Large enhancement of the photovoltaic effect in ferroelectric complex oxides through bandgap reduction.
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.
School of Materials Science and Engineering, Gwangju Institute of Science and Technology, Gwangju 61005, South Korea.
Hyunji
H
An
Department of Electrical Engineering, Gachon University, Seongnam 13120, South Korea.
Jun Young
JY
Han
Faculty of Physics and Center for Computational Materials Science, University of Vienna, Vienna A-1090, Austria.
Bongjae
B
Kim
School of Materials Science and Engineering, Gwangju Institute of Science and Technology, Gwangju 61005, South Korea.
Jaesun
J
Song
School of Materials Science and Engineering, Gwangju Institute of Science and Technology, Gwangju 61005, South Korea.
Sang Yun
SY
Jeong
Faculty of Physics and Center for Computational Materials Science, University of Vienna, Vienna A-1090, Austria.
Cesare
C
Franchini
Department of Electrical Engineering, Gachon University, Seongnam 13120, South Korea.
Chung Wung
CW
Bark
School of Materials Science and Engineering, Gwangju Institute of Science and Technology, Gwangju 61005, South Korea.
Sanghan
S
Lee