32 research outputs found
Improving the thermal stability of top-emitting organic light-emitting diodes by modification of the anode interface
This research was financially supported by the EPSRC NSF-CBET lead agency agreement (EP/R010595/1, 1706207), the DARPA-NESD program (N66001-17-C-4012) and the Leverhulme Trust (RPG-2017-231). Y.D. acknowledges a stipend from the Chinese Scholarship Council (CSC). C.K. acknowledges support from the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2017R1A6A3A03012331). M.C.G. acknowledges support from the Alexander von Humboldt Stiftung through the Humboldt-Professorship.Topâemitting organic lightâemitting diodes (OLEDs) are of interest for numerous applications, in particular for displays with high fill factors. To maximize efficiency and luminance, molecular pâdoping of the hole transport layer (pâHTL) and a highly reflective anode contact, for example, made from silver, are used. Atomic layer deposition (ALD) is attractive for thin film encapsulation of OLEDs but generally requires a minimum process temperature of 80 °C. Here it is reported that the interface between the pâHTL and the silver anode of topâemitting OLEDs degrades during an 80 °C ALD encapsulation process, causing an over fourfold reduction in OLED current and luminance. To understand the underlying mechanism of device degradation, single charge carrier devices are investigated before and after annealing. A spectroscopic study of pâHTLs indicates that degradation is due to the interaction between diffusing silver ions and the pâtype molecular dopant. To improve the stability of the interface, either an ultrathin MoO3 buffer layer or a bilayer HTL is inserted at the anode/organic interface. Both approaches effectively suppress degradation. This work shows a route to successful encapsulation of topâemitting OLEDs using ALD without sacrificing device performance.Publisher PDFPeer reviewe
High brightness, highly directional organic light-emitting diodes as light sources for future light-amplifying prosthetics in the optogenetic management of vision loss
Funding: Engineering and Physical Sciences Research Council (Grant Number(s): EP/R010595/1). National Science Foundation (Grant Number(s): 1706207). Defense Sciences Office, DARPA (Grant Number(s): N66001-17-C-4012). Leverhulme Trust (Grant Number(s): RPG-2017-231). Alexander von Humboldt-Stiftung (Grant Number(s): Humboldt Professur). National Research Foundation of Korea (GrantNumber(s): 2017R1A6A3A03012331). China Sponsorship Council.Optogenetic control of retinal cells transduced with light-sensitive channelrhodopsins can enable restoration of visual perception in patients with vision loss. However, a light intensity orders of magnitude higher than ambient light conditions is required to achieve robust cell activation. Relatively bulky wearable light amplifiers are currently used to deliver sufficient photon flux (>1016 photons/cm2/s in a ±10° emission cone) at a suitable wavelength (e.g., 600 nm for channelrhodopsin ChrimsonR). Here, ultrahigh brightness organic light-emitting diodes (OLEDs) with highly directional emission are developed, with the ultimate aim of providing high-resolution optogenetic control of thousands of retinal cells in parallel from a compact device. The orange-emitting phosphorescent OLEDs use doped charge transport layers, generate narrowband emission peaking at 600 nm, and achieve a luminance of 684 000 cd mâ2 at 15 V forward bias. In addition, tandem-stack OLEDs with a luminance of 1 152 000 cd mâ2 and doubled quantum efficiency are demonstrated, which greatly reduces electrical and thermal stress in these devices. At the photon flux required to trigger robust neuron firing in genetically modified retinal cells and when using heat sinking and realistic duty cycles (20% at 12.5 Hz), the tandem-stack OLEDs therefore show a greatly improved half-brightness lifetime of 800 h.Publisher PDFPeer reviewe
Internal Architectural Patterns of Bar Fingers Within Digitate Shallow-Water Delta: Insights from the Shallow Core, GPR and Delft3D Simulation Data of the Ganjiang Delta, China
Digitate shallow-water deltas are commonly found in modern lakes and bays, as well as within cratonic petroliferous basins. They develop one or multiple sinuous finger-like sands (i.e., bar fingers), including high-RSI (sinuosity ratio of distributary channel and bar finger â„1) and low-RSI (RSI 10°) compared with those in the supplying river. This dip angle exhibits a negative relationship with downstream distance and a positive exponential relationship with lateral migration distance. Silty drapes become dense along the migration direction of the distributary channel. The levee develops multiple horizontal muddy accretion beds. The high-RSI bar finger develops a large number (>3) of accretion beds in mouth bars with high dip angles, and a large number of accretion beds in thick levees, compared with the low-RSI bar finger. The results of this paper provide insights into the prediction and development of cratonic digitate shallow-water delta reservoirs
Photostimulation for in vitro optogenetics with high power blue organic light-emitting diodes
