Flexible Photodetectors Research Articles

Extensible Integrated System for Real-Time Monitoring of Cardiovascular Physiological Signals and Limb Health.

In recent decades, the rapid growth in flexible materials, new manufacturing technologies, and wearable electronics design techniques has helped establish the foundations for noninvasive photoelectric sensing systems with shape-adaptability and "skin-like" properties. Physiological sensing includes humidity, mechanical, thermal, photoelectric, and other aspects. Photoplethysmography (PPG), an important noninvasive method for measuring pulse rate, blood pressure, and blood oxygen, uses the attenuated signal obtained by the light absorbed and reflected from living tissue to a light source to realize real-time monitoring of human health status. This work illustrates a patch-type optoelectronic system that integrates a flexible perovskite photodetector and all-inorganic light-emitting diodes (LEDs) to realize the real-time monitoring of human PPG signals. The pulse rate of the human body and the swelling degree of finger joints can be extracted and analyzed using photodetectors, thus monitoring human health for the prevention and early diagnosis of certain diseases. Specifically, this work develops a 3D wrinkled-serpentine interconnection wire that increases the shape adaptability of the device in practical applications. The PPG signal sensor reported in this study has considerable potential for future wearable intelligent medical applications.

Paper-based MoS2/Bi2S3 heterojunction photodetectors for broadband detection and fast response

Flexible photodetectors are receiving increasing attention due to their promising applications in wearable optoelectronic devices, bendable imaging sensors, and implantable optoelectronic devices. In this work, a novel strategy for constructing flexible photodetectors based on a hybrid heterojunction of Bi2S3 and MoS2 was proposed. The devices are fabricated on a biodegradable paper substrate using a simple hydrothermal process and vacuum filtration techniques and exhibit a broadband photoresponse from ultraviolet to near-infrared (NIR). Especially, the specific detectivity (D*) of the MoS2/Bi2S3 photodetectors is 3.25 × 1010 Jones under 365 nm, and the rise/decay time is 0.053 s/0.119 s in the NIR region. In addition, the performance of Bi2S3/MoS2 photodetectors realizes a maximum responsivity (R) of 27.45 mA/W and a fast response time (∼0.470 s). These devices exhibit a stable photoresponse under repeated bending. Inexpensive materials and easy fabrication techniques provide a viable strategy for the design and performance optimization of flexible bimetallic sulfide photodetectors.

ZnO-Based Flexible UV Photodetector for Wearable Electronic Applications

ZnO-Based Flexible UV Photodetector for Wearable Electronic Applications

Multilayered PdTe2/thin Si heterostructures as self-powered flexible photodetectors with heart rate monitoring ability

Two-dimensional layered material/semiconductor heterostructures have emerged as a category of fascinating architectures for developing highly efficient and low-cost photodetection devices. Herein, we present the construction of a highly efficient flexible light detector operating in the visible-near infrared wavelength regime by integrating a PdTe2 multilayer on a thin Si film. A representative device achieves a good photoresponse performance at zero bias including a sizeable current on/off ratio exceeding 105, a decent responsivity of ~343 mA/W, a respectable specific detectivity of ~2.56 × 1012 Jones, and a rapid response time of 4.5/379 μs, under 730 nm light irradiation. The detector also displays an outstanding long-term air stability and operational durability. In addition, thanks to the excellent flexibility, the device can retain its prominent photodetection performance at various bending radii of curvature and upon hundreds of bending tests. Furthermore, the large responsivity and rapid response speed endow the photodetector with the ability to accurately probe heart rate, suggesting a possible application in the area of flexible and wearable health monitoring.

Recent Application and Progress of Metal Halide Perovskite Photodetector on Flexible Substrates

Comprehensive SummaryIn recent years, flexible photodetectors (FPDs) have received increasing attention due to their applications in electronic eyes, flexible sensing, terminal devices, and wearable devices. In addition, metallic halide perovskite materials are considered as future materials for FPDs due to their compatibility with flexible substrates, low cost, simple synthesis methods, and superior optoelectronic properties. This review provides a comprehensive overview of the relevant cutting‐edge research in the field of flexible perovskite photodetectors (FPPDs) from 2020 to 2022. First, the evaluation criteria for FPPDs are discussed and the development of perovskite stability criteria is emphatically described. Afterwards, the synthesis methods and device construction processes of metal halide perovskite materials commonly used by researchers in the past three years are described. These include single crystals and low‐dimensional materials. Moreover, we have elaborated on the research of self‐powered FPPD and its contributions in wearability, terminals, and portability. Finally, a summary of developments and possibilities in the field of FPPDs from 2020 to 2022 is provided.

