Flexible Photodetectors Research Articles

Scalable and low-cost fabrication of flexible WS2 photodetectors on polycarbonate

We present a low-cost and easy-to-implement technique to fabricate large-area WS2 photodetector devices onto transparent and flexible polycarbonate substrates. The method relies on the deposition of large-area (in the cm scale) thin films (~30 nm thick) of WS2 by a recently introduced abrasion-induced method. Interdigitated electrical contacts are then deposited by thermal evaporation through a shadow mask. The photodetectors present well-balanced performances with an good trade-off between responsivity (up to 144 mA/W at a source-drain voltage of 10 V and illumination power of 1 μW) and response time (down to ~70 µs) and a detectivity value of 108 Jones. We found that the devices perform very reversibly upon several illumination and straining cycles and we found a moderate device-to-device variation.

Large area, self-powered, flexible, fast, and broadband photodetector enabled by the SnSe-Sb2Se3 heterostructure

The Self-powered and flexible photodetector is the future of the optoelectronic industry. For the first time, we have employed an isotype heterostructure, SnSe-Sb2Se3, and showed its photodetection performance under the Vis-NIR range. The large area device exhibits a stable and fast response at zero bias. Even after 1500 bending cycles, the device showed a stable photo-response without change in response time (while recovery time doubled). Also, this isotype structure showed enhanced absorption in the complete Vis-NIR spectra that can be utilized in other applications like solar cells.

ZIF-67 Derivative Decorated MXene for a Highly Integrated Flexible Self-Powered Photodetector.

The rapid development of portable and wearable electronics has promoted the integration of multifunction techniques. Although flexible energy storage systems have been successfully investigated, the compact configuration with photodetector and energy storage components has received less attention. As a new member of the 2D material class, MXene exhibits remarkable electronic and optical properties. Here, through the intentional introduction of ZIF-67 derivatives deposited on the Mo2CTx nanosheets, the synthesized Co-CoOx/NC/Mo2CTx heterostructure not only provided a straightforward pathway for photogenerated electrons to transport but also enhanced the structural stability of Mo2CTx, leading to a high responsivity and short rise/decay time under the illumination of simulated light in the photoelectrochemical (PEC) configuration. The integrated flexible device based on a zinc ion battery and Co-CoOx/NC/Mo2CTx heterostructure shows outstanding photodetection function and retains the intrinsic charge/discharge behaviors, which could monitor 1 day sunlight changes in real time. The paradigm presented here paves the way for realizing the development of miniaturization and multifunction toward next-generation portable and wearable technologies.

Nacre inspired robust self-encapsulating flexible perovskite photodetector

The unique properties of metal halide perovskites give them great potential for applications in portable and wearable optoelectronics. However, the intrinsic brittleness of perovskites favors easy crack propagation that deteriorates the optoelectronic performance of the devices. Inspired by nacre, we propose flexible perovskite thin films fabricated by antisolvent-assisted self-encapsulation of polymer and imprinting techniques during crystallization. Such an approach results in synchronous formation of polymer-glued perovskite grains exhibiting nacre-like “brick-and-mortar” structure. The deformable composite architecture bonding hemisphere-shaped grating (HG) and porous photonic crystal (PC) (HG-PC) improves its crystalline quality and light-harvesting capability. An HG-PC photodetector (PD) with high responsivity of 17.31 A/W and detectivity of 5.02 × 1013 Jones is achieved. Our flexible HG-PC PD retains 95% of the initial photocurrent after 1000 bending cycles at 2 mm curvature radius. This solvent-driven self-encapsulation strategy offers an innovative and universal approach for highly efficient flexible optoelectronics.

Space-confined synthesis of SWNT bundles wrapped by MoS2 crystalline layers as flexible sensors and detectors

Single-walled carbon nanotubes (SWNTs) are ideal template for constructing one-dimensional (1D) heterojunctions with intriguing optical and electrical properties, yet it remains challenging to wrap foreign materials around SWNTs due to their very small diameter and large curvature. Here, we present a space-confined method to synthesize SWNT bundles wrapped by MoS2 crystalline layers (SWNT@MoS2) film by embedding a pristine SWNT film within a porous multi-walled nanotube sponge, which acts as a liquid precursor container for hydrothermal reaction. We find that crystalline MoS2 sheets could be formed around the outer surface of SWNT bundles uniformly and continuously, with tailored number of multi-layers (3–17 layers), for bundle sizes ranging from several to hundreds of nanometers. The resulting SWNT@MoS2 network shows much enhanced light response and gas sensitivity, presenting promising applications as flexible photo-detectors and toxic gas sensors. Our scalable synthesis method and SWNT-based coaxial-cables will be useful in future developing innovated 1D van der Waals heterojunctions and flexible nanoelectronic systems.

