Influence of polymeric electrets on the performance of derived hybrid perovskite-based photo-memory devices

Controlled Growth of Highly Oriented Perovskite Crystals in Polymer Solutions via Selective Solvent Vapor Diffusion

Organic-inorganic hybrid perovskites have garnered significant attention in optoelectronics owing to their outstanding tunable optical characteristics. Controlled growth of perovskite nanocrystals from solutions is key for controlling the emission intensity and photoluminescence lifetime of perovskites. In particular, most studies have focused on controlling the crystallization of perovskite through chemical treatment using chelating ligands or physical treatment via antisolvent diffusion, and there exists a trade-off between the photoluminescence intensity and lifetime of perovskites. Herein, a selective solvent vapor-assisted crystallization with the aid of a functional polymer, which nanoscale perovskite crystals are grown andante from precursor solution, is presented for tuning the crystallization and optical properties of a common halide perovskite, methylammonium lead bromide (MAPbBr3 ). The proposed method here produces perovskite nanocrystals in the range of 200-300 nm. The spin-coated thin film formed from the perovskite solution exhibits strong green photoluminescence with a long lifetime. The effects of the functional group and polymer dosage on the crystallization of MAPbBr3 are systematically investigated, and the crystallization mechanism is explained based on a modified LaMer model. This study provides an advanced solution process for precisely controlling perovskite crystallization to enhance their optical properties for next-generation optoelectronic devices.

Tailoring Wavelength-Adaptive Visual Neuroplasticity Transitions of Synaptic Transistors Comprising Rod-Coil Block Copolymers for Dual-Mode Photoswitchable Learning/Forgetting Neural Functions

The vision-inspired artificial neural network based on optical synapses has drawn a tremendous amount of attention for emulating biological senses. Although photoexcitation-induced synaptic functionalities have been widely studied, optical habituation via the photoinhibitory pathway is yet to be demonstrated for sophisticated biomimetic visual adaptive systems. Here, the first optical neuromorphic block copolymer (BCP) phototransistor is demonstrated as an all-optical operation responding to various wavelengths, fulfilling photoassisted dynamic learning/forgetting cycles via optical potentiation without gate bias. The polyfluorene BCPs were precisely designed to enable wavelength-adaptive responses, benefiting from interfacial semiconductor/electret morphology and the crystallinity/electron affinity of the BCPs. Notably, this is the first work to simultaneously exhibit fully light-controlled short- and long-term memory based on organic material systems. The device presents a high current contrast above 100-fold and long-term retention over 104 s. As a proof-of-concept for neural networks, a 6 × 6 array of photosynapses performed outstanding visual pattern learning/forgetting with high accuracy. This study exploits the design strategy of a conjugated BCP electret to unleash the full potential of wavelength-adaptive visual neuroplasticity transitions. It provides an effective architecture for designing high-performance and high-storage capacity required applications in next-generation neuromorphic systems.

Generation of Long-Lived Excitons in Room-Temperature Phosphorescence 2D Organic and Inorganic Hybrid Perovskites for Ultrafast and Low Power-Consumption Nonvolatile Photomemory

Room-temperature phosphorescence (RTP) two-dimensional (2D) organic-inorganic hybrid perovskites (OIHPs) that possess superior stability and efficient triplet energy transfer between inorganic parts and organic cations have been seen as promising materials in optoelectronic devices. However, the development of RTP 2D OIHP-based photomemory has not been explored yet. In this work, the spatially addressable RTP 2D OIHPs-based nonvolatile flash photomemory is first investigated to explore the function of triplet excitons in elevating the performance of photomemory. Thanks to the triplet excitons generated in RTP 2D OIHP, extremely low photo-programming time of 0.7 ms, multilevel behavior of minimum 7 bits (128 levels), remarkable photoresponsivity of 19.10 AW^-1 and significantly low power consumption of 6.79 × 10^-8 J per bit can be achieved. The current study provides a new prospective in understanding triplet excitons function in nonvolatile photomemory.

