Area Of Light-emitting Diodes Research Articles

Tuning hole transport layers and optimizing perovskite films thickness for high efficiency CsPbBr3 nanocrystals electroluminescence light-emitting diodes

Metal halide perovskite nanocrystals (NCs) have sparked considerable attentions in the area of light-emitting diodes (LED) by virtue of their remarkable color purity and spectral tunability (400–700 nm). However, the optoelectronic performance of LED devices based on perovskite NCs is severely limited by the problem of charge injection since (i) the charge injection layers exhibit significant differences in energy levels and charge mobility, (ii) one thick NCs emitting layer can obstruct the electrons transmission and one thin NCs emitting layer can change the charge recombination region, inducing series of troubles in fabrication and application of LED devices. Herein, a series of LED devices based on cesium lead bromide (CsPbBr3) green-emitting perovskite NCs are reported by adopting Poly-N-vinylcarbazole (PVK)/Poly [9,9-dioctylfluoreneco-N-[4-(3-methylpropyl)]diphenylamine] (TFB) and Poly[bis(4-phenyl) (2,4,6-trimethylphenyl)amine] (PTAA) as the hole transport layer (HTL) materials. With the increase of applied voltage, the CsPbBr3 NCs LED device with PTAA as HTL displays better transport characteristics, such as a lower turn-on voltage and a higher luminance, than that of the device with TFB and PVK as HTL. By optimizing the spin-coating craft parameter of the CsPbBr3 NCs layer, an efficient green-emitting CsPbBr3 NCs LED device with maximum luminance of 4531 cd m−2, current efficiency of 14.4 cd A−1, power efficiency of 14.1 lm W−1 and maximum external quantum efficiency of 4.28% was obtained. These results provide an approach for the practical applications of CsPbBr3 NCs electroluminescence LED devices.

Improved Target Signal Source Tracking and Extraction Method Based on Outdoor Visible Light Communication Using an Improved Particle Filter Algorithm Based on Cam-Shift Algorithm

An improved particle filter algorithm based on Cam-Shift algorithm applied to outdoor visible light communication (outdoor-VLC) is presented in this paper. In the outdoor-VLC system, accurately and completely tracking and extracting the target signal source Light Emitting Diode (LED) area is the premise for realizing communication. However, few existing studies pay attention to it. In the dynamic outdoor environment, there will be a lot of different environmental interferences (such as background interference, similar object interference, etc.), which greatly increases the difficulty of tracking and extracting the target signal source LED area. Therefore, in this paper, an improved tracking algorithm is proposed to solve the problem of how to track and extract the target signal source LED area accurately, stably and in real time in the outdoor-VLC system under various environmental interferences, so as to increase the feasibility of practical application of VLC system in outdoor scenes. This improved algorithm combines the particle filter algorithm and Cam-Shift algorithm originally. Experimental results show that the proposed algorithm has good accuracy, robustness and real-time performance under the environment of multiple interference factors. Accordingly, the proposed algorithm can be applied to the outdoor-VLC system with various environmental interferences, and can realize the actual first step of communication in VLC system based on image sensor well, laying a foundation for feature extraction, data transmission and other subsequent steps.

Liquid film coating of small molecule OLEDs

Organic small molecules typically deposited by vacuum deposition are a promising material for efficient, low-cost, area light-emitting diodes (OLEDs). In this article we discuss methods to apply these materials by solvent-based large area coating methods. As a basis for the technical description of the coating and wetting process, we present material properties, such as viscosity and surface tension of SMOLED solutions and polar and disperse part for the surface energy of typical substrates or semiconducting organic layers. Whereas SM content has little effect on the ink properties, impurities were identified as an important factor for the wetting behavior. Based on the material properties and coating experiments with SMOLED solutions, the coating methods of blade and slot die coating are discussed with respect to film thickness and stability. We found that the film thickness of knife-coated films does depend on velocity, temperature, provided fluid volume, and composition. Calibration curves for commercial materials (NMP and Spiro-MeOTAD) are given. The stability of slot die coating was lower than expected from literature. However, homogeneous SMOLED layers could be produced by slot die coating at gap-to-film-thickness ratios of up to 50.

Energy production and conversion applications of one-dimensional semiconductor nanostructures

One-dimensional semiconductor nanomaterials form the basis for new technologies as well as driving the evolution of existing ones. Although these various technologies are in different stages of development, from nucleation to pilot production, it is difficult to ignore the tremendous potential they carry, overall, for next-generation concepts. One of the several areas that have been revolutionized by one-dimensional nanostructures, and which could not have happened at a more critical time, is energy. This review outlines the impact that one-dimensional semiconductor materials are having on energy production and conversion technologies. Instead of being extensive, we provide key developments in the areas of light-emitting diodes, solar cells, photoelectrochemistry and fuel cells.

Continuous activation of PpIX by daylight is as effective as and less painful than conventional photodynamic therapy for actinic keratoses; a randomized, controlled, single-blinded study

Photodynamic therapy (PDT) is a highly effective treatment for actinic keratoses (AK); however, it is time consuming and often painful for the patient. Daylight-PDT would make the treatment independent of the clinic and less painful due to the continuous activation of small amounts of porphyrins during its formation. The objective of this randomized controlled study was to compare response rates and adverse effects after methyl aminolevulinate (MAL)-PDT using conventional red light-emitting diode (LED) light vs. daylight. Twenty-nine patients with AK of the face and scalp were treated with MAL-PDT in two symmetrical areas. One area was illuminated by red LED light (37 J cm(-2)) after 3-h incubation with MAL under occlusive dressing. The other area was treated with daylight for 2.5 h after the MAL cream had been under occlusion for half an hour. We found no significant difference in the treatment effect between the two treatments (P = 0.13), with a reduction of AK lesions of 79% in the daylight area compared with 71% in the LED area. Treatment response in the daylight area did not depend on the intensity of the daylight. Illumination with LED was more painful than daylight (P < 0.0001). Erythema and crusting occurred after both treatments and were similar in the two areas. PDT of AK by continuous activation of porphyrins by daylight proved to be as effective as conventional PDT. PDT using daylight activation will make the treatment of these extremely common premalignant tumours more time and cost effective, and more convenient for the patient.