Search

Photodetectors based on inorganic semiconductors demonstrate superior responsivity, but their high thermal budget fabrication process is a serious impediment for emerging applications. Hybrid photodetectors based on organic-inorganic heterojunctions synergistically offer the solution-processability and tunability of organic semiconductors, along with the superior absorption coefficient and transport properties of inorganic materials. In this work, a broadband photodetector based on a bulk-heterojunction of hybrid organic-PEDOT:PSS/inorganic-SnSe2 and a subsequent vertical junction on flexible ITO-coated-PET is demonstrated. SnSe2 nanoflakes, synthesized via a facile hydrothermal method, exhibit absorption in both the visible and NIR spectra, and are made into a bulk heterojunction (BHJ) with PEDOT:PSS. The ITO layer exhibits absorption in the UV spectra, onto which the SnSe2-PEDOT:PSS bulk-heterojunction composite is deposited to form a vertical junction. The broadband photodetector exhibits quick response times of 16 ms, 221 ms and 274 ms and superior responsivities of 0.72 A W-1, 0.67 A W-1 and 0.69 A W-1 in the UV, Vis and NIR spectra, respectively. This superior responsivity of the photodetector is related to the enhanced interfacial area between SnSe2-PEDOT:PSS in the bulk-heterojunction, which leads to efficient electron-hole pair separation. Furthermore, the device is subjected to multiple bending cycles (∼3000) and minimal deviation in responsivity is observed. The facile and low-cost approach demonstrated in this work finds potential applications in novel flexible opto-electronic devices. This journal is © the Partner Organisations.

Flexible and compressible sensors have been widely used for various wearable applications; however, the devices are typically planar, expensive and with limited compressibility. In this work, carbon-doped polypyrrole nanoparticles interfaced in a 3D-macroporous melamine foam (C-PPy@MF) composite are used as a low-cost multifunctional sensor for breath monitoring, pressure-, and strain-sensing applications. The C-PPy nanostructures were grown on MF using an ultrasonic irradiation technique to achieve a firm loading of C-PPy on the MF surface and interface. Detailed morphological characterization studies reveal the discrete distribution of C-PPy nanoparticles in the MF matrix. Structural analysis revealed a broad amorphous phase corresponding to the carbon polymer chains. The fabricated C-PPy@MF-based breath sensor displayed a fast response time of 0.9 s and a recovery time of 1.3 s upon continuous exhalation and inhalation cycles. In addition, the breath sensor was used for the monitoring of human breath per minute (bpm) and dehydration of the lungs. The superior response of the breath sensor can be attributed to the surface engineering of MF with the C-PPy nanostructures, which enables an excellent surface reactivity due to their large relative surface area. The C-PPy@MF-based piezoresistive pressure sensor exhibits a sensitivity of 2 kPa-1 in the pressure range of 1-90 kPa and a rapid response time of 160 ms. A 3 × 3 pressure sensor array was developed for precise spatial mapping to demonstrate the practicability of the pressure sensor. The fabricated C-PPy@MF-based strain sensor recorded a maximum gauge factor (GF) of 23.47 and can withstand a maximum strain of 80%, which is higher than most of the previously reported similar yet sophisticated devices. In addition, a constant response was obtained for 1000 bending cycles, demonstrating the excellent mechanical stability of the fabricated C-PPy@MF device. The fabricated C-PPy@MF-based flexible breath, pressure, and

Despite the low cost of paper substrates, the lack of appropriate device fabrication techniques has hampered the overall efficacy of paper-based sensors. Addressing this issue, in this work, we develop a multi-walled carbon nanotube (MWCNTs) coated paper substrate-based biosensor using a novel method of wax deposition followed by vacuum filtration to design dedicated hydrophobic and hydrophilic channels for label-free, highly selective, and sensitive detection of cholesterol. Detailed morphological characterization studies reveal the uniform deposition of MWCNTs on the paper substrate (∼15–20 nm average diameter). Upon exposure to cholesterol, an excellent dynamic range of response over three orders of magnitude from 10 nM −75 µM and 100 µM–8 mM concentration range with a limit of detection of 3.2 nM (3 S/m) was obtained. The Michaelis–Menten constant (Km) was found to be 0.0093 µM. In addition, the fabricated biosensor exhibited excellent reproducibility, stability and high specificity to cholesterol with negligible response from interfering analytes. The excellent response of the fabricated biosensor can be attributed to the modulation of electrical properties due to electrostatic gating effect and direct electron transfer between MWCNTs and cholesterol due to the bioconjugation of Cholesterol oxidase (ChOx). The strategy employed here addresses some major challenges faced by the current methods of using rigid substrates and liquid electrolyte based analytical methods for detection of cholesterol. Furthermore, the sensor could successfully measure concentrations of cholesterol in saliva. This work provides a promising platform for developing low cost, interference free, disposable paper-based biosensors for point of care diagnostics. © 2022 The Korean Society of Industrial and Engineering Chemistry

