Ferroelectric Photovoltaic Effect Research Articles

Colossal Ferroelectric Photovoltaic Effect in Inequivalent Double-Perovskite Bi2FeMnO6 Thin Films.

Double perovskite films have been extensively studied for ferroelectric order, ferromagnetic order, and photovoltaic effects. The customized ion combinations and ordered ionic arrangements provide unique opportunities for bandgap engineering. Here, a synergistic strategy to induce chemical strain and charge compensation through inequivalent element substitution is proposed. A-site substitution of the barium ion is used to modify the chemical valence and defect density of the two B-site elements in Bi2FeMnO6 double perovskite epitaxial thin films. We dramatically increased the ferroelectric photovoltaic effect to ∼135.67 μA/cm2 from 30.62 μA/cm2, which is the highest in ferroelectric thin films with a thickness of less than 100 nm under white-light LED irradiation. More importantly, the ferroelectric polarization can effectively improve the photovoltaic efficiency of more than 5 times. High-resolution HAADF-STEM, synchrotron-based X-ray diffraction and absorption spectroscopy, and DFT calculations collectively demonstrate that inequivalent ion plays a dual role of chemical strain (+1.92 and -1.04 GPa) and charge balance, thereby introducing lattice distortion effects. The reduction of the oxygen vacancy density and the competing Jahn-Teller distortion of the oxygen octahedron are the main phenomena of the change in electron-orbital hybridization, which also leads to enhanced ferroelectric polarization values and optical absorption. The inequivalent strategy can be extended to other double perovskite systems and applied to other functional materials, such as photocatalysis for efficient defect control.

Depolarization Field-Induced Photovoltaic Effect in Graphene/α-In2Se3/Graphene Heterostructures.

The ferroelectric photovoltaic effect (FPVE) enables alternate pathways for energy conversion that are not allowed in centrosymmetric materials. Understanding the dominant mechanism of the FPVE at the ultrathin limit is important for defining the ultimate efficiency. In contrast to the wide band gap conventional thin-film ferroelectrics, 2D α-In2Se3 has an ideal band gap of 1.3 eV and enables the fabrication of ultrathin and stable heterostructures, providing the perfect platform to explore FPVE in the nanoscale limit. Here, we study the ferroelectric layer thickness-dependent FPVE in vertical few-layer graphene/α-In2Se3/graphene heterostructures. We find that the short-circuit photocurrent is antiparallel to the ferroelectric polarization and increases exponentially with decreasing thickness. We show that the observed behavior is predicted by the depolarization field model, originating from the unscreened bound charges due to the finite density of states in semimetal few-layer graphene. As a result, the heterostructures show enhancement of the power conversion efficiency, reaching 2.56 × 10-3% under 100 W/cm2 in 18 nm thick α-In2Se3, approximately 275 times more than the 50 nm thick α-In2Se3. These results demonstrate the importance of the depolarization field at the nanoscale and define design principles for the potential of harnessing FPVE at reduced dimension.

Solution derived transparent PZT/FTO heterojunction and its high-temperature ferroelectric photovoltaic effect

Ferroelectric photovoltaic (PV) materials have garnered considerable interest because of their distinctive switchable PV characteristics. Nevertheless, their ability to function within a wide range of ambient temperatures was previously constrained. This paper describes the construction of ferroelectric capacitors featuring an Au/PZT (Pb(Zr0.40Ti0.60)O3)/FTO (SnO2:F) heterojunction through the utilization of the sol-gel technique. The performance analysis findings indicate that the PZT material, following optimization of annealing temperature, displayed strong ferroelectric properties and notable frequency-dependent dielectric behavior. An increase in temperature (25°C∼300°C) revealed that short-circuit current density Jsc exhibited an upward → downward → upward trend and reached 399.6 μA/cm2 at 300°C. Energy band analysis showed the presence of spontaneous polarization and a large work function difference between the bottom electrode FTO and the top electrode Au (∼0.42 eV) created a strong built-in electric field in the PZT films, which was conducive to the photogenerated carriers' separation and greatly improved the PZT film ferroelectric PV. In this paper, transparent ferroelectric materials were demonstrated for the first time to exhibit a photoelectric responsivity of up to 1.77 mA/W at a temperature of 300°C, offering a practical strategy for the implementation of transparent ferroelectric photovoltaic devices in high-temperature environments, particularly those subjected to intense solar energy harvesting and conversion.

