Dual-Band, High-Performance Phototransistors from Hybrid Perovskite and Organic Crystal Array for Secure Communication Applications

Spacer Engineering Enables Fine-Tuned Thin Film Microstructure and Efficient Charge Transport for Ultrasensitive 2D Perovskite-Based Heterojunction Phototransistors and Optoelectronic Synapses

2D Ruddlesden-Popper phase layered perovskites (RPLPs) hold great promise for optoelectronic applications. In this study, a series of high-performance heterojunction phototransistors (HPTs) based on RPLPs with different organic spacer cations (namely butylammonium (BA+), cyclohexylammonium (CyHA+), phenethylammonium (PEA+), p-fluorophenylethylammonium (p-F-PEA+), and 2-thiophenethylammonium (2-ThEA+)) are fabricated successfully, in which high-mobility organic semiconductor 2,7-dioctyl[1]benzothieno[3,2-b]benzothiophene is adopted to form type II heterojunction channels with RPLPs. The 2-ThEA+-RPLP-based HPTs show the highest photosensitivity of 3.18 × 107 and the best detectivity of 9.00 × 1018 Jones, while the p-F-PEA+-RPLP-based ones exhibit the highest photoresponsivity of 5.51 × 106 A W-1 and external quantum efficiency of 1.32 × 109%, all of which are among the highest reported values to date. These heterojunction systems also mimicked several optically controllable fundamental characteristics of biological synapses, including excitatory postsynaptic current, paired-pulse facilitation, and the transition from short-term memory to long-term memory states. The device based on 2-ThEA+-RPLP film shows an ultra-high PPF index of 234%. Moreover, spacer engineering brought fine-tuned thin film microstructures and efficient charge transport/transfer, which contributes to the superior photodetection performance and synaptic functions of these RPLP-based HPTs. In-depth structure-property correlations between the organic spacer cations/RPLPs and thin film microstructure/device performance are systematically investigated.

Overcoming the Unfavorable Effects of "Boltzmann Tyranny:" Ultra-Low Subthreshold Swing in Organic Phototransistors via One-Transistor-One-Memristor Architecture

Organic phototransistors (OPTs), as photosensitive organic field-effect transistors (OFETs), have gained significant attention due to their pivotal roles in imaging, optical communication, and night vision. However, their performance is fundamentally limited by the Boltzmann distribution of charge carriers, which constrains the average subthreshold swing (SSave ) to a minimum of 60 mV/decade at room temperature. In this study, an innovative one-transistor-one-memristor (1T1R) architecture is proposed to overcome the Boltzmann limit in conventional OFETs. By replacing the source electrode in an OFET with a memristor, the 1T1R device exploits the memristor's sharp resistance state transitions to achieve an ultra-low SSave of 18 mV/decade. Consequently, the 1T1R devices demonstrate remarkable sensitivity to photo illumination, with a high specific detectivity of 3.9 × 109  cm W-1 Hz1/2 , outperforming conventional OPTs (4.9 × 104  cm W-1 Hz1/2 ) by more than four orders of magnitude. The 1T1R architecture presents a potentially universal solution for overcoming the detrimental effects of "Boltzmann tyranny," setting the stage for the development of ultra-low SSave devices in various optoelectronic applications.

Van Der Waals Semiconductor Based Omnidirectional Bifacial Transparent Photovoltaic for Visual-Speech Photocommunication

Omnidirectional photosensing is crucial in optoelectronic devices, enabling a wide field of view (wFoV) and leveraging potential applications for the Internet of Things in sensors, light fidelity, and photocommunication. The wFoV helps overcome the limitations of line-of-sight communication, and transparent photodetection becomes highly desirable as it enables the capture of optical information from various angles. Therefore, developing a photoelectric device with a 360° wFoV, ultra sensitivity to photons, power generation, and transparency is of utmost importance. This study utilizes a heterojunction of van der Waals SnS with Ga2 O3 to fabricate a transparent photovoltaic (TPV) device showing a 360° wFoV with bifacial onsite power production. SnS/Ga2 O3 heterojunction preparation consists of magnetron sputtering and is free from nanopatterning/nanostructuring to achieve the desired wFoV window device. The device exhibits a high average visible transmittance of 56%, generates identical power from bifacial illumination, and broadband fast photoresponse. Careful analysis of the device shows an ultra-sensitive photoinduced defect-modulated heterojunction and photocapacitance, revealed by the impedance spectroscopy, suggesting photon-flux driven charge diffusion. Leveraging the wFoV operation, the TPV embedded visual and speech photocommunication prototype demonstrated, aiming to help visually and auditory impaired individuals, promising an environmental-friendly sustainable future.

