Enhanced Photovoltaic Performance in Polycrystalline BiFeO3Thin Film/ZnO Nanorod Heterojunctions

We demonstrate that the insertion of an n-type ZnO nanorod (NR) layer between a polycrystalline BiFeO3 (BFO) thin film and a poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) buffer layer in a sandwich-like F-doped SnO2 (FTO)/BFO/PEDOT:PSS/Au capacitor leads to the short-circuit current (Jsc) increasing 64-fold from 16.8 μA/cm2 to 1.08 mA/cm2 under the AM1.5G (100 mW/cm2) illumination. When the semitransparent Au electrode is substituted by a transparent Al-doped ZnO (AZO) electrode, the photovoltaic (PV) output can be further improved, with the power conversion efficiency (PCE) reaching 0.17%, which is to our knowledge the highest efficiency that has ever been obtained in the all-solid-state BFO-based capacitor solar devices. It is proposed that the polarization induced FTO/BFO Schottky barrier, the low-resistance ZnO NR/PEDOT:PSS contact, and the carrier transportation characteristics of ZnO NRs contribute to the PV enhancement. A band bending diagram model considering ferroelectric polarization and interface states as well as a schematic energy level diagram of the FTO/BFO/ZnO NR/PEDOT:PSS/Au device is constructed to illustrate the PV enhancement. Our work may provide a new way to utilize ferroelectrics to improve the power conversion efficiency of heterojunction based solar cells and to produce solar cells with tunable PV response and other novel functions.