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Charge injection is known as the major source of dark current under an applied reverse bias, which directly influences the performance of organic photodetectors with diode architecture. However, it is unclear which of various contributions, such as electron flow through the junction, shunt leakage, thermionic emission, and tunnelling, are dominant. This study investigates the thermionic emission and tunneling models to describe the origin of experimentally measured dark current generated in an organic photodetector. To elucidate the dominant mechanism, the barrier energies at anodic contacts are set from 0.6 to 1.0 eV using photosensitive layers composed of different acceptors. A linear relation is found between the natural logarithm of the dark current density under reverse bias and the square root of the barrier height, which strongly suggests direct tunneling as dominant mechanism for dark current injection. This conclusion is strengthened by temperature dependent dark current analysis. Further knowledge of the dominant mechanism by charge injection can help devise an effective strategy to suppress dark current for effective organic photodetector device implementation. 相似文献
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Liang Qin Liping Wu Bhupal Kattel Chunhai Li Yong Zhang Yanbing Hou Judy Wu Wai‐Lun Chan 《Advanced functional materials》2017,27(47)
Graphene field effect transistor sensitized by a layer of semiconductor (sensitizer/GFET) is a device structure that is investigated extensively for ultrasensitive photodetection. Among others, organometallic perovskite semiconductor sensitizer has the advantages of long carrier lifetime and solution processable. A further step to improve the responsivity is to design a structure that can promote electron–hole separation and selective carrier trapping in the sensitizer. Here, the use of a hybrid perovskite–organic bulk heterojunction (BHJ) as the light sensitizer to achieve this goal is demonstrated. Our spectroscopy and device measurements show that the CH3NH3PbI3–PCBM BHJ/GFET device has improved charge separation yield and carrier lifetime as compared to a reference device with a CH3NH3PbI3 sensitizer only. The key to these enhancement is the presence of [6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM), which acts as charge separation and electron trapping sites, resulting in a 30‐fold increase in the photoresponsivity. This work shows that the use of a small amount of electron or hole acceptors in the sensitizer layer can be an effective strategy for improving and tuning the photoresponsivity of sensitizer/GFET photodetectors. 相似文献
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CH3NH3PbI3/C60 heterojunction photodetectors were here fabricated. The peak EQE achieves ∼80% in the visible-light range from 400 to 760 nm. Benefitting from eliminating the leakage current (PEDOT:PSS-free), extremely low dark current density (0.6 nA/cm2) and high specific detectivity (2.7 × 1013 Jones) are acquired. 相似文献
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高灵敏度的有机光电探测器(OPD)具有从可见光到近红外(NIR)的宽带响应和优异的整体器件性能,在包括高质量生物成像在内的各种应用中起到了非常重要的作用。文章使用Silvaco TCAD模拟了一种活性层由宽带隙聚合物PBDTTT-C-T作为给体以及稠合八烷基小分子FOIC作为受体构成的混合物所制成的宽带有机光电探测器。模拟结果表明,器件的暗电流密度、外量子效益、可探测到的最低光强能力等各项指标达到了很好的水平,与实验数据吻合较好。由此,可认为模拟过程中所使用到的参数具有较好的可信度和使用价值,可以为同类型光电探测器的模拟与研究提供有益借鉴。 相似文献
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用金属有机物化学气相沉积法(MOCVD)生长了GaAs/AlGaAs量子阱材料,分别制备了300μm×300μm台面,峰值波长8.5μm,外电极压焊点面积80μm×80μm,内电极压焊点面积20μm×20μm的单元测试样品。用变温液氦制冷机测试系统对两个样品进行50～300K的变温测试,分析了器件在不同偏压条件下的暗电流特性。发现该量子阱红外探测器的背景限温度为50K。不同生长次序中GaAs与AlGaAs界面的不对称性,以及掺杂元素的扩散导致了正负偏压下的I/V曲线呈不对成性。探测器电极压焊点面积大小与位置的不同对暗电流有一定的影响。 相似文献
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Panagiotis E. Keivanidis Peter K. H. Ho Richard H. Friend Neil C. Greenham 《Advanced functional materials》2010,20(22):3895-3903
Organic photodiodes are presented that utilize solution‐processed perylene diimide bulk heterojunctions as the device photoactive layer. The polymer (9,9′‐dioctylfluorene‐co‐benzothiadiazole; F8BT) is used as the electron donor and the N,N′‐bis(1‐ethylpropyl)‐3,4,9,10‐perylene tetracarboxylic diimide (PDI) derivative is used as the electron acceptor. The thickness‐dependent study of the main device parameters, namely of the external quantum efficiency (EQE), the short‐circuit current (ISC), the open‐circuit voltage (VOC), the fill factor (FF), and the dark current (ID) is presented. In as‐spun F8BT:PDI devices the short‐circuit EQE reaches the maximum of 17% and the VOC value is as high as 0.8 V. Device ID is in the nA mm?2 regime and it correlates with the topography of the F8BT:PDI layer. For a range of annealing temperatures ID is monitored as the morphology of the photoactive layer changes. The changes in the morphology of the photoactive layer are monitored via atomic force microscopy. The thermally induced coalescence of the PDI domains assists the dark conductivity of the device. ID values as low as 80 