Flexible Phototransistors Research Articles

Flexible Phototransistor Array Enhanced by Coupling the Piezo‐Phototronic Effect and the Flexoelectric Effect for Strain/Optical Sensing and Imaging

Flexible Phototransistor Array Enhanced by Coupling the Piezo‐Phototronic Effect and the Flexoelectric Effect for Strain/Optical Sensing and Imaging

Broadening spectral responses and achieving environmental stability in SnS2/Ag-NPs/HfO2 flexible phototransistors.

Layered two-dimensional (2D) materials have gained popularity thanks to their atomically thin physique and strong coupling with light. Here, we investigated a wide band gap (≥ 2 eV) 2D material, i.e., tin disulfide (SnS2), and decorated it with silver nanoparticles, Ag-NPs, for broadband photodetection. Our results show that the SnS2/Ag-NPs devices exhibit broadband photodetection ranging from the ultraviolet to near-infrared (250-1050 nm) spectrum with decreased rise/decay times from 8/20 s to 7/16 s under 250 nm wavelength light compared to the bare SnS2 device. This is attributed to the localized surface plasmon resonance effect and the wide band gap of SnS2 crystal. Furthermore, the HfO2-passivated SnS2/Ag-NPs devices exhibited high photodetection performance in terms of photoresponsivity (∼12 500 A W-1), and external quantum efficiency (∼6 × 106%), which are significantly higher compared to those of bare SnS2. Importantly, after HfO2 passivation, the SnS2/Ag-NPs photodetector maintained the stable performance for several weeks with merely ∼5.7% reduction in photoresponsivity. Lastly, we fabricated a flexible SnS2/Ag-NPs photodetector, which shows excellent and stable performance under various bending curvatures (0, 20, and 10 mm), as it retains ∼80% of its photoresponsivity up to 500 bending cycles. Thus, our study provides a simple route to realize broadband and stable photoactivity in flexible 2D material-based devices.

Fabrication of highly sensitive flexible phototransistors through a unidirectional floating film transfer method using P4T2F-HD thin films

Fabrication of highly sensitive flexible phototransistors through a unidirectional floating film transfer method using P4T2F-HD thin films

Low Energy Argon Ion Irradiation Effect on the α-In2Se3 Nanoflakes for Flexible Phototransistors

In this report, we investigate the low-energy argon ion radiation effect on the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\alpha $ </tex-math></inline-formula> -In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Se <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> nanoflakes for flexible phototransistors systematically. The phonon modes, microstructure, piezoelectricity, and photoresponsivity of the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\alpha $ </tex-math></inline-formula> -In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Se <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> nanoflake-based flexible phototransistors are investigated. The irradiation-induced vacancies may affect the metal–semiconductor interface and band structure, and result in photoresponsivity degeneration, but the static strain increases the photoresponsivity by the piezophototronic effect and the piezoresistive effect. After irradiation with a fluence of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$7\times10$ </tex-math></inline-formula> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13</sup> /cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , a compressive strain of −0.506% increases the photocurrent ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$I_{\mathrm {ph}}$ </tex-math></inline-formula> ), responsivity ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$R$ </tex-math></inline-formula> ), external quantum efficiency (EQE), and specific detectivity ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$D^\ast$ </tex-math></inline-formula> ) by 412%, 412%, 412%, and 526%, respectively, when the optical power density is about 8.973 mW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . All these show that the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\alpha $ </tex-math></inline-formula> -In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Se <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> nanoflakes have a relatively high radiation resistance, and the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\alpha $ </tex-math></inline-formula> -In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Se <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> is one of the candidate materials for the flexible phototransistors used in the aerospace or nuclear industries.

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.

A full transparent high-performance flexible phototransistor with an ultra-short channel length

Ultraviolet (UV) photodetectors (PDs), which can convert ultraviolet light into electrical signals for dynamic monitoring, have attracted tremendous attention to protect humans from diseases induced by harmful light radiations.

Microfluidic Approach for Lead Halide Perovskite Flexible Phototransistors

Lead halide perovskites possess outstanding optical characteristics that can be employed in the fabrication of phototransistors. However, due to low current modulation at room temperature, sensitivity to the ambient environment, lack of patterning techniques and low carrier mobility of polycrystalline form, investigation in perovskite phototransistors has been limited to rigid substrates such as silicon and glass to improve the film quality. Here, we report on room temperature current modulation in a methylammonium lead iodide perovskite (MAPbI3) flexible transistor made by an extremely cheap and facile fabrication process. The proposed phototransistor has the top-gate configuration with a lateral drain–channel–source structure. The device performed in the linear and saturation regions both in the dark and under white light in different current ranges according to the illumination conditions. The transistor showed p-type transport characteristics and the field effect mobility of the device was calculated to be ~1.7 cm2 V−1 s−1. This study is expected to contribute to the development of MAPbI3 flexible phototransistors.

