Semitransparent,Flexible, and Self‐Powered Photodetectors Based on Ferroelectricity‐Assisted Perovskite Nanowire Arrays

Transparent and flexible photodetectors hold great promise in next‐generation portable and wearable optoelectronic devices. However, most of the previously reported devices need an external energy power source to drive its operation or require complex fabrication processes. Herein, designed is a semitransparent, flexible, and self‐powered photodetector based on the integrated ferroelectric poly(vinylidene‐fluoride‐trifluoroethylene) (P(VDF‐TrFE)) and perovskite nanowire arrays on the flexible polyethylene naphthalate substrate via a facile imprinting method. Through optimizing the treatment conditions, including polarization voltage, polarization time, and the concentration of P(VDF‐TrFE), the resulting device exhibits remarkable detectivity (7.3 × 10¹² Jones), fast response time (88/154 µs) at zero bias, as well as outstanding mechanical stability. The excellent performance is attributed to the efficient charge separation and transport originating from the highly oriented 1D transport pathway and the polarization‐induced internal electric field within P(VDF‐TrFE)/perovskite hybrid nanowire arrays.     

Micropatterned P(VDF‐TrFE) Film‐Based Piezoelectric Nanogenerators for Highly Sensitive Self‐Powered Pressure Sensors

Here micropatterned poly(vinylidenefluoride‐co‐trifluoroethylene) (P(VDF‐TrFE)) films‐based piezoelectric nanogenerators (PNGs) with high power‐generating performance for highly sensitive self‐powered pressure sensors are demonstrated. The microstructured P(VDF‐TrFE)‐based PNGs reveal nearly five times larger power output compared to a flat film‐based PNG. The micropatterning of P(VDF‐TrFE) polymer makes itself ultrasensitive in response to mechanical deformation. The application is demonstrated successfully as self‐powered pressure sensors in which mechanical energy comes from water droplet and wind. The mechanism of the high performance is intensively discussed and illustrated in terms of strain developed in the flat and micropatterned P(VDF‐TrFE) films. The impact derived from the patterning on the output performance is studied in term of effective pressure using COMSOL multiphysics software.     

Self‐Powered UV–Vis–NIR Photodetector Based on Conjugated‐Polymer/CsPbBr3 Nanowire Array

Perovskite photodetectors have attracted intensive research interest due to promising applications in sensing, communication, and imaging. However, their performance is restricted by the narrow spectrum range, required power source, and instability in ambient environment. To address these issues, a self‐powered photodetector based on the inorganic CsPbBr₃ perovskite nanowire array/conjugated‐polymer hybrid structure is designed. The spectra response range of the device can be extended to 950 nm, along with outstanding stability, fast response speed (111/306 µs), and large detectivity (1.2 × 10¹³ Jones). The performance parameters are comparable to or even better than most reported CsPbBr₃ and conjugated‐polymer photodetectors. The excellent performance is mainly attributed to the efficient carrier generation, separation, and transport resulting from array structure and favorable band structure.     

A Self‐Powered and Stable All‐Perovskite Photodetector–Solar Cell Nanosystem

Hybrid organic–inorganic perovskites have attracted intensive interest as light absorbing materials in solid‐state solar cells. Herein, we demonstrate a high‐performance CH₃NH₃PbI₃‐based perovskite photodetector constructed on the flexible indium tin oxide (ITO) coated substrate even after 200 bending cycles. The as‐fabricated devices show high responsivity, broad spectrum response from ultraviolet to whole visible light, long‐term stability, and high on‐off ratio. Particularly, atomic layer deposition technique was used to deposit the ultrathin Al₂O₃ film on devices, functioning as a protection layer to effectively enhance the stability and durability of perovskite photodetectors. The first all‐perovskite self‐powered nanosystem was successfully assembled by integrating a perovskite solar cell with a perovskite photodetector. Driven by the perovskite solar cell, the photodetector exhibits fast and stable response to illuminated light at a low working voltage less than 1.0 V. This stable integrated nanosystem has promising applications in which photodetectors can work in harsh environments without external power sources.     