High‐Performance Broadband Flexible Photodetectors Based on Ti3C2Tx MXene/Pyramidal Thin Si Heterostructures with Light Trapping Effect for Heart Rate Detection

AbstractHigh‐performance flexible photodetectors are urgently demanded for application in many emerging domains including flexible, wearable, portable, and stretchable optoelectronics. In this work, a highly efficient flexible photodetector made of a Ti3C2Tx MXene/pyramidal thin Si heterostructure is successfully fabricated. Thanks to the remarkable light trapping effect as confirmed by numerical modeling based on finite‐element method, the as‐constructed detector demonstrates excellent photoresponse performance in a broadband wavelength spectrum. The optimal responsivity, specific detectivity, and response speed reach ≈530 mA W−1, ≈1.21 × 1012 Jones and 30/14 µs, respectively, at zero bias under near‐infrared light illumination. Specifically, the responsivity is greatly enhanced by ≈2.65 times, as compared with a planar counterpart. In addition, the light detector can maintain its outstanding photoresponse properties upon 1000 cycles of bending test or at diverse bending radii of curvature, owing to its prominent mechanical flexibility and robust bending endurance. Finally, the capability of monitoring the heart rate of a person in a wideband wavelength spectrum and at various bending radii of curvature is presented. The above results imply the huge potential of the flexible light detector for use in some applications such as wearable health monitoring.

Building Low-Cost, High-Performance Flexible Photodetector Based on Tetragonal Phase VO2 (A) Nanorod Networks.

We present a straightforward and cost-effective method for the fabrication of flexible photodetectors, utilizing tetragonal phase VO2 (A) nanorod (NR) networks. The devices exhibit exceptional photosensitivity, reproducibility, and stability in ambient conditions. With a 2.0 V bias voltage, the device demonstrates a photocurrent switching gain of 1982% and 282% under irradiation with light at wavelengths of 532 nm and 980 nm, respectively. The devices show a fast photoelectric response with rise times of 1.8 s and 1.9 s and decay times of 1.2 s and 1.7 s for light at wavelengths of 532 nm and 980 nm, respectively. In addition, the device demonstrates exceptional flexibility across large-angle bending and maintains excellent mechanical stability, even after undergoing numerous extreme bending cycles. We discuss the electron transport process within the nanorod networks, and propose a mechanism for the modulation of the barrier height induced by light. These characteristics reveal that the fabricated devices hold the potential to serve as a high-performance flexible photodetector.

Electronic and light absorption properties of metal adsorbed In2Se3 monolayer

With its excellent optical and electrical characteristics, two-dimensional (2D) In2Se3 has a lot of potential uses in flexible electronics, photodetectors, and phase-change memory, and so on. In this study, we have systematically investigated the electronic structure and light absorption properties of a metal atom adsorbed monolayers of In2Se3 using density functional theory. The findings indicate that the most stable sites of different metal adsorbed In2Se3 monolayer materials are different. All metal atoms adsorbed In2Se3 (M-In2Se3) systems have good stability. After the adsorption of metal atoms on all M-In2Se3 systems, it can be seen by their energy band structures that all systems exhibit metallic behavior. It is illustrated that the adsorption of metal atoms can modulate the change of In2Se3 material from semiconductor to metal. Similarly, the densities of states plots show the metallic nature of the M-In2Se3 system structure and indicate that adsorbed metal atoms can change the properties of the In2Se3 material itself. And interestingly, in the M-In2Se3 system, the ultraviolet (UV) region exhibits significantly enhanced absorption peaks, demonstrating that the addition of metal atoms can improve the In2Se3 material’s ability to absorb light. Finally, reference light absorption spectrum, it is found that placing spherical metal nanoparticles on top of 100 nm thick In2Se3 nanosheets could excite the localized surface plasmon resonance. And among them, Au nanoparticles have the most impact on the localization of electric fields. It indicates that the introduction of Au significantly enhances the absorption properties of the material. This suggests that the metal atom adsorbed In2Se3 system will be favorable for its application in optical devices as well as electronic devices.