pA mm?2 are achieved with a corresponding EQE of 9%, when an electron‐blocking layer (EB) is used in bilayer EB/F8BT:PDI devices. Electron injection from the hole‐collecting electrode to the F8BT:PDI medium is hindered by the use of the EB layer. The temperature dependence of the ID value of the as‐spun F8BT:PDI device is studied in the range of 296–216 K. In combination with the thickness and the composition dependence of ID, the determined activation energy Ea suggests a two‐step mechanism of ID generation; a temperature‐independent step of electric‐field‐assisted carrier injection from the device contacts to the active‐layer medium and a thermally activated step of carrier transport across the device electrodes, via the PDI domains of the photoactive layer. Moreover, device ID is found to be sensitive to environmental factors. 相似文献
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2D single crystals of down to two‐monolayer thickness are fabricated from a push–pull structure‐based green light absorbing organic n‐type semiconductor, (2E,2′E)‐3,3′‐(2,5‐difluoro‐1,4‐phenylene)bis(2‐(5‐(4‐(trifluoromethyl)phenyl)thiophen‐2‐yl)acrylonitrile) (2F‐4‐TFPTA). The 2F‐4‐TFPTA 2D single crystal exhibits field‐effect electron mobility of 0.9 cm2 V−1 s−1 in the dark and also decent photoresponsivity of 3.6 × 103 A W−1 under green light‐emitting diode irradiation, which is noted as the first demonstration of green‐sensitive 2D organic phototransistors. Photoresponse time of this 2F‐4‐TFPTA 2D single‐crystal device is as fast as 43 ms for the rise and 85 ms for the decay. 相似文献
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We report low dark current small molecule organic photodetectors (OPDs) with an inverted geometry for image sensor applications. Adopting a very thin MoOx:Al cathode interlayer (CIL) in the inverted OPD with a reflective top electrode results in a remarkably low dark current density (Jd) of 5.6 nA/cm2 at reverse bias of 3 V, while maintaining high external quantum efficiency (EQE) of 56.1% at visible wavelengths. The effectiveness of the CIL on the diode performance has been further identified by application to inverted OPDs with a semi-transparent top electrode, leading to a significantly low Jd of 0.25 nA/cm2, moderately high EQE540 nm of 25.8%, and subsequently high detectivity of 8.95 × 1012 Jones at reverse bias of 3 V. Possible origins of reduced dark currents in the OPD by using the MoOx:Al CIL are further described in terms of the change of interfacial energy barrier and surface morphology. 相似文献
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Spectroscopic sensing combined with optical imaging is crucial with respect to today's ever-growing demand for instant analytical techniques to be incorporated in various handheld and wearable devices. Further miniaturization and integration of such types of sensors is critical and wavelength-selective organic photodetectors (OPDs) may provide the required technology. In this progress report, some early OPD applications and their potential are presented. Crucial device parameters such as the specific detectivity, external quantum efficiency, and dark current density of visible and near-infrared wavelength-selective photodetectors are compared and assayed to theoretical and semi-empirical limits. The different organic detector approaches include the use of inherently narrow-band absorbers as well as internally filtered and microcavity devices. Each of these strategies comes with its own specific material and device design criteria, around which material development and selection should be centered to move beyond the current state of the art. As OPD technology matures, device stability becomes important and is hence also briefly discussed. Via this perspective, it is aimed to provide the reader with critical insights into the device physics and chemistry of wavelength-selective OPDs, hereby providing leverage for new ideas to bring this technology to the market. 相似文献
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新型GaAs/AlGaAs量子阱红外探测器暗电流特性 总被引：2，自引：1，他引：2
对基于 Ga As/ Al Ga As系子带间吸收的一种新型量子阱红外探测器 ,采用 Poisson方程和 Schrodinger方程 ,计算了新器件结构的能带结构、电子分布特性 ,在此基础上采用热离子发射、热辅助遂穿模型对器件的暗电流特性进行了模拟 ,计算结果与器件实测的暗电流特性吻合得很好 ,说明热离子发射、热辅助遂穿机制是形成器件暗电流的主要构成机制 ,增加垒高、降低阱中掺杂浓度及降低工作温度是抑制器件暗电流的主要途径 ,计算结果对进一步优化器件的设计将起到重要的理论指导作用 . 相似文献
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Wei Li Yalun Xu Xianyi Meng Zuo Xiao Ruiming Li Li Jiang Lihao Cui Meijuan Zheng Chang Liu Liming Ding Qianqian Lin 《Advanced functional materials》2019,29(20)