Notable Performance Enhancement of CsPbI2Br Solar Cells by a Dual-Function Strategy with CsPbBr3 Nanocrystals

Herein, a dual-function strategy, in which CsPbI2Br is treated by CsPbBr3 nanocrystals (NCs) via addition and surface modification to construct the "electron bridge" and gradient heterojunction, respectively, to notably improve the performance of the CsPbI2Br solar cells, is proposed. The "electron bridge" formed by the CsPbBr3 NCs provides an extra transport channel for the photogenerated electrons in the CsPbI2Br layer, thus facilitating electron transport. Meanwhile, surface modification of CsPbI2Br by the CsPbBr3 NCs forms a gradient heterojunction between the CsPbI2Br layer and the P3HT layer, enhancing hole extraction accordingly. In addition, the CsPbBr3 NC treatment passivates the defects at the bulk and surface of the CsPbI2Br layers, thus suppressing carrier recombination. Thanks to these positive effects of the CsPbBr3 NCs, the demonstration device with a simple configuration of ITO/SnO2/CsPbI2Br/P3HT/Ag achieves a notable power conversion efficiency of 17.03%, which is among the highest efficiencies reported for CsPbI2Br-based solar cells.

Nanocrystal Array Engineering and Optoelectronic Applications of Organic Small-Molecule Semiconductors

Organic small-molecule semiconductor materials have attracted extensive attention because of their excellent properties. Due to the randomness of crystal orientation and growth location, however, the preparation of continuous and highly ordered organic small-molecule semiconductor nanocrystal arrays still face more challenges. Compared to organic macromolecules, organic small molecules exhibit better crystallinity, and therefore, they exhibit better semiconductor performance. The formation of organic small-molecule crystals relies heavily on weak interactions such as hydrogen bonds, van der Waals forces, and π-π interactions, which are very sensitive to external stimuli such as mechanical forces, high temperatures, and organic solvents. Therefore, nanocrystal array engineering is more flexible than that of the inorganic materials. In addition, nanocrystal array engineering is a key step towards practical application. To resolve this problem, many conventional nanocrystal array preparation methods have been developed, such as spin coating, etc. In this review, the typical and recent progress of nanocrystal array engineering are summarized. It is the typical and recent innovations that the array of nanocrystal array engineering can be patterned on the substrate through top-down, bottom-up, self-assembly, and crystallization methods, and it can also be patterned by constructing a series of microscopic structures. Finally, various multifunctional and emerging applications based on organic small-molecule semiconductor nanocrystal arrays are introduced.

Recent Progress on Wavelength-Selective Perovskite Photodetectors for Image Sensing

Spectral sensing plays a crucial part in imaging technologies, optical communication, and other fields. However, complicated optical elements, such as prisms, interferometric filters, and diffraction grating, are required for commercial multispectral detectors, which hampers their advance toward miniaturization and integration. In recent years, metal halide perovskites have been emerging for optical-component-free wavelength-selective photodetectors (PDs) because of their continuously tunable bandgap, fascinating optoelectronic properties, and simple preparation processes. In this review, recent advances in wavelength-selective perovskite PDs, including narrowband PDs, dual-band PDs, multispectral-recognizable PDs, and X-ray PDs, are highlighted, with an emphasis on device structure designs, working mechanisms, and optoelectronic performances. Meanwhile, the applications of wavelength-selective PDs in image sensing for single-/dual-color imaging, full-color imaging, and X-ray imaging are introduced. Finally, the remaining challenges and perspectives in this emerging field are presented.

Split-Ring Structured All-Inorganic Perovskite Photodetector Arrays for Masterly Internet of Things

Photodetectors with long detection distances and fast response are important media in constructing a non-contact human-machine interface for the Masterly Internet of Things (MIT). All-inorganic perovskites have excellent optoelectronic performance with high moisture and oxygen resistance, making them one of the promising candidates for high-performance photodetectors, but a simple, low-cost and reliable fabrication technology is urgently needed. Here, a dual-function laser etching method is developed to complete both the lyophilic split-ring structure and electrode patterning. This novel split-ring structure can capture the perovskite precursor droplet efficiently and achieve the uniform and compact deposition of CsPbBr3 films. Furthermore, our devices based on laterally conducting split-ring structured photodetectors possess outstanding performance, including the maximum responsivity of 1.44 × 105 mA W-1, a response time of 150 μs in 1.5 kHz and one-unit area < 4 × 10-2 mm2. Based on these split-ring photodetector arrays, we realized three-dimensional gesture detection with up to 100 mm distance detection and up to 600 mm s-1 speed detection, for low-cost, integrative, and non-contact human-machine interfaces. Finally, we applied this MIT to wearable and flexible digital gesture recognition watch panel, safe and comfortable central controller integrated on the car screen, and remote control of the robot, demonstrating the broad potential applications.

