Enhancement of Charge Transfer in TiO₂/BiOI Heterojunction Using BiFeO₃ as Interface Modifier for Photoelectrochemical Conversion

Abstract

The solution-processed TiO2/BiFeO3/BiOI ternary heterojunction with cascade energy level alignments was developed for photoelectrochemical conversion, in which, BiOI was deposited on BiFeO3 sensitized TiO2 mesoporous film by spin-coating method. BiFeO3 as ferroelectric material was served here as a mediator for improvement of charge separation and transfer. The photocurrent generation in TiO2/BiFeO3/BiOI sample are very stable, even measured after 50 light on/off cycles with 2000 s. Moreover, compared with the TiO2/BiOI film, TiO2/BiFeO3/BiOI film showed about twice as high photocurrent density and photocatalytic activity. Kelvin probe force microscope showed that the surface potential of TiO2/BiFeO3/BiOI film was 0.456 V, which was obviously larger than 0.226 V in TiO2/BiOI sample. The increased surface potential should originate from the polarization electric-field E self by BiFeO3 interlayer, in which the direction of electric-field was directed toward the BiOI. The presence of E self consequently resulted in the better dissociation of photo-generated electrons and holes. Charge transport dynamics suggested that charge transfer rate increased from 6.813 s−1 of TiO2/BiOI heterojunction to 22.280 s−1 of TiO2/BiFeO3/BiOI heterojunction, and surface charge recombination rate reduced from 10.305 s−1 of the TiO2/BiOI to 7.707 s−1 of TiO2/BiFeO3/BiOI heterojunction, which results in the enhanced photoelectrochemical conversion in TiO2/BiFeO3/BiOI heterojunction.