Ferroelectric, Optical, and Photovoltaic Properties of Morphotropic Phase Boundary Compositions in the PbTiO₃–BiFeO₃–Bi(Ni_1/2Ti_1/2)O₃ System

Ferroelectrics can exhibit the bulk photovoltaic effect (BPVE), which enables a switchable photoresponse and above-band-gap open-circuit voltages (Voc). For these systems a large remnant polarization (Pr) combined with a narrow band gap (Eg) is believed to be critical in optimizing the photovoltaic performance. Here we investigate the PbTiO3–BiFeO3–Bi(Ni1/2Ti1/2)O3 system which exhibits a large bulk Pr and a tunable narrow Eg. To optimize the ferroelectric polarization, ceramic samples were prepared in the vicinity of the ternary morphotropic phase boundary (MPB), and their photovoltaic properties were characterized over a broad range of optical wavelengths. MPB compositions with a direct optical gap ranging from 2.25 to 2.85 eV and Pr = 32–39 μC/cm2 show a BPVE with Voc = 6 V at room temperature and a wavelength-dependent switchable photoresponse. Under 1 sun AM 1.5 G illumination the short-circuit photocurrent (jsc) increased by an order of magnitude as Eg was lowered from 2.85 to 2.25 eV, with ∼0.1 μA/cm2.