Non‐volatile Ferroelectric Poly(vinylidene fluoride‐co‐trifluoroethylene) Memory Based on a Single‐Crystalline Tri‐isopropylsilylethynyl Pentacene Field‐Effect Transistor

A new type of nonvolatile ferroelectric poly(vinylidene fluoride‐co‐trifluoroethylene) (P(VDF‐TrFE)) memory based on an organic thin‐film transistor (OTFT) with a single crystal of tri‐isopropylsilylethynyl pentacene (TIPS‐PEN) as the active layer is developed. A bottom‐gate OTFT is fabricated with a thin P(VDF‐TrFE) film gate insulator on which a one‐dimensional ribbon‐type TIPS‐PEN single crystal, grown via a solvent‐exchange method, is positioned between the Au source and drain electrodes. Post‐thermal treatment optimizes the interface between the flat, single‐crystalline ab plane of TIPS‐PEN and the polycrystalline P(VDF‐TrFE) surface with characteristic needle‐like crystalline lamellae. As a consequence, the memory device exhibits a substantially stable source–drain current modulation with an ON/OFF ratio hysteresis greater than 10³, which is superior to a ferroelectric P(VDF‐TrFE) OTFT that has a vacuum‐evaporated pentacene layer. Data retention longer than 5 × 10⁴ s is additionally achieved in ambient conditions by incorporating an interlayer between the gate electrode and P(VDF‐TrFE) thin film. The device is environmentally stable for more than 40 days without additional passivation. The deposition of a seed solution of TIPS‐PEN on the chemically micropatterned surface allows fabrication arrays of TIPS‐PEN single crystals that can be potentially useful for integrated arrays of ferroelectric polymeric TFT memory.     

Flexible and Self‐Powered Lateral Photodetector Based on Inorganic Perovskite CsPbI3–CsPbBr3 Heterojunction Nanowire Array

Self‐powered perovskite photodetectors mainly adopt the vertical heterojunction structure composed of active layer, electron–hole transfer layers, and electrodes, which results in the loss of incident light and interfacial accumulation of defects. To address these issues, a self‐powered lateral photodetector based on CsPbI₃–CsPbBr₃ heterojunction nanowire arrays is designed on both a rigid glass and a flexible polyethylene naphthalate substrate using an in situ conversion and mask‐assisted electrode fabrication method. Through adding the polyvinyl pyrrolidone and optimizing the concentration of precursors under the pressure‐assisted moulding process, both the crystallinity and stability of perovskite nanowire array are improved. The nanowire array–based lateral device shows a high responsivity of 125 mA W^?1 and a fast rise and decay time of 0.7 and 0.8 ms under a self‐powered operation condition. This work provides a new strategy to fabricate perovskite heterojunction nanoarrays towards self‐powered photodetection.     

Novel p–p Heterojunctions Self‐Powered Broadband Photodetectors with Ultrafast Speed and High Responsivity

Novel inorganic/organic self‐powered UV–vis photodetectors based on single Se microtube and conducting polymers—polyaniline (PANI), polypyrrole (PPy), and poly(3,4‐ethylenedioxythiophene) (PEDOT)—are fabricated. The conducting polymers are directly coated on the surface of a single Se microtube via a facile and low‐cost in situ polymerization method. The integrated Se/PANI photodetector with 45‐nm‐thick PANI layer shows excellent self‐powered behavior under UV–vis light illumination. In particular, it exhibits high on/off ratio of 1.1 × 10³, responsivity (120 mA W^?1), large detectivity (3.78 × 10¹¹ Jones), and ultrafast response speed (rise time of 4.5 µs and fall time of 2.84 ms) at zero bias at 610 nm (0.434 mW cm^?2)‐light illumination. Moreover, the individual Se/PPy and Se/PEDOT self‐powered photodetectors also exhibit fast and stable responses, including responsivity of 70 and 5.5 mA W^?1, rise time of 0.35 and 1.00 ms, fall time of 16.97 and 9.78 ms, respectively. Given the simple device architecture and low cost fabrication process, this work provides a promising way to fabricate inorganic/organic, high‐performance, self‐powered photodetectors.     

An Ultrahigh Responsivity (9.7 mA W−1) Self‐Powered Solar‐Blind Photodetector Based on Individual ZnO–Ga2O3 Heterostructures

Highly crystallized ZnO–Ga₂O₃ core–shell heterostructure microwire is synthesized by a simple one‐step chemical vapor deposition method, and constructed into a self‐powered solar‐blind (200–280 nm) photodetector with a sharp cutoff wavelength at 266 nm. The device shows an ultrahigh responsivity (9.7 mA W^?1) at 251 nm with a high UV/visible rejection ratio (R _{251 nm}/R _{400 nm}) of 6.9 × 10² under zero bias. The self‐powered device has a fast response speed with rise time shorter than 100 µs and decay time of 900 µs, respectively. The ultrahigh responsivity, high UV/visible rejection ratio, and fast response speed make it highly suitable in practical self‐powered solar‐blind detection. Additinoally, this microstructure heterojunction design method would provide a new approach to realize the high‐performance self‐powered photodetectors.     