Solution processed photodetectors with high responsivities and simple fabrication schemes are high on demand for variety of emerging opto-electronic applications. However, these devices suffer from sluggish response and recovery times. In this work, we demonstrate the simultaneous enhancement of the responsivity, response time and spectral range of detection in a solution-processed device based on organic/inorganic hybrid junction. A solution-processed flexible CdS photodetector is fabricated using a facile and economical chemical bath deposition technique. The fabricated pristine-CdS device exhibits responsivity and response time of 50 mA/W and 5.4 s. The resultant device exhibits enhanced responsivity and response time of around 740 mA/W and 0.6 s, respectively, upon modification with the PEDOT:PSS conducting polymer. These values of PEDOT-modified device are one order larger than pristine-CdS detector. Further, PEDOT:PSS modification also extends the responsivity of the device from UV-Vis to NIR spectra. NIR responsivity in the hybrid device, is imputed to the photothermal property of the PEDOT:PSS layer. Thus, the overall device spectral response is accredited to the simultaneous existence of photoelectric and photo-thermal phenomena. The observed responsivity and faster response time is ascribed primarily to the built-in potential at interface of CdS-PEDOT:PSS, which not only facilitates efficient separation of photo carriers but also leads to a reduction in the recombination of excitons. Given the simple approach and excellent enhancement in the device performance, the idea demonstrated here could be useful to design high performance opto-electronic device based on solution-processed techniques. © 2022 Elsevier B.V.

Transition Metal Dichalcogenides based flexible photodetectors have gained importance owing to the excellent absorption and photo conductivity. However, the fabrication of layered materials requires complex processes, high thermal budget, fabrication conditions using toxic precursors with expensive experimental facilities. In this work, we report a novel combination i.e., layered bimetallic chalcogenides Bi2S3/RuS2 hybrid heterojunctions with engineered interfacial structures facilitating wide range of absorption for broadband photodetector applications. The bimetallic sulphides were grown on biodegradable cellulose paper substrate using one-step hydrothermal method and optimized to get desired 1D/1D morphology. Detailed characterization studies demonstrate the formation of 1D-Bi2S3 microneedles with an orthorhombic phase and 1D-RuS2 nano-rods with a cubic phase structure providing clear evidence of 1D/1D hybrid heterostructure formation. The fabricated photodetector displayed excellent photo response in the UV, Visible and NIR region with a maximum responsivity of 58.2 mA/W towards visible light. A maximum EQE of 78% was obtained with fast response time of 0.6, 0.4 and 0.7 s for UV, VIS and NIR light respectively, which are far more superior considering the cost-effective, scalable cleanroom free fabrication technique employed. The obtained response can be ascribed to the superior absorption property of RuS2 in the UV region and Bi2S3 in the visible and NIR region. The discrete distribution of RuS2 on the Bi2S3 device facilitates the formation of local electric fields and the contact engineering by collecting charge carriers from the Bi2S3 results in efficient separation of photogenerated charge carriers.This work demonstrates the first paper-based-bimetallic sulphides with unexplored bismuth and ruthenium complexes-based hybrid heterojunction based broadband photodetector with excellent flexibility, low cost, the strategy outlined here is ideal for various applica

Despite their high absorption coefficients, most two-Dimensional (2D) Transition Metal Dichalcogenides (TMDC) based photodetectors have a narrow range of light absorption and employ sophisticated fabrication methods. To overcome this, we propose a 2D–0D hybrid heterojunction-based broadband photodetector with Tin Diselenide (SnSe2)/Tin Oxide (SnO2) hybrid structure to enhance the range of detection and performance of the photodetector. The 2D and 0D nanoparticles were synthesized using a simple, cost-effective, one-step hydrothermal method. Detailed physicochemical characterization studies demonstrate the formation of 2D hexagonal layers of SnSe2 nanoflakes with absorption in visible and near IR regions and rutile tetragonal structure of SnO2 Quantum dots (QDs) with absorption in UV region. The fabricated photodetector shows superior responsivity of 47.9, 16.8, and 6.51 mA/W in UV, VIS, and NIR light with enhanced light-matter interaction. The SnSe2/SnO2 heterostructures demonstrated an efficient interlayer charge transfer due to the strong coupling. The superior performance of the photodetector can be attributed to the sizeable tuning of bandgap upon optical excitation in the bulk heterojunction wherein the photocarriers are injected into the SnSe2 nanoflakes for efficient light absorption in the broadband spectrum. The response time of this device was observed to be 0.5, 0.5, and 0.93 s under the illumination of UV, visible, and NIR lights, respectively. The flexibility studies display excellent robustness and mechanical stability for ~2000 bending cycles at ambient conditions. Hence, due to its flexibility, low power, and low cost, the strategy outlined here is ideal for applications like wearable electronics, flexible security, and surveillance systems.

Pencil (graphite) on paper (PoP) electronics has gained significant attention due to its low cost and versatility in developing customizable disposable electronics. Despite the convenience of the PoP methodology in device fabrication its application in developing electronics is limited due to the absence of a bandgap in graphite. The present work is the first demonstration of the direct writing of 2D MoS2 trace on paper which was utilized as a pressure and strain sensor. Detailed characterization studies revealed the formation of rhombohedral and hexagonal phased MoS2 micro-flowers. XPS studies revealed the formation of mixed 1T (metallic) and 2H (semiconducting) phases of MoS2. With the increase in the number of traces of 2D MoS2 on paper, the resistance of the channel decreased owing to the increase in conducting channels. The as-fabricated pressure sensor displayed a sensitivity of 2.21 kPa-1 and strain sensor displayed a GF of 13. Also, the sensor displayed an excellent durability for 1600 cycles. The superior response of the sensor can be attributed to the synergistic properties of micro fibrous paper substrate and piezo-dependent electron transfer of 2D-MoS2. The presented technique enables 'make it yourself' multifunctional device that have numerous potential applications in the field of consumer electronics and personal healthcare monitoring.