Low-voltage-modulated perovskite/organic dual-band photodetectors for visible and near-infrared imaging

Visible and near-infrared (NIR) light dual-band photodetectors (PDs) have potential applications in signal detection, bioimaging, optical communications and safety monitoring. Herein, we report an ultrafast perovskite/organic heterojunction dual-mode PD with a voltage-modulated photoresponse range in visible and NIR spectra. The PD, comprising a perovskite layer to absorb visible light (500-810 nm) and an organic bulk heterojunction layer for NIR light absorption (810-950 nm), exhibited a switchable spectral response in the visible or NIR bands. The voltage-modulated visible and NIR photoresponses of the PD were attributable to controlled charge photogeneration in perovskite and organic blend thin films under different bias polarities. The device exhibited peak responsivities of 93.5 and 102.2 mA/W in the visible and NIR bands, respectively; a high detectivity of 4.3 × 109 Jones (at forward bias of 0.7 V and incident 625 nm light) and 1.6 × 1012 Jones (at reverse bias of -1.5 V and incident 900 nm light); a fast microsecond response time; and a wide dynamic range (>120 dB) both in the visible mode and NIR mode. Also, this voltage-modulated dual-band PD shows promising applications in visible light and NIR imaging, which is proven by demonstrating a PD array with 25 pixels (5 × 5).

Fabrication Strategies and Optoelectronic Applications of Perovskite Heterostructures

Metal halide perovskites (MHPs) are emerging low‐cost and multifunctional semiconductor materials. They have been widely used in optoelectronic devices such as perovskite solar cells, light‐emitting diodes, photodetectors, memristors, and lasers. Developing new MHPs, defects passivation, optimizing device structures, and packaging techniques are all effective methods to improve photoelectric performance and stability of perovskite devices. Particularly, the fabrication of perovskite/perovskite heterostructures (PPHSs) is a novel and arresting method to obtain stable and high‐performing optoelectronic perovskite devices since it can passivate defects, regulate energy gaps, and provide new carrier transmission modes of MHPs for multiple semiconductor applications. In this paper, representative fabrication strategies of PPHSs including films and single‐crystal heterostructures are reviewed, and their applications in optoelectronic devices are summarized. Furthermore, the challenges and prospects of PPHSs are discussed based on the current status.

A Review on Solution-Processed Organic Phototransistors and Their Recent Developments

Today, more disciplines are intercepting each other, giving rise to “cross-disciplinary” research. Technological advancements in material science and device structure and production have paved the way towards development of new classes of multi-purpose sensory devices. Organic phototransistors (OPTs) are photo-activated sensors based on organic field-effect transistors that convert incident light signals into electrical signals. The organic semiconductor (OSC) layer and three-electrode structure of an OPT offer great advantages for light detection compared to conventional photodetectors and photodiodes, due to their signal amplification and noise reduction characteristics. Solution processing of the active layer enables mass production of OPT devices at significantly reduced cost. The chemical structure of OSCs can be modified accordingly to fulfil detection at various wavelengths for different purposes. Organic phototransistors have attracted substantial interest in a variety of fields, namely biomedical, medical diagnostics, healthcare, energy, security, and environmental monitoring. Lightweight and mechanically flexible and wearable OPTs are suitable alternatives not only at clinical levels but also for point-of-care and home-assisted usage. In this review, we aim to explain different types, working mechanism and figures of merit of organic phototransistors and highlight the recent advances from the literature on development and implementation of OPTs for a broad range of research and real-life applications.