Ultra-High Responsivity and Enhanced Trap Assisted Charge Transfer by utilizing Ti3C2TX(MXene) as a Transport Layer for ReS2 based Flexible Broadband Photodetector: A better Alternative to Graphene

Even though there are many reports on low-cost flexible broadband photodetector the main issue is the low value of the responsivity due to non-uniformity of the substrate. The reason is the lack of suitable transport material. Graphene has proven to be the best till date, but, on unconventional substrates such as biodegradable paper, responsivity values still remain an unresolved issue. This report demonstrates for the first time the use of Ti3C2TX(MXene) as transport layer, utilizing 2D ReS2 as active material on paper substrate as broadband photodetector and further compared its performance with graphene. Responsivity values calculated for ReS2/MXene and ReS2/graphene under visible and NIR illumination are 40.8 AW−1, 26.9 AW−1, and 26.5 AW−1, 17.5 AW−1, respectively, which suggests that MXene as transport layer largely enhances performance. To understand the phenomena, detailed mechanisms studies are presented in terms of density of surface states and energy band diagram. Surface states density was found to be larger in MXene compared to graphene structure, suggests that the lifetime of the carrier is high with MXene as transport layer compared to Graphene due to trap assisted charge transfer. This ReS2/MXene heterostructure based environment friendly photodetector can find potential applications in future flexible optoelectronics.

Low-temperature process for self-powered lead-free Cs2AgBiBr6 perovskite photodetector with high detectivity

In recent years, solution-processed lead halide perovskites have obtained great achievements in the field of optoelectronic devices. However, the instability and the toxicity of lead halide materials limit their commercial development. As a kind of lead-free perovskite, bismuth (Bi)-based double perovskite materials have become a research hot spot due to their high thermal stability and non-toxicity. Unfortunately, in the current preparation process, the solution-processed, high-quality Bi-based double perovskites need to suffer high post-treatment temperature, which seriously affects the interfaces between the perovskite/transport layer and is not friendly to the flexibility. Herein, by optimizing the DMF content in the Cs2AgBiBr6 precursor solution and spin coating speed, we obtained the optimal performance of the control device. On this basis, by adding ionic liquid to the optimal Cs2AgBiBr6 perovskite precursor, we greatly reduced the fabrication temperature of the Cs2AgBiBr6 from 285 to 150 °C, improved the stability of the device and the high-performance, flexible Cs2AgBiBr6 perovskite photodetectors (PDs) were fabricated at first. Through optimization, our low-temperature prepared Cs2AgBiBr6 perovskite PD showed high device performance with the switching ratio of 1.66 × 104, the linear dynamic range of 100 dB, the detectivity of up to 1.87 × 1012 Jones, and our flexible Cs2AgBiBr6 perovskite PDs also achieved the detectivity up to 8.04 × 1011 Jones with good flexible stability. This work provides a facile way to fabricate lead-free perovskites at low temperature.

ZnS Nanosheets in a Polyaniline Matrix as Metallopolymer Nanohybrids for Flexible and Biofriendly Photodetectors

The current research work reports on the functionalization of a poly-toluenesulfonic acid (p-TSA)-doped polyaniline matrix by ZnS nanosheets. Structural analysis has been performed by X-ray diffraction and X-ray photoelectron spectroscopy. The Rietveld refinement confirms the cubic phase of ZnS as well as the XPS reveals the binding energies of Zn 2p1/2 and Zn 2p3/2 at 1045.85 and 1022.83 eV, respectively, establishing the Zn2+ state. Scanning electron microscopy of ZnS–polyaniline exhibits a different-sized mist-like morphology on both paper and cotton substrates. The tunneling electron microscopy images reveal the ZnS nanosheet with an interplanar spacing of 0.31 nm incorporated in the polyaniline matrix. Further, analysis was carried out through UV–visible spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, and dynamic light scattering. The metal–metallopolymer nanohybrid-metal device of this metal–polymer framework was fabricated on flexible and eco-friendly cellulose paper and cotton substrates. The density functional theory approach was adopted for better insight understanding about the synthesized material in terms of band gap, electron affinity, and electronegativity. Ohmic as well as the space charge-limited behavior of current is found responsible for the current–voltage characteristics. This flexible device exhibited an ultrahigh photoresponsivity of 396.479 A W–1 and a giant external quantum efficiency of 1.344 × 105%. Paper and cotton substrate-based devices show significant responsivities of 3.671 and 1.740 mA/W with detectivities of 3.092 × 1010 and 3.470 × 1010 Jones even at 0 V, respectively.

