A ferroelectric field effect in the bulk heterojunction was found when an external electric field (EEF) was applied on the active layer of polymer solar cells (PSCs) during the annealing process of the active layer spin-coated with poly (3-hexylthiophene):[6,6]-phenyl-C61 butyric acid methyl ester (P3HT:PCBM). For one direction field, the short circuit current density of PSCs was improved from 7.2 to 8.0 mA/cm2, the power conversion efficiency increased from 2.4 to 2.8%, and the incident photon-to-current conversion efficiency increased from 42 to 49% corresponding to the different EEF magnitude. For an opposite direction field, the applied EEF brought a minus effect on the performance mentioned above. EEF treatment can orientate molecular ordering of the polymer, and change the morphology of the active layer. The authors suggest a explanation that the ferroelectric field has been built in the active layer, and therefore it plays a key role in PSCs system. A needle-like surface morphology of the active film was also discussed.
We present a fully quantum-mechanical model of the electronic dynamics of primary photoexcitations in a polymeric semiconductor heterojunction, which includes both polymer stacking and phonon relaxation. By examining the phonon-induced fluctuations in the state-to-state energy gaps and the exact golden-rule rate constants, we conclude that resonant tunnelling between the primary exciton to delocalized interchain charge-transfer states may be the initial step in the formation of charge-carriers in polymer-based bulk-heterojunction photovoltaic diodes.
A ferroelectric junction transistor memory made from switchable van der Waals p-n heterojunctions
Zhejiang University（浙江大学）；King Abdullah University of Science and Technology（阿卜杜拉国王科技大学）；Wenzhou University（温州大学）；Chinese Academy of Sciences（中国科学院）；South China Normal University（华南师范大学）；Xidian University（西安电子科技大学）
We report a simple one pot process for the preparation of lead sulphide (PbS) nanocrystals in the conjugated polymer MEH-PPV, and we demonstrate electronic coupling between the two components.
Recombination of photogenerated charge carriers in polymer bulk heterojunction (BHJ) solar cells reduces the short circuit current (Jsc) and the fill factor (FF). Identifying the mechanism of recombination is, therefore, fundamentally important for increasing the power conversion efficiency. Light intensity and temperature dependent current-voltage measurements on polymer BHJ cells made from a variety of different semiconducting polymers and fullerenes show that the recombination kinetics are voltage dependent and evolve from first order recombination at short circuit to bimolecular recombinat…
Two-dimensional transition metal dichalcogenides (TMDCs) have recently attracted attention due to their superlative optical and electronic properties. In particular, their extraordinary optical absorption and semiconducting band gap have enabled demonstrations of photovoltaic response from heterostructures composed of TMDCs and other organic or inorganic materials. However, these early studies were limited to devices at the micrometer scale and/or failed to exploit the unique optical absorption properties of single-layer TMDCs. Here we present an experimental realization of a large-area type-I…
In this paper we consider the essential electronic excited states in parallel chains of semiconducting polymers that are currently being explored for photovoltaic and light-emitting diode applications. In particular, we focus upon various type II donor-acceptor heterojunctions and explore the relation between the exciton binding energy to the band off-set in determining the device characteristic of a particular type II heterojunction material. As a general rule, when the exciton binding energy is greater than the band off-set at the heterojunction, the exciton will remain the lowest energy exc…
We observe a universal feature in the frequency dependence of intensity modulated photocurrent Iph based on studies of a variety of efficient bulk-heterojunction polymer solar cells (BHJ-PSCs). This feature of Iph appears in the form of a local maximum in the 5 kHz < frequency < 10 kHz range and is observed to be largely independent of the external parameters such as modulated light intensity (Lac), wavelength, temperature (T), and external field (EF) over a wide range. Simplistic kinetic models involving carrier generation, recombination and extraction processes are used to interpret the over…
