High-performance Phototransistors Research Articles

Enhanced Photodetection Performance of an In Situ Core/Shell Perovskite-MoS2 Phototransistor.

While two-dimensional transition metal dichalcogenides (TMDCs)-based photodetectors offer prospects for high integration density and flexibility, their thinness poses a challenge regarding low light absorption, impacting photodetection sensitivity. Although the integration of TMDCs with metal halide perovskite nanocrystals (PNCs) has been known to be promising for photodetection with a high absorption coefficient of PNCs, the low charge mobility of PNCs delays efficient photocarrier injection into TMDCs. In this study, we integrated MoS2 with in situ formed core/shell PNCs with short ligands that minimize surface defects and enhance photocarrier injection. The PNCs/MoS2 heterostructure efficiently separates electrons and holes by establishing type II band alignment and consequently inducing a photogating effect. The synergistic interplay between photoconductive and photogating effects yields a high responsivity of 2.2 × 106 A/W and a specific detectivity of 9.0 × 1011 Jones. Our findings offer a promising pathway for developing low-cost, high-performance phototransistors leveraging the advantages of two-dimensional (2D) materials.

Two-dimensional perovskite oxide high-κ dielectric for high-performance phototransistors

Two-dimensional perovskite oxide high-κ dielectric for high-performance phototransistors

Tunable Light Response Modulated by the Organic Interface Charge Transfer Effect

AbstractThe combination of a donor (D) and an acceptor (A) is viewed as a promising approach to achieve high performance phototransistors, owing to their advantages in exciton dissociation and charge trapping. The electronic properties at the D‐A interface can vary substantially with the choice of materials, and how to precisely control the interface properties to achieve a controllable light response behavior is still an open question. Herein, a series of D‐A heterostructure is reported with varying electronic structures of the acceptor and demonstrate the ability to tune the performance and photocurrent decay behaviors. Two distinct types of charge transfer phenomena, ground state, and excited state charge transfer, are identified originating from the specific different energy level alignment and lead to the improved photoresponsivity up to 104 AW−1 and the significantly varied photosensitivity ranging from 102 to approaching 107. Furthermore, the distinct charge transfer scenarios elicit diverse temporal responses, encompassing both short‐term synaptic behavior as well as persistent memory characteristics. These findings shed light on the importance of understanding and controlling charge transfer property for phototransistor performance and applications. The ability to modulate the temporal responses opens up new possibilities for designing devices with desired memory and synaptic functionalities.

Laser shock introduces strained wrinkling of CVD monolayer MoS2 and atomic gapping of plasmonic phototransistors

Monolayer MoS2, an atomic direct bandgap 2D material with excellent mechanical properties, is considered one of the top candidates for next-generation electronics. However, the phototransistor based on MoS2 synthesized through chemical vapor deposition (CVD) has relatively weak optical emissivity and absorption, low field-effect mobility, and a narrow response spectral range These limitations hinder the widespread application of MoS2 in optoelectronic devices. Here, to improve the performance of CVD 2D electronic devices in large-scale applications, we designed a hybrid nano-system with laser shock-enhanced plasmon and strain coupling. Wrinkles of CVD monolayers of MoS2 sandwiched between two layers of Ag nanoparticles (NPs) are tensile strained to form gap-mode localized surface plasmon resonance (LSPR). The strain of the laser shock (LS) leads to the co-deformation of MoS2 and Ag NPs, achieving an extremely narrow gap LSPR (<1 nm). The residual inhomogeneous elastic strain, remaining after the shock, not only enhances the LSPR but also modulates the band structure of MoS2 favorably. In comparison to a phototransistor employing CVD-monolayer MoS2 on a flat substrate (1L-MoS2), the laser-shock phototransistor (LS_Ag-MoS2) is improved by nearly 50 times, the response range is extended to near-infrared, and the field effect mobility is increased by 30 times. In addition, the response time is reduced from 1.28 s to 20 ms, which is comparable to the current high-K dielectric multilayer MoS2 phototransistor. Our work presents an advanced and scalable fabrication method for future applications of ultra-thin and high-performance phototransistors utilizing CVD two-dimensional materials.