Human Skin-Inspired Electrospun Patterned Robust Strain-Insensitive Pressure Sensors and Wearable Flexible Light-Emitting Diodes

Wearable skin-inspired electronic skins present remarkable outgrowth in recent years because their promising comfort device integration, lightweight, and mechanically robust durable characteristics led to significant progresses in wearable sensors and optoelectronics. Wearable electronic devices demand real-time applicability and factors such as complex fabrication steps, manufacturing cost, and reliable and durable performances, severely limiting the utilization. Herein, we nominate a scalable solution-processable electrospun patterned candidate capable of forming ultralong mechanically robust nano-microdimensional fibers with higher uniformity. Nanofibrous patterned substrates present surface energy and silver nanoparticle crystallization shifts, contributing to strain-sensitive and -insensitive conductive electrodes (10 000 cycles of 50% strain). Synergistic robust stress releasing and durable electromechanical behavior engenders stretchable durable health sensors, strain-insensitive pressure sensors (sensitivity of ∼83 kPa^-1 and 5000 durable cycles), robust alternating current electroluminescent displays, and flexible organic light-emitting diodes (20% improved luminescence and 300 flex endurance of 2 mm bend radius).

Low-Energy-Consumption and Electret-Free Photosynaptic Transistor Utilizing Poly(3-hexylthiophene)-Based Conjugated Block Copolymers

Neuromorphic computation possesses the advantages of self-learning, highly parallel computation, and low energy consumption, and is of great promise to overcome the bottleneck of von Neumann computation. In this work, a series of poly(3-hexylthiophene) (P3HT)-based block copolymers (BCPs) with different coil segments, including polystyrene, poly(2-vinylpyridine) (P2VP), poly(2-vinylnaphthalene), and poly(butyl acrylate), are utilized in photosynaptic transistor to emulate paired-pulse facilitation, spike time/rate-dependent plasticity, short/long-term neuroplasticity, and learning-forgetting-relearning processes. P3HT serves as a carrier transport channel and a photogate, while the insulating coils with electrophilic groups are for charge trapping and preservation. Three main factors are unveiled to govern the properties of these P3HT-based BCPs: i) rigidity of the insulating coil, ii) energy levels between the constituent polymers, and iii) electrophilicity of the insulating coil. Accordingly, P3HT-b-P2VP-based photosynaptic transistor with a sought-after BCP combination demonstrates long-term memory behavior with current contrast up to 10⁵ , short-term memory behavior with high paired-pulse facilitation ratio of 1.38, and an ultralow energy consumption of 0.56 fJ at an operating voltage of -0.0003 V. As far as it is known, this is the first work to utilize conjugated BCPs in an electret-free photosynaptic transistor showing great potential to the artificial intelligence technology.

Contribution of Polymers to Electronic Memory Devices and Applications

Electronic memory devices, such as memristors, charge trap memory, and floating-gate memory, have been developed over the last decade. The use of polymers in electronic memory devices enables new opportunities, including easy-to-fabricate processes, mechanical flexibility, and neuromorphic applications. This review revisits recent efforts on polymer-based electronic memory developments. The versatile contributions of polymers for emerging memory devices are classified, providing a timely overview of such unconventional functionalities with a strong emphasis on the merits of polymer utilization. Furthermore, this review discusses the opportunities and challenges of polymer-based memory devices with respect to their device performance and stability for practical applications.

Comprehensive Non-volatile Photo-programming Transistor Memory via a Dual-Functional Perovskite-Based Floating Gate

Photonic transistor memory has received increasing attention as next-generation optoelectronic devices for light fidelity (Li-Fi) application due to the attractive advantages of ultra-speed, high security, and low power consumption. However, most transistor-type photonic memories developed to date still rely on electrical bias for operation, imposing certain limits on data transmission efficiency and energy consumption. In this study, the dual manipulation of "photo-writing" and "photo-erasing" of a novel photonic transistor memory is successfully realized by cleverly utilizing the complementary light absorption between the photoactive material, n-type BPE-PTCDI, in the active channel and the hybrid floating gate, CH₃NH₃PbBr₃/poly(2-vinylpyridine). The fabricated device not only can be operated under the full spectrum but also shows stable switching cycles of photo-writing (PW)-reading (R)-photo-erasing (PE)-reading (R) (PW-R-PE-R) with a high memory ratio of ∼10⁴, and the memory characteristics possess a stable long-term retention of >10⁴ s. Notably, photo-erasing only requires 1 s light illumination. Due to the fully optical functionality, the rigid gate electrode is removed and a novel two-terminal flexible photonic memory is fabricated. The device not only exhibits stable electrical performance after 1000 bending cycles but also manifests a multilevel functional behavior, demonstrating a promising potential for the future development of photoactive electronic devices.