Magnetically controllable and flexible phototransistor for artificial intelligent skin with additional perception

With rational design, emerging artificial intelligent systems enable to possess capabilities far beyond human beings. Here, we report a novel magnetically controllable and flexible phototransistor using a tandem structure composed of an organic solar cell (OSC) of ITO/ZnO/P3HT:PC61BM/MoO3/Ag and a magnetic micropyramid array film of FeNi/PDMS composite covered with silver nanowires (AgNWs) (FeNi/PDMS/AgNWs) separated by an air gap. The FeNi/PDMS/AgNWs micropyramid structure takes the advantage of the Ag electrode of the bottom OSC forming a magnetoelectronic device. This novel seamless integrated device can interact with external stimuli, including pressure, light and magnetic field, forming an intriguing type of transistor. The output current of the developed transistor can be modulated by both optical excitation and magnetic field simultaneously, making it possess new functionalities. Additionally, the phototransistor carries several outstanding features, including fast photo/magnetic-response time, non-contact magnetic/optical control, and mechanical flexibility. These promising properties diversify the applications of the proposed phototransistor for the implementation in wearable electronics, touchless technology, and optical communication.

Silicon nanomembrane phototransistor flipped with multifunctional sensors toward smart digital dust.

The sensing module that converts physical or chemical stimuli into electrical signals is the core of future smart electronics in the post-Moore era. Challenges lie in the realization and integration of different detecting functions on a single chip. We propose a new design of on-chip construction for low-power consumption sensor, which is based on the optoelectronic detection mechanism with external stimuli and compatible with CMOS technology. A combination of flipped silicon nanomembrane phototransistors and stimuli-responsive materials presents low-power consumption (CMOS level) and demonstrates great functional expansibility of sensing targets, e.g., hydrogen concentration and relative humidity. With a device-first, wafer-compatible process introduced for large-scale silicon flexible electronics, our work shows great potential in the development of flexible and integrated smart sensing systems for the realization of Internet of Things applications.

Defect repair for enhanced piezo-phototronic MoS2 flexible phototransistors

Suppression of the screening effect and thus the enhancement of piezo-phototronic modulation were achieved in monolayer MoS2 through defect engineering.

Fabrication of Flexible Image Sensor Based on Lateral NIPIN Phototransistors.

Flexible photodetectors have been intensely studied for the use of curved image sensors, which are a crucial component in bio-inspired imaging systems, but several challenging points remain, such as a low absorption efficiency due to a thin active layer and low flexibility. We present an advanced method to fabricate a flexible phototransistor array with an improved electrical performance. The outstanding electrical performance is driven by a low dark current owing to deep impurity doping. Stretchable and flexible metal interconnectors simultaneously offer electrical and mechanical stabilities in a highly deformed state. The protocol explicitly describes the fabrication process of the phototransistor using a thin silicon membrane. By measuring I-V characteristics of the completed device in deformed states, we demonstrate that this approach improves the mechanical and electrical stabilities of the phototransistor array. We expect that this approach to a flexible phototransistor can be widely used for the applications of not only next-generation imaging systems/optoelectronics but also wearable devices such as tactile/pressure/temperature sensors and health monitors.

Flexible and Transparent Organic Phototransistors on Biodegradable Cellulose Nanofibrillated Fiber Substrates

AbstractThis work demonstrates flexible, transparent phototransistors that can detect visible light with nontoxic organic active materials on biodegradable substrates toward environment‐friendly electronics. The molybdenum trioxide (MoO3)‐buffered indium zinc oxide as high‐performance hole injector and transparent electrodes is applied for the first time to organic phototransistors on cellulose nanofibrillated fiber substrates to achieve more than 70% of transmittance in the visible range (400–750 nm) while showing high conductivity under multiple bendings. Excellent electrical switching characteristics are obtained from transistors using a pentacene active layer with a saturation mobility value of 1.40 cm2 V−1 s−1. The phototransistors, which can detect visible light and perform in two operation modes, exhibit a maximum responsivity of 54.8 A W−1 and a photosensitivity of 24.4 under white light illumination at an intensity of 0.12 mW cm−2. Moreover, the devices show a stable operation during mechanical bending tests with radii ranging from 100 to 5 mm and cyclic bending tests of up to 2000 cycles at a fixed radius of 5 mm. The results suggest that these flexible phototransistors with properties of transparency and biodegradability have considerable potential for use in low‐cost and eco‐friendly disposable sensor systems.

