Photovoltaic Effect in Ferroelectric Pt/(Bi_0.9La_0.1)(Fe_0.97Ta_0.03)O₃/Graphene Hetrostructures

Abstract

Recently, observation of switchable polarization-induced ferroelectric photovoltaic effect (FEPV) in BiFeO3 (BFO) has attracted great interest. In order to improve its FEPV properties, co-substituted [Bi0.9La0.1][Fe0.97Ta0.03]O3 (BLFTO) films were fabricated on Pt/TiO2/SiO2/Si substrates by pulsed laser deposition (PLD). The phase formation of the films was confirmed by X-ray diffraction, Raman spectroscopy, and XPS studies. The FEPV properties in La and Ta co-doped BiFeO3 (BFO) thin films were evaluated under illumination using sandwich configuration with a transparent conducting electrode (TCE) graphene as top electrode. The TCE electrode was transferred by chemical method on BLFTO thin films. The band gap of the films was determined to be 2.66 eV from spectrophotometric measurements, which is very close to that of pure BFO (2.7 eV). The ferroelectric nature of the films was characterized by P-E loop measurements, which indicated that leakage was still the prominent factor for not getting good polarization hysteresis. The piezo-force microscopy (PFM) studies however confirmed the ferroelectric nature of the films. The photovoltaic effect of the films was studied in both geometries, namely top-bottom and planar electrodes configurations. We will present aforementioned investigations and discuss possible photovoltaic applications of the above structure.