Ferroelectric photovoltaic effect engineered by phase transition and defect neutralization in K0.5Na0.5NbO3 film

As an excellent light transmission material, K0.5Na0.5NbO3 (KNN) shows considerable potential in ferroelectric photovoltaics. However, poor leakage and non-intrinsic polarization limit their photoelectric conversion since they play important roles in the generation, separation and transport of photogenerated carriers. This work realizes the simultaneous improvement of bandgap, ferroelectric and leakage by the introduction of charged group BiFeO3 (BFO), which neutralizes the defects and reduces the leakage current of the films by about two orders of magnitude and increases the remanent polarization to 15.4 μC/cm2 due to the phase transition. Meanwhile, the addition of Fe also introduces impurity energy levels into the KNN films and reduces the bandgap. The open-circuit voltage of the 0.98KNN-0.02BFO film is increased by about 2.5 times. This work provides a feasible way to enhance the ferroelectric photovoltaic performance of KNN films and accelerate their application.

Field-induced structural and orbital transformations leading to large bulk photovoltaic response in modified barium titanate

Ferroelectric systems are gaining importance in the perspective of capitalizing on their potential in energy applications. In particular, the ferroelectric photovoltaic effect is one of the attractive fields because of the reported above bandgap photovoltage. Although numerous efforts are being made to understand the ferroelectric photovoltaic mechanism, correlations among the structural, orbital, and photovoltaic characteristics, useful to engineer the system for applications, are rarely being investigated. Here, such correlations are established in electric field-induced studies carried out on the lead-free ferroelectric Ba0.875(Bi0.5Li0.5)0.125TiO3 system. Upon poling, x-ray diffraction studies reveal a twofold enhancement in the orthorhombic phase fraction at the expense of the tetragonal phase in comparison with the unpoled sample. The ex situ and in situ Raman studies demonstrate the field-induced changes in the structural characteristics. Furthermore, the Rayleigh analysis validates the field-induced lattice deformation in accordance with x-ray diffraction and Raman studies. Notably, the Ba0.875(Bi0.5Li0.5)0.125TiO3 sample exhibits anomalous open-circuit voltage (12 V) under the poling condition. To substantiate the experimental finding, density functional theory calculations are carried out. The theoretical calculations elucidate that the conduction band edge of the orthorhombic phase has a vital contribution from z character orbitals, which is further enhanced under poling to give rise to a higher shift current and, hence, a better photovoltaic response. However, the tetragonal phase's orbital characters are robust upon poling. Overall, these studies pave the way for designing ferroelectric systems for better photovoltaic properties.

Dielectric and ferroelectric photovoltaic properties of epitaxial BiFeO3 film with La0.5Sr0.5CoO3 bottom electrode

In order to deeply investigate the dielectric and ferroelectric photovoltaic properties of BiFeO3 (BFO) thin films, the Pt/BFO/La[Formula: see text]Sr[Formula: see text]CoO3 (LSCO) heterostructure ferroelectric capacitor grown on (001) SrTiO3 (STO) substrate is successfully fabricated by off-axis magnetron sputtering. The X-ray diffraction (XRD) and Phi scanning results show that the STO-based BFO and LSCO films are both (001) epitaxial structure. Although the BFO ferroelectric film exhibits an obvious dielectric dispersion phenomenon, a remarkable ferroelectric photovoltaic performance is obtained with open circuit voltage ([Formula: see text]) of 0.38[Formula: see text]V and short-circuit current ([Formula: see text]) of 0.23[Formula: see text]mA/cm2, respectively. With increasing test temperatures, [Formula: see text] decreases slowly and then rapidly, while [Formula: see text] increases rapidly and then decreases. At a critical temperature of 80∘C, the BFO ferroelectric film exhibits a faster photovoltaic response, in which the values of [Formula: see text] and [Formula: see text] are about 0.19[Formula: see text]V and 0.28[Formula: see text]mA/cm2, respectively. Moreover, the energy band analysis indicates that a large work function difference ([Formula: see text][Formula: see text]eV) between LSCO and Pt leads to a strong built-in electric field in the BFO film, which is beneficial to separate the photo-generated carriers and improve ferroelectric photovoltaic effect. In all, this study not only shows that BFO is an excellent and environmentally friendly photovoltaic candidate material, but also provides a practical strategy for improving the performance of BFO ferroelectric photovoltaic devices.