The quantum-dynamical mechanism of photoinduced subpicosecond exciton dissociation and the concomitant formation of a charge-separated state at a TFB:F8BT polymer heterojunction is elucidated. The analysis is based upon a two-state vibronic coupling Hamiltonian including an explicit 24-mode representation of a phonon bath comprising high-frequency (C$=$C stretch) and low-frequency (torsional) modes. The initial relaxation behavior is characterized by coherent oscillations, along with the decay through an extended nonadiabatic coupling region. This region is located in the vicinity of a conical…
A polysquaraine low band gap polymer was synthesized by Yamamoto coupling of a monomeric dibromo indolenine squaraine dye. The resulting polymer has a weight average molar mass in the order of Mw ~30.000-50.000 and a polydispersity of ca. 1.7 as determined by gel-permeation chromatography (GPC). The electronic properties of monomer and polymer were investigated by cyclic voltammetry, absorption and emission spectroscopy. Owing to exciton coupling the absorption bands of the polymer are red-shifted and strongly broadened compared to the monomer squaraine dye. Bulk heterojunction solar cells wer…
Mixed-dimensional van der Waals heterojunctions comprising polymer and twodimensional (2D) semiconductors have many characteristics of an ideal charge separation interface for optoelectronic and photonic applications. However, the photoelectron dynamics at polymer- 2D semiconductor heterojunction interfaces are currently not sufficiently understood to guide the optimization of devices for these applications. This manuscript is a report of a systematic exploration of the time-dependent photophysical processes that occur upon photoexcitation of a type-II heterojunction between the polymer PTB7 a…
Organic solar cells have the potential to be low-cost and efficient solar energy converters, with a promising energy balance. They are made from carbon-based semiconductors, which exhibit favourable light absorption and charge generation properties, and can be manufactured by low temperature processes such as printing from solvent-based inks, which are compatible with flexible plastic substrates or even paper. In this review, we will present an overview of the physical function of organic solar cells, their state-of-the-art performance and limitations, as well as novel concepts to achieve a be…
Four modifications of the corona triode are described for charging polar polymers with ferroelectric or non-linear optical properties. Advantages of the constant current modification of corona poling are illustrated and discussed.
The effect of interfaces and confinement in polymer ferroelectric structured is discussed. Results on confinement under different geometries are presented and the comparison of all of them allows to evidence that the presence of an interface in particular cases stabilizes a ferroelectric phase that is not spontaneously formed under normal bulk processing conditions
In polymeric semiconductors, charge carriers are polarons, which means that the excess charge deforms the molecular structure of the polymer chain that hosts it. This effect results in distinctive signatures in the vibrational modes of the polymer. We probe polaron photo- generation dynamics at polymer:fullerene heterojunctions by monitoring its time-resolved resonance-Raman spectrum following ultrafast photoexcitation. We conclude that polarons emerge within 200 fs, which is nearly two orders of magnitude faster than exciton localisation in the neat polymer film. Surprisingly, further vibrati…
Light induced polarons in solid films of polymer-fullerene blends were studied by applying photoluminescence (PL), photo induced absorption (PIA) techniques as well as electron spin resonance (ESR). The materials used were poly(3-hexylthiophene) (P3HT) and poly-[2-methoxy, 5-(2'-ethyl-hexyloxy) phenylene vinylene] (MEH-PPV) as donors. As acceptors we used [6,6]-phenyl-C61-butyric acid methyl ester ([C60]PCBM) and various soluble C70-derivates: [C70]PCBM, diphenylmethano[70]fullerene oligoether (C70-DPM-OE), C70-DPM-OE2, and two fullerene dimers, C70-C70 and C60-C70 (all shown in figure 1). In …
Experimental results are presented on anomalous behavior of absorption currents in PVDF during the stepwise increase of the voltage applied through a corona. These results, supplemented with the dynamics of the time constant of the electret potential decay are consistent with a hypothesis assuming deep trapping of the charge carriers during the polarization buildup in ferroelectric polymers. Model calculations are made on distribution of the potential energy at the surface of the polarized crystallites proving that additional sites for the charge trapping are created there.
