Solid-state dye-sensitized TiO₂ solar cells based on a sensitizer covalently wired to a hole conducting polymer

We report on the molecular wiring efficiency of a ruthenium polypyridine complex acting as a sensitizer connected to a poly(3-hexyl)thiophene chain acting as hole transporting material. We have developed an efficient synthetic strategy to covalently connect via an ethanyl spacer a regioregular poly(3-hexyl)thiophene chain to a ruthenium complex. Solid-state dye-sensitized solar cells were prepared either with the latter system or with a similar ruthenium sensitizer but lacking the polymer chain (reference system). The comparison of the photocurrent–photovoltage characteristics of the cells recorded under AM1.5 indicates a two fold improvement of the overall photoconversion efficiencies when the sensitizer is grafted to the hole transporting material (η = 0.27%) relative to the reference system (η = 0.13%). The higher photovoltaic performance can be attributed to the better diffusion-like propagation of the holes from the sensitizer to the counter electrode through the covalently linked polythiophene chain.