High-performance Organic Photodetectors Research Articles

Study of OPD based on PC60BM+P3HT bulk heterojunction

Junction organic photodetectors (OPD) based on the principle of photovoltaic generation have been widely studied. Firstly, this paper introduces the bulk heterojunction OPDs using ZnO for electron transport layer, PC60BM+P3HT for active layer structure, and MoO3 for hole transport layer to improve the photoelectric conversion efficiency. Secondly, the OPD device was prepared by specific experimental scheme, and the advantages of using the polymer-organic small molecular heterojunction were pointed out. Finally, the performance of the device was analyzed, including external quantum efficiency (EQE), responsiveness, specific detectivity, dark current and so on in different bands. Finally, the shortcomings of the device are pointed out, and the improvement scheme and possible improvement direction are put forward to improve the photoelectric conversion efficiency and fabricate high performance organic photodetectors.

Octupole moment driven free charge generation in partially chlorinated subphthalocyanine for planar heterojunction organic photodetectors

In this study, high-performance organic photodetectors are presented which utilize a pristine chlorinated subphthalocyanine photoactive layer. Optical and optoelectronic analyses indicate that the device photocurrent is primarily generated through direct charge generation within the chlorinated subphthalocyanine layer, rather than exciton separation at layer interfaces. Molecular modelling suggests that this direct charge generation is facilitated by chlorinated subphthalocyanine high octupole moment (−80 DÅ2), which generates a 200 meV shift in molecular energetics. Increasing the thickness of chlorinated subphthalocyanine leads to faster response time, correlated with a decrease in trap density. Notably, photodetectors with a 50 nm thick chlorinated subphthalocyanine photoactive layer exhibit detectivities approaching 1013 Jones, with a dark current below 10−7 A cm−2 up to −5 V. Based on these findings, we conclude that high octupole moment molecular semiconductors are promising materials for high-performance organic photodetectors employing single-component photoactive layer.

UV‐A/B High‐Sensitivity Organic Photodetectors Containing Butterfly‐Shaped Furan‐Fused BN‐Dihydropyrene with Push‐Pull Electron “Wings” toward Image Sensor

AbstractReplacement of C─C unit with its isoelectronic B─N unit in aromatics provides a new class of molecules with appealing properties. Herein, Five novel butterfly‐shaped furan‐fused bis‐BN dihydropyrenes (FBN) derivatives are synthesized with different push‐pull electron “wings”. These compounds exhibit prominent UV‐A/B absorption, high energy levels, and p‐type characteristics. Thanks to the side‐chain engineering and BN dipole manipulation, their intramolecular dipole moments and intermolecular stacking mode are effectively regulated to improve intra‐ and inter‐molecular charge transfer, thus achieving high hole mobilities. Five FBN‐X compounds are doped with PC71BM as heterojunction photosensitive layers to fabricate solution‐processed high performance organic photodetectors (OPDs), which exhibit self‐powered effect and high sensitivity to UV‐A/B. Especially, the FBN‐CN‐based device presents a high detectivity up to 1.72 × 1012 Jones, a peak external quantum efficiency of 19.1%, and an extremely low dark current density of 8.90 × 10−10 A cm−2 under 320 nm at 0 V. To the best of authors knowledge, it is the first report of photodiode‐type UV‐OPDs containing BN‐doped polycyclic aromatic hydrocarbons as active layer to date. And the optimal device shows a significant advantage over the reported 300–380 nm UV‐OPDs. In addition, a 10 × 10 array of organic image sensor is successfully demonstrated, which showcases excellent low‐light imaging capability.

Design and Fabrication of High-Performance Organic Photodetector for Ambient Light PPG Sensor

Design and Fabrication of High-Performance Organic Photodetector for Ambient Light PPG Sensor

Development of high-performance organic photodetectors by understanding origin of dark current density with synthesis of photoconductive polymers

Photoconductive polymers (PCPs) are key materials that determine the static and dynamic performance of p-n bulk heterojunction organic photodetectors (OPDs). Herein, we developed benzo[1,2-d:4,5-d']bis(oxazole)-based novel PCPs with π-spacer molecular engineering to promote charge-transport while maintaining low dark-current densities (Jd) in OPDs. The origin of Jd was elucidated by measuring hole charge-transfer (CT) state energy. We found that the degree of hole accumulation at the CT state rather than the CT state energy was crucial to maintaining a low Jd and promoting a fast signal response in the devices. The optimized OPDs showed highly promising responsivity (R) of 0.43 A/W and specific detectivity (D*) of 6.85 × 1012 Jones at −1 V under 532 nm LED (5.0 mW cm−2) illumination, which are superior to those of the control device (R = 0.29 A/W and D* = 5.46 × 1011 Jones). In addition, the dynamic properties were significantly improved by the introduction of π-spacers on the PCPs. −3 dB cut-off frequency was 200.4 kHz, and the rising and falling response times was ultrafast as 2.3 and 2.8 μs, respectively. Understanding the origin of Jd through the molecular engineering of PCPs is expected to contribute greatly toward expanding the knowledge required to develop high-performance OPDs.

