最新刊期
卷 53 ， 期 4 ， 2022
- 摘要：Organic/polymer photodetectors have attracted extensive attentions due to their adjustable responding spectra, solution processed procedure and capability of flexible device fabrication. In recent years, with the rapid development of organic semiconducting materials, the performances of organic/polymer photodetectors have been significantly improved. Organic photodetectors show comparable performance to that of commercial silicon-based photodetectors in visible light region, while outdo that in the near-infrared region. The study on organic photodetectors also widens their potential applications. Especially in medical and healthcare area, where lighter, thinner and more flexible organic/polymer photodetectors have aroused research interests, paving a new way for the development of novel portable healthcare monitoring device. For example, photoplethysmography signal monitoring is essentially important for the development of both wearable devices and clinical medicine area. By using flexible organic photodetectors, high resolution photoplethysmography signals were obtained. Organic light-emitting diodes with organic photodetectors are further integrated on flexible substrates via solution processed approach, and skin-like healthcare devices with real-time photoplethysmography, blood oxygen monitoring capabilities were realized. Focusing on both fundamental research and extending applications of organic/polymer photodetector, we summarized recent developments of organic/polymer photodetector for healthcare technology. In this review, the material design principles and outlook for high performance organic/polymer photodetectors toward medical and healthcare applications are discussed. In the first chapter, we describe the working principle of organic photodetectors. The representative near-infrared sensitive organic semiconductors were reviewed. Then, practical applications of the organic photodetectors for healthcare techniques were subsequently introduced. Finally, the current challenges in this field and prospects for the future development were concluded in the last part.关键词：Organic/polymer photodetector;Optoelectronic polymer;Photoplethysmography;Healthcare monitoring;Short-wave infrared sensor
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发布时间：2024-10-08 - 摘要：This review systematically summarizes the development, working mechanism, performance optimization and relevant application exploration of photomultiplication type organic photodetectors (PM-OPDs). In 2015, Prof. Fujun Zhang's group firstly reported PM-OPDs on the basis of active layers with single carrier transport channels. Electron traps are formed with acceptor surrounded by donor in active layers with the weight ratio of donor to acceptor as about 100:1. The working mechanism of PM-OPDs is attributed to hole tunneling injection assisted by interfacial trapped electron. Dark current density of PM-OPDs can be well suppressed due to the single carrier transport in active layers with rather less acceptor. New concept of "charge injection narrowing" was firstly proposed to prepare ultra-narrowband PM-OPDs, which is realized by adjusting thickness of active layers to control interfacial trapped electron distribution. Broadband PM-OPDs can be obtained via ternary strategy or double-layer scheme. Double-layer scheme consists of one absorption layer and one PM layer, which are individually employed to tune spectral response range of PM-OPDs and achieve external quantum efficiency greater than 100%. The advantages of photodiode type photodetectors and PM-OPDs can be integrated into one device by employing double-layer scheme. PM-OPDs with broad and flat spectral response can be achieved via optimizing interfacial trapped electron distribution, which can be regulated by inserting optical field adjusting layer or incorporating wide bandgap semiconductor materials into active layers. The PM-OPDs have been successfully applied in many fields, such as heart rate monitoring, single pixel imaging and optical switch. The successful practical applications indicate good development prospect of PM-OPDs.关键词：photomultiplication type Organic photodetectors;tunnelling injection;external quantum efficiency;spectral range
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发布时间：2024-10-08 - 摘要：Photodetectors are the foundation of modern science and industrial systems. Organic semiconductors have developed rapidly in the past decade due to their appealing properties such as low-cost manufacturing, flexibility, light-weight, and large-area scalability. Near-infrared organic photovoltaic photodetectors have drawn extensive attention because of their wide applications in bioimaging, quality inspection, image sensing, optical communication and night surveillance. Owing to the highly tuneable optical and electrical properties of organic semiconductor materials, narrow-band, low noise, visible-blind near-infrared organic photodetectors have been achieved. The research on near-infrared organic photovoltaic photodetectors has aroused widespread interest at home and abroad. Chinese scholars have made great contributions to the development of this research field, and a series of important innovations have been made in the preparation of near-infrared organic materials and the design of near-infrared organic photodiode devices. This article aims to summarize and review the research progress of near-infrared organic photovoltaic photodetectors and their future development in the fields of imaging sensing, biomedicine and spectral analysis. In the first section, we briefly introduce the basic overview of the device structures, applications and important figures of merit of organic photodetectors. In the second section, we summarized the materials used in the active layer of the near-infrared photovoltaic organic photodetectors in the past decade, which are simply classified into organic near-infrared polymer materials and near-infrared small-molecule materials. In the third section, we reviewed the device optimization and design strategies of near-infrared organic photovoltaic photodetectors, including the adjustment of active layer film thickness, charged carrier blocking layers, the strategies of charge collecting narrowing and exciton dissociation narrowing. In the fourth section, the specific applications and their scientific principles of near-infrared organic photodetectors are introduced, including real-time biological monitoring, spectral analysis and near-infrared imaging applications. In the last section, we briefly summarized the achievements which have been made, the current challenges and the future prospects of near-infrared organic photovoltaic photodetectors.