Thickness modulation of incline-grown Bi2O2Se for the construction of high-performance phototransistors

Newly emerging two-dimensional (2D) Bi2O2Se has received intense research interest due to its unique band structure and ultrafast optical properties. However, the device performance of Bi2O2Se-based photodetectors is far from the expectation because of the undesirable contact issues of the contaminates from the fabrication process or the high Schottky barrier caused by the large work function mismatch. In this work, highly efficient photodetection based on an “all-Bi2O2Se” device geometry has been demonstrated. By controlling the growth conditions, Bi2O2Se flakes with thicknesses of 8–15 nm (thin) and &amp;gt;40 nm (thick) are obtained. The thin one is a typical n-type semiconductor, while the thick one shows the degenerated n-type behavior with a higher Fermi level. Two thick flakes are adopted as 2D contacts for the absorption layer of thin flake, leading to the upward movement of the thin flake band structures. By tailoring the Schottky barrier frame at the interface junction, the high barriers are eliminated, which boost the transport and collection of photo-generated electrons. The photodetector demonstrates strong photoresponse to visible and near-infrared light. High photoresponsivity and specific detectivity of 3.34 × 104 A/W and 6.61 × 1013 Jones, respectively, are achieved under the 640 nm light illumination.

High-Performance Phototransistor Memory with an Ultrahigh Memory Ratio Conferred Using Hydrogen-Bonded Supramolecular Electrets

As the research of photonic electronics thrives, the enhanced efficacy from an optic unit cell can considerably improve the performance of an optoelectronic device. In this regard, organic phototransistor memory with a fast programming/readout and a distinguished memory ratio produces an advantageous outlook to fulfill the demand for advanced applications. In this study, a hydrogen-bonded supramolecular electret is introduced into the phototransistor memory, which comprises porphyrin dyes, meso-tetra(4-aminophenyl)porphine, meso-tetra(p-hydroxyphenyl)porphine, and meso-tetra(4-carboxyphenyl)porphine (TCPP), and insulated polymers, poly(4-vinylpyridine) and poly(4-vinylphenol) (PVPh). To combine the optical absorption of porphyrin dyes, dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT) is selected as a semiconducting channel. The porphyrin dyes serve as the ambipolar trapping moiety, while the insulated polymers form a barrier to stabilize the trapped charges by forming hydrogen-bonded supramolecules. We find that the hole-trapping capability of the device is determined by the electrostatic potential distribution in the supramolecules, whereas the electron-trapping capability and the surface proton doping originated from hydrogen bonding and interfacial interactions. Among them, PVPh:TCPP with an optimal hydrogen bonding pattern in the supramolecular electret produces the highest memory ratio of 1.12 × 108 over 104 s, which is the highest performance among the reported achievements. Our results suggest that the hydrogen-bonded supramolecular electret can enhance the memory performance by fine-tuning their bond strength and cast light on a potential pathway to future photonic electronics.

Molecular template growth of organic heterojunctions to tailor visual neuroplasticity for high performance phototransistors with ultralow energy consumption.

The optical and charge transport properties of organic semiconductors are strongly influenced by their morphology and molecular structures. Here we report the influence of a molecular template strategy on anisotropic control via weak epitaxial growth of a semiconducting channel for a dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT)/para-sexiphenyl (p-6P) heterojunction. The aim is to improve charge transport and trapping, to enable tailoring of visual neuroplasticity. The proposed phototransistor devices, comprising a molecular heterojunction with optimized molecular template thickness, exhibited an excellent memory ratio (ION/IOFF) and retention characteristics in response to light stimulation, owing to the enhanced orientation/packing of DNTT molecules and a favorable match between the LUMO/HOMO levels of p-6P and DNTT. The best performing heterojunction exhibits visual synaptic functionalities, including an extremely high pair-pulse facilitation index of ∼206%, ultralow energy consumption of 0.54 fJ, and zero-gate operation, under ultrashort pulse light stimulation to mimic human-like sensing, computing, and memory functions. An array of heterojunction photosynapses possess a high degree of visual pattern recognition and learning, to mimic the neuroplasticity of human brain activities through a rehearsal learning process. This study provides a guide to the design of molecular heterojunctions for tailoring high-performance photonic memory and synapses for neuromorphic computing and artificial intelligence systems.