A Direct surface modification strategy of ITO anodes enables high-performance organic photodetectors

A direct modification strategy of indium tin oxide (ITO) for high-performance organic photodetectors (OPDs) is developed. By using chlorinated ITO (ITO-Cl) as the anode, the OPD device exhibits superior performance than ITO/PEDOT:PSS-based device.

Effects of charge injection barrier on the dark current of organic photodiodes

In this work, we investigated the effect of charge injection barrier on the dark current density of organic photodetectors. The photosensitive layer of these photodetectors contains an electron-donating polymer PNTOD, and the derivatives of the widely used non-fullerene acceptor, namely ITIC, IT-2F and IT-4F. All devices showed similar absorption profiles and external quantum efficiencies, while different dark current density and thus specific detectivity. It is interesting to note that both electron and hole injection barriers of devices decreased with increased fluorine substituents in end groups of the non-fullerene acceptor ITIC. The electron injection barriers reduced from 1.37 eV for ITIC to 1.02 eV for IT-4F, and the corresponding hole injection barriers slightly dropped from 0.75 eV for ITIC to 0.57 eV for IT-4F, leading to an increased dark current at reversed bias. These findings verified the importance of rational energy level alignment of photosensitive materials for achieving high-performance organic photodetectors. • The effects of charge injection barrier on the dark current density of organic photodetectors were investigated. • OPDs based on ITIC derivatives showed similar photocurrent and responsivity, while obviously different dark current density and detectivity. • Increasing F-substituents of ITIC derivatives leads to decreased charge injection barrier and thus increased dark current density.

High-performance organic photodetectors enabled by a refined fibrillar multiphase morphology

Film morphology of donor:acceptor blend layers plays a critical role in photon-to-current efficiency and dark/noise current of organic photodetectors (OPDs). One effective approach to manipulate crystallization and mesoscale phase separation of such blend layers is sequential casting (SC). However, the guiding strategies to control the morphology and the impacts on OPD performance of the SC films remain elusive, as the film structural evolution during SC is different from conventional blend casting (BC). Here, a refined fibrillar multiphase morphology is demonstrated by SC in an NT812:IEICO-4F blend film, where the high-quality IEICO-4F crystallites infiltrate the robust NT812 fibril network from the surface to the bulk. Such a morphology leads to improved charge generation and collection, reduced trap states, and enhanced charge block capability of resultant device, enabling simultaneous achievement of high external quantum efficiency and low dark/noise current. A maximum special detectivity of 5 × 1013 Jones is achieved at 860 nm under –0.1 V, which is among the highest detectivities for vis-to-NIR OPDs. The linear dynamic range and response speed are also improved. Such enhancements are parallelly observed from OPD devices based on other blend systems with similar fibrillar refinement, which provides guidelines for film structure manipulation towards high OPD performance.

Thieno[3,4-b]pyrazine-containing D-A conjugated polymer-based photodetectors with high performance and UV–visible dual-band response for color temperature sensor and encrypted optical communication

Three thieno[3,4-b]pyrazine (TP)-containing D-A type conjugated polymers are successfully used to develop multifunctional high-performance organic photodetectors (OPDs). The TP acceptor units are respectively coupled with three different donor units to effectively regulate their molecular energy levels and carrier mobilities. The resultant polymers exhibit dual-band absorbance in the UV–visible region, intramolecular charge transfer (ICT) effect and efficient ambipolar transport characteristics. They are evaluated as the single photosensitive layers in OPDs for the first time. The optimal device based on TP-Si presents a peak external quantum efficiency (EQE) over 40% and a high specific detectivity (D∗) of 3.35×1012 Jones with fast temporal response under 560 nm at −1.5 V, which are superior to the most of reported single-active-layer OPDs. The high performance could be ascribed to the well-balanced photogenerated carriers and the efficient charge separation and transport in the device. Noteworthy, this dual-band response device can be used as a novel color temperature (CT) sensor for complementary white light illumination, and an encrypted UV–visible light communication scheme has been successfully demonstrated. The results show that these ambipolar D-A polymers have a broad application prospect in secure optical communication in the future.

