Semiconducting ferroelectric perovskites with intermediate bands via B -site Bi5+ doping

We propose B-site Bi5+-doped ferroelectric perovskite materials as suitable candidates for the bulk photovoltaic effect and related solar applications. The low-lying 6s empty states of the electronegative Bi atom produce empty bands in the energy gap of the parent materials, effectively lowering the band gap by 1-2 eV, depending on the composition of the ferroelectric end member and the concentration of Bi5+ in the solid solution. The polarization decreases but survives upon doping, which enables the "shift-current" mechanism for photocurrent generation, while the decreased band gap allows absorption of much of the visible spectrum. The magnitude of shift-current response is calculated for 0.75Pb2InNbO6-0.25Ba2InBiO6 (PIN-BIB) and 0.75Pb2ScNbO6-0.25Ba2ScNbO6 (PSN-BSB) and is predicted to exceed the visible-light bulk photovoltaic response of all previously reported materials, including BiFeO3. Furthermore, the existence of their intermediate bands and multiple band gaps, combined with Fermi-level tuning by A-site co-doping, also allows for their potential application in traditional p-n junction-based solar cells as broad-spectrum photoabsorbers.