Six‐arm Stellat Dendritic‐PbS Flexible Infrared Photodetector for Intelligent Healthcare Monitoring

AbstractThe flexible photodetector plays an important role in improving human medical health status. However, the narrow spectral detection range, poor stress stability, and non‐degradation of traditional flexible photodetectors greatly hinder the further development of wearable medical devices. In this paper, a novel flexible infrared photodetector is proposed for intelligent healthcare monitoring using high purity lead sulfide (PbS) nanoparticles on paper‐based flexible substrate synthesized by hydrothermal method and physical friction. The excellent performance of the detector is attributed to the 1.01 eV band gap and six‐arm stellate dendritic structure of PdS, a good combination between PbS and paper substrate via physical friction. As a result, our photodetector demonstrates wide‐spectrum detection capabilities from 365 to 1550 nm. The photodetector at 980 nm (50.4 μW cm−2) shows responsivity of 6.45 mA W−1, detectivity of 6.4 × 1010 Jones, response recovery time of 0.36 s/0.41 s, with good mechanical stability. By comparison, our detector has a wider detection range, better weak signal detection performance, and shorter response time than the performance of the former paper‐based detector. Furthermore, the paper‐based PbS photodetector as a dual‐wavelength photoplethysmography sensor is applied to analyze the oxygen saturation and develop an intelligent bandage to monitor wound healing. This paper‐based PbS photodetector has tremendous potential in the field of wearable medical devices and intelligent medical applications are expected.

Room-Temperature High-Detectivity Flexible Near-Infrared Photodetectors with Chalcogenide Silver Telluride Nanoparticles.

Herein, flexible near-infrared (NIR) photodetectors were prepared using silver telluride (Ag5Te3) nanoparticles (NPs) for optoelectronic applications. For the main channel materials of the photodetectors, Ag5Te3 NPs were used, which were synthesized in an aqueous solution. Moreover, Ag5Te3 thin films were successfully fabricated on plastic substrates at 150 °C using redistributed Ag5Te3 NPs in aqueous inks. The crystal structure, chemistry, and optoelectronic properties of the synthesized photodetectors were studied. The fabricated flexible Ag5Te3-based photodetectors achieved a detectivity of 6.27 × 109 cm Hz1/2 W–1 (>109) at room temperature under ∼0.35% compressive and tensile strains. The obtained detectivity value exceeds those of two-dimensional inorganic layered material phototransistors—such as MoS2—or commercial thermistor bolometers at room temperature (∼109). Furthermore, the proposed novel method for the synthesis of Ag5Te3 thin films on plastic substrates can be applied to other Ag5Te3-based applications in the future.

1D NiO–3D Fe2O3 mixed dimensional heterostructure for fast response flexible broadband photodetector

Conventional heterojunction photodetectors rely on planar junction architecture which suffer from low interfacial contact area, inferior light absorption characteristics and complex fabrication schemes. Heterojunctions based on mixed dimensional nanostructures such as 0D-1D, 1D-2D, 1D-3D etc have recently garnered exceptional research interest owing to their atomically sharp interfaces, tunable junction properties such as enhanced light absorption cross-section. In this work, a flexible broadband UV–vis photodetector employing mixed dimensional heterostructure of 1D NiO nanofibers and 3D Fe2O3 nanoparticles is fabricated. NiO nanofibers were synthesized via economical and scalable electro-spinning technique and made composite with Fe2O3 nanoclusters for hetero-structure fabrication. The optical absorption spectra of NiO nanofibers and Fe2O3 nanoparticles exhibit peak absorption in UV and visible spectra, respectively. The as-fabricated photodetector displays quick response times of 0.09 s and 0.18 s and responsivities of 5.7 mA W−1 (0.03 mW cm−2) and 5.2 mA W−1 (0.01 mW cm−2) for UV and visible spectra, respectively. The fabricated NiO–Fe2O3 device also exhibits excellent detectivity in the order of 1012 jones. The superior performance of the device is ascribed to the type-II heterojunction between NiO–Fe2O3 nanostructures, which results in the localized built-in potential at their interface, that aids in the effective carrier separation and transportation. Further, the flexible photodetector displays excellent robustness when bent over ∼1000 cycles thereby proving its potential towards developing reliable, diverse functional opto-electronic devices.