Ferroelectric field-effect transistors (FE-FETs) consisting of tunable dielectric layers are utilized to investigate interfacial transport processes. Large changes in the dielectric constant as a function of temperature are observed in FE-FETs in conjunction with the ferroelectric to paraelectric transition. The devices offer a test bed to evaluate specific effects of polarization on the electrical processes. FE-FETs have dominant contributions from polarization-fluctuation rather than static dipolar disorder prevalent in high k paraelectric dielectric-based FETs. Additionally, photo-excitatio…
The ongoing depletion of fossil fuels has led to an intensive search for additional renewable energy sources. Solar-based technologies could provide sufficient energy to satisfy the global economic demands in the near future. Photovoltaic (PV) cells are the most promising man-made devices for direct solar energy utilization. Understanding the charge separation and charge transport in PV materials at a molecular level is crucial for improving the efficiency of the solar cells. Here, we use light-induced EPR spectroscopy combined with DFT calculations to study the electronic structure of charge …
The major loss mechanism of photogenerated polarons was investigated in P3HT:PCBM solar cells by the photo-CELIV technique. For pristine and annealed devices, we find that the experimental data can be explained by a bimolecular recombination rate reduced by a factor of about ten (pristine) and 25 (annealed) as compared to Langevin theory. Aided by a macroscopic device model, we discuss the implications of the lowered loss rate on the characteristics of polymer:fullerene solar cells.
We investigated photogeneration yield and recombination dynamics in blends of poly(3-hexyl thiophene) (P3HT) and poly[2-methoxy-5-(30,70-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) with [6,6]- phenyl-C61 butyric acid methyl ester (PC61BM) by means of temperature dependent time delayed collection field (TDCF) measurements. In MDMO-PPV:PC61BM we find a strongly field dependent polaron pair dissociation which can be attributed to geminate recombination in the device. Our findings are in good agreement with field dependent photoluminescence measurements published before, supporting a scena…
We investigate the electronic dynamics of model organic photovoltaic (OPV) system consisting of polyphenylene vinylene (PPV) oligomers and [6,6]-phenyl C61-butyric acid methylester (PCBM) blend using a mixed molecular mechanics/quantum mechanics (MM/QM) approach. Using a heuristic model that connects energy gap fluctuations to the average electronic couplings and decoherence times, we provide an estimate of the state-to-state internal conversion rates within the manifold of the lowest few electronic excitations. We find that the lowest few excited states of a model interface are rapidly mixed …
Hybrid conjugated polymer/fullerene filaments based on MEH-PPV/PVP/PCBM are prepared by electrospinning, and their properties assessed by scanning electron, atomic and lateral force, tunnelling, and confocal microscopy, as well as by attenuated total reflection Fourier transform-infrared spectroscopy, photoluminescence quantum yield and spatially-resolved fluorescence. Highlighted features include ribbon-shape of the realized fibers, and the persistence of a network serving as a template for heterogeneous active layers in solar cell devices. A set of favorable characteristics is evidenced in t…
We investigate the mechanical properties of $π$-conjugated polymeric materials composed of regioregular poly(3-hexylthiophene) (P3HT) and fullerene C$_{60}$ using coarse-grained molecular dynamics simulations. Specifically, we perform tensile simulations of P3HT:C$_{60}$ composites with varied degrees of polymerization and C$_{60}$ mass fractions to obtain their stress-strain responses. Decomposition of stress tensor into kinetic energy and virial contributions indicates that the tensile moduli of the pure P3HT samples are greatly dependent on non-bonded interactions and on bonded interactions…
Colloidal zinc oxide (ZnO) nanoparticles are frequently used in the field of organic photovoltaics for the realization of solution-producible, electron-selective interfacial layers. Despite of the widespread use, there is a lack of detailed investigations regarding the impact of structural properties of the particles on the device performance. In this work, ZnO nanoparticles with varying surface-area-to-volume ratio were synthesized and implemented into polymer-fullerene bulk heterojunction solar cells with a gas-permeable top electrode. By comparing the electrical characteristics before and a…
We report on the fabrication and electrical characterization of few-layer graphene (FLG) devices coated with a ferroelectric polymer layer of poly(vinylidene fluoride/trifluoroethylene) [P(VDF/TrFE)]. Highly stable and reliable resistance changes were observed under floating conditions, which were dependent on the back gate voltage applied beforehand. Nonvolatile memory functionality in the hybrid FLG-P(VDF/TrFE) devices is attributed to a remanent electric field induced by the ferroelectric polarization of the P(VDF/TrFE) layer.