Infrared Detection Using Transparent and Flexible Field‐Effect Transistor Array with Solution Processable Nanocomposite Channel of Reduced Graphene Oxide and P(VDF‐TrFE)

Photodetectors using optically responsive graphene (Gr) or reduced graphene oxide (R‐GO) on rigid substrates have showed promising results for detection of broad band light including infrared (IR). However, there have been only a few reports on Gr or R‐GO photodetectors with new functionalities such as optical transparency and/or flexibility. Herein, a new kind of transparent and flexible IR photodetector is presented using a field‐effect transistor (FET) structure in which an IR‐responsive nanocomposite layer of R‐GO and poly(vinylidenefluoride‐co‐trifluoroethylene) (P(VDF‐TrFE)) is employed as the channel. The IR photodetector exhibits high IR responsivity, stability, and reproducibility under mechanical strain and ambient conditions. In addition, the capability of measuring the distribution of responses from each device in the transparent and flexible nanocomposite FET array under IR radiation from the human body is also demonstrated. Therefore, the development of a flexible IR photodetector with high responsivity, transparency, ease of integration, and stability in an ambient environment is a suitable alternative approach for achieving the stable monitoring of IR in many flexible and transparent electronic systems.     

High Quality Perovskite Crystals for Efficient Film Photodetectors Induced by Hydrolytic Insulating Oxide Substrates

A high quality perovskite film is a key factor in determining the device performance, such as photovoltaic cells, light‐emission diodes, lasers, and photodetectors. Here, a method is presented to improve the crystalline quality of perovskite films on surface‐oxygen‐rich insulating oxide substrates, which can promote the growth of both the polycrystalline and single crystals and enhance the adhesion between the perovskites and the substrates. A much longer carrier diffusion length of exceeding 5 µm together with significantly reduced trap density and nonradiative recombination is achieved for the film. These perovskite films show much better lasing and photodetector performance, indicating promising applications for the light emitting, lasing, and detector devices.     

Optimization of Solubility,Film Morphology and Photodetector Performance by Molecular Side‐Chain Engineering of Low‐Bandgap Thienothiadiazole‐Based Polymers

A series of donor–acceptor (D‐A) type low‐bandgap polymers containing the terthiophene and thieno[3,4‐b]thiadiazole units in the main chain but different numbers of identical side chains are designed and synthesized in order to study the effect of side chain on the polymer properties and optimize the performance of polymer photodetectors. Variation in the side chain content can influence the polymer solubility, molecular packing, and film morphology, which in turn affects the photodetector performance, particularly with regard to the photoresponsivity and dark current. X‐ray diffraction patterns indicate that molecular ordering increases with more side chains. Atomic force microscopy shows that appropriate morphology of the active layer in the polymer photodetector is necessary for high photocurrent and low dark current. Using BCP as a hole blocking layer (10 nm), the photodetector based on P4 exhibits the optimized performance with specific detectivity of 1.4 × 10¹² Jones at 800 nm, which is among the best reported values for polymer photodetectors and even comparable to that of a silicon photodetector.     

Solution‐Processed Self‐Powered Transparent Ultraviolet Photodetectors with Ultrafast Response Speed for High‐Performance Communication System

Transparent ultraviolet (UV) photodetectors are an essential component of next‐generation “see‐through” electronics. However, the current photodetectors often suffer from relatively slow response speeds and high driving voltages. Here, all‐solution‐processed UV photodetectors are reported that are facilely prepared from environmentally friendly and abundant materials. The UV photodetectors are composed of a titanium dioxide thin film as the photosensitive layer sandwiched between two different transparent electrodes to form asymmetric Schottky junctions. The photodetector with high optical transparency can operate at zero bias because of spontaneous separation of photogenerated electron–hole pairs by the built‐in electric field. The resulting self‐powered photodetector displays high sensitivity to broadband UV light (200–400 nm). In particular, an ultrafast response speed up to 44 ns is obtained, representing a significant improvement over those of the conventional transparent photodetectors. Moreover, the photodetector has been successfully applied, for the first time, in a UV communication system as the self‐powered signal receiver. This work uniquely combines the features of high optical transparency and self‐power ability into UV photodetectors and would enable a broad range of optoelectronic applications.     

