Decreasing the band gap: Highly polarized oxides for solar conversion

Solar energy is a promising long-term solution for future energy requirements; however, current solar energy conversion devices are plagued by low efficiency. The use of ferroelectric perovskite oxides is one approach for boosting conversion efficiency. Ferroelectric oxides possess spontaneous polarization and have been shown to produce a bulk photovoltaic effect, in which charged carriers separate to prevent recombination. Currently, most solid oxide ferroelectrics have a band gap of at least 3 eV, absorbing primarily in the UV region. To improve the efficiency of solar hydrogen production, new materials with a decreased band gap and large polarization are needed. Substitutions in perovskites with elements whose bonds with oxygen are less ionic and more covalent should reduce the band gap. We use first-principles density functional theory (DFT) calculations to investigate the ground state structures of precious metal (PM) doped PbTiO₃. They are promising candidates to be used as semi-conductive ferroelectric-based substrates for solar conversion devices.