Synergistic effect of interface engineering and bulk photovoltaic effect enhanced self-powered Ta2NiS5/ α -In2Se3/WSe2 van der Waals heterojunction for photodetection

The discovery of van der Waals ferroelectric materials with narrow bandgaps has opened up opportunities for the extensive adoption of self-powered ferroelectric devices that rely on the bulk photovoltaic effect. However, it still needs to overcome the challenges related to the weak ferroelectric polarization and bulk photovoltaic effect in ultrathin van der Waals ferroelectric materials. In this report, we present a synergistic effect of interface engineering and bulk photovoltaic effect in the Ta2NiS5/α-In2Se3/WSe2 van der Waals heterojunction for photodetection. The heterojunction can detect the light with a wide range of wavelengths from near-ultraviolet to near-infrared without requiring external power sources. The output current density of the self-powered heterojunction shows a linear relationship with the optical power intensity at a specific wavelength. Moreover, it accurately identifies the wavelength of light at the same optical power intensity. The on/off ratio is 1.1 × 104, 3.9 × 104, 1 × 104, and 17, respectively, when the optical power density is 100 mW/cm2 for 405, 660, 808, and 1064 nm light. The self-powered Ta2NiS5/α-In2Se3/WSe2 van der Waals photodetector exhibits high specific detectivity of 1.56 × 1011, 1.79 × 1012, 9.16 × 1010, and 1.26 × 105 Jones for wavelengths of 405, 660, 808, and 1064 nm, respectively. These results validate our strategy for enhancing the detection performance in self-powered ferroelectric van der Waals photodetectors, thus opening up possibilities for future self-powered photodetection technologies.

The effect of defects induced by polarization on bandgap evolution and photovoltaic performance in KN-based semiconducting ferroelectric ceramics

The high-field polarization enables bandgap-engineered ferroelectric perovskite oxides to further enhance their photovoltaic performance. However, research on the mechanism of the high-field polarization-enhanced ferroelectric photovoltaic effect lacks understanding in terms of bandgap evolution. In this work, the ceramics [KNbO3]1−x−[SrNi0.5Hf0.5O3−δ]x(KNSNH100x, x = 0.02 − 0.08), prepared by the solid phase method, exhibit good ferroelectricity and four absorption bandgaps, three of which have sub-bandgaps generated by Ni. The effect of increased defects induced by high-field polarization on bandgap evolution and photovoltaic properties was investigated. The increase in defect concentration in KNSNH2 induced by high-field polarization is the cause of the variation in bandgap structure in KNSNH2. Structural refinement suggests that the change in the bandgap after polarization can be induced by the lattice distortion. The evolution of bandgap structure after polarization in KNSNH2 lead to an enhancement of visible light absorption, which further improve the photovoltaic performance by produced more carriers. A two-fold enhancement of short-circuit photocurrent density (Jsc) under simulated solar irradiation is achieved in the KNSNH2 sample by polarization. This work provides new insights into the effect of defect induced by polarization on enhancing ferroelectric photovoltaic performance and the mechanism of bandgap evolution.

Ferroelectric Photovoltaic Effect in the Ordered Smectic Phases of Chiral π-Conjugated Liquid Crystals: Improved Current-Voltage Characteristics by Efficient Fixation of Polar Structure

Abstract We synthesized four liquid-crystalline (LC) compounds with extended π-conjugation, incorporating a chiral branched-alkoxy chain. These compounds displayed ferroelectric chiral smectic C (SmC*) and ordered smectic phases. The carrier transport properties in the LC phases were characterized using the time-of-flight (TOF) method. Although all four chiral phenylterthiophene derivatives exhibited nondispersive hole conduction in the SmC* phases, nondispersive transient curves in the ordered smectic phases were limited. Notably, clear nondispersive photocurrent decays were observed in the ordered smectic phase of an LC compound containing an (R)-3-octyloxy moiety as the chiral unit. This compound achieved hole mobility of 4 × 10−3 cm2 V−1 s−1 in the ordered phase at 114 °C. The polar structure induced by poling treatment in the ferroelectric SmC* phase of the chiral LC compound was successfully stabilized with a lower electric field than previously reported systems. We confirmed the presence of the ferroelectric bulk photovoltaic effect in the polarized structure of the chiral-ordered smectic phase. Furthermore, we observed an enhancement in the output performance for the bulk photovoltaic effect due to the efficient stabilization of the polar structure.

