Acta Physica Sinica, Volume. 68, Issue 21, 217701-1(2019)
Ferroelectrics materials, as a candidate of materials, have recently received attention, for they possess applications in photovoltaic devices and can couple the light absorption with other functional properties. In these materials, the strong inversion symmetry is broken, which is because the spontaneous electric polarization promotes the desirable separation of photo-excited carriers and allows voltages higher than the band-gap, thus permitting efficiency beyond the maximum possible value in a conventional p-n junction solar cell. Much effort has been made to study the ferroelectric photovoltaic effect in several families of ferroelectric perovskite oxides, such as Pb(Zr,Ti)O3, LiNbO3, BaTiO3, KNbO3, Na0.5Bi0.5TiO3-BaTiO3, AgNbO3and BiFeO3. However, their photo-electric conversion efficiency is now still very low though this field is being studied. The observed output photocurrent is very low due to the negative influence of a wide band-gap and small absorption coefficient, which is caused by the wide band-gaps for most of ferroelectric materials such as Pb(Zr,Ti)O3(~3.5 eV), and BaTiO3 (~3.3 eV), especially. Although the BiFeO3 system with low band-gap (2.7 eV), which can absorb most visible light for electron transition, is considered as a potential photovoltaic material, it is difficult to synthesize pure perovskite structure. The BiFeO3-BaTiO3 (BF-BT) ferroelectric material with excellent piezoelectric and ferroelectric properties has been widely concerned by researchers in recent years. However, it is still unclear whether this system has the same advantages as BiFeO3 materials with excellent photovoltaic properties. In this work, the Bi(Fe0.96Mg0.02–xTi0.02+x)O3-0.3BaTiO3 ferroelectric ceramics are prepared by the conventional synthesis method to uncover the piezoelectric and ferroelectric properties, as well as the photovoltaic performance with different ratios of Mg2+/Ti4. Because of the electronic production caused by replacing Mg2+ ions with Ti4+ ions, the conductivity of sample increases, and thus its piezoelectric and ferroelectric properties deteriorate. The piezoelectric coefficient d33 decreases from 195 pC/N at x = 0 to 27 pC/N at x = 0.02. Conversely, the range of absorption spectrum increases when the Mg2+ ions are replaced by Ti4+ ions. The band gap of sample decreases from 1.954 eV at x = 0 to 1.800 eV at x = 0.02. The photocurrent of sample increases from 3.71 nA/cm2 at x = 0 to 32.45 nA/cm2 at x = 0.02 because of the combined action of reducing the band gap and internal bias field.
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Li-Feng Zhu, Wen-Yuan Pan, Yan Xie, Bo-Ping Zhang, Yang Yin, Gao-Lei Zhao.
Received: Jun. 28, 2019
Accepted: --
Published Online: Sep. 17, 2020
The Author Email: Zhao Gao-Lei (zhaogaolei@mail.ioa.ac.cn)