Boosting Phototransistor Performance in Monolayer TMDs via Multiple Reflections from DBR.

Transition-metal dichalcogenides (TMDs) are intensively studied for high-performance phototransistors. However, the device performance is limited by the single photoexcitation. Here, we show a unique strategy in which phototransistor performance can be boosted by fabricating the device on top of a distributed Bragg reflector (DBR). Monolayer molybdenum disulfide (MoS2) and tungsten disulfide (WS2) phototransistors were fabricated on DBR and SiO2 substrates for comparison. Furthermore, phototransistor performances including photocurrent, responsivity, photoinduced mobility, and subthreshold swing highlight 582 times enhancement in photoresponsivity ratio and 350 times enhancement in photocurrent ratio in the DBR sample using transparent graphene electrode and hBN encapsulation.

Interfacial Engineering of High-Performance, Solution-Processed Sb2S3 Phototransistors.

Antimony sulfide, as a binary chalcogenide, has attracted great attention in the field of optoelectronics in recent years, particularly in photovoltaics, because of its striking merits such as earth elements abundance, excellent stability, chemical versatility, and solution processability. With the rapid development of fabrication techniques and device engineering, the device performance of Sb2S3 solar cells has experienced an unprecedented success. However, photodetectors based on Sb2S3 were barely reported, especially based on the transistor configuration. In this work, we prepared high quality Sb2S3 thin films via a sol-gel method, and Sb2S3 thin films were deposited on zinc-tin oxide based field-effect transistors. Furthermore, an additional electron transport layer was inserted between the Sb2S3 layers and the zinc-tin oxide channels and archived high-performance phototransistors with proper interfacial engineering. The optimized devices exhibited extremely high photosensitivity (106), low dark current (∼10 pA) and noise (∼11 fA Hz-1/2), high detectivity (1 × 1013 Jones), and superior device stability, indicating great potential for next generation solution-processed photodetectors.

Highly Sensitive Broadband Phototransistors Based on Gradient Tin/Lead Mixed Perovskites.

Highly sensitive broadband photodetectors are critical to numerous cutting-edge technologies such as biomedical imaging, environment monitoring, and night vision. Here, phototransistors based on mixed Sn/Pb perovskites are reported, which demonstrate ultrahigh responsivity, gain and specific detectivity in a broadband from ultraviolet to near-infrared region. The interface properties of the perovskite phototransistors are optimized by a special three-step cleaning-healing-cleaning treatment, leading to a high hole mobility in the channel. The highly sensitive performance of the mixed Sn/Pb perovskite phototransistors can be attributed to the vertical compositional heterojunction automatically formed during the film deposition, which is helpful for the separation of photocarriers thereby enhancing a photogating effect in the perovskite channel. This work demonstrates a convenient approach to achieving high-performance phototransistors through tuning compositional gradient in mixed-metal perovskite channels.

Optoelectronic Modulation of Silver Antimony Sulfide Thin Films for Photodetection.

Silver antimony sulfide, as a ternary chalcogenide, has attracted great attention in the field of optoelectronics in recent years. In particular, it has appealing properties, such as excellent stability, solution processability, and versatile composition tunability. Benefiting from the recent development of processing techniques, AgSbS2 has emerged as a promising candidate for next-generation, thin-film photovoltaics. On the contrary, AgSbS2-based photodetectors have been barely reported. In this work, we systematically investigated the composition engineering of silver antimony sulfide compounds with a precursor route. Their optoelectronic properties were fully characterized, and the composition was optimized for photodetection. High-performance phototransistors were first reported based on field-effect thin film transistors with interfacial modification. The obtained AgSbS2 phototransistors exhibited relatively high photosensitivity, low dark current and noise, superior device stability, and excellent detectivity covering the whole range from ultraviolet to near-infrared, highlighting the great potential for next-generation photodetection.