Funding: Leverhulme Trust (RPG-2017-231), the EPSRC NSF-CBET lead agency agreement (EP/R010595/1, 1706207), the DARPA NESD programme (N66001-17-C-4012) and the RS Macdonald Charitable Trust. C.M. acknowledges funding by the European Commission through a Marie Sklodowska-Curie Individual Fellowship (703387). Y. L. Deng acknowledges support from the Chinese Scholarship Council (CSC).Optogenetics, photostimulation of neural tissues rendered sensitive to light, is widely used in neuroscience to modulate the electrical excitability of neurons. For effective optical excitation of neurons, light wavelength and power density must fit with the expression levels and biophysical properties of the genetically encoded lightâsensitive ion channels used to confer light sensitivity on cellsâmost commonly, channelrhodopsins (ChRs). As light sources, organic lightâemitting diodes (OLEDs) offer attractive properties for miniaturized implantable devices for in vivo optical stimulation, but they do not yet operate routinely at the optical powers required for optogenetics. Here, OLEDs with doped charge transport layers are demonstrated that deliver blue light with good stability over millions of pulses, at powers sufficient to activate the ChR, CheRiff when expressed in cultured primary neurons, allowing live cell imaging of neural activity with the red genetically encoded calcium indicator, jRCaMP1a. Intracellular calcium responses scale with the radiant flux of OLED emission, when varied through changes in the current density, number of pulses, frequency, and pulse width delivered to the devices. The reported optimization and characterization of highâpower OLEDs are foundational for the development of miniaturized OLEDs with thinâlayer encapsulation on bioimplantable devices to allow singleâcell activation in vivo.Publisher PDFPeer reviewe
Narrowband organic light-emitting diodes for fluorescence microscopy and calcium imaging
Funding: Leverhulme Trust (RPG-2017-231), the EPSRC NSF-CBET lead agency agreement (EP/R010595/1, 1706207), the DARPA NESD program (N66001-17-C-4012) and the RS Macdonald Charitable Trust. C.M. acknowledges funding from the European Commission through a Marie SkĆodowska Curie individual fellowship (703387). A.M. acknowledges funding through an individual fellowship of the Deutsche Forschungsgemeinschaft (404587082). Y.D. acknowledges support from the Chinese Scholarship Council (CSC). L.T. acknowledges studentship funding through the EPSRC CM-CDT (EP/L015110/1). M.S. acknowledges funding by the Royal Society (Dorothy Hodgkin Fellowship, DH160102).Fluorescence imaging is an indispensable tool in biology, with applications ranging from singleâcell to wholeâanimal studies and with live mapping of neuronal activity currently receiving particular attention. To enable fluorescence imaging at cellular scale in freely moving animals, miniaturized microscopes and lensless imagers are developed that can be implanted in a minimally invasive fashion; but the rigidity, size, and potential toxicity of the involved light sources remain a challenge. Here, narrowband organic lightâemitting diodes (OLEDs) are developed and used for fluorescence imaging of live cells and for mapping of neuronal activity in Drosophila melanogaster via genetically encoded Ca2+ indicators. In order to avoid spectral overlap with fluorescence from the sample, distributed Bragg reflectors are integrated onto the OLEDs to block their longâwavelength emission tail, which enables an image contrast comparable to conventional, much bulkier mercury light sources. As OLEDs can be fabricated on mechanically flexible substrates and structured into arrays of cellâsized pixels, this work opens a new pathway for the development of implantable light sources that enable functional imaging and sensing in freely moving animals.PostprintPeer reviewe
Higher fibrinogen and neutrophil-to-lymphocyte ratio are associated with the early poor response to intravenous thrombolysis in acute ischemic stroke
BackgroundInflammation and platelet activation play pivotal roles in acute ischemic stroke (AIS) pathogenesis. Early response to thrombolysis is a vital indicator for the long-term prognosis of AIS. However, the correlation between fibrinogen or the neutrophil-to-lymphocyte ratio (NLR) and the early response to intravenous thrombolysis in patients with AIS remains unclear.MethodsAIS patients undergoing intravenous thrombolysis were enrolled between January 2018 and May 2023. Blood cell counts were sampled before thrombolysis. A good response was defined as a National Institutes of Health Stroke Scale (NIHSS) score decreased â„4 or complete recovery 24 h after thrombolysis treatment. A poor response was defined as any increase in the NIHSS score or a decrease in the NIHSS score <4 at the 24 h after thrombolysis treatment compared with that at admission. Logistic regression analysis was performed to explore the relationship of the fibrinogen level and NLR with a poor thrombolysis response. Receiver operating characteristic (ROC) analysis was used to assess the ability of the fibrinogen level and NLR to discriminate poor responders.ResultsAmong 700 recruited patients, 268 (38.29%) were diagnosed with a good response, and 432 (61.71%) were diagnosed with a poor response to intravenous thrombolysis. A binary logistic regression model indicated that an elevated fibrinogen level (odds ratio [OR], 1.693; 95% confidence interval [CI] 1.325â2.122, P < 0.001) and NLR (OR, 1.253; 95% CI, 1.210â2.005, P = 0.001) were independent factors for a poor response. The area under the curve (AUC) values for the fibrinogen level, NLR and fibrinogen level combined with the NLR for a poor response were 0.708, 0.605, and 0.728, respectively.ConclusionsOur research indicates that the levels of fibrinogen and NLR at admission can be used as a prognostic factor to predict early poor response to intravenous thrombolysis
