The Role of Dielectric Screening in Organic Shortwave Infrared Photodiodes for Spectroscopic Image Sensing

Wu, Zhenghui; Zhai, Yichen; Yao, Weichuan; Eedugurala, Naresh; Song, Zhanqian; Huang, Lifeng; Gu, Xiaodan; Azoulay, Jason D.; Ng, Tse Nga

doi:10.1002/adfm.201805738

Cited by 87 publications

(117 citation statements)

References 39 publications

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“…As the exciton binding energy is lowered, photogeneration can become independent of the electric field, 33 because the dissociation process would not need an external bias to assist in separating electron−hole pairs. The devices here are not fully free of dissociation problems, 9,23 but the screening effect explains the characteristics in Figure 1b, which shows lower electric-field dependence as ε increases, when the D:A ratio is adjusted from 1:1 to 1:4.…”

Section: Acs Applied Electronic Materialsmentioning

confidence: 95%

Organic Bulk Heterojunction Infrared Photodiodes for Imaging Out to 1300 nm

Yao

Huang

et al. 2019

ACS Appl. Electron. Mater.

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This work studies organic bulk heterojunction photodiodes with a wide spectral range capable of imaging out to 1.3 μm in the shortwave infrared. Adjustment of the donor-to-acceptor (polymer:fullerene) ratio shows how blend composition affects the density of states (DOS) which connects materials composition and optoelectronic properties and provides insight into features relevant to understanding dispersive transport and recombination in the narrow bandgap devices. Capacitance spectroscopy and transient photocurrent measurements indicate the main recombination mechanisms arise from deep traps and poor extraction from accumulated space charges. The amount of space charge is reduced with a decreasing acceptor concentration; however, this reduction is offset by an increasing trap DOS. A device with 1:3 donor-to-acceptor ratio shows the lowest density of deep traps and the highest external quantum efficiency among the different blend compositions. The organic photodiodes are used to demonstrate a single-pixel imaging system that leverages compressive sensing algorithms to enable image reconstruction.

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Section: Acs Applied Electronic Materialsmentioning

confidence: 95%

Organic Bulk Heterojunction Infrared Photodiodes for Imaging Out to 1300 nm

Yao

Huang

et al. 2019

ACS Appl. Electron. Mater.

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“…The photodetector current was amplified by a low-noise amplifier and subsequently recorded by a lock-in amplifier (SRS 510). [42][43][44] Long-pass filters with cut-off wavelength at 455, 780, and 1100 nm were used to eliminate second-order harmonics in the spectra. During the optical measurements, the sample charge/discharge current was simultaneously monitored by the SP-200 potentiostat.…”

Section: Methodsmentioning

confidence: 99%

Wide Potential Window Supercapacitors Using Open‐Shell Donor–Acceptor Conjugated Polymers with Stable N‐Doped States

Wang

Huang

Eedugurala

et al. 2019

Advanced Energy Materials

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IntroductionSupercapacitors are electrochemical energy storage devices that store charge through fast, reversible redox reactions, enable load-leveling, regenerative energy harvesting, and high power applications. [1][2][3][4][5][6] The energy density of a supercapacitor (E = CV 2 /2) is linearly dependent on the specific capacitance C and proportional to the square of the operational voltage V. The main strategies to increase energy depend upon the mechanism of charge storage, whether capacitive or Faradaic. Capacitive electrodes store charge on the surface; hence, research is focused on strategies to increase the surface area, typically based on high surface area carbons. [7][8][9] Faradaic materials undergo redox reactions and offer the ability to tune the operating voltage. There has been considerable success in tuning the cathode voltage and delivering high capacitance systems operating at the upper limit of prototypical nonaqueous electrolytes. [1,7] However, the device voltage and energy remain limited by a lack of complementary high power electrodes for the anode. [10,11] In the absence of new high voltage electrolytes, there is no room to further extend the cathode potential, because over-potential may lead to hazardous runaway reactions between the highly oxidized cathodes and flammable nonaqueous electrolytes. In contrast, it is generally safe for nonaqueous electrolytes to operate down to −2 V relative to the Ag/AgCl electrode, and the development of anode materials is critical to increase the energy densities of supercapacitors.Consequently, there is an urgent need for strategies aimed at extending the operational voltage toward negative potentials to improve the energy density and cell voltage of supercapacitors. As an alternative to metal oxides, redox-active macromolecules offer mechanical flexibility, low-cost, and scalability relevant for small and large scale applications. [12][13][14][15][16] In radical polymers, [17][18][19][20] the redox sites are at pendant radical groups distributed along a polymer backbone. Due to the insulating nature of the backbone and low conductivity, devices based on these materials require blending with additional conductive materials for electron transport, ultimately lowering the electrode energy Supercapacitors have emerged as an important energy storage technology offering rapid power delivery, fast charging, and long cycle lifetimes. While extending the operational voltage is improving the overall energy and power densities, progress remains hindered by a lack of stable n-type redox-active materials. Here, a new Faradaic electrode material comprised of a narrow bandgap donor−acceptor conjugated polymer is demonstrated, which exhibits an open-shell ground state, intrinsic electrical conductivity, and enhanced charge delocalization in the reduced state. These attributes afford very stable anodes with a coulombic efficiency of 99.6% and that retain 90% capacitance after 2000 charge-discharge cycles, exceeding other n-dopable organic materials. Redox cycling proce...

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“…[17] A dozen NIR photoactive organic materials have been reported to date, with only a minor fraction showing photodetection up to 1400 nm. [18][19][20][21] Roomtemperature values for D* in this wavelength regime are in the order of 10 10 Jones and hence one to two orders of magnitude Organic photodetectors (OPDs) with a performance comparable to that of conventional inorganic ones have recently been demonstrated for the visible regime. However, near-infrared photodetection has proven to be challenging and, to date, the true potential of organic semiconductors in this spectral range (800-2500 nm) remains largely unexplored.…”

Section: Doi: 101002/adma202003818mentioning

confidence: 99%