Abstract
Tuning the bandgap in ferroelectric complex oxides is a possible route for improving the photovoltaic activity of materials. Here, we report the realization of this effect in epitaxial thin films of the ferroelectric complex oxide Bi3.25La0.75Ti3O12 (BLT) suitably doped by Fe and Co. Our study shows that Co (BLCT) doping and combined Fe, Co (BLFCT) doping lead to a reduction of the bandgap by more than 1 eV compared to undoped BLT, accompanied by a surprisingly more efficient visible light absorption. Both BLCT and BLFCT films can absorb visible light with a wavelength of up to 500 nm while still exhibiting ferroelectricity, whereas undoped BLT only absorbs UV light with a wavelength of less than 350 nm. Correlated with its bandgap reduction, the BLFCT film shows a photocurrent density enhanced by 25 times compared to that of BLT films. Density functional theory calculations indicate that the bandgap contraction is caused by the formation of new energy states below the conduction bands due to intermixed transition metal dopants (Fe, Co) in BLT. This mechanism of tuning the bandgap by simple doping can be applied to other wide-bandgap complex oxides, thereby enabling their use in solar energy conversion or optoelectronic applications.
Highlights
Tuning the bandgap in ferroelectric complex oxides is a possible route for improving the photovoltaic activity of materials
Ferroelectrics are not applicable to photovoltaic devices owing to their large energy bandgaps (Eg), which lead to insufficient light absorption and limit the photocurrent[7]
Correspondence and requests for materials should be addressed to C.W.B. or S.L. www.nature.com/scientificreports/. Based on this point of view, we studied the adjustment of the Eg of a ferroelectric Bi3.25La0.75Ti3O12 (BLT) film using a simple doping method based on a theoretical study
Summary
Tuning the bandgap in ferroelectric complex oxides is a possible route for improving the photovoltaic activity of materials. The Eg of ferroelectric BiT is decreased from 3.55 to 2.65 eV through the site-specific substitution of the Co ion on the B site of the perovskite octahedral (BO6) between the BiT and LCO interfaces[3] This approach may not be preferred for practical photovoltaic applications because fabrication of this material requires the precise control of superlattice periodicity and the use of a complex process with multiple targets. A conventional doping approach is widely used for tuning Eg because of its easy process compared to that required for the fabrication of superlattice thin films Based on this point of view, we studied the adjustment of the Eg of a ferroelectric Bi3.25La0.75Ti3O12 (BLT) film using a simple doping method based on a theoretical study. The large enhancement of the photocurrent density in BLCT and BLFCT confirms the significant reduction of the bandgaps by simple doping
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