Elevated Voltage on Sandwiched Semiconductor/Ferroelectric Photovoltaics

A sandwiched semiconductor/ferroelectric/semiconductor thin film composed of n-type TiO2/BiFeO3/p-type NiO was meticulously designed to bolster photovoltaic performance. In this configuration, TiO2 and NiO function as electron and hole transport layers, respectively. Besides, similar to p-i-n heterojunction devices, the formation of two depletion layers at the TiO2/BiFeO3 and BiFeO3/NiO interfaces generates an extra internal electric field, which facilitates electron–hole separation. Attributed to the two effects mentioned above, the current density is increased to 2.89 mA/cm2. Furthermore, the polarization direction in ferroelectric bismuth ferrite is “pinned” by the two internal electric fields; therefore, the open-circuit voltage doubles from 0.70 to 1.50 V compared to TiO2/BiFeO3 devices, resulting in a power conversion efficiency of 1.61%, surpassing the performance of both pure ferroelectric photovoltaics utilizing BiFeO3 and traditional TiO2/NiO p-n junction cells.