Flexible self-powered solar-blind UV photodetectors based on amorphous Ga2O3 modified carbon fiber cloth

Self-powered solar-blind ultraviolet (UV) photodetectors are gaining increasing recognition as green, efficient, and sustainable devices, representing a development trend in the evolution of next-generation optoelectronics. Much efforts have been devoted to carbon-based materials for their excellent conductivity. Among these materials, commercial carbon fiber sheets stand out due to their distinctive 3D structure, impressive conductivity, cost-effectiveness, and flexibility, rendering them highly suitable for a wide range of photosensitive applications. The realm of flexible optoelectronic devices has garnered substantial interest owing to its pivotal role in diverse domains. However, the utilization of carbon cloth (CC) as a substrate for photodetectors remains an area ripe for exploration. This study aims to fabricate self-powered solar-blind UV photodetectors based on amorphous Ga2O3 (a-Ga2O3) thin films modified CC using a concise and efficient physical vapor deposition technique (magnetron sputtering). The results show that the optimal responsivity of the a-Ga2O3/CC photodetector is 16.98 mA/W, with response times of 0.16/0.10 s (rise/decay time). Even after 300 cycles of bending treatment, this self-powered photodetector maintains excellent cyclic stability and repeatability. Furthermore, first-principles calculation reveals a significant built-in electric field around the interface between a-Ga2O3 and CC, which can effectively separate photogenerated electrons and holes and suppress carriers’ recombination. This inherent mechanism allows the a-Ga2O3/CC-based photodetector to exhibit remarkable self-powered characteristics and prominent solar-blind detection ability.

Tunable Contacts of Bi2 O2 Se Nanosheets MSM Photodetectors by Metal-Assisted Transfer Approach for Self-Powered Near-Infrared Photodetection.

Owing to the Fermi pinning effect arose in the metal electrodes deposition process, metal-semiconductor contact is always independent on the work function, which challenges the next-generation optoelectronic devices. In this work, a metal-assisted transfer approach is developed to transfer Bi2 O2 Se nanosheets onto the pre-deposited metal electrodes, benefiting to the tunable metal-semiconductor contact. The success in Bi2 O2 Se nanosheets transfer is contributed to the stronger van der Waals adhesion of metal electrodes than that of growth substrates. With the pre-deposited asymmetric electrodes, the self-powered near-infrared photodetectors are realized, demonstrating low dark current of 0.04 pA, high Ilight /Idark ratio of 380, fast rise and decay times of 4 and 6ms, respectively, under the illumination of 1310nm laser. By pre-depositing the metal electrodes on polyimide and glass, high-performance flexible and omnidirectional self-powered near-infrared photodetectors are achieved successfully. This study opens up new opportunities for low-dimensional semiconductors in next-generation high-performance optoelectronic devices.

Optimized photoelectric performance of MoS2/graphene heterostructure device induced by swift heavy ion irradiation

Two-dimensional materials with exceptional electronic and photoelectric properties are expected to develop a new-generation of ultrathin, high efficiency, broadband, and flexible photodetectors. For the potential application towards outer space exploration, the harsh irradiation environment must be taken into consideration. In this work, irradiation effects of MoS2/Graphene heterostructure field effect transistors (MoS2/G FETs) induced by swift heavy ions (SHIs) were explored. After irradiation, a new Raman peak denoted as D peak emerged, which demonstrated that SHI irradiation induced damage in graphene. Photoluminescence investigation of MoS2 indicated that SHI irradiation activated the excitation conversion of trion A− to excitation A0. Latent tracks were observed on MoS2/G/SiO2 by using atomic force microscope. The decreased resistance and increased carrier mobilities were detected at fluence lower than 5 × 1010 ions/cm2, which could be ascribed to the localized annealing of graphene during irradiation. The increased photocurrent and responsivity at fluence lower than 1 × 1010 ions/cm2 could be interpreted as the enhanced photoinduced gate voltage resulting from the SHI irradiation induced defects in MoS2/G FET. The devices were deteriorated at fluence of 1 × 1011 ions/cm2. The optimized and degraded properties of the devices could be ascribed to competition among doping, local annealing and defect scattering.

Self-powered flexible UV photodetectors based on MOCVD-grown Ga2O3 films on mica

Self-powered flexible UV photodetectors based on MOCVD-grown Ga2O3 films on mica

Multilayered Nanometer Thick Films of n-MoS2 QD/n-MoS2/p-CuO as p–n Heterojunctions for Self-Powered Flexible Photodetectors

Multilayered Nanometer Thick Films of n-MoS₂ QD/n-MoS₂/p-CuO as p–n Heterojunctions for Self-Powered Flexible Photodetectors

Laser-Induced Graphene-based Flexible Substrate with Photothermal Conversion and Photoresponse Performance on Polyimide Film.

