Wearable Optoelectronic Devices Research Articles

Visible-light photoelectric performance and bending stability of flexible LaCoO3/Mica thin films

New energy sources such as solar energy have been developed and utilized due to the shortage of non-renewable energy, and photoelectric materials have attracted more attention, accordingly. Moreover, flexible optoelectronic devices are crucial in the fields of wearable artificial intelligence, portable energy, and smart medical care. At present, photoelectric devices based on traditional perovskite cobalt oxide rigid films have problems such as inability to bend and deformation, which limits their application environment. Here, natural mica with atomically flat surface, high thermal stability, high transparency and good mechanical flexibility was selected as the substrate for preparing a series of LaCoO3 flexible photoelectric films. These films exhibit excellent photoelectric properties and flexible properties. More importantly, the flexible film still has fast response speed and reproducible light response after 500 bending cycles. It reveals that all-inorganic perovskite LaCoO3 is a promising candidate for designing high-performance, flexible and wearable optoelectronic devices.

Surface Energy-Assisted Patterning of Vapor Deposited All-Inorganic Perovskite Arrays for Wearable Optoelectronics.

Solution-based methods for fabricating all-inorganic perovskite film arrays often suffer from limited control over nucleation and crystallization, resulting in poor homogeneity and coverage. To improve film quality, advanced vapor deposition techniques are employed for continuous film. Here, the vapor deposition strategy to the all-inorganic perovskite films array, enabling area-selective deposition of perovskite through substrate modulation is expanded. It can yield a high-quality perovskite film array with different pixel shapes, various perovskite compositions, and a high resolution of 423dpi. The resulting photodetector arrays exhibit remarkable optoelectronic performance with an on/off ratio of 13 887 and responsivity of 47.5AW-1. The device also displays long-term stability in a damp condition for up to 12h. Moreover, a pulse monitoring sensor based on the perovskite films array demonstrates stable monitoring for pulse signals after being worn for 12h and with a low illumination of 0.055mWcm-2, highlighting the potential application in wearable optoelectronic devices.

Electrical, optical and mechanical properties of monolayer MoTe2 for applications in wearable optoelectronic devices

Transition metal dichalcogenides (TMDs) have excellent optical and mechanical properties and have potential application value in wearable optoelectronic response devices. MoTe2, a representative material of TMDs, is studied by first-principles calculation in this paper. The results show that the MoTe2 monolayer has a direct band gap of 1.110eV, which has a strong light absorption capacity and can produce a high concentration of photogenerated charge carriers after light absorption. The material is soft and exhibits the unique mechanical properties of layered materials. The effects of biaxial strain and defects on the properties of the materials were analyzed. The results show that the biaxial compression strain can enhance the light absorption curve of the material, enhance the light absorption of the photogenerated carrier, and expand the range of its energy distribution. The tensile strain decreases the value of the photon absorption curve and decreases the range of energy distribution of photogenerated carriers. The Mo vacancy defect increases the absorption curve value in the low energy region and broadens the optical response range of the material. The two types of vacancy defects both induce a ‘discrete’ distribution of photogenerated carriers. The Mo vacancy significantly affects the elastic modulus and anisotropy properties of the material, resulting in the material changing from ductile to brittle. When Mo vacancy is added, the spatial distribution of the elastic modulus of the material also changes greatly. Therefore, MoTe2 has potential application in flexible optoelectronic devices, and its performance can be controlled by strains and defects.

Interface‐Confined Assembly of Layered Molecular Crystal Arrays Toward Wearable UV‐Radiation Monitor

AbstractOrganic semiconductors have significant potential for wearable optoelectronics due to their designable molecular structures, tunable photoelectronic properties, and flexibility. For their integration into optoelectronic devices, organic semiconductors need to be assembled into single‐crystalline arrays with both precise alignment of micro‐/nanostructures and long‐range order of molecules. In this study, an interface‐confined lithography technique is developed for fabricating organic single‐crystalline microwire arrays with layered molecular stacking and ordered crystallographic orientation toward wearable UV radiation monitor. This interface‐confined strategy introduces parallel gas–liquid–solid three‐phase contact line (TPCL) arrays to suppress the lateral growth of single crystals. Meanwhile, TPCLs with controlled dewetting direction promote longitudinal growth, thus universally yielding 1D arrays based on various organic semiconducting small molecules. These 1D single‐crystalline arrays exhibit high average mobility of 12.5 cm2 V−1 s−1 with uniform electronic properties of 9.3% variation, and good mechanical stability after 1000 bending times. Based on organic 1D arrays, wearable devices with robust photoresponsivity of 8.26 × 103 A W−1 and high mechanical flexibility achieve real‐time monitoring of UV radiation to prevent skin disease. This confined‐assembly strategy opens a new avenue to construct wearable optoelectronic devices for health monitoring.