Dual-functional optoelectronic memories based on ternary hybrid floating gate layers

Optoelectronic memories based on organic field-effect transistors (OFETs) have been extensively investigated, and great progress has been made in improving memory performance and reducing operating power consumption. Despite these achievements, optoelectronic memories reported so far have only a single storage function, such as light-assisted memory, light writing memory, or light-erasing memory, which may not meet the requirements of multi-functional storage in the future. Here, the dual-functional optoelectronic memories are demonstrated by employing ternary hybrid films as floating gate layers. Integrating the advantages of hole trapping in [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) and photoinduced electron trapping in CsPbBr3 quantum dots (QDs), the dual-functional storages including electric programming holes and light programming electrons can be realized in one device. Owing to the complementary charge trapping advantages in CsPbBr3 QDs and PCBM, the devices also show a short light erasing time of 0.05 s and low erasing gate bias within -35 V. In addition, the devices exhibit decent endurance for 500 continuous light programming-reading-electric programming-reading cycling tests and admirable electron and hole retention time of 10 000 s with negligible charge leakage. This study may offer a feasible path for the development of new-generation memory.

Nonvolatile Multilevel Photomemory Based on Lead-Free Double Perovskite Cs2AgBiBr6 Nanocrystals Wrapped Within SiO2 as a Charge Trapping Layer

Floating gate transistor photomemory (FGTPM) has been regarded as one of the most prospective nonvolatile photomemory devices because of its compatibility with transistor-based circuits, nondestructive reading, and multilevel storage. Until now, owing to the excellent photoelectric properties, lead-based perovskite nanocrystals (PNCs) have been applied in most of the perovskite-based FGTPM devices and embedded in the polymer matrix as the charge trapping layer. However, the polymer matrix and its solvent would degrade the structure of the PNCs, resulting in the loss of their unique photoresponse ability. In addition, lead-based perovskites have environmental unfriendliness and poor stability. Hence, a novel nonvolatile FGTPM based on oligomeric silica (OS) wrapped lead-free double perovskite Cs₂AgBiBr₆ NCs was demonstrated for the first time. Acting synchronously as the protection layer for the discrete Cs₂AgBiBr₆ NCs and charge tunneling layer for the FGTPM device, the OS layer can achieve controllable thickness by adjusting the process parameters, leading to an adjustment of storage properties with a larger memory window (58 V). Owing to the excellent photoresponse ability of the Cs₂AgBiBr₆@OS composite layer, the FGTPM device exhibited high-performance with repeatable multilevel nonvolatile photomemory and precise photoresponse ability of wavelength/time/power-dependent photoirradiation without extra gate biasing.

High-Performance Nonvolatile Organic Photonic Transistor Memory Devices using Conjugated Rod-Coil Materials as a Floating Gate

A novel approach for using conjugated rod-coil materials as a floating gate in the fabrication of nonvolatile photonic transistor memory devices, consisting of n-type Sol-PDI and p-type C10-DNTT, is presented. Sol-PDI and C10-DNTT are used as dual functions of charge-trapping (conjugated rod) and tunneling (insulating coil), while n-type BPE-PDI and p-type DNTT are employed as the corresponding transporting layers. By using the same conjugated rod in the memory layer and transporting channel with a self-assembled structure, both n-type and p-type memory devices exhibit a fast response, a high current contrast between "Photo-On" and "Electrical-Off" bistable states over 10⁵ , and an extremely low programing driving force of 0.1 V. The fabricated photon-driven memory devices exhibit a quick response to different wavelengths of light and a broadband light response that highlight their promising potential for light-recorder and synaptic device applications.

Two-Dimensional Cs2Pb(SCN)2Br2-Based Photomemory Devices Showing a Photoinduced Recovery Behavior and an Unusual Fully Optically Driven Memory Behavior