Flexible thin-film photodetectors based on solution-processed molybdenum disulphide nanosheets

Flexible thin-film photodetectors based on solution-processed molybdenum disulphide nanosheets

Large-scale preparation of ultra-long ZnSe–PbSe heterojunction nanowires for flexible broadband photodetectors

Flexible photodetectors show great applications in wearable electronics such as health monitoring and the Internet of Things. In this study, we have prepared ultralong ZnSe–PbSe heterojunction nanowires with a length of 20 μm in gram-scale by an in-situ cation exchange reaction. The produced PbSe nanoparticles on the ZnSe nanowire configuration are close to an ideal heterojunction system due to the small lattice mismatch of 7.4% in the (111) direction. The Ohmic contact is formed for nanowire photodetectors. The ZnSe–PbSe heterojunction nanowire photodetector exhibits a broadband photoresponse with the peak responsivity of 40 A W −1 while the ZnSe nanowire photodetector shows a narrowband photoresponse of 5 A W −1 , as a result of its extended absorption across the entire UV-visible-NIR. Electrons are transported from PbSe to ZnSe while holes are trapped at PbSe, and electrons are extracted to an external circuit by an Al electrode, resulting in a high gain of the photoconductor. The broadband photoresponse, the large linear dynamic range of 66 dB, the fast response speed of 0.02 s and the protracted cycle of 5000 show the feasibility of the flexible heterojunction photodetector.

Enhanced performance of MgZnO flexible ultraviolet photodetectors

Enhanced performance of MgZnO flexible ultraviolet photodetectors

Low‐Cost Copper Electrode for High‐Performance Panchromatic Multiplication‐Type Organic Photodetectors with Optical Microcavity Effect

AbstractLow‐cost and flexible panchromatic organic photodetectors (OPDs) are one of the most promising alternatives in next‐generation wearable electronics, but they still face the formidable challenges of replacing brittle indium tin oxide electrode and suffer from low near‐infrared (NIR) photo‐response. Herein, the low‐cost metal copper (Cu) is used as a semi‐transparent anode to fabricate high‐performance panchromatic multiplication‐type OPDs. Because of the advantages of smooth surface, lower sheet resistance, and good transmittance, high‐quality optical resonant cavity forming between Cu anode and aluminum cathode greatly enhanced the weak sub‐bandgap response of intermolecular charge transfer states in NIR region, while also retaining a good response in the UV–vis region. Due to the good hole‐collecting ability, the Cu electrode is suitable for realizing the photo‐multiplication effect. Accordingly, the resulting OPDs achieve a panchromatic response ranging from the UV (300 nm) to NIR (900 nm) region. The maximum external quantum efficiency (EQE) reaches 117 040% at 350 nm, and the relatively high EQE of 25 468% is realized even at 765 nm. Furthermore, a flexible OPD is successfully fabricated by using polyethylene terephthalate substrate with Cu anode to achieve the real‐time detection of human blood oxygen pulse signals.

Non‐Fullerene Acceptor Organic Photodetector for Skin‐Conformable Photoplethysmography Applications

AbstractCommercial photoplethysmography (PPG) sensors and other biomedical devices that require near‐infrared (NIR) light detection are limited by rigid photodetector architectures that cannot interface comfortably with skin. Flexible organic photodetectors could potentially solve this problem; however, organic photodetectors suffer from low NIR sensitivity, largely due to the early absorption cutoffs originating from the use of fullerene acceptors. This work details a new flexible organic photodiode (OPD) based on narrow bandgap non‐fullerene‐acceptor (NFA) bulk heterojunction (BHJ) incorporating a PTB7‐Th and COTIC‐4F blend. The photodetector developed for this study reaches an external an external quantum efficiency (EQE) to 60% in the 600–1000 nm range and responsivity (R) as high as ≈0.42 A W–1. Through the integration of a PEDOT:PSS and PDINO interfacial layers, undesired carrier injection is suppressed, and a detectivity (D*) in the order of ≈1013 Jones is achieved. In addition, oxygen saturation and heart rate are successfully measured by integrating the developed photodiode in a PPG sensor.