High-Performance Flexible Broadband Photoelectrochemical Photodetector Based on Molybdenum Telluride.

Flexible broadband photodetectors are desired but challenging to be fabricated for next-generation wearable intelligent optoelectronic devices. Considering the narrow bandgap and strong light absorption, molybdenum telluride (MoTe2 ) based photoelectrochemical photodetectors are successfully assembled by liquid phase exfoliation accompanied with the electrophoretic deposited method. This MoTe2 -based photodetector shows a broadband detection in ultraviolet-near-infrared band, long-term stability within 18000s, and fast response in millisecond-level (response time≈19ms, recovery time≈26ms). More importantly, even though the MoTe2 photodetector is bent and twisted at a high degree for several hundred times, it still shows excellent flexibility with stable on-off switching characteristics. Additionally, this photodetector displays a good response for rotation angles in the range from 0° to 360°, and the extracted Iph maintain almost the same value approximately 0.97µAcm-2 , suggesting an omnidirectional detection capability. This work demonstrates the proposed flexible photoanode shows a great potential in future broadband omnidirectional detection systems.

Spatial dynamic image planning based on wearable optoelectronic devices for tactical simulation of table tennis tournaments

Spatial dynamic image planning based on wearable optoelectronic devices for tactical simulation of table tennis tournaments

High-Performance Flexible Broadband Photothermoelectric Photodetectors Based on Tellurium Films.

Mid- and far-infrared photodetectors that can operate at room temperature are essential for both civil and military applications. However, the widespread use of mid-to-far-infrared photonic technology faces challenges due to the need for low-temperature cooling of existing commercial semiconductors and the limited optical absorption efficiency of two-dimensional materials. We have utilized the photothermoelectric effect to fabricate a self-powered, broadband, and high-performance photodetector based on a one-dimensional tellurium nanorod array film. The device surpasses energy band gap limitations, functioning even at wavelengths up to approximately 10,600 nm. In particular, the detectivity of the device can reach 4.8 × 109 Jones at 4060 nm under room-temperature conditions, which is an order of magnitude higher than that of commercially available photodetectors. It demonstrates fast response and recovery times of 8.3 and 8.8 ms. Furthermore, the device demonstrates outstanding flexibility withstanding over 300 bending cycles and environmental stability. These results suggest a viable approach for designing and developing high-performance, room-temperature, wearable optoelectronic devices.

Organic High-Temperature Synaptic Phototransistors for Energy-Efficient Neuromorphic Computing.

Organic optoelectronic synaptic devices that can reliably operate in high-temperature environments (i.e., beyond 121°C) or remain stable after high-temperature treatments have significant potential in biomedical electronics and bionic robotic engineering. However, it is challenging to acquire this type of organic devices considering the thermal instability of conventional organic materials and the degradation of photoresponse mechanisms at high temperatures. Here, high-temperature synaptic phototransistors (HTSPs) based on thermally stable semiconductor polymer blends as the photosensitive layer are developed, successfully simulating fundamental optical-modulated synaptic characteristics at a wide operating temperature range from room temperature to 220°C. Robust optoelectronic performance can be observed in HTSPs even after experiencing 750 h of the double 85 testing due to the enhanced operational reliability. Using HTSPs, Morse-code optical decoding scheme and the visual object recognition capability are also verified at elevated temperatures. Furthermore, flexible HTSPs are fabricated, demonstrating an ultralow power consumption of 12.3 aJ per synaptic event at a low operating voltage of -0.05mV. Overall, the conundrum of achieving reliable optical-modulated neuromorphic applications while balancing low power consumption can be effectively addressed. This research opens up a simple but effective avenue for the development of high-temperature and energy-efficient wearable optoelectronic devices in neuromorphic computing 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.

Coexistence of Electrochromism and Bipolar Nonvolatile Memory in a Single Viologen.

