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Enhancing Light Outcoupling in OLEDs by Integration of Scattering Electrodes
摘要： Limited outcoupling efficiencies are still a big problem in organic light-emitting devices (OLEDs). In this contribution, a simple and general approach for enhancing the outcoupling efficiency of OLEDs is presented: by using a three-step process including electro-spray deposition of a sacrificial material (step i), thin metal-layer deposition (step ii), and elution of the sacrificial material (step iii), scattering metal structures can be fabricated that can be used in cavity OLEDs. The integration into green-emitting vacuum-processed OLEDs yields in an increased luminous efficiency and EQE by 30% and 27%, respectively.
关键词： OLED,Electrospray Deposition,Organic Electronics,Light Outcoupling
更新于2025-11-14 15:25:21
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Mobility Evaluation of BTBT Derivatives: Limitation and Impact on Charge Transport
摘要： Amongst contemporary semiconductors many of the best performing materials are based on [1]benzothieno[3,2-b][1]benzothiophene (BTBT). Alkylated derivatives of these small molecules not only provide high hole mobilities but can also be easily processed by thermal vacuum or solution deposition methods. Over the last decade numerous publications have been investigating molecular structures and charge transport properties to elucidate what makes these molecules so special. However, the race towards ever higher mobilities resulted in significantly deviating values, which exacerbates linking molecular structure to electronic properties. Moreover, a recently arisen debate on overestimation of organic field-effect transistor mobilities calls for a revaluation of these numbers. We synthesised and characterised four BTBT derivatives with either one or two alkyl chains (themselves consisting of either eight or ten carbon atoms), and investigated their spectroscopic, structural and electrical properties. By employing two probes, gated 4-point probe and gated van der Pauw measurements, we compare field effect mobility values at room and low temperatures, and discuss their feasibility and viability. We attribute mobility changes to different angles between molecule planes and core-to-core double layer stacking of asymmetric BTBT derivatives and show higher mobilities in the presence of more and longer alkyl chains. A so called “zipper effect” brings BTBT cores in closer proximity promoting stronger intermolecular orbital coupling and hence higher charge transport.
关键词： charge transport,mobility,BTBT,organic electronics,organic transistors
更新于2025-10-23 16:08:52
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Spatially Uniform Shallow Trap Distribution in an Ultrathin Organic Transistor
摘要： In organic electronic materials, charge carrier transport is often limited by disorder-induced trap states very close in energy to the ideal band transport states. We directly view the location and impact of these 'shallow' traps on an ultrathin transistor active layer using Kelvin Probe Force Microscopy. As the transistor turns on, dramatic fluctuations in the surface potential of the active channel suddenly arise due to charge trapping and release processes. Importantly, the spatial distribution of rapid fluctuations in surface potential is uniform throughout the active channel. These facts strongly constrain the microscopic origin of shallow charge traps, and associated efforts to optimize the mobility and noise performance baseline in device applications.
关键词： disorder,charge traps,electrical noise,organic electronics
更新于2025-09-23 15:23:52
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[IEEE 2018 International Flexible Electronics Technology Conference (IFETC) - Ottawa, ON, Canada (2018.8.7-2018.8.9)] 2018 International Flexible Electronics Technology Conference (IFETC) - Flexible Printed Organic Thin-Film Transistor Devices and Integrated Circuit Applications
摘要： The latest developments in flexible and printed electronics technology based on organic thin-film transistor (OTFT) devices as well as printable electronic materials are briefly reported on in this paper. The successful fabrication and operation of printed OTFT devices and a variety of integrated circuit applications such as flip-flop logic gates and operational amplifiers will be demonstrated.
