Enhanced performance of I₂-free solid-state dye-sensitized solar cells with conductive polymer up to 6.8%

An iodine-free solid-state dye-sensitized solar cell (ssDSSC) is reported here, with 6.8% energy conversion efficiency-one of the highest yet reported for N719 dye-as a result of enhanced light harvesting from the increased transmittance of an organized mesoporous TiO₂ interfacial layer and the good hole conductivity of the solid-state-polymerized material. The organized mesoporous TiO₂ (OM-TiO₂) interfacial layer is prepared on large-area substrates by a sol-gel process, and is confirmed by scanning electron microscopy (SEM) and grazing incidence small-angle X-ray scattering (GISAXS). A 550-nm-thick OM-TiO₂ film coated on fluorine-doped tin oxide (FTO) glass is highly transparent, resulting in transmittance increases of 8 and 4% compared to those of the bare FTO and conventional compact TiO₂ film on FTO, respectively. The high cell performance is achieved through careful control of the electrode/hole transport material (HTM) and nanocrystalline TiO₂/conductive glass interfaces, which affect the interfacial resistance of the cell. Furthermore, the transparent OM-TiO₂ film, with its high porosity and good connectivity, exhibits improved cell performance due to increased transmittance in the visible light region, decreased interfacial resistance (Î