The rapid development of Internet of Things and big data has made the conventional storage devices face the need of reforming. Rather than using electrical pulses to store data in one of two states, photomemory exploiting optical stimulation to store light information emerges as a revolutionary candidate for the optoelectronic community. However, fully optically driven photomemory with fast data transmission speed and outstanding energy saving capability suffers from less exploration. Herein, a transistor-type photomemory using a 2D Cs₂Pb(SCN)₂Br₂/polymer hybrid floating gate is explored and three host polymers, polystyrene, poly(4-vinylphenol), and poly(vinylpyrrolidone) (PVP), are investigated to understand the relationship between polymer matrix selection and memory performance. All devices show a photoinduced recovery memory behavior but with two distinctly different photomemory behaviors. In addition to the demonstration of a regular nonvolatile photomemory showing a high on/off ratio of >10⁶ over 10⁴ s, an unusual fully optically driven memory behavior is intriguingly accomplished in the Cs₂Pb(SCN)₂Br₂/PVP photomemory. Using white light as the driver of programming and a blue laser as the main performer of erasing, this device can be switched between two distinguishable states and possesses acceptable data discriminability, as evidenced by its fully optically driven writing (programing)-reading-erasing-reading switching function that shows an on/off current ratio of 10³. This study not only presents the first 2D perovskite-based photomemory but also shows a novel fully optically driven memory that has been rarely reported in the literature.

Nano-Micro Dimensional Structures of Fiber-Shaped Luminous Halide Perovskite Composites for Photonic and Optoelectronic Applications

Perovskite nanomaterials have been revealed as highly luminescent structures regarding their dimensional confinement. In particular, their promising potential lies behind remarkable luminescent properties, including color tunability, high photoluminescence quantum yield, and the narrow emission band of halide perovskite (HP) nanostructures for optoelectronic and photonic applications such as lightning and displaying operations. However, HP nanomaterials possess such drawbacks, including oxygen, moisture, temperature, or UV lights, which limit their practical applications. Recently, HP-containing polymer composite fibers have gained much attention owing to the spatial distribution and alignment of HPs with high mechanical strength and ambient stability in addition to their remarkable optical properties comparable to that of nanocrystals. In this review, the fabrication methods for preparing nano-microdimensional HP composite fiber structures are described. Various advantages of the luminescent composite nanofibers are also described, followed by their applications for photonic and optoelectronic devices including sensors, polarizers, waveguides, lasers, light-down converters, light-emitting diode operations, etc. Finally, future directions and remaining challenges of HP-based nanofibers are presented.

Improving the Performance and Stability of Perovskite Light-Emitting Diodes by a Polymeric Nanothick Interlayer-Assisted Grain Control Process

CsPbBr₃ is a promising light-emitting material due to its wet solution processability, high photoluminescence quantum yield (PLQY), narrow color spectrum, and cost-effectiveness. Despite such advantages, the morphological defects, unsatisfactory carrier injection, and stability issues retard its widespread applications in light-emitting devices (LEDs). In this work, we demonstrated a facile and cost-effective method to improve the morphology, efficiency, and stability of the CsPbBr₃ emissive layer using a dual polymeric encapsulation governed by an interface-assisted grain control process (IAGCP). An eco-friendly low-cost hydrophilic polymer poly(vinylpyrrolidone) (PVP) was blended into the CsPbBr₃ precursor solution, which endows the prepared film with a better surface coverage with a smoothened surface. Furthermore, it is revealed that inserting a thin PVP nanothick interlayer at the poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS)/emissive layer interface further promotes the film quality and the performance of the derived LED. It is mainly attributed to three major consequences: (i) reduced grain size of the emissive layer, which facilitates charge recombination, (ii) reduced current leakage due to the enhanced electron-blocking effect, and (iii) improved color purity and air stability owing to better defect passivation. As a result, the optimized composite emissive film can retain the luminescence properties even on exposure to ambient conditions for 80 days and ∼62% of its initial PL intensity can be preserved after 30 days of storage without any encapsulation.

Multilevel Photonic Transistor Memory Devices Using Conjugated/Insulated Polymer Blend Electrets

