Ferroelectric, Optical, and Photovoltaic Properties of Morphotropic Phase Boundary Compositions in the PbTiO₃–BiFeO₃–Bi(Ni1/2Ti1/2)O₃ System

Ferroelectrics can exhibit the bulk photovoltaic effect (BPVE), which enables a switchable photoresponse and above-band-gap open-circuit voltages ( V oc ). For these systems a large remnant polarization ( P r ) combined with a narrow band gap ( E g ) is believed to be critical in optimizing the photovoltaic performance. Here we investigate the PbTiO 3 –BiFeO 3 –Bi(Ni 1/2 Ti 1/2 )O 3 system which exhibits a large bulk P r and a tunable narrow E g . 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 P r = 32–39 μC/cm 2 show a BPVE with V oc = 6 V at room temperature and a wavelength-dependent switchable photoresponse. Under 1 sun AM 1.5 G illumination the short-circuit photocurrent ( j sc ) increased by an order of magnitude as E g was lowered from 2.85 to 2.25 eV, with ∼0.1 μA/cm 2 .