II . K . 3 Efficient H 2 Production via Novel Molecular Chromophores and Nanostructures

This work involves a basic research program that will ultimately enable new solar technology for a highly efficient and low cost water splitting system. The system consists of a unique tandem cell where the sunlight is first incident upon a photocathode, and light transmitted through the photocathode is absorbed in the photoanode. The photocathode generates two electrons per absorbed photon through singlet fission in unique molecular chromophores bound to a nanocrystalline TiO2 support. The photoanode consists of hole-injecting molecular chromophores or semiconductor quantum dots supported on a hole-conducting nanocrystalline film. If the photoanode also generates two electrons per absorbed photon through singlet fission or multiple exciton generation (MEG) in semiconductor quantum dots, the maximum cell efficiency for water splitting at zero overvoltage is 46%. A tandem cell with two photoelectrodes both producing just one electron per absorbed photon has a maximum efficiency of 40% at zero overvoltage; a cell with just one photoelectrode has a maximum efficiency of about 32% independent of whether one or two electrons are produced per absorbed photon.