Graphene-based flexible electronic devices are widely used in photoelectric components and photodetectors. However, it remains a huge challenge to fabricate graphene-based flexible devices efficiently and economically. Compared with the flexible electronic devices made by combining the flexible film with metal and semiconductor materials, the graphene-based flexible substrate (GFS) can be efficiently and conveniently induced by laser direct writing on the flexible film. In this paper, the GFS with a resistance of as low as 15 Ω was successfully induced by CO2 laser on a polyimide (PI) film in one step, and the GFS surface covered with carbon nanoparticles (GFSC) with a resistance of 25 Ω was further induced by femtosecond (fs) laser reprocessing. Benefiting from the laser-induced porous graphene structure, the absorptivity of GFS is up to 90% in the wavelength range of 200-2000 nm. The formation of carbon nanoparticles on the GFSC surface further improves the absorptivity to 97.5% in a wide spectral range. Under white light irradiation of 1 sun, the surface temperature of GFS reaches 65.7 °C and that of GFSC is up to 70.8 °C within 2 min. Under the irradiation of a light-emitting diode (LED) with a central wavelength of 365 nm, the highest photoresponsivity of GFS and GFSC was 8.8 and 1.3 mA/W, respectively. The response time and recovery time of GFS are 8 and 7.3 s, and those of GFSC are 8.3 and 6.7 s, respectively. Importantly, GFSC has a more stable photoresponse performance due to the better electron capture and transfer capability of carbon nanoparticles. It is believed that GFS and GFSC have great application potential in flexible photodetectors and sensors.

Flexible infrared photodetector based on polyethylene terephthalate (PET) supported lead sulfide thin film

Flexible photodetectors are thought to have uses in optoelectronics, biological imaging, and smart wearable systems. The goal of this work was to develop a simple and low-cost method for fabricating a flexible infrared photodetector based on a lead sulfide (PbS) thin film produced on a PET substrate utilizing a simple low-temperature spray pyrolysis technique. The device has a highest sensitivity to infrared light (562%), a high responsivity (1.06 mA/W), and a short response time (1 ms) at an intensity of 1.72 mW/cm2. During 100 bending tests at a 40° angle, the performance of this flexible devices showed no signs of significant deterioration. The device exhibits a good, reproducible, and steady photoresponse even after bending (under tensile strain). This implies that this Ag/PbS-PET/Ag photodetector will find uses in wearable technology that require the detection of infrared radiation.

Highly Responsive, Polarization‐Sensitive, Flexible, and Stable Photodetectors Based on Highly Aligned CsCu2I3 Nanowires

AbstractAs a new inorganic lead‐free perovskite, cesium copper iodide (CsCu2I3) has attracted wide attention in the field of photodetectors due to its non‐toxicity, good air and thermal stability, and excellent optoelectronic properties. However, the random growth and disordered distribution of CsCu2I3 crystals during their preparation results in poor crystal quality, seriously limiting their applications. Highly ordered CsCu2I3 crystal formation with high crystal quality for high‐performance photodetectors remains a major challenge. Here, an ingenious nanoimprinting technology is utilized to obtain high‐performance photodetectors based on highly aligned CsCu2I3 nanowires (NWs). Owing to the high crystal quality, the photodetector exhibits excellent responsivity of 12.35 A W−1 (310 nm) and 89.73 mA W−1 (365 nm), respectively, as well as good polarization light detection with a dichroism ratio of up to 2.28. Additionally, the device on a flexible substrate retains its initial level of performance even after being bent 2000 times. Remarkably, the device exhibits superior stability and maintains excellent performance after being placed in the natural environment for 1 month without any encapsulation.

Polymer-Derived Carbon Nanofiber and Its Photocurrent-Switching Responses of Carbon Nanofiber/Cu Nanocomposite in Wide Ranges of Excited Light Wavelength.