Giant Polarization Sensitivity via the Anomalous Photovoltaic Effect in a Two-Dimensional Perovskite Ferroelectric.

Polarization sensitivity, which shows great potential in photoelectric detection, is expected to be significantly improved by the ferroelectric anomalous photovoltaic (APV) effect. However, it is challenging to explore new APV-active ferroelectrics due to severe polarization fatigue induced by the leakage current of photoexcited carriers. For the first time, we report a strong APV effect in a 2D hybrid perovskite ferroelectric assembled by alloying mixed organic cations, (HA)2(EA)2Pb3Br10 (1, where HA+ is n-hexylammonium and EA+ is ethylammonium), which has a large spontaneous polarization ∼3.8 μC/cm2 and high a Curie temperature ∼378 K. Its ferroelectricity allows a strong APV effect with an above-bandgap photovoltage up to 7.4 V, which exceeds its bandgap (∼2.7 eV). Most strikingly, based on the dependence on polarized-light angle, this strong APV effect renders the highest level of polarization sensitivity with a giant current ratio of ∼25, far beyond other 2D single-phase materials. This study sheds light on the exploration of APV-active ferroelectrics and inspires their future high-performance optoelectronic device applications.

Evolution between ferroelectric photovoltaic effect and resistance switching behavior engineered by the polarization field and barrier characteristics.

The bandgap and polarization field play a key role in the ferroelectric photovoltaic effect. However, narrow bandgap induced electrical conductivity always brings out a depression of the photovoltaic performances. Based on the mechanisms of the photovoltaic effect and resistance switching behaviors in ferroelectric materials, this work realizes an evolution between the two effects by engineering the polarization field and barrier characteristics, which addresses the trade-off issues between the bandgap and polarization for ferroelectric photovoltaic effect. SrCoOx (SC, 2.5≤x≤3) with multivalent transition is introduced into Na0.5Bi0.5TiO3 (NBT) matrix material to engineered the polarization field and barrier characteristics. (1-x)NBT-xSC (x=0.03, 0.05, 0.07) solid solution films present an evolution of ferroelectric photovoltaic effect to grow out of nothing again to the disappearance of the photovoltaic effect and the appearance of resistance switching behavior. The 0.95NBT-0.05SC film achieve the open-circuit voltage of 0.81 V and the short-circuit current of 23.52 µA/cm2, and the 0.93NBT-0.07SC film obtains the resistive switching behavior with switch ratio of 100. This work provides a practicable strategy to achieve the fascinating evolution between photovoltaic effect and resistive switching.

Plasmonic-enhanced photovoltaic output in bismuth ferrite films

Recently, the ferroelectric photovoltaic effect of BiFeO3 has attracted much attention due to its above-bandgap photovoltage and switchable photocurrent. However, the very low photocurrent density hinders its practical application. In this paper, elaborate photovoltaic heterostructures were constructed by BiFe0.9375Ti0.0625O3 (BFTiO) film and Au nanoparticles layer. The results and analysis demonstrate that these heterostructures exhibit a huge enhancement in photocurrent density. A possible mechanism for the enhanced photocurrent density is proposed herein based on the Local Surface Plasmon Resonance (LSPR) effect. First, the incident light reaching the Au nanoparticles is amplified by the LSPR effect and reflected into the BFTiO film, thus improving its light absorption. Second, the photogenerated electrons in the vicinity of the BFTiO-Au interface are accelerated by the enhanced electromagnetic field caused by the LSPR effect, thereby promoting the separation efficiency of the photogenerated carriers. Consequently, the LSPR effect significantly increases the photocurrent density of the BFTiO film.

