80 research outputs found
Role of domain walls in the abnormal photovoltaic effect in BiFeO3
Recently, the anomalous photovoltaic (PV) effect in BiFeO3 (BFO) thin
films, which resulted in open circuit voltages (V-oc) considerably
larger than the band gap of the material, has generated a revival of the
entire field of photoferroelectrics. Here, via temperature-dependent PV
studies, we prove that the bulk photovoltaic (BPV) effect, which has
been studied in the past for many non-centrosymmetric materials, is at
the origin of the anomalous PV effect in BFO films. Moreover, we show
that irrespective of the measurement geometry, V-oc as high as 50V can
be achieved by controlling the conductivity of domain walls (DW). We
also show that photoconductivity of the DW is markedly higher than in
the bulk of BFO
Strain-gradient mediated local conduction in strained bismuth ferrite films
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 BiFeO3 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 [Formula: see text]-phase. This work offers insight and implication of the strain gradient on the electronic properties in both optoelectronic and photovoltaic devices
Photovoltaic effect in multi-domain ferroelectric perovskite oxides
We propose a device model that elucidates the role of domain walls in the
photovoltaic effect in multi-domain ferroelectric perovskites. The model
accounts for the intricate interplay between ferroelectric polarization, space
charges, photo-generation and electronic transport. When applied to bismuth
ferrite, results show a significant electric potential step across both
71-degree and 109-degree domain walls, which in turn contributes to the
photovoltaic (PV) effect. We also find a strong correlation between
polarization and oxygen octahedra tilts, which indicates the nontrivial role of
the latter in the PV effect. The domain wall-based PV effect is further shown
to be additive in nature, allowing for the possibility of generating
above-bandgap voltag
Photoferroelectric oxides
Giant photovoltaic effect due to bulk photovoltaic effect observed in
multiferroic BiFeO3 thin films has triggered a renewed interest on
photoferroelectric materials for photovoltaic applications. Tremendous advance
has been done to improve power conversion efficiency (up to up to 8.1%) in
photoferroelectrics via absorption increase using narrow bandgap
ferroelectrics. Other strategies, as it is the more efficient use of
ferroelectric internal electric field, are ongoing. Moreover, as a by-product,
several progress have been also achieved on photostriction that is the
photo-induced deformation phenomenon. Here, we review ongoing and promising
routes to improve ferroelectrics photoresponse
Substantial bulk photovoltaic effect enhancement via nanolayering.
Spontaneous polarization and inversion symmetry breaking in ferroelectric materials lead to their use as photovoltaic devices. However, further advancement of their applications are hindered by the paucity of ways of reducing bandgaps and enhancing photocurrent. By unravelling the correlation between ferroelectric materials' responses to solar irradiation and their local structure and electric polarization landscapes, here we show from first principles that substantial bulk photovoltaic effect enhancement can be achieved by nanolayering PbTiO3 with nickel ions and oxygen vacancies ((PbNiO2)x(PbTiO3)(1-x)). The enhancement of the total photocurrent for different spacings between the Ni-containing layers can be as high as 43 times due to a smaller bandgap and photocurrent direction alignment for all absorption energies. This is due to the electrostatic effect that arises from nanolayering. This opens up the possibility for control of the bulk photovoltaic effect in ferroelectric materials by nanoscale engineering of their structure and composition
Ferroelectric materials for photovoltaics
En col·laboració amb la Universitat Autònoma de Barcelona (UAB), la Universitat de Barcelona (UB) i l’Institut de Ciències Fotòniques (ICFO)Ferroelectric photovoltaic has been intensively studied during the last years due to possible high efficient charge separation by presence of an internal electric field. Ferroelectric materials show permanent electrical polarization. Ideally, electric contacts would screen the polarization, but if screening is not perfect, it results in the generation of depolarization field. In this report, we study the photoelectric response of LuMnO3 that shows a small bandgap compared to archetypical ferroelectric materials and a sizeable internal polarization. We have studied its photoresponse dependence on polarization state
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