Large ferroelectric-polarization-modulated photovoltaic effects in bismuth layered multiferroic/semiconductor heterostructure devices

Ferroelectrics are appealing candidates for photovoltaic applications. In this study, Bi5FeTi3O15 (BFTO) single layer and ZnO/BFTO bilayer films were deposited onto 0.7 wt% Nb-doped SrTiO3 (NSTO) electrically conducting single-crystal substrates to form Ag/BFTO/NSTO and Ag/ZnO/BFTO/NSTO photovoltaic devices. It was found that the insertion of an n-type semiconducting ZnO layer eliminates the built-in electric field between the Ag electrode and the BFTO film and results in the formation of a BFTO/ZnO p–n junction with a built-in electric field whose direction points to the BFTO film. These effects, together with the depolarization field within the BFTO film, provide a favorable energy level alignment for efficient electron extraction. As a result, the short circuit photocurrent density (Jsc) was improved by nearly 50 fold to 2.2 mA cm−2 and the output power density was increased by 15 fold to 0.09 mW cm−2 under ultraviolet light (λ = 405 nm) illumination. Upon the reversal of the ferroelectric polarization direction from downward to upward, the Jsc and the open circuit voltage (Voc) were increased by 2.5 and 4 fold for the Ag/BFTO/NSTO device and by 2.83 and 8.5 fold for the Ag/ZnO/BFTO/NSTO device, respectively. This work provides an effective way for developing efficient ferroelectric and semiconductor based photovoltaic devices.