Exceptionally Strong Self-Powered Polarization Behaviors Involving with Bulk Photovoltaics in Highly Anisotropic 2D Hybrid Perovskite Ferroelectric Crystals

Two-dimensional (2D) hybrid perovskites take an emerging position in optoelectronics. Especially, ferroelectric crystals in this family can be potentially used as polarized light detectors because photocurrent, induced by the ferroelectric bulk photovoltaic effect (BPVE), is the function of the intersection angle between the polarization directions of polarized light and the spontaneous polarization (Ps) direction of ferroelectric crystals. Herein, exceptionally strong polarization responses to polarized light are achieved in ferroelectric crystals of (isopentylammonium)2CsPb2Br7 (1), which is closely involved with the Ps-directed BPVE. Structurally, the alternate packing of organic spacers and inorganic sheets leads to its intrinsic anisotropy of optical dichroism (αc/αa ∼ 3.1), thus creating sinusoidal photocurrents with a polarization ratio of ∼1.2 at 10 V bias. It is noteworthy that the exceptional polarization responses with a large polarization ratio of ∼7.2 can be further obtained based on its BPVE at zero bias (self-powered mode). This figure-of-merit is significantly superior to that of some 2D materials, nanowires, and homologues, e.g., ReS2 (∼3.5), GeSe (∼2.16), CsPbBr3 nanowire (∼2.6), and (n-butylammonium)2(methylammonium)Pb2Br7 (∼2.0). This work sheds light on the optimization of photoelectric behaviors on the targeted optoelectronic device applications by ferroelectric BPVE.

Flexible BaTiO3 Thin Film-Based Coupled Nanogenerator for Simultaneously Scavenging Light and Vibration Energies

Ferroelectric materials have a variety of properties, such as piezoelectricity, pyroelectricity, and the ferroelectric photovoltaic effect, which enable them to obtain electrical energy from various external stimuli. Here, we report a coupled nanogenerator based on flexible BTO ferroelectric films with a cantilevered beam structure. It combines the photovoltaic and flexoelectric effects in a ferroelectric materials-based coupled nanogenerator for simultaneously scavenging vibration energy and light energy, thus improving energy scavenging performance. As compared with the photovoltaic effect individually, simultaneous vibration and light illumination under a light intensity of 57 mW/cm2 at 405 nm can produce a photo-flexoelectric coupling current of 85 nA, where the current peak has been enhanced by 121%. Due to the photo-flexoelectric coupling effect, the device has outstanding charging performance, where a 4.7 μF capacitor can be charged to 60 mV in 150 s. These devices have potential applications in multi-energy scavenging and self-powered sensors.

Stress-tuning the bulk photovoltaic response in polycrystalline bismuth ferrite films

Bulk or anomalous photovoltaic effect in ferroelectrics has recently sparked interest due to the generation of switchable photovoltages that are not limited by the bandgap of the material. The development of strategies to tune its magnitude is a key for the development of light-driven devices, e.g., photostrictive actuators, photostrictive sensors, or reconfigurable waveguides. In this paper, the bulk photovoltaic effect of polycrystalline solution-deposited bismuth ferrite thin films is studied under different stress conditions induced by different substrates and quantified using a direct strain assessment via x-ray diffraction. An increase in the short-circuit bulk photovoltaic current of 150% is observed with a change from a compressive stress of 0.54 GPa to a tensile stress of 0.93 GPa. This change is attributed to intrinsic piezophotovoltaic effect, demonstrating the potential to strain engineer the bulk photovoltaic effect in thin films.

Revisiting the Ferroelectric Photovoltaic Properties of Vertical BiFeO3 Capacitors: A Comprehensive Study.

The ferroelectric photovoltaic effect has been extensively studied for possible applications in energy conversion and photo-electrics. The reversible spontaneous polarization gives rise to a switchable photovoltaic behavior. However, despite its long history, the origin of the ferroelectric photovoltaic effect still lacks a full understanding since multiple mechanisms such as bulk and Schottky-barrier-related interface effects are involved. Herein, we report a comprehensive study on the photovoltaic response of BiFeO3-based vertical heterostructures, using multiple strategies to clarify its origin. We found that, under white light illumination, polarization-modulated Schottky barrier at the interface is the dominating mechanism. By varying the top metal contacts, only the photovoltaic effect of the polarization downward state is strongly modulated, suggesting selective interface contribution in different polarization states. A Schottky-barrier-free device shows negligible photovoltaic effect, suggesting the lack of bulk photovoltaic effect in vertical heterostructures under white light illumination.