关键词： Organic electronics,Flexible electronics,Organic thin-film transistor,Printed electronics
更新于2025-09-23 15:22:29
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Tuning Contact Resistance in Top-Contact <i>p</i> -Type and <i>n</i> -Type Organic Field Effect Transistors by Self-Generated Interlayers
摘要： Contact resistance significantly limits the performance of organic field-effect transistors (OFETs). Positioning interlayers at the metal/organic interface can tune the effective work-function and reduce contact resistance. Myriad techniques offer interlayer processing onto the metal pads in bottom-contact OFETs. However, most methods are not suitable for deposition on organic films and incompatible with top-contact OFET architectures. Here, a simple and versatile methodology is demonstrated for interlayer processing in both p- and n-type devices that is also suitable for top-contact OFETs. In this approach, judiciously selected interlayer molecules are co-deposited as additives in the semiconducting polymer active layer. During top contact deposition, the additive molecules migrate from within the bulk film to the organic/metal interface due to additive-metal interactions. Migration continues until a thin continuous interlayer is completed. Formation of the interlayer is confirmed by X-ray photoelectron spectroscopy (XPS) and cross-section scanning transmission electron microscopy (STEM), and its effect on contact resistance by device measurements and transfer line method (TLM) analysis. It is shown that self-generated interlayers that reduce contact resistance in p-type devices, increase that of n-type devices, and vice versa, confirming the role of additives as interlayer materials that modulate the effective work-function of the organic/metal interface.
关键词： organic electronics,TLM,self-generated interlayers,organic field-effect transistors
更新于2025-09-23 15:22:29
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Polythiophene–PCBM-Based All-Organic Electrochromic Device: Fast and Flexible
摘要： A fast and ?exible all-organic electrochromic device, fabricated using polythiophene and PCBM as active materials and plastic substrate, which shows very good power e?ciency as well, has been reported here. The device shows quanti?able improvement in electrochromic performance using parameters like switching speed, coloration e?ciency, color contrast, and cycle life. Spectroscopic investigations have been carried out using Raman and UV?vis to establish a bias induced redox switching based mechanism for the reported improvement in the performance. The device shows switching between magenta (OFF) and transparent states (ON) with a very small bias of ±1 V, an optical modulation of 50% and an absorbance switching contrast of 91%. An enhanced stability for a duration of longer than 2500 s and 250 cycles has been reported with an ultrafast response of few hundred milliseconds. A very high coloration e?ciency of 321 cm2/C is achieved, making the proposed device one of the best reported P3HT-based electrochromic devices.
关键词： PCBM,electrochromic,polythiophene,?exible devices,organic electronics
更新于2025-09-23 15:22:29
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Bay-Linked Perylenediimides are Two Molecules in One: Insights from Ultrafast Spectroscopy, Temperature Dependence, and Time-Dependent Density Functional Theory Calculations
摘要： Bay-linked di-perylenediimide (di-PDI) molecules are finding increasing use in organic electronics due to their steric hindrance that 'twists' the two monomer units relative to one another, decreasing molecular aggregation. In this paper we explore the electronic spectroscopy and ultrafast dynamics of the singly-linked β-β-S-di-PDI (2,9'-di(undecan-5-yl)-2',9-di(undecan-6-yl)-[5,5'-bianthra[2,1,9-def:6,5,10-d'e'f']diisoquinolin]-1,1',3,3',8,8',10,10'(2H,2'H,9H,9'H)-octaone). Excitation-emission spectroscopy reveals two distinct emitting species, which are further characterized by time-dependent density functional theory (TD-DFT), demonstrating that the bay-linked PDI dimers exist in two geometrical conformations. These conformations are an 'open' geometry, where the two monomer sub-units are oriented nearly at right angles, giving them more J-like coupling, and a 'closed' geometry, in which the two monomer sub-units are nearly π-stacked, resulting in more H-like coupling. Given the extent of through-space and through-bond coupling, however, neither di-PDI conformer can be well-described simply in terms of independently-coupled monomers; instead, a full quantum chemistry description is required to understand the electronic structure of this molecule. Temperature-dependent experiments and the TD-DFT calculations indicate that the 'closed' conformer is ～70 meV more stable than the 'open' conformer, so that both conformers are important to the behavior of the molecule at room temperature and above. We use a combination of steady-state and femtosecond transient absorption and emission spectroscopies to globally fit the multiple electronic transitions underlying the spectra of both the 'closed' and 'open' conformers, which agree well with the TD-DFT calculations. The fact that di-PDI molecules are molecular species that adopt two distinct quasi-independent chemical identities has important ramifications for charge trapping and mobility in the organic electronic devices employing these materials.