Viologens are fascinating redox-active organic compounds that have been widely explored in electrochromic devices (ECDs). However, the combination of electrochromic and resistive random-access memory in a single viologen remains unexplored. We report the coexistence of bistate electrochromic and single-resistor (1R) memory functions in a novel viologen. A high-performance electrochromic function is achieved by combining viologen (BzV2+2PF6) with polythiophene (P3HT), enabling a "push-pull" electronic effect due to the efficient intermolecular charge transfer in response to an applied bias. The ECDs show high coloration efficiency (ca. 1150 ± 10 cm2 C-1), subsecond switching time, good cycle stability (>103 switching cycles), and low-bias operation (±1.5 V). The ECDs require low power for switching the color states (55 μW cm-2 for magenta and 141 μW cm-2 for blue color). The random-access memory devices (p+2-Si/BzV2+2PF6/Al) exhibit distinct low and high resistive states with an ON/OFF ratio of ∼103, bipolar and nonvolatile characteristics that manifest good performances, and "Write"-"Read"-"Erase" (WRE) functions. The charge conduction mechanism of the RRAM device is elucidated by the Poole-Frenkel model where SET and RESET states arise at a low transition voltage (VT = ±1.7 V). Device statistics and performance parameters for both electrochromic and memory devices are compared with the literature data. Our findings on electrochromism and nonvolatile memory originated in the same viologen could boost the development of multifunctional, smart, wearable, flexible, and low-cost optoelectronic devices.

Gate Controlled Photocurrent Generation Mechanism in Air-Grown Organic Single Crystals for High-Speed Multiband Imaging.

Organic semiconductors herald new opportunities for fabricating high-performance flexible and wearable optoelectronic devices owing to their intrinsic mechanical flexibility, excellent optical absorption, and cool-free operation. The photocurrent generation mechanisms are of multiple physical origins, including photoconductive, photovoltaic, and photogating effects, and the influence of individual effects on the device figures-of-merit is still not well understood. Here we fabricated a high-performance pentacene single-crystal transistor employing graphene electrodes and demonstrated the modulation from the photogating mechanism to the photoconduction effect by controlling gate bias. Control experiments indicate that the calculation based on transfer curves tends to overestimate the responsivity due to nearby trap states. Using a high frequency-modulated light signal to suppress the trapping process, we successfully measured its intrinsic -3 dB bandwidth of 75 kHz. Finally, high-resolution and UV-NIR high-speed imaging capability was demonstrated. Our work provides new guidelines for understanding the photophysical process and intrinsic performances of organic devices and also confirms the potential of organic single crystals in high-speed imaging applications.

Large‐Area Freestanding Bi2S3 Nanofibrous Membranes for Fast Photoresponse Flexible IR Imaging Photodetector (Adv. Funct. Mater. 24/2023)

Flexible IR Imaging Photodetectors In article number 2300159, Jinzhong Wang, Shiyong Gao, and co-workers, successfully prepared, a large-area freestanding Bi2S3 nanofibrous membrane (NFM) with high flexibility, which is self-assembled from ultralong Bi2S3 nanowires. The flexible photodetector based on the as-prepared Bi2S3 NFM exhibits high responsivity, fast response, excellent stability and splendent imaging capability under both flat and bent state. The as-prepared Bi2S3 NFM has great potential in flexible and wearable optoelectronic devices.

Flexible, Stretchable, and Luminescent Hydrogels Based on a Polydimethylsiloxane-Coated CsPbBr3 Nanostructure for Elastomers

Cesium lead halide perovskite nanocrystals (PNCs) have attracted great attention in optoelectronic devices due to their excellent optical properties, such as tunable emission wavelengths, long carrier lifetime, and narrow full width at half-maximum (fwhm). However, the poor stability of PNCs in water or humid environments greatly limits their wide-spreading applications. It is challenging to prepare PNCs with long-term stability in water. Herein, we successfully prepared CsPbBr3@PDMS microspheres by using the emulsification method. Due to the protection of the PDMS layer, the CsPbBr3@PDMS microspheres exhibit good optical properties and stability in water, acid, and alkali solutions. In addition, to expand the application of CsPbBr3 NCs in flexible optical devices and wearable devices, we first prepared stretchable, stable, and photoluminescent hydrogel with a CsPbBr3@PDMS microsphere (hydrogel/CsPbBr3@PDMS) by using the emulsification method. The hydrogel/CsPbBr3@PDMS elastomer exhibits good stability and stretchability. Furthermore, the hydrogel/CsPbBr3@PDMS elastomer retains bright green emission and stability under different mechanical deformations. This work provides a method to improve the CsPbBr3 PNCs with high stability by emulsification, which could also expand the applications of PNCs in underwater display, wearable, and flexible optoelectronic devices.