The behavior of ferroelectricity at the nanoscale is the focus of increasing research activity because of intense interest in the fundamental nature of spontaneous order in condensed-matter systems and because of the many practical applications of ferroelectric thin films to, for example, electromechanical transducers, infrared imaging sensors, and nonvolatile random-access memories. Ferroelectricity, in analogy with its namesake ferromagnetism, is the property of some crystalline systems to maintain a permanent, but reversible, electrical polarization in the absence of an external electric fi…
Blends of polymer and C$_{60}$-derived molecules are in the spotlight in recent years for application in organic photovoltaics, forming what is known as bulk-heterojunction active layers. The character of the heterojunction is determinant, with clear relevance of morphology and phase separation. To better understand the morphology of the systems, we present a classical molecular dynamics (CMD) simulation of polymer/fullerene (P3HT/C$_{60}$) blends, coming from different starting points, using the specifically designed Nanomol Force Field based on the Universal Force Field. We use not-so-short …
We report piezo-response force microscopy studies of the static and dynamic properties of domain walls (DWs) in 11 to 36 nm thick films of crystalline ferroelectric poly(vinylidene-fluoride-trifluorethylene). The DW roughness exponent ζ ranges from 0.39 to 0.48 and the DW creep exponent μ varies from 0.20 to 0.28, revealing an unexpected effective dimensionality of ~1.5 that is independent of film thickness. Our results suggest predominantly 2D ferroelectricity in the layered polymer and we attribute the fractal dimensionality to DW deroughening due to the correlations between the in-plane and…
The possibility of controlling the domain structure in spherical nanoparticles of uniaxial and multiaxial ferroelectrics using a shell with tunable dielectric properties is studied in the framework of Landau-Ginzburg-Devonshire theory. Finite element modeling and analytical calculations are performed for Sn2P2S6 and BaTiO3 nanoparticles covered with high-k polymer, temperature dependent isotropic paraelectric strontium titanate, or anisotropic liquid crystal shells with a strongly temperature dependent dielectric permittivity tensor. It appeared that the tunable paraelectric shell with a tempe…
School of Emergent Soft Matter, State Key Laboratory of Advanced Papermaking and Paperbased Materials, South China University of Technology（华南理工大学 emergent 软物质学院，先进造纸及纸基材料国家重点实验室）；Guangdong Provincial Key Laboratory of Functional and Intelligent Hybrid Materials and Devices, Guangdong Basic Research Center of Excellence for Energy & Information Polymer Materials, South China University of Technology（华南理工大学广东省功能与智能杂化材料与器件重点实验室，广东省能源与信息高分子材料基础研究中心）；Eindhoven University of Technology（埃因霍温理工大学）
Nanoscaled room-temperature ferroelectricity is ideal for developing advanced non-volatile high-density memories. However, reaching the thin film limit in conventional ferroelectrics is a long-standing challenge due to the possible critical thickness effect. Van der Waals materials, thanks to their stable layered structure, saturate interfacial chemistry and weak interlayer couplings, are promising for exploring ultra-thin two-dimensional (2D) ferroelectrics and device applications. Here, we demonstrate a switchable room-temperature ferroelectric diode built upon a 2D ferroelectric α-In2Se3 la…
Polymer-piezoceramic 0-3 composites combine the flexibility of the polymers and the excellent piezoelectric properties of the ferroelectric based ceramic. While grain size of the ceramic powder is one of the important considerations in the fabrication of such composites, a correlation relating poling field induced structural changes and its possible influence on the overall piezoelectric response of the composite is still lacking. In this paper, we examine this issue on a 0-3 piezo-composite comprising of a ceramic powders of a low-lead piezoelectric alloy (x)Bi(Ni1/2Zr1/2O3-(1-x)PbTiO3 in pro…
We present experimental evidence for hexagonal domain faceting in the ferroelectric polymer PVDF-TrFE films having the lower orthorhombic crystallographic symmetry. This effect can arise from purely electrostatic depolarizing forces. We show that in contrast to magnetic bubble shape domains where such type of deformation instability has a predominantly elliptical character, the emergence of more symmetrical circular harmonics is favored in ferroelectrics with high dielectric constant.
