Photovoltaic effect and photopolarization in Pb[(Mg1/3Nb2/3)0.68<

Abstract

Ferroelectric materials are an alternative to semiconductor-based photovoltaics and offer the advantage of above bandgap photovoltage generation. However, there are few known compounds, and photovoltaic efficiencies remain low. Here, we report the discovery of a photovoltaic effect in undoped lead magnesium niobate-lead titanate crystal and a significant improvement in the photovoltaic response under suitable electric fields and temperatures. The photovoltaic effect is maximum near the electric-field-driven ferroelectric dipole reorientation, and increases threefold near the Curie temperature (T c ). Moreover, at ferroelectric saturation, the photovoltaic response exhibits clear remanent and transient effects. The transient-remanent combinations together with electric and thermal tuning possibilities indicate photoferroelectric crystals as emerging elements for photovoltaics and optoelectronics, relevant to all-optical information storage and beyond. DOI: 10.1103/PhysRevMaterials.2.012401 Photoferroelectrics are remarkable materials that have great potential for multifunctional applications [1]. These materials that exhibit (multi)ferroic order are particularly interesting, because they offer advanced electric operation that is related to multiple electric polarization switching states [2]. The field was rejuvenated after the discovery of the photovoltaic effect in the multiferroic BiFeO 3 [3,4], resulting in the revival of ferroelectric-based photovoltaic operation and related materials [5][6][7][8]. Based on recent progress in photovoltaic efficiency of Bi 2 FeCrO 6 films [9], ferroelectric (FE) cells might become competitors for conventional photovoltaics in the near future. In this respect, better insight into photoinduced changes of electrical properties over a wide range of temperatures and electric fields would be helpful. Such a study, however, requires high-quality crystals that are free from the surface/interface effects occurring in thin films [10] and the grain size dependence occurring in ceramics [11]. This task is challenging because the total number of currently known photovoltaicferroelectric compounds is well below 20 [5][6][7][8] We also detail the remanent photopolarization properties originating from the photocarrier generation-distribution mechanism, and demonstrate how the photovoltaic response can be tuned by varying the applied electric field and temperature.The crystals had (001) orientation, and were square shaped with edges along the [010] and [100] directions [ Fig. 1(a)]. In-* Corresponding author: kundysATipcms.unistra.fr dependent energy-dispersive x-ray spectroscopy (EDS) analysis confirmed the PMN-32%PT composition of the crystal. The sample's dimensions were 901 μm × 272 μm × 2161 μm, and both electrodes were formed with silver paste covering the edges in the planes parallel to yz [ Fig. 1(a)]. This experimental geometry was chosen to minimize light power loss and to avoid possible extrinsic contributions related to light-assisted charge injection from electrodes. The hyster...

Larger photovoltaic effect and hysteretic photocarrier dynamics in Pb[(Mg1/3Nb2/3)0.70Ti0.30]O3 crystal

“…At ferroelectric remanence the voltage change versus light intensity shows a~20-times larger effect than in the PMN-PT32% crystal (figure 2) in agreement with much larger effect of the light on the FE loop ( figure 1(a) and [29]). The nonlinear behavior as a function of light intensity with a characteristic peak is observed for both compounds.…”

“…As a consequence of free charge generation by light, the sample becomes leakier FE with apparent increase in the both FE polarization and FE coercive force ( figure 1(b)). The observed light-induced change in the ferroelectric loop largely exceeds in magnitude all previous observations [29,[32][33][34]. The corresponding voltampere characteristics further illustrate the photoinduced change in electric properties ( figure 1(b)).…”

“…As light intensity decreases, this process is reversed, and the majority of carriers become free again, but now move in the opposite direction, in agreement with the sign change of the photocurrent (see 'release from traps' part in figure 3). Subsequent illumination reveals a smaller magnitude of the photocurrent, because a part of photo-excited carriers had recombined irreversibly, diminishing surface charges, and therefore decreasing polarization [29]. The role of polarization magnitude in the PV effect can be verified by comparing ferroelectric loops of both compounds in darkness ( figure 4).…”

“…Although this mechanism is possible, its contribution is unlikely dominant here because the piezoelectric coefficients do not differ by the order of magnitude in both compounds [30]. The intrinsic mechanism of light induced charge generation may come into play deserving a separate study including symmetry dependent [29] and defect dependent [42] arguments.…”

Optical Control of Ferroelectric Domains: Nanoscale Insight into Macroscopic Observations

“…Warren et al manifested that it is also possible to tune the state of spontaneous polarization merely by the exposure of light . Fundamental understanding of this mechanism is likely to offer new device prospects especially in optoelectronics and information storage . It is to be noted that the photovoltaic effect in ferroelectrics is well known since the 1960s and has been investigated for the optical reading of ferroelectric random‐access memories, photodiodes, and photovoltaic applications.…”