Exciplexes formed by intermolecular charge transfer between electron-donating and electron-accepting molecules have attracted much attention because of their triplet harvesting characteristics for highly efficient OLEDs. Similar to thermally activated delayed fluorescence (TADF), exciplex exhibit an extremely small singlet-triplet energy splitting, and allow upconversion from triplet states to singlet states. Here, we will show our recent results on high performance OLEDs based on exciplex hosts and emitters.
Phosphorescent white OLEDs with simple structure were successfully fabricated by doping a blue emitter in the exciplex host and then inserting an ultrathin nondoped orange layer within the blue emissive zone. By optimizing the location of the orange emitter, a high power efficiency of 75.3 lm/W was achieved in the phosphorescent white OLED with reduced efficiency roll-off.
Hybrid white OLEDs were fabricated by using exciplex as both of the blue fluorescent emitter and the host for phosphorescent emitters. An exciplex-sandwich emissive architecture was designed to precisely manipulate the exciton allocation. And a high external quantum efficiency of 28.3% and a high power efficiency of 102.9 lm/W were realized in the hybrid white OLEDs, which remain as high as 25.8% and 63.5 lm/W at 1000 cd/m2.
Most recently, we proposed a method by exciplex engineering to fabricate fluorescent OLEDs with high efficiency and low efficiency roll-off, which could open a useful avenue to design all-fluorescent white OLEDs without TADF emitters for high performance lighting.
We report the fabrication of high performance inverted polymer solar cells with simply modified indium tin oxide (ITO) by an ultrathin aluminum (Al) and sodium chloride (NaCl) composite layer. The device efficiency and stability were both improved. The optimized device with poly(3-hexylthiophene) as the donor and [6,6]-phenyl-C61-butyric acid methylester as the acceptor under AM 1.5 (100 mw cm−2) radiation achieved a high power conversion efficiency of 3.88% with an open-circuit voltage of 0.60 V and a fill factor of 0.61, which is significantly higher than those of the inverted devices with only Al or NaCl as modification interlayer, respectively. Moreover, the stability is enhanced by about 70% more than that of the conventional device. The significant enhancement is attributed to the reduced work function of ITO electrode from 4.75 to 3.90 eV by modification as well as the improvement of the electrode interface.
Organic light-emitting diodes (OLEDs) have drawn increasing attention as the next generation displays and lighting sources. High efficiency and long lifetime are necessary for OLEDs in practical applications. In conventional OLEDs, the charge carriers are directly injected into the organic transport layers from electrodes, the injection barriers between the organic transport layers and electrodes are unavoidable due to the mismatch between the work function of metal electrode and the energy level of charge-transport layer, which greatly affects the performance of fabricated OLEDs. Furthermore, tandem OLEDs, which are fabricated by vertically connecting several individual electroluminescent (EL) units together in series via an appropriate charge generation layer (CGL) with the entire device driven by a single power source can significantly enhance current efficiency and stability, but their performance is strongly dependent on the used CGL, especially the power efficiency is difficult to enhance due to the increase of working voltage. Recently we found that organic semiconductor heterojunctions show efficient charge generation effect and as CGL, not only double the luminance and current efficiency, but also greatly improve the power efficiency, which is difficult in tandem OLEDs based on conventional CGLs. We also realized electrode-independent charge injection by using organic semiconductor heterojuncrions as injectors in OLEDs, and obtained comparable electroluminescent (EL) performance with that of conventional OLEDs. Here, we report the results of tandem OLEDs based on organic semiconductor heterojunctions as CGL and OLEDs using organic semiconductor heterojunctions as injectors, and discuss this working mechanism in detail.
Two bisindolylmaleimide derivatives were prepared in good yields, characterized and successfully employed in the fabrication of organic light-emitting-diodes (OLEDs). The absorption spectra and photoluminescence spectra of the compounds in solution and in thin film were also measured and they show larger Stokes shifts (>100nm). With the electroluminescence devices configured as ITO/NPB/dopant:Alq3 /Alq3/LiF/Al, they exhibit yellow (A) and orange (B) color. In particularly, the two devices can be turned on at 5.2 V (device A) and 5.9V (device B), and reached the maximum brightness of 15066 and 8593cd/m2 at 21V, respectively. From the cyclic voltammetry and the onset absorption, the highest occupied molecule orbital (HOMO) and the lowest unoccupied molecule orbital (LUMO) energy levels can be estimated as A (5.3, 2.9eV) and B (5.4, 3.1eV).
Conference Committee Involvement (6)
Organic and Hybrid Light Emitting Materials and Devices XXVI
21 August 2022 | San Diego, California, United States
Organic and Hybrid Light Emitting Materials and Devices XXV
2 August 2021 | San Diego, California, United States
Organic and Hybrid Light Emitting Materials and Devices XXIV
24 August 2020 | Online Only, California, United States
Organic and Hybrid Light Emitting Materials and Devices XXIII
11 August 2019 | San Diego, California, United States
Organic Light Emitting Materials and Devices XXII
19 August 2018 | San Diego, California, United States
Organic Light Emitting Materials and Devices XXI
6 August 2017 | San Diego, California, United States
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