Photoelectric effect of hybrid ultraviolet-sensitized phototransistors from an n-type organic semiconductor and an all-inorganic perovskite quantum dot photosensitizer

Low-dimensional all-inorganic perovskite quantum dots (QDs) have been increasingly developed as photo-sensing materials in the field of photodetectors because of their strong light-absorption capability and broad bandgap tunability. Here, solution-processed hybrid phototransistors built by a dithienothiophenoquinoid (DTTQ) n-type organic semiconductor transport channel mixing with a colloidal CsPbBr₃ perovskite QD photosensitizer are demonstrated by manipulating the relative volume ratio from 10 : 0 to 9 : 1, 7 : 3, 5 : 5, 3 : 7, 1 : 9, and 0 : 10. This results in a significantly enhanced photodetection performance owing to the advantages of a high UV absorption cross-section based on the perovskite QDs, efficient carrier transport abilities from the DTTQ semiconductor, and the photogating effect between the bulk heterojunction photocarrier transfer interfaces. The optimized DTTQ : QD (3 : 7) hybrid phototransistor achieves a high photoresponsivity (R) of 7.1 × 10⁵ A W^-1, a photosensitivity (S) of 1.8 × 10⁴, and a photodetectivity (D) of 3.6 × 10¹³ Jones at 365 nm. Such a solution-based fabrication process using a hybrid approach directly integrated into a sensitized phototransistor potentially holds promising photoelectric applications towards advanced light-stimulated photodetection.

Perovskite photodetectors and their application in artificial photonic synapses

Organic-inorganic hybrid perovskites exhibit superior optoelectrical properties and have been widely used in photodetectors. Perovskite photodetectors with excellent detectivity have great potential for developing artificial photonic synapses which can merge data transmission and storage. They are highly desired for next generation neuromorphic computing. The recent progress of perovskite photodetectors and their application in artificial photonic synapses are summarized in this review. Firstly, the key performance parameters of photodetectors are briefly introduced. Secondly, the recent research progress of photodetectors including photoconductors, photodiodes, and phototransistors is summarized. Finally, the applications of perovskite photodetectors in artificial photonic synapses in recent years are highlighted. All these demonstrate the great potential of perovskite photonic synapses for the development of artificial intelligence.

Circularly Polarized Photodetectors Based on Chiral Materials: A Review

Circularly polarized light (CPL) plays an important role in many photonic techniques, including tomographic scanning based on circular polarization ellipsometry, optical communication and information of spin, and quantum-based optical calculation and information processing. To fully exploit the functions of CPL in these fields, integrated photoelectric sensors capable of detecting CPL are essential. Photodetectors based on chiral materials can directly detect CPL due to their intrinsic optical activity, without the need to be coupled with polarizers and quarter-wave plates as in conventional photodetectors. This review summarizes the recent research progress in CPL photodetectors based on chiral materials. We first briefly introduce the CPL photodetectors based on different types of chiral materials and their working principles. Finally, current challenges and future opportunities in the development of CPL photodetectors are prospected.

Recent Advances in Perovskite Photodetectors for Image Sensing

In recent years, metal halide perovskites have been widely investigated to fabricate photodetectors for image sensing due to the excellent photoelectric performance, tunable bandgap, and low-cost solution preparation process. In this review, a comprehensive overview of the recent advances in perovskite photodetectors for image sensing is provided. First, the key performance parameters and the basic device types of photodetectors are briefly introduced. Then, the recent developments of image sensors on the basis of different dimensional perovskite materials, including 0D, 1D, 2D, and 3D perovskite materials, are highlighted. Besides the device structures and photoelectric properties of perovskite image sensors, the preparation methods of perovskite photodetector arrays are also analyzed. Subsequently, the single-pixel imaging of perovskite photodetectors and the strategies to fabricate narrowband perovskite photodetectors for color discrimination are discussed. Finally, the potential challenges and possible solutions for the future development of perovskite image sensors are presented.

Color-Selective Schottky Barrier Modulation for Optoelectric Logic

The limitation on signal processes implementable using conventional semiconductor circuits based on electric signals necessitates a revolutionary change in device structures such that they can exploit photons or light. Herein, we introduce optoelectric logic circuits that convert optical signals with different wavelengths corresponding to different colors into binary electric signals. Such circuits are assembled using unit devices in which the electric current through the semiconductor channel is effectively gated by lights of different colors. Color-selective optical modulation of the device is cleverly achieved using graphene decorated with different organic dyes as the electrode of a Schottky diode structure. The drastic change in the electrode work function under illumination induces a change in the height of the Schottky barrier formed at the electrode/semiconductor junction and consequent modulation of the electric current; we term the developed device a photonic barristor. We construct logic circuits using an array of photonic barristors and demonstrate that they execute the functions of conventional NAND and NOR gates from optical input signals.

