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 similar to 4.30 and 3.30 eV and keep the ionization potential at similar to-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.