High-sensitive phototransistor based on vertical HfSe2/MoS2 heterostructure with broad-spectral response

Van der Waals heterostructures based on the two-dimensional (2D) semiconductor materials have attracted increasing attention due to their attractive properties. In this work, we demonstrate a high-sensitive back-gated phototransistor based on the vertical HfSe2/MoS2 heterostructure with a broad-spectral response from near-ultraviolet to near-infrared and an efficient gate tunability for photoresponse. Under bias, the phototransistor exhibits high responsivity of up to 1.42×103 A/W, and ultrahigh specific detectivity of up to 1.39×1015 cm⋅Hz1/2⋅W−1. Moreover, it can also operate under zero bias with remarkable responsivity of 10.2 A/W, relatively high specific detectivity of 1.43×1014 cm⋅Hz1/2⋅W−1, ultralow dark current of 1.22 fA, and high on/off ratio of above 105. These results should be attributed to the fact that the vertical HfSe2/MoS2 heterostructure not only improves the broadband photoresponse of the phototransistor but also greatly enhances its sensitivity. Therefore, the heterostructure provides a promising candidate for next generation high performance phototransistors.

BN-Anthracene for High-Mobility Organic Optoelectronic Materials through Periphery Engineering.

Despite the remarkable synthetic accomplishments in creating diverse polycyclic aromatic hydrocarbons with B-N bonds (BN-PAHs), their optoelectronic applications have been less exploited. Herein, we report the achievement of high-mobility organic semiconductors based on existing BN-PAHs through a "periphery engineering" strategy. Tetraphenyl- and diphenyl-substituted BN-anthracenes (TPBNA and DPBNA, respectively) are designed and synthesized. DPBNA exhibits the highest hole mobility of 1.3 cm2 V-1 s-1 in organic field-effect transistors, significantly outperforming TPBNA and all the reported BN-PAHs. Remarkably, this is the first BN-PAH with mobility over 1 cm2 V-1 s-1 , which is a benchmark value for practical applications as compared with amorphous silicon. Furthermore, high-performance phototransistors based on DPBNA are also demonstrated, implying the high potential of BN-PAHs for optoelectronic applications when the "periphery engineering" strategy is implemented.

Fast Photoresponsive Phototransistor Memory Using Star-Shaped Conjugated Rod-Coil Molecules as a Floating Gate.

With the explosive growth in data generation, photomemory capable of multibit data storage is highly desired to enhance the capacity of storage media. To improve the performance of phototransistor memory, an organic-molecule-based electret with an elaborate nanostructure is of great importance because it can enable multibit data storage in a memory device with high stability. In this study, a series of star-shaped rod-coil molecules consisting of perylenediimide (PDI) and biobased solanesol were synthesized in two-armed (PDI-Sol2), four-armed (PDI-Sol4), and six-armed (PDI-Sol6) architectures. Their molecular architecture-morphology relationships were investigated, and phototransistor memory was fabricated and characterized to evaluate the structure-performance relationship of these rod-coil molecules. Accordingly, the memory devices were enabled by photowriting with panchromatic light (405-650 nm) and electrical erasing using a gate bias. The PDI-Sol4-based memory device showed high memory ratios of 10 000 over 10 000 s and a rapid multilevel photoresponse of 50 ms. This achievement is related to the favorable energy-level alignment, isolated nanostructure, and face-on orientation of PDI-Sol4, which eliminated the charge tunneling barrier. The results of this study provide a new strategy for tailoring nanostructures in organic-molecule-based electrets by using a star-shaped rod-coil architecture for high-performance phototransistor memory.

High-performance floating-gate organic phototransistors based on n-type core-expanded naphthalene diimides

In the field of organic phototransistor, achieving both broad-spectral and high photosensitivity has always been a big challenge. The innovation of device structure has previously proven to be a possible solution to this problem. Here in this study, a novel organic phototransistor based on a high mobility n-type small molecule as the conducting layer and an isolated bulk heterojunction light-absorbing layer as the floating gate has been demonstrated in this study. With the special designed device structure, the phototransistor shows extremely high sensitivity to broad spectral and weak light irradiation, and the photoresponsivity and photocurrent/dark-current ratio of the device can reach up to 4840 mA/W and 1.8 × 105 respectively. For conclusion, this study suggests a potential way to obtain high-performance phototransistors at room temperature, which will further promote the commercial application of organic phototransistors.