Enhanced Optical Absorption in Perovskite/Si Tandem Solar Cells with Nanoholes Array

Perovskite solar cells are used in silicon-based tandem solar cells due to their tunable band gap, high absorption coefficient and low preparation cost. However, the relatively large optical refractive index of bottom silicon, in comparison with that of top perovskite absorber layers, results in significant reflection losses in two-terminal devices. Therefore, light management is crucial to improve photocurrent absorption in the Si bottom cell. In this paper, nanoholes array filled with TiO₂ is introduced into bottom cells design. By finite-difference time-domain methods, the absorption efficiency and photocurrent density in the range of 300-1100 nm has been analyzed, and the structural parameters have been also optimized. Our calculations show the photocurrent density which tends to be saturated with the increase in the height of the nanoholes. The absorption enhancement modes of photons at different wavelengths have been analyzed intuitively by the distribution of electric field. These results enable a viable and convenient route toward high efficiency design of perovskite/Si tandem solar cells.

Graphene-Quantum-Dots-Induced Centimeter-Sized Growth of Monolayer Organic Crystals for High-Performance Transistors

Monolayer organic crystals have attracted considerable attention due to their extraordinary optoelectronic properties. Solution self-assembly on the surface of water is an effective approach to fabricate monolayer organic crystals. However, due to the difficulties in controlling the spreading of organic solution on the water surface and the weak intermolecular interaction between the organic molecules, large-area growth of monolayer organic crystals remains a great challenge. Here, a graphene quantum dots (GQDs)-induced self-assembly method for centimeter-sized growth of monolayer organic crystals on a GQDs solution surface is reported. The spreading area of the organic solution can be readily controlled by tuning the pH value of the GQDs solution. Meanwhile, the π-π stacking interaction between the GQDs and the organic molecules can effectively reduce the nucleation energy of the organic molecules and afford a cohesive force to bond the crystals, enabling large-area growth of monolayer organic crystals. Using 2,7-didecyl benzothienobenzothiopene (C₁₀-BTBT) as an examples, centimeter-sized monolayer C₁₀-BTBT crystal with uniform molecular packing and crystal orientation is attained. Organic field-effect transistors based on the monolayer C₁₀-BTBT crystals exhibit a high mobility up to 2.6 cm² V^-1 s^-1, representing the highest mobility value for solution-assembled monolayer organic crystals. This work provides a feasible route for large-scale fabrication of monolayer organic crystals toward high-performance organic devices.

Bioinspired Multifunctional Organic Transistors Based on Natural Chlorophyll/Organic Semiconductors

Inspired by the photosynthesis process of natural plants, multifunctional transistors based on natural biomaterial chlorophyll and organic semiconductors (OSCs) are reported. Functions as photodetectors (PDs) and light-stimulated synaptic transistors (LSSTs) can be switched by gate voltage. As PDs, the devices exhibit ultrahigh photoresponsivity up to 2 × 10⁶ A W^-1 , detectivity of 6 × 10¹⁵ Jones, and I_photo /I_dark ratio of 2.7 × 10⁶ , which make them among the best reported organic PDs. As LSSTs, important synaptic functions similar to biological synapses are demonstrated, together with a dynamic learning and forgetting process and image-processing function. Significantly, benefiting from the ultrahigh photosensitivity of chlorophyll, the lowest operating voltage and energy consumption of the LSSTs can be 10^-5 V and 0.25 fJ, respectively. The devices also exhibit high flexibility and long-term air stability. This work provides a new guide for developing organic electronics based on natural biomaterials.

Organic Transistor Nonvolatile Memory with Three-Level Information Storage and Optical Detection Functions

By the current processing technology, it is a challenge to obtain ultrahigh-density information storage in the conventional binary floating-gate-based organic field-effect transistor (FG-OFET) nonvolatile memories (NVMs). To develop a multilevel memory in one cell is a feasible solution. In this work, we demonstrate FG-OFET NVMs with an integrated polymer floating-gate/tunneling (I-FG/T) layer consisting of poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) and polystyrene. The photoelectric effect of organic/polymer semiconductors is used to improve the controllability of the polarity and the number of the charges stored in the floating-gate. The FG-OFET NVMs integrate light sensitivity and nonvolatile information storage functions. By selecting suitable optical and electrical programming/erasing conditions, three-level information storage states, corresponding to electron storage, approximate neutrality, and hole storage in the floating-gate, are achieved and freely switched to each other. The memory mechanism and the dependence of the memory performances on the F8BT contents in I-FG/T layers are investigated. As a result, good memory performances, with mobility larger than 1.0 cm² V^-1 s^-1, reliable three-level switching endurance over 100 cycles, and stable three-level retention capability over 20 000 s, are achieved in our memory. Furthermore, an imaging system with a nonvolatile information storage function is demonstrated in a 16 × 5 array of FG-OFET NVMs.