A visible to near-infrared nanocrystalline organic photodetector with ultrafast photoresponse

A high performance organic photodetector with an ultrafast photoresponse of 1.8 μs, a high responsivity of 680 mA W−1 and a detectivity of 6.35 × 1013 Jones was fabricated. The small Frenkel exciton binding energy ensures that excitons can be efficiently dissociated.

High-Performance Organic Photodetectors Enabled by a Refined Fibrillar Multiphase Morphology

High-Performance Organic Photodetectors Enabled by a Refined Fibrillar Multiphase Morphology

Diminished Trap-Induced Leakage Current at the Organic/Electrode Interface for High-Performance Organic Photodetectors

Diminished Trap-Induced Leakage Current at the Organic/Electrode Interface for High-Performance Organic Photodetectors

Identifying the Molecular Origins of High-Performance in Organic Photodetectors Based on Highly Intermixed Bulk Heterojunction Blends

A bulk-heterojunction (BHJ) structure of organic semiconductor blend is widely used in photon-to-electron converting devices such as organic photodetectors (OPD) and photovoltaics (OPV). However, the impact of the molecular structure on the interfacial electronic states and optoelectronic properties of the constituent organic semiconductors is still unclear, limiting further development of these devices for commercialization. Herein, the critical role of donor molecular structure on OPD performance is identified in highly intermixed BHJ blends containing a small-molecule donor and C60 acceptor. Blending introduces a twisted structure in the donor molecule and a strong coupling between donor and acceptor molecules. This results in ultrafast exciton separation (<1 ps), producing bound (binding energy ∼135 meV), localized (∼0.9 nm), and highly emissive interfacial charge transfer (CT) states. These interfacial CT states undergo efficient dissociation under an applied electric field, leading to highly efficient OPDs in reverse bias but poor OPVs. Further structural twisting and molecular-scale aggregation of the donor molecules occur in blends upon thermal annealing just above the transition temperature of 150 °C at which donor molecules start to reorganize themselves without any apparent macroscopic phase-segregation. These subtle structural changes lead to significant improvements in charge transport and OPD performance, yielding ultralow dark currents (∼10-10 A cm-2), 2-fold faster charge extraction (in μs), and nearly an order of magnitude increase in effective carrier mobility. Our results provide molecular insights into high-performance OPDs by identifying the role of subtle molecular structural changes on device performance and highlight key differences in the design of BHJ blends for OPD and OPV devices.

High-Performance Solution-Processed Pentacene/Al Schottky Ultraviolet Photodiode With Pseudo Photovoltaic Effect

This article reports a solution-processed pentacene/Al Schottky photodiode for ultraviolet (UV) detection. A low-cost dispersion method is used to fabricate the pentacene film on ITO substrates. The surface morphology, crystalline properties, electrical, and optical properties of the pentacene film have been investigated in detail by X-ray diffraction (XRD), AFM, SEM, UV-visible(Vis), and Hall measurements. Also, the UV detection characteristics were studied. The mechanism attributes to a pseudo photovoltage developed at the Schottky junction. The device shows a high sensitivity of 5.7 (372 nm), a detectivity of 1.25 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> Jones (364 nm), and a quantum efficiency of 1502% (362 nm) at 1-V applied bias. This work paves the way for developing future-generation high-performance organic photodetectors suitable for optoelectronic applications.

Processes Controlling the Distribution of Vertical Organic Composition in Organic Photodetectors by Ultrasonic-Assisted Solvent Vapor Annealing

Regulating the vertical composition distribution of an organic electronic donor and acceptor is an effective strategy for the fabrication of high-performance organic photodetectors (OPDs). In this ...

Self-filtering narrowband high performance organic photodetectors enabled by manipulating localized Frenkel exciton dissociation

The high binding energy and low diffusion length of photogenerated Frenkel excitons have long been viewed as major drawbacks of organic semiconductors. Therefore, bulk heterojunction structure has been widely adopted to assist exciton dissociation in organic photon-electron conversion devices. Here, we demonstrate that these intrinsically “poor” properties of Frenkel excitons, in fact, offer great opportunities to achieve self-filtering narrowband organic photodetectors with the help of a hierarchical device structure to intentionally manipulate the dissociation of Frenkel excitons. With this strategy, filter-free narrowband organic photodetector centered at 860 nm with full-width-at-half-maximum of around 50 nm, peak external quantum efficiency around 65% and peak specific detectivity over 1013 Jones are obtained, which is one the best performed no-gain type narrowband organic photodetectors ever reported and comparable to commercialized silicon photodetectors. This novel device structure along with its design concept may help create low cost and reliable narrowband organic photodetectors for practical applications.

Dark Current Reduction Strategy via a Layer-By-Layer Solution Process for a High-Performance All-Polymer Photodetector.