High-Performance Organic Phototransistors Based on D18, a High-Mobility and Unipolar Polymer

Organic optoelectronics has progressed excitingly in recent years, mainly due to the innovation of donor and acceptor systems. Organic photodetectors based on novel semiconductor materials and well-designed device architectures have also been reported with improved device performance. However, most of them were photodiodes, and it is challenging to integrate them into the well-established readout circuits. Organic phototransistors are mainly based on the hybrid strategy, composed of either hybrid films or multilayer device structures, which complicates charge transfer and charge transport. Most of the organic devices also suffer from poor stability. In this work, we introduce a recently developed p-type copolymer, D18, to fabricate high-performance phototransistors. D18 possesses excellent charge generation, high mobility, and unipolar charge transport, which fulfill the generic design rule of organic phototransistors. The optimized phototransistors based on D18 exhibited extremely low dark current (∼10 pA) and noise (∼10 fA/Hz1/2), a high detectivity of 4 × 1013 Jones, a swift response of <5 ms, and excellent device stability. We also demonstrated flexible phototransistors with decent performance metrics, indicating great potential for next-generation solution-processed photodetectors and flexible electronic devices.

Few-layered organic single-crystalline heterojunctions for high-performance phototransistors

Few-layered organic single-crystalline heterojunctions for high-performance phototransistors

Ultra-thin two-dimensional molecular crystals grown on a liquid surface for high-performance phototransistors.

A novel strategy for the growth of molecularly thin two-dimensional molecular crystals (2DMCs) of organic semiconductors with poor solubility was developed. Large-area bilayer 2DMCs were grown on a liquid surface at elevated temperatures, with record mobility and superior photoresponse.

High-Performance Vertical Organic Phototransistors Enhanced by Ferroelectrics

Organic phototransistors with high sensitivity and responsivity to light irradiance have great potential applications in national defense, meteorology, industrial manufacturing, and medical security. However, undesired dark current and photoresponsivity limit their practical applications. Here, a novel vertical organic phototransistor combined with ferroelectric materials is developed. The device structure has nanometer channel length, which can effectively separate photogenerated carriers and reduce the probability of carrier recombination and defect scattering, thus improving the device performance of phototransistors. Moreover, by inserting the poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) ferroelectric layer, the Schottky barrier at the interface between the semiconductor and source can be adjusted by the polarization of the external electric field, which can effectively reduce the dark current of the phototransistor to further improve the device performance. Therefore, our phototransistors exhibit a high photoresponsivity of more than 5.7 × 105A/W, an outstanding detectivity of 1.15 × 1018 Jones, and an excellent photosensitivity of 5 × 107 under 760 nm light illumination, which are better than those of conventional lateral organic phototransistors. This work provides a new approach for the development of high-performance phototransistors, which opens a new pathway for organic phototransistors in practical application.

Light-modulated vertical heterojunction phototransistors with distinct logical photocurrents

The intriguing carrier dynamics in graphene heterojunctions have stimulated great interest in modulating the optoelectronic features to realize high-performance photodetectors. However, for most phototransistors, the photoresponse characteristics are modulated with an electrical gate or a static field. In this paper, we demonstrate a graphene/C60/pentacene vertical phototransistor to tune both the photoresponse time and photocurrent based on light modulation. By exploiting the power-dependent multiple states of the photocurrent, remarkable logical photocurrent switching under infrared light modulation occurs in a thick C60 layer (11 nm) device, which implies competition of the photogenerated carriers between graphene/C60 and C60/pentacene. Meanwhile, we observe a complete positive-negative alternating process under continuous 405 nm irradiation. Furthermore, infrared light modulation of a thin C60 (5 nm) device results in a photoresponsivity improvement from 3425 A/W up to 7673 A/W, and we clearly probe the primary reason for the distinct modulation results between the 5 and 11 nm C60 devices. In addition, the tuneable bandwidth of the infrared response from 10 to 3 × 103 Hz under visible light modulation is explored. Such distinct types of optical modulation phenomena and logical photocurrent inversion characteristics pave the way for future tuneable logical photocurrent switching devices and high-performance phototransistors with vertical graphene heterojunction structures.