Tunable negative photoconductivity in encapsulated ambipolar tellurene for functional optoelectronic device applications

Two-dimensional tellurium (2D Te) is a promising material for functional optoelectronic applications due to its narrow band gap and high carrier mobility. However, its light−matter interactions typically induce positive photoconductivity (PPC), leading to low photoresponsivity in 2D Te-based photodetectors due to their high dark current and the indirect 2D Te band gap. Here, we report novel tunable negative photoconductivity (NPC) in an Al2O3-encapsulated ambipolar 2D Te device, with excellent photoresponsivity of up to 6.9 × 104 A W−1, outperforming most previously reported 2D single-element chalcogen-based photodetectors. The NPC is attributed to the lower carrier mobility due to phonon scattering induced by the enhanced photothermal effect in the encapsulated Te layer. The threshold voltage can be tuned in the encapsulated 2D Te transistor under high-energy laser irradiation, demonstrating a new strategy for controlled 2D Te doping. Well-controlled gate-tunable negative and positive persistent photocurrents are achieved in the encapsulated 2D Te transistor, thus emulating biological synapse activity. An encapsulated 2D Te device with a flexible substrate also exhibits stable NPC after 1000 bending cycles, highlighting its potential use in wearable optoelectronic devices. The construction of ambipolar 2D Te phototransistors may pave the way for the development of novel functional optoelectronic devices.

A Centimeter-Scale Type-II Weyl Semimetal for Flexible and Fast Ultra-Broadband Photodetection from Ultraviolet to Sub-Millimeter Wave Regime.

Flexible photodetectors with ultra-broadband sensitivities, fast response, and high responsivity are crucial for wearable applications. Recently, van der Waals (vdW) Weyl semimetals have gained much attention due to their unique electronic band structure, making them an ideal material platform for developing broadband photodetectors from ultraviolet (UV) to the terahertz (THz) regime. However, large-area synthesis of vdW semimetals on a flexible substrate is still a challenge, limiting their application in flexible devices. In this study, centimeter-scale type-II vdW Weyl semimetal, Td -MoTe2 films, are grown on a flexible mica substrate by molecular beam epitaxy. A self-powered and flexible photodetector without an antenna demonstrated an outstanding ability to detect electromagnetic radiation from UV to sub-millimeter (SMM) wave at room temperature, with a fast response time of ≈20 µs, a responsivity of 0.53mA W-1 (at 2.52 THz), and a noise-equivalent power (NEP) of 2.65 nW Hz-0.5 (at 2.52 THz). The flexible photodetectors are also used to image shielded items with high resolution at 2.52 THz. These results can pave the way for developing flexible and wearable optoelectronic devices using direct-grown large-area vdW semimetals.

Mosaic Charge Distribution-Based Sliding and Pressing Triboelectrification under Wavy Configuration

As high-voltage output and fast response devices, triboelectric nanogenerators (TENGs) are widely used for sensors with fast and high-sensitivity performance. As a primary electrical signal, the waveform output provides an accurate and rapid response to external stimulus parameters such as press and slide. Here, based on mosaic charging and residual charge theories, the contact charging principle of TENGs is further discussed. Moreover, a wavy structure is obtained in the vertical contact separation and lateral sliding modes to further study the influence of external parameters applied to TENGs, which thus helps further the understanding of the output waveforms. The experimental results show that wavy TENGs have output properties that are excellent compared to those of TENGs with flat structures, such as longer charging and discharging times and more complex waveforms. By researching the waveform in depth, our work will provide new prospects for application in various sensors of interactive wearable systems, intelligent robots, and optoelectronic devices based on TENGs.

High performance flexible photodetector based on 0D-2D perovskite heterostructure

Flexible photodetectors (PDs) comprised of low-dimensional organic-inorganic hybrid perovskites having perovskite quantum dots are the next generation wearable optoelectronic devices. Here, a flexible Vis-NIR PD is designed containing 2D DJ perovskite (4AMP)(MA) 2 Pb 3 I 10 (4AMP = 4-(aminomethyl)piperidinium, MA = methylammonium) (n3) and the micro concentration of CsPbI 3 perovskite quantum dots (QDs) layered heterostructures. The device response under 660 nm light is increased to 615% controlled by the optimal concentration of QDs. The device combination as per the mass of QDs depicts strong photosensitivity and high-power output. The band gap between the two is minimal forming a matching structure which lowers the energy barrier of carrier transport process. QDs layer fills the gap of perovskite film forming an almost defect-free heterostructure. QDs layer isolates water and passivates the perovskite layer for the high-performance of optoelectronic devices. The degradation of PDs with the optimal concentration of QDs under up to 5000 bending cycles and different bending angles can be ignored, and the devices show a self-healing phenomenon with the increase of bending cycles. The optimized strategy will develop flexible, wearable, high-performance and low-cost PDs. QDs-concentration-dependent based on 0D-2D perovskite heterostructure was applied to enhance the performance of flexible photodetector.