Structural Design and Pyroelectric Property of SnS/CdS Heterojunctions Contrived for Low‐Temperature Visible Photodetectors

The traditional photodetectors based on photoelectric effect exhibit inferior response or even out of operation with the decrease of temperature. However, cryogenic visible light detection is increasingly demanded in deep space and polar exploration. Herein, a self‐powered visible photodetector coupling pyroelectricity and photoelectricity to optimize the cryogenic detecting performance is designed in which hydrothermally grown CdS nanorod array is covered by SnS nanoflakes. The choice of SnS allows the detector with strong visible light absorption and great photoelectric conversion efficiency, while the CdS nanorod structure with pyroelectricity can effectively modulate the behavior of photogenerated carriers at low temperatures. It is found that the response characteristics of the photodetector are dominated by the combination of pyroelectric and photoelectric effects, which becomes more significant with the reduced temperature. Specifically, at 130 K temperature, the photoresponse current under 650 nm light is improved by 7.5 times as that at room temperature, while the ratio of pyroelectric current to photocurrent can be increased to 400%. Meanwhile, the responsivity and detectivity are as high as 10.4 mA W^?1 and 3.56 × 10¹¹ Jones, respectively. This work provides a promising approach to develop high‐performance self‐powered visible photodetectors with low‐temperature operating capability.     

High‐Performance Ferroelectric Memory Based on Phase‐Separated Films of Polymer Blends

High‐performance polymer memory is fabricated using blends of ferroelectric poly(vinylidene‐fluoride‐trifluoroethylene) (P(VDF‐TrFE)) and highly insulating poly(p‐phenylene oxide) (PPO). The blend films spontaneously phase separate into amorphous PPO nanospheres embedded in a semicrystalline P(VDF‐TrFE) matrix. Using low molecular weight PPO with high miscibility in a common solvent, i.e., methyl ethyl ketone, blend films are spin cast with extremely low roughness (R_rms ≈ 4.92 nm) and achieve nanoscale phase seperation (PPO domain size < 200 nm). These blend devices display highly improved ferroelectric and dielectric performance with low dielectric losses (<0.2 up to 1 MHz), enhanced thermal stability (up to ≈353 K), excellent fatigue endurance (80% retention after 10⁶ cycles at 1 KHz) and high dielectric breakdown fields (≈360 MV/m).     

Engineering the Exciton Dissociation in Quantum‐Confined 2D CsPbBr3 Nanosheet Films

Recent years have witnessed a rapid development of all‐inorganic halide perovskite in optoelectronic devices. Ultrathin 2D CsPbBr₃ nanosheets (NSs) with large lateral dimensions have demonstrated exceptional photophysical properties because of their analogous exciton electronic structure to quantum wells. Despite the incredible progress on device performance, the photophysics and carrier transportation parameters of quantum‐confined CsPbBr₃ NSs are lacking, and the fundamental understanding of the exciton dissociation mechanism is far less developed. Here, a ligands rearrangement mechanism is proposed to explain why annealed NS films have an increased charge transfer rate and a decreased exciton binding energy and lifetime, prompting tunneling as a dominant way of exciton dissociation to separate photogenerated excitons between neighboring NSs. This facile but efficient method provides a new insight to manipulate perovskite nanocrystals coupling. Moreover, ultrathin 2D CsPbBr₃ NS film is demonstrated to have a enhanced absorption cross section and high carrier mobility of 77.9 cm² V^?1 s^?1, contributing to its high responsivity of 0.53 A W^?1. The photodetector has a long‐term stability up to three months, which are responsible for reliable perovskite‐based device performance.     

High‐Performance Flexible Broadband Photodetector Based on Organolead Halide Perovskite

Organolead halide perovskites have attracted extensive attentions as light harvesting materials for solar cells recently, because of its high charge‐carrier mobilities, high photoconversion efficiencies, low energy cost, ease of deposition, and so on. Herein, with CH₃NH₃PbI₃ film deposited on flexible ITO coated substrate, the first organolead halide perovskite based broadband photodetector is demonstrated. The organolead halide perovskite photodetector is sensitive to a broadband wavelength from the ultraviolet light to entire visible light, showing a photo‐responsivity of 3.49 A W^?1, 0.0367 A W^?1, an external quantum efficiency of 1.19×10³%, 5.84% at 365 nm and 780 nm with a voltage bias of 3 V, respectively. Additionally, the as‐fabricated photodetector exhibit excellent flexibility and robustness with no obvious variation of photocurrent after bending for several times. The organolead halide perovskite photodetector with high sensitivity, high speed and broad spectrum photoresponse is promising for further practical applications. And this platform creates new opportunities for the development of low‐cost, solution‐processed and high‐efficiency photodetectors.     