Organic semiconductors have attracted tremendous attention in the past few years, thanks to their excellent flexibility, solution‐processability, low‐cost, chemical versatility, etc. Particularly, organic solar cells based on ternary heterojunctions have shown remarkable device performance, with the recent development of nonfullerene acceptor materials. These novel materials are also promising for photodetection. However, there are several key limits facing organic photodetectors, such as relatively large bandgaps, poor charge transport, and stability. In this work, a novel nonfullerene acceptor—COi8DFIC—is introduced, blended with a fullerene derivative and a donor to form ternary heterojunctions. After optimization, photodiodes based on such ternary blends exhibit compelling performance metrics, including low dark current, decent responsivity, large linear dynamic range, fast response, and excellent stability. This device performance is actually on a par with the established silicon technology, suggesting great potential for photodetection and imaging. 相似文献
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我们报道了一种基于SnS2/InSe垂直异质结的宽带光电探测器,其光谱范围为365-965 nm。其中,InSe作为光吸收层,有效扩展了光谱范围,SnS2作为传输层,与InSe形成异质结,促进了电子-空穴对的分离,增强了光响应。该光电探测器在365 nm下具有813 A/W的响应度。并且,在965nm光照下它仍然具有371 A/W的高响应度,1.3×105%的外量子效率,3.17×1012 Jones的比探测率,以及27 ms的响应时间。该研究为高响应宽带光电探测器提供了一种新的方法。 相似文献
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从理论与实验两方面对截止波长为1.7μm(x=0.53),1.9μm(x=0.6)和2.2μm(x=0.7)p in InxGa1-xAs探测器性能进行了研究.对探测器暗电流的研究结果表明,扩展波长In0.6Ga0.4As,In0.7Ga0.3As探测器在反向偏置低压区,欧姆电流占据主导地位;在反向偏置高压区,缺陷隧穿电流占主导地位;且扩展波长In0.6Ga0.4As,In0.7Ga0.3As探测器的暗电流比In0.53Ga0.47As探测器增加较大.对探测器R0A随温度及i层载流子浓度变化关系的研究结果表明,在热电制冷温度下探测器性能可得到较大提高,i层的轻掺杂可使探测器的R0A得到改善. 相似文献
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Electron traps, hole traps, and the dominant recombination-generation (R-G) centers have been investigated with deep level
transient spectroscopy and current-voltage/temperature measurements in heteroepitaxial GexSi1-x alloys with x ranging from 0.15 to 1, grown on graded Gey.Si1−y/Si substrates. For all samples with compositions x < 0.85, which retain the Si-like conduction band structure, we detect
a dominant electron trap and R-G center whose activation energy is ΔE = 0.5 eV, independent of composition. This energy agrees
with that of electron traps previously reported for plastically deformed (PD) Si, suggesting a connection to the Si-like band
structure. This 0.5 eV level dominates the reverse leakage current over a wide range of growth and annealing conditions for
the 30% Ge samples, indicating that the electronic state at ΔE = 0.5 eV is a very efficient R-G center, as would be expected
from its midgap position. Alternatively, for strain relaxed, pure Ge (< 1), we detect electron traps at Ec − 0.42 eV and Ec − 0.28 eV, in agreement with the literature on PD Ge and Ge bicrystals. These energies are significantly different from those
observed for x < 0.85, and we conclude that these changes in activation energy are due to changes in the conduction band structure
for high Ge content. Moreover, in contrast with the Si-like samples (x < 0.85), the reverse leakage current in the relaxed
Ge cap layer is not controlled by deep levels, but is rather dictated by intrinsic, band-to-band generation due to the reduced
bandgap of Ge as compared to Si-like alloys. Only for reverse bias magnitudes which incorporate a significant portion of the
graded buffer within the depletion region do R-G centers dominate the reverse leakage current. These results confirm the high
quality of the strain-relaxed, pure Ge cap region which was grown on a GeySi1−y/Si step graded heterostructure (where y was increased from 0 to 1) by ultra high vacuum chemical vapor deposition. Finally,
we report for the first time, what is apparently the dislocation kink site state at Ec − 0.37 eV, in a GexSi1−x alloy. 相似文献
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Michael P. Hughes Katie D. Rosenthal Niva A. Ran Martin Seifrid Guillermo C. Bazan Thuc‐Quyen Nguyen 《Advanced functional materials》2018,28(32)
The photovoltaic and electrical properties of organic semiconductors are characterized by their low dielectric constant, which leads to the formation of polarons and Frenkel excitons. The low dielectric constant of organic semiconductors has been suggested to be significantly influential in geminate and bimolecular recombination losses in organic photovoltaics (OPVs). However, despite the critical attention that the dielectric constant has received in literature discussions, there has not yet been a thorough study of the dielectric constant in common organic semiconductors and how it changes when blended. In fact, there have been some inconsistent and contradictory reports on such dielectric constants, making it difficult to identify trends. Herein, at first a detailed explanation of a specific methodology to determine the dielectric constant in OPV materials with impedance spectroscopy is provided, including guidelines for possible experimental pitfalls. Using this methodology, the analysis for the dielectric constant of 17 common neat organic semiconductors is carried out. Furthermore, the relationship between the dielectric constant and blend morphology are studied and determined. It is found that the dielectric constant of a blend system can be very accurately predicted solely based on the dielectric constants of the neat materials, scaled by their respective weight ratios in the blend film. 相似文献