Photonic data storage has diverse optoelectronic applications such as optical sensing and recording, integrated image circuits, and multibit-storage flash memory. In this study, we employ conjugated/insulated polymer blends as the charge storage electret for photonic field-effect transistor memory devices by exploring the blend composition, energy level alignment, and morphology on the memory characteristics. The studied conjugated polymers included poly(9,9-di-n-octylfluorenyl-2,7-diyl) (PF), poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV), poly[{2,5-di(3',7'-dimethyloctyloxy)-1,4-phenylene-vinylene}-co-{3-(4'-(3″,7″-dimethyloctyloxy)phenyl)-1,4-phenylenevinylene}-co-{3-(3'-(3',7'-dimethyloctyloxy)phenyl)-1,4-phenylenevinylene}] (SY-PPV), and poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(benzo[2,1,3]thiadiazol-4,8-diyl)] (F8BT), and the insulated polymers were polystyrene (PS) and poly(methyl methacrylate) (PMMA). The photonic memory device using the PF/PS blend electret exhibited a dynamic switching behavior with light-writing and voltage-erasing processes both within only 1 s, along with a high contrast on the current on/off ratio between "Photo-On" and "Electrical-OFF" over 10⁶ and the decent retention time for more than 3 months. In addition, the multilevel memory behavior could be observed using different light sources of 405, 450, and 520 nm or energy intensity, which was supported by surface potential analysis. The characteristics were superior to those of the devices using PF/PMMA blend due to the higher charge storage behavior of PS supported by fluorescence analysis. The PF/PS blend film prepared from the chlorobenzene solvent exhibited mesh-like and aggregated PF domains in the PS matrix and enhanced the contact surface area between the semiconductor and blend electret, leading to a higher memory window. The photonic memory behavior was also observed in the blend electrets of PS with the low band gap polymer, MEH-PPV, SY-PPV, or F8BT, by changing the photoresponsive light sources. Our study demonstrated a new electret system to apply on the multilevel photonic memory devices.

Two-Dimensional WSe2/Organic Acceptor Hybrid Nonvolatile Memory Devices Based on Interface Charge Trapping

Two-dimensional (2D) materials, with atomic thickness and unique electronic structure, hold great potentials in electronic device applications. Charge transfer at the interface of 2D materials further provides a versatile platform for applications in electronics. Here, we report nonvolatile memory devices based on interface charge trapping between 2D WSe₂ and organic electron acceptors. The 2D WSe₂-organic acceptor hybrid structure exhibits a high storage performance, such as large gate memory windows, high on/off ratios (>10³), and long retention time (>1000 s). Further analysis revealed that organic acceptors with a stronger electron affinity (i.e., higher redox potential) have a larger electron-trapping ability and hence a better memory performance.

Light enhanced low-voltage nonvolatile memory based on all-inorganic perovskite quantum dots

Light enhanced low-voltage nonvolatile memory was prepared using all-inorganic perovskite quantum dots (QDs) as a semiconductor layer and Ag nanoparticles (NPs) as a floating gate layer. The photo-induced carriers can be produced in CsPbBr₃ QDs under ultraviolet light and trapped in Ag NPs under the action of an external electric field. With the assistance of light, the device exhibited a significantly larger memory window (ΔV _th) under low programming and erasing voltages of ±5 V owing to the use of CsPbBr₃ QDs. Furthermore, we proved that the ΔV _th of the memory strongly depended on the applied bias voltage (V _DS) as well as still remaining at 79.3% after 10⁵ s at V _DS of 1.4 V. The facile memory provides a new approach to trap a photo-induced charge and reduce operating voltages by combining QDs with metal NPs.

Stretchable and Ambient Stable Perovskite/Polymer Luminous Hybrid Nanofibers of Multicolor Fiber Mats and Their White LED Applications

We report the fabrication and optical/mechanical properties of perovskite/thermoplastic polyurethane (TPU)-based multicolor luminescent core-shell nanofibers and their large-scale fiber mats. One-step coaxial perovskite/TPU nanofibers had a high photoluminescence quantum yield value exceeding 23.3%, surpassing that of its uniaxial counterpart, due to the homogeneous distribution of perovskite nanoparticles (NPs) by the confinement of the TPU shell. The fabricated core-shell nanofibers exhibited a high mechanical endurance owing to the well elastic properties of TPU and maintained the luminescence intensity even under a 100% stretched state after 1000 stretching-relaxing cycles. By taking advantage of the hydrophobic nature of TPU, the ambient and moisture stability of the fabricated fibers were enhanced up to 1 month. Besides, large-area stretchable nanofibers with a dimension of 15 cm × 30 cm exhibiting various visible-light emission peaks were fabricated by changing the composition of perovskite NPs. Moreover, a large-scale luminescent and stretchable fiber mat was successfully fabricated by electrospinning. Furthermore, the white-light emission from the fabricated fibers and mats was achieved by incorporating orange-light-emitting poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] into the TPU shell and coupling the turquoise blue-light-emitting perovskite NPs in the core site. Finally, the integrity of the perovskite-based TPU fibers was realized by fabricating a light-emitting diode (LED) device containing the orange-light-emitting fibers embedded in the polyfluorene emissive layer. This work demonstrated an effective way to prepare stable and stretchable luminous nanofibers and the integration of such nanofibers into LED devices, which could facilitate the future development of wearable electronic devices.