The separation of photogenerated polaron pairs in organic bulk heterojunction solar cells is the intermediate but crucial step between exciton dissociation and charge transport to the electrodes. In state-of-the-art devices, above 80% of all polaron pairs are separated at fields of below $10^7$V/m. In contrast, considering just the Coulomb binding of the polaron pair, electric fields above $10^8$V/m would be needed to reach similar yields. In order to resolve this discrepancy, we performed kinetic Monte Carlo simulations of polaron pair dissociation in donor--acceptor blends, considering deloc…
We studied the recombination dynamics of charge carriers in organic bulk heterojunction solar cells made of the blend system poly(2,5-bis(3-dodecyl thiophen-2-yl) thieno[2,3-b]thiophene) (pBTCT-C12):[6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) with a donor--acceptor ratio of 1:1 and 1:4. The techniques of charge carrier extraction by linearly increasing voltage (photo-CELIV) and, as local probe, time-resolved microwave conductivity (TRMC) were used. We observed a difference in the initially extracted charge carrier concentration in the photo-CELIV experiment by one order of magnitude, w…
Graphene has exceptional optical, mechanical and electrical properties, making it an emerging material for novel optoelectronics, photonics and for flexible transparent electrode applications. However, the relatively high sheet resistance of graphene is a major constrain for many of these applications. Here we propose a new approach to achieve low sheet resistance in large-scale CVD monolayer graphene using non-volatile ferroelectric polymer gating. In this hybrid structure, large-scale graphene is heavily doped up to 3{\times}1013 cm-2 by non-volatile ferroelectric dipoles, yielding a low she…
Ferroelectric materials can switch their polarization in response to an applied electric field. In this work, ferroelectricity at the single molecule level is proposed and investigated using density functional theory (DFT) calculations. Several bowl-shaped molecules, both synthetically reported and hypothetically proposed, are shown to invert polarization in response to external applied electric fields. Such a polarization inversion relies on the conformational change of a single molecule, unlike its traditional counterparts of which ferroelectricity originates from the switch of an asymmetric…
Organic bulk-heterojunctions (BHJ) and solar cells containing the trimetallic nitride endohedral fullerene 1-[3-(2-ethyl)hexoxy carbonyl]propyl-1-phenyl-Lu3N@C80 (Lu3N@C80-PCBEH) show an open circuit voltage (VOC) 0.3 V higher than similar devices with [6,6]-phenyl-C[61]-butyric acid methyl ester (PC61BM). To fully exploit the potential of this acceptor molecule with respect to the power conversion efficiency (PCE) of solar cells, the short circuit current (JSC) should be improved to become competitive with the state of the art solar cells. Here, we address factors influencing the JSC in blend…
Inclusion of heavy metal atoms in a polymer backbone allows transitions between the singlet and triplet manifolds. Interfacial dissociation of triplet excitons constitutes a viable mechanism for enhancing photovoltaic (PV) efficiencies in polymer heterojunction-based solar cells. The PV efficiency from polymer solar cells utilizing a ladder-type poly (para-phenylene) polymer (PhLPPP) with trace quantity of Pd atoms and a fullerene derivative (PCBM) is much higher than its counterpart (MeLPPP) with no Pd atom. Evidence is presented for the formation of a weak ground-state charge-transfer comple…
Understanding of degradation mechanisms in polymer:fullerene bulk-heterojunctions on the microscopic level aimed at improving their intrinsic stability is crucial for the breakthrough of organic photovoltaics. These materials are vulnerable to exposure to light and/or oxygen, hence they involve electronic excitations. To unambiguously probe the excited states of various multiplicities and their reactions with oxygen, we applied combined magneto-optical methods based on multifrequency (9 and 275 GHz) electron paramagnetic resonance (EPR), photoluminescence (PL), and PL-detected magnetic resonan…
