs

TiO₂ photoanodes for I₂-free solid-state dye-sensitized solar cells (ssDSSCs) were prepared from multifunctional new TiO₂ nanostructures to enhance light harvesting and charge collection efficiency in ssDSSCs using poly(3,4-ethylenedioxythiophene)s (PEDOTs). A new type of TiO₂ paste containing TiO₂ nanowires (TNW) was prepared and successfully transformed to TiO₂ nanoparticulate-wire hybrids (TNPW) with a large surface area of 61.4 m² g^-1 through thermal annealing. The thickness of the TNPW layer could be controlled up to 17 μm without cracks. As a as hole transport material, PEDOTs were infiltrated into the TNPW photoanode through in situ solid-state polymerization (SSP-PEDOTs) and N719 dyes were adsorbed to give ssDSSCs. The SSP-PEDOTs based ssDSSCs with TNPW photoanodes recorded a high cell efficiency (η) of 6.4% and short-circuit current (J_sc) of 14.3 mA cm^-2 without scattering particles, which were 30.6 and 22.2% higher than those of traditional TiO₂ nanoparticles (TNP) in the same conditions. Furthermore, liquid-state DSSCs with the TNPW photoanode attained a η of 8.4%, which was superior to that of a reference TNP cell (7.3%). The maximum η values were 7.1 and 9.9% for ssDSSCs and liquid type DSSCs, respectively, in the presence of additional scattering layers to support the importance of TNPWs. These enhanced photovoltaic performances of TNPW cells could be attributed to the unique TNPW structure that is advantageous for high charge collection with a long electron diffusion path and large surface area required for high dye adsorption efficiency.