Photovoltaic Effect in ITO/Rgo/BFO/Au Heterostructures

Abstract

In recent years, BiFeO3 (BFO) thin films showed promising potential towards photovoltaic applications due to its superior ferroelectric properties and optical bandgap lies in the visible region. Among other wide bandgap ferroelectric photovoltaic (Fe-PV) materials (i.e. BaTiO3, LiNbO3 and Pb(Zr,Ti)O3), BFO exhibits large open circuit voltage (VOC), tunable output, and switchable photovoltaic effect. It has been reported that insertion of semiconductor layer to a conventional metal/ferroelectric/metal structure can result into novel heterostructures based photovoltaic cells. However, integration of novel carbon materials in ferroelectric photovoltaic devices has not been very popular. We have studied photovoltaic effect in In2O3-Sn2O3 (ITO)/reduced graphene oxide (rGO)/BiFeO3/Au (metal/semiconductor/ferroelectric/metal heterostructure). We have synthesized graphene oxide using modified hummers method. We spin coated GO solution on ITO substrate and dried overnight at 50oC to achieve thin films. Resultant GO thin films were annealed in NH3:H2 (3:1) atmosphere at 600oC. Electrical measurements confirmed n-type doping in thermally reduced GO (rGO) films. Whereas, BFO act as p-type semiconductor due to charge defects mainly, Oxygen vacancies. BFO films were grown using pulsed laser deposition technique. ITO/rGO/BFO/Au heterostructures shows a reasonable photovoltaic response. Such heterostructure shows short-cicuit current density of 86 µA/cm2. We believe that two built-in fields generated at Au/BFO and BFO/rGO interface are responsible for separation and transport of photo-excited electron-hole pairs. Our work may provide a new way to integrate carbon materials to ferroelectrics to produce heterojunction based solar cells.