Chemical Solution Deposition of Single‐Phase BiFeO₃ Thin Films on Transparent Substrates

Abstract

The production of high‐quality BiFeO3 thin films on cost‐effective transparent electrodes for visible light harvesting applications and devices remains a challenge. Here, the production of single‐phase nanostructured BiFeO3 thin films via chemical solution deposition (CSD) on transparent conductive fluorine‐doped tin oxide FTO glass substrates is reported. It is shown that BiFeO3 is of high purity using a variety of analytical tools and that the as‐obtained BiFeO3 thin films have a single‐grain single‐domain structure exhibiting ferroelectric switching under poling. The BiFeO3 samples show visible light absorption with a bandgap of 2.7 eV under all processing conditions. By changing the annealing atmosphere, it was possible to modify the photocurrent produced, which were (at 1.23 VNHE) 0.07 (O2‐annealed), 0.02 (air‐annealed), and 0.01 mA cm−2 (Ar‐annealed). This indicates a change in the mobile carriers available. The results show that it is possible to produce single‐phase BiFeO3 on a transparent conductive electrode system with controllable photoconductivity.

Role of Excess Bi on the Properties and Performance of BiFeO3 Thin-Film Photocathodes

“…Makarovic et al also show a number of examples from the literature of p-type BFO formed when the annealing was done in air, which supports the results of Wefring et al Solution-based synthesis that involves annealing in ambient air leads to formation of p-type material, whereas vapor deposition techniques mostly operating under low partial pressures of oxygen (like pulsed laser deposition) form n-type materials . Consequently, BFO can be used as a photocathode − or photoanode. ,− Since Bi is volatile, an excess of Bi is often used in the synthesis to compensate for the loss of Bi when subjected to high temperatures. − However, excess Bi can also lead to the formation of additional phases, like Bi 2 O 3 and Bi 2 Fe 4 O 9 , which could affect the PEC performance of BFO . A 10% excess of Bi is generally added to compensate for the loss of Bi from thin films during annealing, while at the same time preventing the formation of other phases of the Bi–Fe–O system .…”

Understanding the impact of Bi stoichiometry towards optimised BiFeO3 photocathodes: structure, morphology, defects and ferroelectricity

“…Also, Wang et al found that O 2 -annealed BFO acted as photoanode and exhibited the photocurrent density of 70 mA cm −2 at 1.23 V NHE . 19 The commonly used methods to prepare BiFeO 3 nanoparticles or lms are solid-state synthesis 20,21 and chemical solution deposition (CSD). Both need an annealing process with a high temperature above 500 °C.…”

Highly transparent Bi4Ti3O12 thin-film electrodes for ferroelectric-enhanced photoelectrochemical processes

“…30 Besides photo-catalysis, adopting ferroelectric semiconductors can be particularly effective in photoelectrochemical (PEC) cells as photo-electrode materials, considering the possibility to modify cell efficiency towards the desired reaction by simply polarizing the photo-electrode, thus representing a great operational advantage. A lot of work has been published on the study and development of poled ferroelectric photo-electrode such as BiFeO 3 , [31][32][33][34][35][36][37][38][39][40] BaTiO 3 , [41][42][43][44][45] Li/Na/K-NbO 3 , [45][46][47][48][49] PbTiO 3 -PbZrTiO 3 , 50-53 SrTiO 3 , 54,55 for the PEC water-splitting reaction, but the use of ferroelectric photocathodes for CO 2 PEC reduction has not been exploited yet. On the other hand, some works on the production of BiTO ferroelectric layers have been reported for photovoltaic applications, [56][57][58] and only one preliminary work in photoelectrocatalysis, where thin films BiOI/BiTO electrodes were fabricated via a metering rod method for the photoelectrochemical characterization of this heterostructure, as photo-anode in the ferroelectric-assisted water-splitting reaction.…”

“…A lot of work has been published on the study and development of poled ferroelectric photoelectrodes such as BiFeO 3 , [31][32][33][34][35][36][37][38][39][40] BaTiO 3 , [41][42][43][44][45] Li/Na/K-NbO 3 , [45][46][47][48][49] PbTiO 3 -PbZrTiO 3 , [50][51][52][53] and SrTiO 3 , 54,55 for the PEC water-splitting reaction, but the use of ferroelectric photocathodes for CO 2 PEC reduction has not been exploited yet. On the other hand, some studies on the production of BiTO ferroelectric layers have been reported for photovoltaic applications, [56][57][58] and only one preliminary work on photo-electrocatalysis has been reported, where thin lm BiOI/BiTO electrodes were fabricated via a metering rod method for the photo-electrochemical characterization of this heterostructure, as a photoanode in the ferroelectric-assisted water-splitting reaction.…”