Enhanced Fill Factor and Power Conversion Efficiency of Single Oxide Ferroelectric Photovoltaic Devices with Designed Nanostructures

AbstractThe ferroelectric photovoltaic effect has promising potential for the next generation of solar cells. However, due to disadvantages such as wide bandgap and low fill factor (FF), the power conversion efficiency (PCE) values reported in ferroelectric photovoltaic devices remain considerably below expectations. Herein, enhanced photovoltaic effect in the films with the nanostructure of ferroelectric nanocrystalline particles embedded in the amorphous or poor crystalline matrix is investigated. The nanostructures are realized by controlled crystallization and doping in Zn0.92‐xCux(Fe0.04Li0.04)O (ZCFLO) films. Benefiting from the improved carrier dynamic regulation in ferroelectric/boundary nanostructures and narrowed bandgap, the designed ZCFLO photoferroelectrics films exhibit high efficiency photovoltaic effect under AM 1.5G light, manifesting above‐bandgap photovoltage, markedly improved FF (83.4%), switchable photoresponse (50.3 mA W−1), and high PCE (14.4%). Meanwhile, the simple method presented in this work is fully compatible with large‐scale manufacturing processes and may find applications in cost‐efficiency optoelectronic devices.

Coupling oxygen vacancy gradient distribution and flexoelectric effects for enhanced photovoltaic performance in bismuth ferrite films

Coupling oxygen vacancy gradient distribution and flexoelectricity for the enhancement of ferroelectric photovoltaic effects.

Broadband, high-sensitivity self-powered ferroelectric LuMnO3-based photodetector with large photocurrent output

The broadband spectrum detection from ultraviolet to near-infrared is hankered in the photoelectric applications of imaging, sensing and communication. Here, a new self-powered photodetector based on ferroelectric LuMnO3 thin film with a narrow bandgap of 1.46 eV exhibits high-sensitivity ultraviolet–visible–near infrared photodetection properties. The responsivity (R) and detectivity (D*) in sunlight are 0.4 A/W and 7.05 × 1011 Jones, which are much higher than that of other ferroelectric photodetectors. Moreover, under the monochromatic light (900 nm), the R and D* can reach 0.39 A/W and 6.89 × 1011 Jones. The outstanding photodetection performances owed to the large photocurrent output, where the short-circuit current density can reach 10.5 mA/cm2 under 1 sun illumination. The synergistic effect of ferroelectric photovoltaic effect and interface barrier effect demonstrates that the multi-driving forces can achieve high dissociation efficiency for photon-generated carriers. The excellent photodetection performances open up new application of ferroelectric materials in broadband self-powered photodetectors.

Maxwell–Wagner polarization engineering in ferroelectric photovoltaic effect

Ferroelectric photovoltaic cells have attracted particular interest owing to their potential applications in the green energy field. But there are two drawbacks: weak polarization and wide bandgap, which make them suffer from the limitation of energy conversion efficiency. In this study, the key issue is solved in Ag2O nanoparticle-dispersed Bi5Ti3FeO15 composites. In order to clarify the mechanism, performances of the bandgap, polarization-dependent J–V curves, dielectric response, and switchable photocurrents were investigated. The Maxwell–Wagner polarization effect is confirmed by permittivity Cole–Cole plots with two or more semicircles overlapping. The spatial polarization gradient matrices can reduce the effective mass of the electron–hole pairs and further promote their separation via the Maxwell–Wagner polarization effect. The synchronous mobility of the separated carriers is enhanced. An improved ferroelectric photovoltaics is achieved in Bi5Ti3FeO15⋅3%Ag2O composites, and the key parameters are as follows: VOC ∼ −3.1 V, energy converse efficiency 9.2 × 10−4%. Furthermore, this work shows the first step toward polarization gradient composites for application in ferroelectric photovoltaic cells.