关键词：Organic photodetector;Organic photodiode;Conjugated polymer materials;Conjugated small-molecule material;Near-infrared response
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发布时间：2024-10-08 - 摘要：Visual information processing and memory in brain is carried out through the manipulation of synaptic plasticity. Light-responsive synaptic devices are the key to realizing artificial visual systems and neuromorphic computing with low energy consumption. Thus, organic photoelectric synaptic devices, which can realize the sensing and memory of optical information, have attracted increasing attention in recent years. This article first introduces that the function of organic photoelectric synaptic devices is integration of organic photodetectors and organic memristors. Then basic synaptic behavioural performance (excitatory/inhibitory post-synaptic current, paired-pulse facilitation/depression, short/long-term plasticity, learning experience and spiking-timing/rate-dependent plasticity) and important parameter indexes (energy consumption, retention time and linearity) of photoelectric synaptic devices are listed. Next, the mechanisms of organic photoelectric synaptic devices are divided into photo-induced carrier trapping and de-trapping, persistent photoconductivity and photochemical reaction/conformational change based on the device structures. Then four applications of photoelectric synaptic devices are reviewed, which is associative learning, image memory, image recognition and neuromorphic computing. Finally, the current problems and challenges of this field are summarized, and the future development trend is prospected. Nowadays, the design principle of organic molecules for organic photoelectric synaptic devices is ambiguous, so more researches and summaries on structure-property relationship should be carried out. Moreover, the evaluation criteria of synaptic devices should be established and more biological synaptic behaviors need to be emulated. As a multidisciplinary research topic of organic electronics, neuromorphology, microelectronics, etc., organic photoelectric synapses will gradually develop from a single device into a large-area, large-scale, multi-functional integrated system, which greatly promotes the development of artificial intelligence.关键词：Organic photoelectric sensing;Neural synapse;Memristor;Bionic vision;Artificial intelligence
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发布时间：2024-10-08
Review
- 摘要：A novel charge transfer cocrystal BPEA-PMD was prepared by solution method using 9,10-diphenylacetylene anthracene (BPEA) as donor molecule and pyromellitic diimide (PMD) as acceptor molecule. The D-A cocrystals show a mixed stacking mode with a molar ratio of 2:1. A series of spectral analyses prove that there is a charge transfer characteristic in the BPEA-PMD cocrystals, which narrows the band gap of the cocrystals and further makes the cocrystals system show excellent photoelectric properties. BPEA-PMD cocrystals exhibit red fluorescence emission, and the PL lifetime is 1.14 ns, showing a single exponential decay process, which indicates that the luminescence process of BPEA-PMD cocrystals is derived from only one excited state. In addition, BPEA-PMD cocrystals display p-type transport properties with hole mobility up to 8.33×10-2 cm2·V-1·s-1. Based on its excellent electrical properties, photoresponsive transistors device was prepared. Under the illumination of 450 nm light, the source-drain current of the phototransistors based on BPEA-PMD increases significantly. Moreover, photosensitivity (P), photoresponsivity (R), and detectivity (D*) are several key parameters for evaluating the photoelectric detection capability. The phototransistors for BPEA-PMD cocrystals demonstrate the Pmax of 37.38, Rmax of 1.67×103 A·W-1, and D*max of 2.06×1013 Jones, which proves the great potential of the organic cocrystals in the application of photoelectric detectors.关键词：Organic cocrystals;Charge transfer;Red fluorescence;P-type transport;Photoresponse
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发布时间：2024-10-08 - 摘要：High-performance near-infrared (NIR) organic photodetectors (OPDs) have widespread application prospects in artificial vision, biological imaging, flexible wearable electronic devices. Ascribed to high absorption coefficient and charge-carrier mobility, the narrow-bandgap polymer DPPDTT displayed a great potential for NIR OPDs. However, due to the nature of narrow bandgap and strong intermolecular interactions, the DPPDTT-based OPDs exhibit a low detectivity (D*(λ)). Here, we introduced PCBM as the acceptor material to construct bulk-heterojunction photodiodes, which improved the efficiency of exciton separation and charge transfer, so that the D*(λ) can be simultaneously enhanced. Moreover, when the narrow-bandgap acceptor Y6 is utilized instead of PCBM to afford a "double narrow-bandgap absorption" heterojunction structure, the superposition of absorption in the near-infrared region could effectively enhance the light response capability of devices. Finally, by adopting the inverted structure and inserting barrier layers, the dark current is further reduced by one order of magnitude, and the D*(λ) is increased to 8.28×1011 Jones under 850 nm at a light irradiation of 0.53 μW·cm-2. With the increase of the measurement frequency, the response speed and the D*(λ) of the device were kept at same value, and it still showed good cycle stability under the condition of 120 frames per second. Thus, the above results confirm that this type of device will show promising applications in photoelectric communication, NIR imaging, physiological testing, and so forth.关键词：narrow-bandgap DPP-based polymer;High performance;diode;near-infrared organic photodetectors
