Strain-gradient mediated local conduction in strained bismuth ferrite films

Abstract

It has been recently shown that the strain gradient is able to separate the light-excited electron-hole pairs in semiconductors, but how it affects the photoelectric properties of the photo-active materials remains an open question. Here, we demonstrate the critical role of the strain gradient in mediating local photoelectric properties in the strained BiFeO 3 thin films by systematically characterizing the local conduction with nanometre lateral resolution in both dark and illuminated conditions. Due to the giant strain gradient manifested at the morphotropic phase boundaries, the associated flexo-photovoltaic effect induces on one side an enhanced photoconduction in the R -phase, and on the other side a negative photoconductivity in the morphotropic -phase. This work offers insight and implication of the strain gradient on the electronic properties in both optoelectronic and photovoltaic devices.

Structural and photoelectric properties of tensile strainedBiFeO3

“…7. Another possible explanation could involve the flexophotovoltaic effect where strain gradients between tetragonal and rhombohedral phases produce both enhanced and inhibited photoconductance [36]. It could therefore be possible that strain gradients between the mixed phases in the BFO films examined here might play an important role.…”

Structure, Performance, and Application of BiFeO3 Nanomaterials

“…Adapted with permission from Ref. [ 114 ]. d The photocurrent under different light intensities in heating and cooling states.…”

“…Strain gradient can separate the light-excited electron–hole pairs and affect the photoelectric properties of photoferroelectrics as reported. Yang et al [ 114 ] used the BFO thin films to demonstrate the role of the strain gradient in mediating photoelectric properties. We can see that the photocurrent (bright stripes in Fig.…”

“…c 3 Profile comparison between the photocurrent and surface morphology of the area marked by blue arrow in c 1 . Adapted with permission from Ref [114]…”

Flexophotovoltaic Effect in Potassium Sodium Niobate/Poly(Vinylidene Fluoride‐Trifluoroethylene) Nanocomposite

“…[21,22] In 2019, Yang et al at Alexe's group found that the nonpiezoelectric SrTiO 3 thin film can easily generate a large strain gradient in the out-of-plane direction, causing a large flexo-polarization, which can significantly affect the photovoltaic effect on the SrTiO 3 thin films. [23] Recently, Shu et al at Catalan's group studied the photoflexoelectric effect on the perovskite CH 3 NH 3 PbBr 3 film and found that under a combination of light illumination and mechanical vibration, the film can generate orders of magnitude higher flexoelectricity than in the dark. [24] In this investigation, the flexoelectricity generated from a bending curvature is used to improve the photovoltaic current of PVDF-based nanocomposites.…”