Hole transporting dye as light harvesting antenna in dye-sensitized TiO 2 hybrid solar cells

We herein demonstrate the viability of utilizing the hole transporting medium of solid-state dye-sensitized solar cells for light harvesting. When using a hole transporting dye (HTD) in addition to an interface dye (ID) bound to the surface of the mesoporous metal oxide scaffold, both are shown to contribute to the photocurrent. Efficient energy transfer (ET) from the HTD to the ID was accomplished by spectrally matching two triphenylamine dyes. The photoluminescence of the HTD was found to be quenched in the presence of the ID. In nanosecond transient absorption measurements, rapid formation of the oxidized HTD was observed after photoexcitation of the ID, demonstrating fast regeneration of the oxidized ID by the HTD. In solar cell devices comprising both the ID and HTD, the spectral response of the external quantum efficiency shows that both dyes contribute to the photocurrent, resulting in a doubling of the photocurrent. In comparison with devices comprising only TiO2 and the HTD, devices with the additional ID exhibited an increased photovoltage due to more efficient charge-carrier separation and energy transfer. Combining and matching HTDs with IDs for optimal ID regeneration but also providing ET is thus a viable means to optimize hybrid solar cells based on mesoporous TiO2.