Chemical vapor deposition growth of nonlayered γ-In2Se3 nanosheets on SiO2/Si substrates and its photodetector application

Two-dimensional (2D) In2Se3 with excellent optical and electrical properties has great application potential for flexible devices, photodetectors, and phase change memories. Here, we report the successes of growing In2Se3 nanosheets on SiO2/Si substrates by chemical vapor deposition (CVD) and fabricating broadband photodetector based on In2Se3. The Raman spectroscopy and transmission electron microscopy studies indicate that our 2D In2Se3 is in γ-phase. Our 2D γ-In2Se3 photodetector shows a broadband response range from near ultraviolet (350 nm) to infrared (1000 nm). The stable broadband response provides opportunities for the application of 2D γ-In2Se3-based devices and also a reference for the preparation and application of other 2D materials.

Highly-Responsive Broadband Photodetector Based on Graphene-PTAA-SnS2 Hybrid.

The development of wearable systems stimulate the exploration of flexible broadband photodetectors with high responsivity and stability. In this paper, we propose a facile liquid-exfoliating method to prepare SnS2 nanosheets with high-quality crystalline structure and optoelectronic properties. A flexible photodetector is fabricated using the SnS2 nanosheets with graphene-poly[bis(4-phenyl) (2,4,6-trimethylphenyl) amine (PTAA) hybrid structure. The liquid-exfoliated SnS2 nanosheets enable the photodetection from ultraviolet to near infrared with high responsivity and detectivity. The flexible broadband photodetector demonstrates a maximum responsivity of 1 × 105 A/W, 3.9 × 104 A/W, 8.6 × 102 A/W and 18.4 A/W under 360 nm, 405 nm, 532 nm, and 785 nm illuminations, with specific detectivity up to ~1012 Jones, ~1011 Jones, ~109 Jones, and ~108 Jones, respectively. Furthermore, the flexible photodetector exhibits nearly invariable performance over 3000 bending cycles, rendering great potentials for wearable applications.

Flexible computational photodetectors for self-powered activity sensing

Conventional vision-based systems, such as cameras, have demonstrated their enormous versatility in sensing human activities and developing interactive environments. However, these systems have long been criticized for incurring privacy, power, and latency issues due to their underlying structure of pixel-wise analog signal acquisition, computation, and communication. In this research, we overcome these limitations by introducing in-sensor analog computation through the distribution of interconnected photodetectors in space, having a weighted responsivity, to create what we call a computational photodetector. Computational photodetectors can be used to extract mid-level vision features as a single continuous analog signal measured via a two-pin connection. We develop computational photodetectors using thin and flexible low-noise organic photodiode arrays coupled with a self-powered wireless system to demonstrate a set of designs that capture position, orientation, direction, speed, and identification information, in a range of applications from explicit interactions on everyday surfaces to implicit activity detection.

Channel Scaling Dependent Photoresponse of Copper-Based Flexible Photodetectors Fabricated Using Laser-Induced Oxidation.

Copper (Cu) oxide compounds (CuxO), which include cupric (CuO) and cuprous (Cu2O) oxide, have been recognized as a promising p-channel material with useful photovoltaic properties and superior thermal conductivity. Typically, deposition methods or thermal oxidation can be used to obtain CuxO. However, these processes are difficult to apply to flexible substrates because plastics have a comparatively low glass transition temperature. Also, additional patterning steps are needed to fabricate applications. In this work, we fabricated a metal-semiconductor-metal photodetector using laser-induced oxidation of thin Cu films under ambient conditions. Raman spectroscopy, scanning electron microscopy-energy-dispersive X-ray spectroscopy, and atomic force microscopy were used to study the composition and morphology of our devices. Moreover, the photoresponse of this device is reported herein. We performed an in-depth analysis of the relationship between the channel size and number of carriers using scanning photocurrent microscopy. The carrier transport behaviors were identified; the photocurrent decreased as the length and width of the channel increased. Furthermore, we verified the suitability of the device as a flexible photodetector using a variety of bending tests. Our in-depth analysis of this Cu-based flexible photodetector could play an important role in understanding the mechanisms of other flexible photovoltaic applications.