Flexible organic N-channel phototransistor and integrated logic devices

A flexible organic field-effect transistor (OFET) and flexible phototransistor have been fabricated using self-assembled single crystals of a small molecule, viz, N,N’-dioctyl-3,4,9,10-perylene tetracarboxylic diimide (PTCDI-C8). The solution processed single crystals of PTCDI-C8 with strong molecular ordering showed excellent OFET performances having mobility μ∼0.2cm2/Vs. The absence of grain boundaries, traps and intrinsically defect-free nature of the single crystals contributed to the improved device performances in PTCDI-C8 crystalline OFET. The device exhibited high sensitivity to photo-illumination with photoresponsivity value upto Ca. 3A/W and photo to dark current ratio ∼103. Both the transistor and photosensing characteristics of the OFET device were retained even under extreme bending of the flexible substrate, exhibiting robust mechanical flexibility of the OPT. To realize OFET based electro-optical logic circuits, we have suitably integrated the photo signal and electrical signal and demonstrated that binary NOT and OR operations could be performed on the OFET device with light as one of the input signal. The large area deposition of self-assembled organic single crystals with multifunctional activity, such as, photosensing with switching, signal amplification, and electro-optical logic operation opens up immense possibilities for flexible organic logic device and promises great potential for future low-cost plastic optoelectronic applications.

Printable and Flexible Phototransistors Based on Blend of Organic Semiconductor and Biopolymer

Printable and flexible organic phototransistors (OPTs) make comprehensive requirements for the organic semiconductors (OSCs), including high photosensitivity, decent transistor characteristics, appropriate solution viscosity, and good film flexibility. It has been challenging to obtain such semiconductors. Here, we demonstrated that by taking advantage of the interfacial charge effect, printable and flexible OPTs with high performance can be successfully fabricated through simply blending common OSCs with polymers. Using 2,7‐dioctyl[1]benzothieno[3,2‐b][1]benzothiophene and an insulating biopolymer polylactide, OPTs with blended and layered structure are both fabricated and investigated. The photoresponses of the OPTs can be modulated by gate voltage over 1000 times, and their responsivities are measured up to 400 A W−1. As compared to the layered OPTs, the blended ones exhibit higher photocurrent to dark current ratio (up to 105) and better light detection limit (lower than 0.02 mW cm−2). The improvements are attributed to larger interfacial area and more intensive charge trapping effect. The flexible OPTs are further fabricated by inkjet printing the blended solution. This work presents OPTs with comprehensive advantages including low cost, enhanced photosensitivity, great flexibility, and printability, which are realized by simply blending common OSC with polymer, and thus provide an inspiration for the design of novel organic electronics.

Flexible Phototransistors Based on Single‐Crystalline Silicon Nanomembranes

In this work, flexible phototransistors with a back gate configuration based on transferrable single‐crystalline Si nanomembrane (Si NM) have been demonstrated. Having the Si NM as the top layer enables full exposure of the active region to an incident light and thus allows for effective light sensing. Flexible phototransistors are performed in two operation modes: 1) the high light detection mode that exhibits a photo‐to‐dark current ratio of 105 at voltage bias of VGS &lt; 0.5 V, and VDS = 50 mV and 2) the high responsivity mode that shows a maximum responsivity of 52 A W−1 under blue illumination at voltage bias of VGS = 1 V, and VDS = 3 V. Due to the good mechanical flexibility of Si NMs with the assistance of a polymer layer to enhance light absorption, the device exhibits stable responsivity with less than 5% of variation under bending at small radii of curvatures (up to 15 mm). Overall, such flexible phototransistors with the capabilities of high sensitivity light detection and stable performance under the bending conditions offer great promises for high‐performance flexible optical sensor applications, with easy integration for multifunctional applications.

Flexible phototransistors based on graphene nanoribbon decorated with MoS2 nanoparticles

This paper presents highly efficient, flexible, and low-cost photo-transistors based on graphene nanoribbon (GNR) decorated with MoS2 nanoparticles (NPs). Due to high carrier mobility, GNR has been used as carrier transport channel and MoS2 NPs provide strong advantage of high gain absorption and the generation of electron-hole pairs. These pairs get separated at the interface between GNR and MoS2 NPs, which leads to electron transfer from NPs towards GNR. The fabricated devices based on GNR-MoS2 hybrid material show a high photo-responsivity of 66AW−1 and fast rise-time (tr) and decay-time (td) of 5ms and 30ms, respectively, under blue laser illumination with a wavelength of 385nm and power density of 2.1μW. The achieved photo-responsivity is 1.3×105 and 104 times larger than that of the first reported pristine graphene and MoS2 photo-transistors, respectively. Furthermore, fabricated devices show a high stability for bending radii larger than 6mm. The simple solution based process, high gain and reproducible operation of fabricated photo-transistors indicate potential applications of them in state of the art photo-detectors and imaging systems.