Semiconducting ferroelectric perovskites with intermediate bands via B-site Bi 5+ 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.