Transformation into electric or photoelectric functional composite from non-conjugated polymers is a great challenge due to the presence of a large number of locative states. In this paper, carbon nanofiber was synthesized via hydrothermal carbonization utilizing carboxymethyl cellulose as a precursor, and the carbon nanofiber/Cu nanocomposite was constructed for defect passivation. The results indicated that the resulting nanocomposites exhibited good absorbance in visible light range and NIR (near-infrared). The photoconductive responses to typical weak visible light (650 nm et al.) and NIR (808, 980, and 1064 nm) were studied based on Au gap electrodes on flexible polymer substrates. The results exhibited that the nanocomposite's solid thick film showed photocurrent-switching behaviors to visible light and NIR, the switch-ratio was depending on the wavelengths and power of incident lights. The positive and negative photoconductance responses phenomenon was observed in different compositions and changing excited wavelengths. Their photophysical mechanisms were discussed. This illustrated that the nanocomposites easily produce free electrons and holes via low power of incident light. Free electrons and holes could be utilized for different purposes in multi-disciplinary fields. It would be a potential application in broadband flexible photodetectors, artificial vision, simulating retina, and bio-imaging from visible light to NIR. This is a low-cost and green approach to obtain nanocomposite exhibiting good photocurrent response from the visible range to NIR.

Enabling low-drift flexible perovskite photodetectors by electrical modulation for wearable health monitoring and weak light imaging

Metal halide perovskites are promising for next-generation flexible photodetectors owing to their low-temperature solution processability, mechanical flexibility, and excellent photoelectric properties. However, the defects and notorious ion migration in polycrystalline metal halide perovskites often lead to high and unstable dark current, thus deteriorating their detection limit and long-term operations. Here, we propose an electrical field modulation strategy to significantly reduce the dark current of metal halide perovskites-based flexible photodetector more than 1000 times (from ~5 nA to ~5 pA). Meanwhile, ion migration in metal halide perovskites is effectively suppressed, and the metal halide perovskites-based flexible photodetector shows a long-term continuous operational stability (~8000 s) with low signal drift (~4.2 × 10−4 pA per second) and ultralow dark current drift (~1.3 × 10−5 pA per second). Benefitting from the electrical modulation strategy, a high signal-to-noise ratio wearable photoplethysmography sensor and an active-matrix photodetector array for weak light imaging are successfully demonstrated. This work offers a universal strategy to improve the performance of metal halide perovskites for wearable flexible photodetector and image sensor applications.

Sunflower‐Inspired Light‐Tracking System and Spatial Encryption Imaging based on Linear Flexible Perovskite Photodetector Arrays

AbstractLight‐tracking systems and wide‐angle imaging are garnering increasing interest in the field of artificial intelligence due to their benefits to improve the light collection efficiency. Perovskite photodetectors have become the mainstream choice for their high adsorption coefficient, flex‐compatible properties, and low‐cost solution process. However, the fabrication of precise angle‐sensitive flexible detectors remains challenging due to the uncontrollable deposition of photosensitive layers. Herein, wide‐angle‐sensitive linear flexible perovskite photodetector arrays are successfully fabricated. The device exhibits a broad range of 144°, high‐resolution of 2.8°, and long‐term stability of 3000 cycles. As a proof‐of‐concept demonstration, a sunflower‐inspired light‐tracking system with adaptive following performance is illustrated. Furthermore, spatially encrypted imaging is achieved using linear perovskite photodetector arrays coupled with algorithms. This work confirms the superiority of flexible perovskite photodetectors in angle‐sensing and encryption imaging.

Recent Advances in Materials, Structures, and Applications of Flexible Photodetectors

AbstractFlexible photodetectors (FPDs), which provide excellent advantages such as great wearability, portability, even implantability, have attracted tremendous interest in wearable healthcare monitoring, bendable imaging sensors, portable optical communication, etc. Recently, organic and perovskite‐based photoactive materials have been considered promising candidates for FPDs due to their superior optoelectronic performance, appealing mechanical flexibility, low‐temperature solution processability, and cost‐effectiveness. In this review, the milestone progress of organic, perovskite, and organic‐perovskite hybrid‐based FPDs and their applications in artificial intelligence are summarized. First, a brief introduction of device configurations, working principles, and key parameters for FPDs are presented. Subsequently, functional materials in FPDs, especially flexible photoactive materials of organic, perovskite, and organic‐perovskite hybrids, are summarized and analyzed. More importantly, representative applications of FPDs are summarized, including wearable healthcare monitoring, imaging sensors, and optical communication. The outlook and challenges for the field are proposed at the end. The purpose of this review is to not only elaborate on the fundamental design principles of FPDs, but also serve as a roadmap for next‐generation artificial intelligence sensing technologies.