Organic Chromophores Designed for Hole Injection into Wide-Band-Gap Metal Oxides for Solar Fuel Applications

The power conversion efficiency of tandem dye-sensitized photoelectrosynthesis cells is limited by the number of p-type metal oxide semiconductors and chromophores available for the photocathode. Here, we introduce a new class of donor–acceptor–donor organic chromophores with deep highest occupied molecular orbital (HOMO) levels to target hole injection into PbTiO3, a wide-band-gap metal oxide alternative to NiO. Electrochemical measurements show that we can tune the range of the chromophores’ electron affinity between ∼4.30 and 3.30 eV and keep the ionization potential at ∼−6.50 eV. The absorption profiles for these chromophores span throughout the visible region. The new chromophore reported here, benzobis(thiadiazole)bis(thiophene-3-carboxylic acid), T2-BBT, adsorbed onto PbTiO3, obtained a maximum absorbed photon-to-current conversion efficiency of 54%. These results highlight the importance of designing chromophores with favorable redox potentials to study promising p-type wide-band-gap metal oxides for photocathodic applications.