Development of very high luminance pâiân junction-based blue fluorescent organic light-emitting diodes
This research was financially supported by the EPSRC NSFâCBET lead agency agreement (EP/R010595/1, 1706207), the DARPAâNESD programme (N66001â17âCâ4012), and the Leverhulme Trust (RPGâ2017â231). Y.L.D. acknowledges a stipend from the Chinese Scholarship Council (CSC). C.M. acknowledges funding by the European Commission through a Marie SkĆodowska Curie Individual Fellowship (703387). C.K. acknowledges support from the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2017R1A6A3A03012331).Organic lightâemitting diodes (OLEDs) can emit light over much larger areas than their inorganic counterparts, offer mechanical flexibility, and can be readily integrated on various substrates and backplanes. However, the amount of light they emit per unit area is typically lower and the required operating voltage is higher, which can be a limitation for emerging applications of OLEDs, e.g., in outdoor and highâdynamicârange displays, biomedical devices, or visibleâlight communication. Here, highâluminance, blueâemitting (λpeak = 464 nm), fluorescent pâiân OLEDs are developed by combining three strategies: First, the thickness of the intrinsic layers in the device is decreased to reduce internal voltage loss. Second, different electronâblocking layer materials are tested to recover efficiency losses resulting from this thickness reduction. Third, the geometry of the anode contact is optimized, which leads to a substantial reduction in the inâplane resistive voltage losses. The OLEDs retain a maximum external quantum efficiency of 4.4% as expected for an optimized fluorescent device and reach a luminance of 132 000 cd mâ2 and an optical power density of 2.4 mW mmâ2 at 5 V, a nearly eightfold improvement compared to the original reference device.PostprintPeer reviewe
Improving the thermal stability of top-emitting organic light-emitting diodes by modification of the anode interface
Topâemitting organic lightâemitting diodes (OLEDs) are of interest for numerous applications, in particular for displays with high fill factors. To maximize efficiency and luminance, molecular pâdoping of the hole transport layer (pâHTL) and a highly reflective anode contact, for example, made from silver, are used. Atomic layer deposition (ALD) is attractive for thin film encapsulation of OLEDs but generally requires a minimum process temperature of 80 °C. Here it is reported that the interface between the pâHTL and the silver anode of topâemitting OLEDs degrades during an 80 °C ALD encapsulation process, causing an over fourfold reduction in OLED current and luminance. To understand the underlying mechanism of device degradation, single charge carrier devices are investigated before and after annealing. A spectroscopic study of pâHTLs indicates that degradation is due to the interaction between diffusing silver ions and the pâtype molecular dopant. To improve the stability of the interface, either an ultrathin MoO3 buffer layer or a bilayer HTL is inserted at the anode/organic interface. Both approaches effectively suppress degradation. This work shows a route to successful encapsulation of topâemitting OLEDs using ALD without sacrificing device performance
Improving the Thermal Stability of Top-Emitting Organic Light-Emitting Diodes by Modification of the Anode Interface
Top-emitting organic light-emitting diodes (OLEDs) are of interest for numerous applications, in particular for displays with high fill factors. To maximize efficiency and luminance, molecular p-doping of the hole transport layer (p-HTL) and a highly reflective anode contact, for example, made from silver, are used. Atomic layer deposition (ALD) is attractive for thin film encapsulation of OLEDs but generally requires a minimum process temperature of 80 degrees C. Here it is reported that the interface between the p-HTL and the silver anode of top-emitting OLEDs degrades during an 80 degrees C ALD encapsulation process, causing an over fourfold reduction in OLED current and luminance. To understand the underlying mechanism of device degradation, single charge carrier devices are investigated before and after annealing. A spectroscopic study of p-HTLs indicates that degradation is due to the interaction between diffusing silver ions and the p-type molecular dopant. To improve the stability of the interface, either an ultrathin MoO3 buffer layer or a bilayer HTL is inserted at the anode/organic interface. Both approaches effectively suppress degradation. This work shows a route to successful encapsulation of top-emitting OLEDs using ALD without sacrificing device performance
Unusual spectroscopic properties of PPE/TiO2 composite and its sensor response to TNT
A composite from a broad bandgap polymer, poly(phenylene ethylene) (PPE), and nano-sized TiO2 particles was found to be able to sense 2,4,6-trinitrotoluene (TNT) for TNT sensor. Fluorescence quenching induced by charge transfer from PPE to nano-sized TiO2 was observed in toluene solution. At high TiO2 composition, a strong exciplex band occurred at 550 nm. Under prolonged light irradiation at 400 nm, unusual fluorescence gains took place at 460 nm, companied with a very small change in the UV–vis absorbance. After 30 min light irradiation, the fluorescence at 460 nm reached a maximum, but the peak at 550 nm disappeared. This composite showed amplified sensor response to TNT compared to the pristine PPE film, which can be potentially used as sensing material for detecting TNT based explosives.<br /