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发布时间：2024-10-08 - 摘要：Narrowband photodetectors, which only respond to the spectral bands of interest but not to other spectral ranges, are widely used in biological sensors, medical monitoring, intelligent communication and other fields. Recent developments in artificial intelligence and wearable electronic devices have fostered a growing demand for visible-blind near-infrared (NIR) narrowband photodetectors. Herein, a novel hierarchical device structure based on the exciton dissociation narrowing (EDN) mechanism is proposed to realize NIR narrowband organic photodetectors (OPDs) with a response peak at 940 nm. Compared with traditional EDN type narrowband OPDs, the new device has a significantly higher peak external quantum efficiency (EQE) at 940 nm. The transient photocurrent measurement results show that the differences in device performance arise from diversity in the dynamics of the carrier trapping and de-trapping processes. Impedance analysis shows that the central trap energy levels of the two devices are located at different trap depths. Deep Gaussian trap density of states distributions cause unfavorable space-charge effects, counteract the internal electric field, and increase the recombination loss, resulting in a significant difference in the EQE of the two devices. The visible-blind NIR OPD with optimized device structure can effectively resist the interference of ambient light, in addition, the sensitivity of the narrowband OPD in the NIR window at 940 nm has been enhanced by trap density of states distribution control. Therefore, it has a strong detection ability for weak infrared radiation. We also fabricated a flexible photodetector based on the optimized device structure with a sensitive area of 1.152 cm2. The device was attached to the surface of human skin, and the noninvasive real-time monitoring of human heart-rate was successfully realized by the reflective PPG technology with a flexible narrowband photodetector for the first time, demonstrating the superiority of this new structure in making high performances narrowband NIR OPDs for practical application.关键词：Near-infrared;Density of states;Narrowband photodetectors;Flexible sensors
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发布时间：2024-10-08 - 摘要：In order to obtain high photoelectric responses in the near-infrared (NIR) region, in this work, an A-D-A type organic electron acceptor, TCIC, is designed and synthesized. Due to the strong quinoid effect of the thieno[3,4-b]thiophene core, TCIC has strong absorptions in the NIR range of 780‒1000 nm and suitable energy levels, which match well with those of the commonly used polymer donor, PCE10. Thus, two device structures are adopted to fabricate the self-powered (at 0 V bias) organic photodetectors (OPDs) based on PCE10:TCIC blended films. Compared to the conventional device, the inverted device is beneficial to suppress dark current and total noise current. Finally, the inverted device achieves the specific detectivities of more than 1013 Jones across the broad spectrum of 410‒1000 nm, and exhibits an ultra-wide linear dynamic range of ~180 dB and an extremely fast response speed of ~6.5 μs under illumination of lights at 940 nm, giving excellent figure-of-merits comparable to those of the best OPDs reported so far. Therefore, this work provides important guidance for the molecular design of high-performance NIR acceptors.关键词：Near-infrared electron acceptors;Thieno[3;4-b]thiophene;Organic photodetectors;Specific detectivity
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发布时间：2024-10-08 - 摘要：The wide-bandgap polymer (PTzBI-Cl) contains an electron-deficient [1,2,3]triazolo[4,5-f]isoindole-5,7(2H,6H)-dione (TzBI) unit, which can be used as an electron-donating polymer to combine with a non-fullerene acceptor, namely Y6DT, to fabricate organic photodetectors (OPDs) that bear inverted device structure. The devices based on high molecular weight PTzBI-Cl-H exhibited lower dark current density and thus superior photodetectivity. The dark current density can be significantly suppressed by optimizing the film thickness of active layer, while the external quantum efficiency can be maintained at a relatively high level. The combination of these advantages leads to an obvious increase in the detectivity. When the active layer thickness increased up to 330 nm, the device exhibited a very low dark current density of 2.3×10-10 A·cm-2 at -0.1 V, and the rectification ratio is 106 in the range of ±2 V. Under -0.1 V bias, the detectivity of the device is higher than 1013 cm·Hz-1/2·W-1 in the range of 500-880 nm, with a maximum of 6.1×1013 cm·Hz-1/2·W-1 and a responsivity of 0.52 A·W-1 at a working wavelength of 830 nm, both of which are among the highest values of thus far reported OPDs based on the inverted structure at the working wavelength of 830 nm without extra gains.关键词：Organic photodetector;near infrared;Molecular weight;thick-film devices
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发布时间：2024-10-08
Research Article
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