Outstanding photoelectrical response in BiFeO3 hollow microspheres deposited by ultrasonic spray pyrolysis technique

Abstract

Nowadays, it is well known that BiFeO3 exhibits a low photoresponse and, in consequence, small short-circuit current density (Jsc≪μA/cm2). This event is considered a problem for which multiple solutions have been explored, from the formation of complex heterostructures, as well as doping with several materials, alternatives that are expensive and, in many cases, complicated. In this context, we report a simple and low-cost technique (Spray Pyrolysis) that has been carried out to obtain microstructures forming hollow BiFeO3 spheres and circular flower-shaped composed by BiFeO3-Bi2O3 with an outstanding photoresponse. These microstructures show a photocurrent increase of more than six magnitude orders (Jsc=3.5 mA/cm2) and an external quantum efficiency reaching a maximum value of 10.7% at a wavelength of 431 nm applying 0 V (photovoltaic effect). Furthermore, a photoresponse variation is also observed when applying positive or negative electrical polarization. The improvement of the photoelectrical response is attributed to the structure type, composition and the oxygen vacancies present by the same process of formation of these microstructures, which is discussed as an Ostwald ripening and a Kirkendall diffusion process. The morphology of the described microstructures was observed using scanning electron microscopy (SEM), while the structural and compositional analysis were performed using X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) techniques. In the case of electrical measurements, an ITO/BFO/Si-n heterojunction was fabricated being this heterojunction formed by intrinsic semiconductor (perovskite) and an n-type oxide semiconductor (ITO).