We have performed resistivity measurements of poly[3,4-ethylenedioxythiophene]: poly[styrenesulfonate] (PEDOT:PSS) films with varying concentrations of glycerol. Resistivity is seen to decrease exponentially from roughly 3 ohm-cm for pure PEDOT:PSS to 3x10-2 ohm-cm for 35 mg/cm3 glycerol in PEDOT:PSS. Beyond this concentration adding glycerol does not significantly change resistivity. Bulk heterojunction polymer solar cells using these variously doped PEDOT:PSS layers as electrodes were studied to characterize the effects on efficiency and lifetime. Although our data display significant scatte…
Herein, we elucidate the impact of tubular confinement on the structure and relaxation behaviour of poly(vinylidene difluoride) (PVDF) and how these affect the para-/ferroelectric behavior of this polymer. We use PVDF nanotubes that were solidified in anodic aluminum oxide (AAO) templates. Dielectric spectroscopy measurements evidence a bimodal relaxation process for PVDF nanotubes: besides the bulk-like -relaxation, we detect a notably slower relaxation that is associated with the PVDF regions of restricted dynamics at the interface with the AAO pore. Strickingly, both the bulk-like and the i…
Over the past decades, there has been significant interest in new cooling technology based on the electrocaloric effect. The large electrocaloric effect observed in polymeric and inorganic ferroelectric materials made possible development of dielectric cooling devices of a new generation. We report a significant impact of annealing on the electrocaloric effect observed in 12/65/35 PLZT bulk ceramics. The electrocaloric data were obtained by direct measurements. Electrocaloric results confirm the existence of the significant electrocaloric response in this relaxor ferroelectric PLZT composition…
Organic solar cells (OSCs) containing an active layer consisting of a nanostructured blend of a conjugated polymer like poly(3-hexylthiophene) (P3HT) and an electron acceptor molecule have the potential of competing against silicon-based photovoltaic panels. However, this potential is unfulfilled primarily due to interrelated production and stability issues. The generally employed spin coating process for fabricating organic solar cells cannot be scaled up. Recently, He et al., have reported that the gelation of P3HT with [6,6]-phenyl-C61-butyric acid methyl ester (PC60BM) under sub-ambient co…
First-principles calculations based on density-functional theory in the pseudo-potential approach have been performed for the total energy, crystal structure and cell polarization for SrTaO$_2$N/SrTiO$_3$ heterostructures. Different heterojunctions were analyzed in terms of the termination atoms at the interface plane, and periodic or non-periodic stacking in the perpendicular direction. The calculations show that the SrTaO$_2$N layer is compressed along the $ab$-plane, while the SrTiO$_3$ is elongated, thus favoring the formation of P4mm local environment on both sides of the interface, leadi…
Polyvinylidenefluoride (PVDF) a semicrystalline pieozoelectric polymer was synthesized with varying process conditions and its ferroelectric domain orientations were studied using piezoresponse force microscope (PFM). PVDF thin films fabricated using tape casting technique with precursor solutions of varying viscosities reveal that the polarization components transform from a dominant planar component to an out-of-plane polarization components with increase in viscosity. Interestingly the planar components possessed a head to head or tail to tail kind of paired domains separated by a distance …
The extrinsic size effect in Piezoresponse Force Microscopy of ferroelectric and piezoelectric thin films on non-polar dielectric substrate is analyzed. Analytical expressions for effective piezoresponse, object transfer function components, and Rayleigh two-point resolution are obtained. These results can be broadly applied for effective piezoelectric response calculations in thin piezoelectric and ferroelectric films as well as surface polar layers e.g. in organic materials and bio-polymers. In particular, the effective piezoresponse strongly decreases with film thickness whereas the sharpne…