Coaxial SnS2/SnS Nanostructures on the Ag Fiber Substrate for Flexible Self-Powered Photodetectors

Sustainable and stable photodetectors with self-powering nature and superior performance are necessary to address the growing demand for flexible and wearable optoelectronic devices. This work demonstrates a flexible, self-powered, coaxial p–n heterojunction photodetector using SnS2/SnS on an Ag fiber substrate by coupling the photoexcitation property, semiconductor nature, and piezoelectric effect. Detailed characterization studies confirm the formation of hexagonal and orthorhombic crystal planes of SnS2 and SnS nanoflakes, respectively, with a piezoelectric coefficient (d33) of 175 pm/V for SnS2. The photoabsorption is maximum in the visible region with a direct band gap of 2.1 eV. The electrical studies display a tunable photoresponse under zero-bias conditions. Upon compressive strain of 0.43%, the photoresponse increases by 36%. The Ion/Ioff ratio of the fabricated photodetector was 102 at a zero bias, and the rise and decay times shorter than 1 s were obtained. The maximum external quantum efficiency of the fabricated photodetector was found to be 54.2%, owing to the superior piezo-phototronic properties. The band diagram and the charge transfer mechanism are studied to investigate the piezo-phototronic effect. The uniform strain on the Ag fiber substrate and the piezo-potential distribution upon compressive and tensile strain promotes carrier separation in the coaxial interfaces of the p–n junction. The demonstrated strategy provides a direction for developing fiber-based photodetectors with self-powering behavior and enhanced photoresponsivity for next-generation smart wearable textile-based applications.

High-performance flexible broadband photodetectors enabled by 2D Ta2NiSe5 nanosheets

Flexible broadband optoelectronic devices play a prominent role in the areas of daily life including wearable optoelectronic systems, health care, and bio-imaging systems. Two-dimensional (2D) narrow-bandgap materials with atomic thickness, adjustable bandgap, mechanical flexibility, as well as excellent optical and electrical properties exhibit great potential for applications in flexible optoelectronic devices. Here, we demonstrate a high-performance photodetector based on high-quality ternary Ta2NiSe5 nanosheets with a narrow bandgap of 0.25 eV. The photodetectors exhibit broadband photodetection capability in the visible-infrared (IR) spectrum (405–2200 nm) at room temperature. The maximum values of responsivity can reach up to 280 A W−1 at the wavelength of 405 nm. Meanwhile, the high responsivity of 63.9 A W−1 and detectivity of 3.8 × 109 Jones are achieved at the wavelength of 2200 nm, respectively. In addition, the obtained Ta2NiSe5-based photodetector shows excellent flexibility and the photodetection performance is almost insignificantly degraded after 1000 bending cycles. These results indicate that the 2D Ta2NiSe5 semiconductor has great potential in future wearable IR optoelectronic devices.

A Tunable Polarization Field for Enhanced Performance of Flexible BaTiO3@TiO2 Nanofiber Photodetector by Suppressing Dark Current to pA Level

AbstractThe flexible titanium dioxide (TiO2) nanofibers (NFs) film are promising candidates for high‐performance wearable optoelectronic devices. However, the TiO2 ultraviolet photodetectors (UV PDs) generally suffer from low photosensitivity, which limits the practical applications. Herein, a TiO2 (TO) NFs film flexible photodetector integrated by ferroelectric BaTiO3 (BTO) NFs is developed via electrospinning technology with double sprinklers and in situ heat treatment. Compared with TO NFs PD with poor on/off ratio ≈44, the BTO@TO NFs PD‐2 exhibits an excellent on/off ratio of ≈1.5 × 104 due to the dramatically restrained dark current. The ultralow dark current (pA level) is attributed to the depletion of photogenerated carriers by the space high‐resistance state induced by the downward self‐polarization field in ferroelectric BaTiO3 NFs. The ferroelectric domain with larger downward orientation in polarized BTO@TO NFs exhibits stronger self‐polarization field to modify the directional transport of photogenerated carriers and enhances the band bending level, which improves the photocurrent of device. The special structure woven by ferroelectric nanofiber with self‐polarization will provide a promising approach for improving the performance of flexible photodetectors.