关键词： TD-DFT calculations,ultrafast spectroscopy,conformational isomers,organic electronics,Bay-linked perylenediimides
更新于2025-09-23 15:22:29
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A flexible organic reflectance oximeter array
摘要： Transmission-mode pulse oximetry, the optical method for determining oxygen saturation in blood, is limited to only tissues that can be transilluminated, such as the earlobes and the fingers. The existing sensor configuration provides only single-point measurements, lacking 2D oxygenation mapping capability. Here, we demonstrate a flexible and printed sensor array composed of organic light-emitting diodes and organic photodiodes, which senses reflected light from tissue to determine the oxygen saturation. We use the reflectance oximeter array beyond the conventional sensing locations. The sensor is implemented to measure oxygen saturation on the forehead with 1.1% mean error and to create 2D oxygenation maps of adult forearms under pressure-cuff–induced ischemia. In addition, we present mathematical models to determine oxygenation in the presence and absence of a pulsatile arterial blood signal. The mechanical flexibility, 2D oxygenation mapping capability, and the ability to place the sensor in various locations make the reflectance oximeter array promising for medical sensing applications such as monitoring of real-time chronic medical conditions as well as postsurgery recovery management of tissues, organs, and wounds.
关键词： flexible electronics,wearable sensors,oximetry,organic electronics,bioelectronics
更新于2025-09-23 15:21:21
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Growth mechanisms of F4-TCNQ on inorganic substrates and nanostructures
摘要： The organic semiconductor tetrafluorotetracyanoquinodimethane (F4-TCNQ) is a promising candidate for the doping of organic semiconductors, two-dimensional materials and inorganic compounds, such as ZnO, and also to enhance the charge carrier injection at contacts in organic electronics. In order to evaluate its applicability as a functionalization material or as an electrically active part in devices, we present a systematic study on the growth mode of F4-TCNQ beyond the first few monolayers on different inorganic substrates that cover a broad variety regarding their physical, chemical and morphological surface properties. The materials used are silicon, silicon carbide, graphene on silicon, sapphire, nanocrystalline diamond, as well as gallium nitride (GaN) layers and nanowire arrays. While the surface termination influences the shape and morphology of the islands of F4-TCNQ which form on all substrates investigated, no significant dependence of the growth mode on the substrate doping type and concentration is observed. GaN nanowires are found to act as nucleation sites for F4-TCNQ islands and to be covered by few monolayers of F4-TCNQ forming a closed coaxial shell. In conclusion, F4-TCNQ is identified to nucleate via Stranski-Krastanov growth consisting of monolayers and islands of different size and shape. The findings in this work provide basic growth information for the implementation of F4-TCNQ as functionalization material for nanowire-based applications.
关键词： GaN nanowires,surface functionalization,growth mode,organic semiconductors,organic electronics,surface doping,F4-TCNQ
更新于2025-09-23 15:21:01
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[SpringerBriefs in Applied Sciences and Technology] Air-Stable Inverted Organic Light-Emitting Diodes ||
摘要： We introduce the importance of air stability on the basis of the principles and the history of organic light-emitting diodes (OLEDs), and the way of realising air-stable OLEDs finally. OLEDs are current-driven self-emitting devices that, in principle, have the features of lightness and thinness. Therefore OLEDs are expected to have unprecedented flexibility. However, it is difficult to achieve air stability in OLEDs, which is the key property for the realisation of flexible devices, because it has been essential to use air-active materials in consideration of the operational mechanism.
关键词： organic electronics,air stability,OLEDs,encapsulation,flexibility
更新于2025-09-23 15:21:01