▎ 摘　　要

We report on the enhancement of photovoltaic performance in a graphene/polycrystalline BiFeO3 (BFO)/Pt heterojunction for the first time. The unique properties of the graphene electrode lead to a short circuit current density of 61 mu A/cm(2) and an open circuit voltage of 0.52V in the heterojunction. These values are much higher than the results reported in polycrystalline BFO with indium tin oxide as the top electrode. A theoretical band diagram model and an equivalent electrical model considering the ferroelectric polarization, interface states, and energy band bending effect are constructed to depict the carrier transport behavior. Important photovoltaic parameters, such as conversion efficiency, illumination intensity response, ON/OFF characteristics, minority carrier lifetime, and external quantum efficiency, are investigated experimentally and theoretically. To improve the photovoltaic performance of the graphene/polycrystalline BFO/Pt heterojunction, HNO3 treatment, and CdSe quantum dots (QDs) filling/sensitizing, as two independent chemical and physical routines, were processed and compared. It can be seen that the photocurrent density exhibits a significant improvement from 61 mu A/cm(2) to 8.67 mA/cm(2) (similar to 150 fold) after HNO3 treatment, while a considerable enhancement of similar to 5 fold is seen with QDs filling/sensitizing. We also present and investigate an optical application of our graphene/polycrystalline BFO/Pt heterojunction as a photosensitive detector. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4748876]