Poly(vinylidenefluoride-co-trifluoroethylene) (P(VDF-TrFE)) based pyroelectric as well as magnetoelectric materials offer great promises for energy harvesting for flexible and wearable applications. Hence, this work focus on solar energy harvesting as well as magnetoelectric phenomenon in two phase nanocomposite film where the constituting phases are manganese ferrite (MnFe2O4) nanoparticles and P(VDF-TrFE) polymer. Composite films have been prepared using solution casting technique. X-ray diffraction result shows higher crystallinity of these films. The ferroelectric, magnetic and magnetoelec…
Electroluminescence (EL) spectra from hybrid charge transfer excitons at metal oxide/organic type-II heterojunctions exhibit pronounced bias-induced spectral shifts. The reasons for this phenomenon have been discussed controversially and arguments for both electric field-induced effects as well as filling of trap states at the oxide surface have been put forward. Here, we combine the results from EL and photovoltaic measurements to eliminate the disguising effects of the series resistance. For SnOx combined with the conjugated polymer MeLPPP, we find a one-to-one correspondence between the blu…
Online training of deep neural networks (DNN) can be significantly accelerated by performing in-situ vector matrix multiplication in a crossbar array of analog memories. However, training accuracies often suffer due to device non-idealities such as nonlinearity, asymmetry, limited bit precision and dynamic weight update range within constrained power budget. Here, we report a three-terminal Ferroelectric-Field-Effect-Transistor based on low thermal budget processes that can work efficiently as an analog synaptic transistor. Ferroelectric polymer P(VDF-TrFE) as the gate insulator and 2D semicon…
Open circuit voltage decay measurements are performed on methylammonium lead iodide (CH3NH3PbI3) perovskite solar cells to investigate the charge carrier recombination dynamics. The measurements are compared to the two reference polymer-fullerene bulk heterojunction solar cells based on P3HT:PC60BM and PTB7:PC70BM blends. In the perovskite devices, two very different time domains of the voltage decay are found, with a first drop on a short time scale that is similar to the organic solar cells. However, two major differences are also observed. 65-70% of the maximum photovoltage persists on much…
For pyroelectric sensor application, materials having large ferroelectric polarization at low applied field and high pyroelectric sensitivity are required. PVDF is one of the ferroelectric polymers, which is being used for pyroelectric detector application. Following properties of PVDF such as low density, low acoustic impedance, wide bandwidth, flexibility, toughness, and ease of fabrication into complex patterns and arrays make it suitable for large area detector applications. But the PVDF has low value of pyroelectric coefficient (p). High field (above 1200kV/cm) is required to pole the PVD…
Using Landau-Ginzburg-Devonshire theory and effective medium approximation, we analytically calculate typical dependences of the pyroelectric and electrocaloric coefficients on external electric field, temperature and radius for spherical single-domain ferroelectric nanoparticles. The considered physical model corresponds to the nanocomposite with small fraction of ferroelectric nanoparticles. Within the framework of the analytical model we establish how the size changes determine the temperature and field behavior pyroelectric and electrocaloric coefficients on example of BaTiO3 nanoparticles…
Recent findings of a large electrocaloric (EC) effect in polymeric and inorganic ferroelectric materials open a potential possibility of development of solid-state cooling or heating devices of new generation with better energy efficiency that may be less harmful for the environment. We investigate by using direct measurements, the temperature and electric field dependence of the electrocaloric response in Pb1-xLax(ZryTi1-y)1-x/4O3 bulk ceramics (PLZT) with x=0.06 and 0.12. Here, the properties of the EC response were probed in a part of the PLZT composition phase diagram with low y=0.40 compo…