Control of Current Hysteresis of Networked Single‐Walled Carbon Nanotube Transistors by a Ferroelectric Polymer Gate Insulator

Films made of 2D networks of single‐walled carbon nanotubes (SWNTs) are one of the most promising active‐channel materials for field‐effect transistors (FETs) and have a variety of flexible electronic applications, ranging from biological and chemical sensors to high‐speed switching devices. Challenges, however, still remain due to the current hysteresis of SWNT‐containing FETs, which has hindered further development. A new and robust method to control the current hysteresis of a SWNT‐network FET is presented, which involves the non‐volatile polarization of a ferroelectric poly(vinylidene fluoride‐trifluoroethylene) (P(VDF‐TrFE)) gate insulator. A top‐gate FET with a solution‐processed SWNT‐network exhibits significant suppression of the hysteresis when the gate‐voltage sweep is greater than the coercive field of the ferroelectric polymer layer (≈50 MV m^?1). These near‐hysteresis‐free characteristics are believed to be due to the characteristic hysteresis of the P(VDF‐TrFE), resulting from its non‐volatile polarization, which makes effective compensation for the current hysteresis of the SWNT‐network FETs. The onset voltage for hysteresis‐minimized operation is able to be tuned simply by controlling the thickness of the ferroelectric film, which opens the possibility of operating hysteresis‐free devices with gate voltages down to a few volts.     

Environmentally Robust Black Phosphorus Nanosheets in Solution: Application for Self‐Powered Photodetector

Large‐size 2D black phosphorus (BP) nanosheets have been successfully synthesized by a facile liquid exfoliation method. The as‐prepared BP nanosheets are used to fabricate electrodes for a self‐powered photodetector and exhibit preferable photoresponse activity as well as environmental robustness. Photoelectrochemical (PEC) tests demonstrate that the current density of BP nanosheets can reach up to 265 nA cm^?2 under light irradiation, while the dark current densities fluctuate near 1 nA cm^?2 in 0.1 M KOH. UV–vis and Raman spectra are carried out and confirm the inherent optical and physical properties of BP nanosheets. In addition, the cycle stability measurement exhibits no detectable distinction after processing 50 and 100 cycles, while an excellent on/off behavior is still preserved even after one month. Furthermore, the PEC performance of BP nanosheets‐based photodetector is evaluated in various KOH concentrations, which demonstrates that the as‐prepared BP nanosheets may have a great potential application in self‐powered photodetector. It is anticipated that the present work can provide fundamental acknowledgement of the performance of a PEC‐type BP nanosheets‐based photodetector, offering extendable availabilities for 2D BP‐based heterostructures to construct high‐performance PEC devices.     

Self‐Powered Flexible TiO2 Fibrous Photodetectors: Heterojunction with P3HT and Boosted Responsivity and Selectivity by Au Nanoparticles

A novel inorganic–organic heterojunction (TiO₂/P3HT (poly(3‐hexylthiophene)) is easily prepared by a combination of anodization and vacuumed dip‐coating methods, and the constructed flexible fibrous photodetector (FPD) exhibits high‐performance self‐powered UV–visible broadband photoresponse with fast speed, high responsivity, and good stability, as well as highly stable performance at bending states, showing great potential for wearable electronic devices. Moreover, Au nanoparticles are deposited to further boost the responsivity and selectivity by regulating the sputtering intervals. The optimal Au/TiO₂/P3HT FPD yields an ≈700% responsivity enhancement at 0 V under 350 nm illumination. The sharp cut‐off edge and high UV–visible rejection ratio (≈17 times higher) indicate a self‐powered flexible UV photodetector. This work provides an effective and versatile route to modulate the photoelectric performance of flexible electronic devices.     

Electrode Dependence of Tunneling Electroresistance and Switching Stability in Organic Ferroelectric P(VDF‐TrFE)‐Based Tunnel Junctions

Ferroelectric tunnel junctions (FTJs) are promising candidates for nonvolatile memories and memristor‐based computing circuits. Thus far, most research has focused on FTJs with a perovskite oxide ferroelectric tunnel barrier. As the need for high‐temperature epitaxial film growth challenges the technological application of such inorganic junctions, more easily processable organic ferroelectrics can serve as alternative if large tunneling electroresistance (TER) and good switching durability would persist. This study reports on the performance of FTJs with a spin‐coated ferroelectric P(VDF‐TrFE) copolymer tunnel barrier. The use of three different bottom electrodes, indium tin oxide (ITO), La_0.67Sr_0.33MnO₃, (LSMO), and Nb‐doped SrTiO₃ (STO) are compared and it is shown that the polarity and magnitude of the TER effect depend on their conductivity. The largest TER of up to 10⁷% at room temperature is measured on FTJs with a semiconducting Nb‐doped STO electrode. This large switching effect is attributed to the formation of an extra barrier over the space charge region in the substrate. The organic FTJs exhibit good resistance retention and switching endurance up to 380 K, which is just below the ferroelectric Curie temperature of the P(VDF‐TrFE) barrier.