The ideal bulk-heterojunction for high-performance organic photodetectors prefersa morphology with a vertically gradient component to suppress the leaking current. Here, we demonstrate an all-polymer photodetector with a segregated bulk-heterojunction active layer. This all-polymer photodetector exhibits a dramatically reduced dark current density because of its built-in charge blocking layer, with a responsivity of 0.25 A W-1 at a wavelength ofapproximately 600 nm and specific detectivity of 5.68 × 1012 cm Hz1/2 W-1 as calculated from the noise spectra at 1 kHz. To our knowledge, this is among the bestperformances reported for photodetectors based on both polymeric donor and acceptor in the photoactive layer. These findings present a facile approach to improving the specific detectivity of polymer photodetectors via a layer-by-layer solution process.

High-Performance Organic Photodetectors from a High-Bandgap Indacenodithiophene-Based π-Conjugated Donor–Acceptor Polymer

A conjugated donor-acceptor polymer, poly[4,4,9,9-tetrakis(4-hexylphenyl)-4,9-dihydro- s-indaceno[1,2- b:5,6- b']dithiophene-2,7-diyl- alt-5-(2-ethylhexyl)-4 H-thieno[3,4- c]pyrrole-4,6(5 H)-dione-1,3-diyl] (PIDT-TPD), is blended with the fullerene derivative [6,6]phenyl-C61-butyric acid methyl ester (PC61BM) for the fabrication of thin and solution-processed organic photodetectors (OPDs). Systematic screening of the concentration ratio of the blend and the molecular weight of the polymer is performed to optimize the active layer morphology and the OPD performance. The device comprising a medium molecular weight polymer (27.0 kg/mol) in a PIDT-TPD:PC61BM 1:1 ratio exhibits an external quantum efficiency of 52% at 610 nm, a dark current density of 1 nA/cm2, a detectivity of 1.44 × 1013 Jones, and a maximum 3 dB cutoff frequency of 100 kHz at -5 V bias. These results are remarkable among the state-of-the-art red photodetectors based on conjugated polymers. As such, this work presents a functional organic active material for high-speed OPDs with a linear photoresponse at different light intensities.

Thin film organic photodetectors for indirect X-ray detection demonstrating low dose rate sensitivity at low voltage operation

Developments in the field of organic semiconductors have generated organic photodetectors with high quantum efficiency, wide spectral sensitivity, low power consumption, and unique form factors that are flexible and conformable to their substrate shape. In this work, organic photodetectors coupled with inorganic CsI(Tl) scintillators are used to showcase the low dose rate sensitivity that is enabled when high performance organic photodetectors and scintillator crystals are integrated. The detection capability of these organic-inorganic coupled systems to high energy radiation highlights their potential as an alternative to traditional photomultiplier tubes for nuclear spectroscopy applications. When exposed to Bremsstrahlung radiation produced from an X-ray generator, SubPc:C60, AlPcCl:C70, and P3HT:PC61BM thin film photodetectors with active layer thicknesses less than 100 nm show detection of incident radiation at low and no applied bias. Remarkably low dose rates, down to at least 0.18 μGy/s, were detectable with a characteristic linear relationship between exposure rate and photodetector current output. These devices also demonstrate sensitivities as high as 5.37 mC Gy−1 cm−2 when coupled to CsI(Tl). Additionally, as the tube voltage across the X-ray generator was varied, these organic-inorganic systems showed their ability to detect a range of continuous radiation spectra spanning several hundred keV.

Rigid, Conjugated Macrocycles for High Performance Organic Photodetectors.

Organic photodetectors (OPDs) are attractive for their high optical absorption coefficient, broad wavelength tunability, and compatibility with lightweight and flexible devices. Here we describe a new molecular design that enables high performance organic photodetectors. We use a rigid, conjugated macrocycle as the electron acceptor in devices to obtain high photocurrent and low dark current. We make a direct comparison between the devices made with the macrocyclic acceptor and an acyclic control molecule; we find that the superior performance of the macrocycle originates from its rigid, conjugated, and cyclic structure. The macrocycle's rigid structure reduces the number of charged defects originating from deformed sp2 carbons and covalent defects from photo/thermoactivation. With this molecular design, we are able to suppress dark current density while retaining high responsivity in an ultrasensitive nonfullerene OPD. Importantly, we achieve a detectivity of ∼1014 Jones at near zero bias voltage. This is without the need for extra carrier blocking layers commonly employed in fullerene-based devices. Our devices are comparable to the best fullerene-based photodetectors, and the sensitivity at low working voltages (<0.1 V) is a record for nonfullerene OPDs.