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Upon optimizing the periodic structures for blue, green and red OLEDs, we fabricate white OLEDs on a corrugated ITO substrate prepared from a specific mixing ratio of PS spheres in different sizes. Eventually, white OLEDs show a significant enhancement in current and power efficiencies. The CIE coordinates are located in a warm white light region even at different viewing angles. [ABSTRACT FROM AUTHOR]

Inter-molecular charge transfer-based donor–acceptor combination – with type-II energy transfer and known as an exciplex – has been extensively studied as a host for organic light-emitting diodes (OLEDs) due to the benefit of high efficiency. However, the broad spectral emission and full width at half maximum (FWHM) of the resulting electroluminescence lead to poor color purity, limiting their potential use in flat panel displays. We here propose a combination strategy that unites an exciplex host and a micro-cavity to resolve the color purity issue. The proposed strategy enables OLEDs to exhibit 2-fold narrower FWHM (26 nm vs. 71 nm) and a record current efficiency (CE) of 180.2 cd A−1 (CE remains 167 cd A−1 at 1000 cd m−2) without any external light-extraction techniques. This work offers a new strategy to achieve high efficiency and high color-purity OLEDs simultaneously. [ABSTRACT FROM AUTHOR]

Trapped light in an organic light-emitting diode (OLED) can be extracted through the construction of periodic structures on the substrates. However, these periodic structures can merely enhance the light emission of a specific wavelength, but not the white light for lighting application. In this work, indium tin oxide (ITO) with a corrugated structure is prepared by reactive ion etching of a polystyrene (PS) sphere matrix with diameters of 300 and 350 nm, which can apparently reduce the losses produced by the waveguide mode and surface plasmon polariton (SPP) mode in the RGB-based white OLED. The extractions of the waveguide mode and SPP mode are investigated theoretically and experimentally. This special corrugated ITO structure with the pitches of 300 and 350 nm, as an internal light out-coupling structure, is useful for the extraction of bluish green and red emission, respectively. More importantly, there are significant enhancements in both the current and power efficiencies of white OLEDs, and the CIE coordinates are located in the warm white region with different viewing angles. Using different weight ratios of the mixed PS spheres, the electroluminescent spectra of white OLEDs can be easily adjusted. [ABSTRACT FROM AUTHOR]

Ideal microlens array (IMLA) based on polystyrene (PS) microspheres with small diameters has been introduced to the surface of indium tin-oxide (ITO) glass substrates to enhance the out-coupling efficiency of organic light-emitting diode (OLED) devices. IMLA was fabricated by a replica molding process using annealed closely packed PS spheres as the template. IMLA is used to extract the waveguide mode which is limited in glass substrate. Experiment results show that the best performance of OLED devices is achieved when the diameter of IMLA is about 6 μm. The enhancement of current efficiency, power efficiency and EQE of green-emitting OLED devices with IMLA with a diameter of 6 μm is 56.4%, 63.5% and 58.8%, respectively, relative to devices without any light out-coupling structures in the forward direction. In addition, we also demonstrate that the IMLA with a diameter of 6 μm can also be applied for the extraction of red, blue and white light. Furthermore, the use of IMLA is not detrimental to the electrical and optical performance of the OLED devices. Image 1 • Small-diameter ideal microlens array (IMLA) was achieved by using annealed packed PS spheres as the template. • IMLA used as the out-coupling structure is not detrimental to the electrical and optical performance of the OLEDs. • The green OLED with IMLA which has a diameter of 6 µm has the best performance: 108.1 cd/A and 99.6 lm/W. • In addition, IMLA with a diameter of 6 μm can also be applied for the extraction of red, blue and white light. [ABSTRACT FROM AUTHOR]

Nano-modified indium tin-oxide (ITO) glass substrates are fabricated for an internal light-extraction structure to enhance the out-coupling efficiency of green organic light-emitting diode (OLED) devices. This nano-modified anode with low haze was prepared by wet chemical etching. Polystyrene (PS) hemispheres, which were distributed randomly on the ITO anode surface, were used as the etching mold. With the help of nano-modified ITO glass substrate, the light trapped by the internal waveguide mode can be extracted effectively compared with conventional planar OLED devices. When OLED devices are incorporated with a nano-modified ITO anode, the highest enhancements of current efficiency (CE), power efficiency (PE) and external quantum efficiency (EQE) are about 40.7%, 37.1% and 36.9%, respectively, relative to a standard device without any light out-coupling structure in the forward direction. To further improve the performance of OLED devices, an ideal microlens array (IMLA) is introduced to the air-side of the glass substrate to extract substrate waveguide. With both internal and external out-coupling structures, the CE, PE and EQE of OLED devices are enhanced by 101.5%, 100% and 96%, reaching 119.3 cd A−1, 108.8 lm W−1 and 31.4% in the forward direction, respectively. Moreover, the nano-modified ITO anode with low haze has no detrimental effect on the performance of OLED devices and is suitable for lighting and display application. [ABSTRACT FROM AUTHOR]

Abstract To realize energy-saving and environmental green illumination by simplified white organic light-emitting devices (WOLEDs) structure and fabricate process, herein, we successfully fabricate a novel simplified efficient WOLED structure using energy transfer from interface exciplexes to complementary color dyes as undoped ultrathin emissive layers (UEMLs) based on tandem OLEDs structure. (Acetylacetonato)bis[2-(thieno[3,2- c ]pyridin-4-yl)phenyl]iridium(III) (PO-01) and iridium(III) bis[(4,6-difluorophenyl)-pyridinato- N ,C2′]-picolinate (FIrpic) are applied as yellow and blue UEMLs, respectively. Particularly, the designed WOLED with Commission Internationale De L'Eclairage chromaticity coordinate (0.36, 0.41) obtaining a peak of 41.5 cd/A (EQE = 18.59%) without light out-coupling technology, achieving high current efficiency among reported WOLEDs all emitters applied UEMLs. Moreover, the designed white OLEDs generally emit warm white spectrum with low correlative color temperature of 3686 K–4700 K, which show are available for healthy illumination. Therefore, we believe our work help to further develop ideal simplified WOLEDs structure and fabricate process for energy-conservation and environment-friendly healthy illumination with high efficiency, simplified fabrication, low reagent consumption and cost, simultaneously. Graphical abstract Image 1 Highlights • Highly simplified efficient tandems WOLEDs using energy transfer from interface exciplexes are successfully fabricated. • High current efficiency of 41.5 cd/A (EQE = 18.59%) is achieved among reported WOLEDs all emitters applied undoped UEMLs. • The WOLEDs generally emit warm white spectrum with low CCT of 3686 K–4700 K, which are available for healthy illumination. [ABSTRACT FROM AUTHOR]

Herein, we show a kind of novel tandem white OLED (WOLED) with interface exciplex, which obtaining a high current efficiency of 40.53 cd/A (EQE=18.15%) without light out‐coupling technology. The WOLEDs generally show simpler device structure and lower working voltage. Moreover, the designed WOELDs generally emit warm white spectrum with low correlative color temperature of 3701K~4699K. [ABSTRACT FROM AUTHOR]

Herein we report a novel design philosophy of tandem OLEDs incorporating a doping-free green phosphorescent bis[2-(2-pyridinyl-N)phenyl-C](acetylacetonato)iridium(III) (Ir(ppy) 2 (acac)) as an ultrathin emissive layer (UEML) into a novel interface-exciplex-forming structure of 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) and 1,3,5-tri(p-pyrid-3-yl-phenyl)benzene (TmPyPB). Particularly, relatively low working voltage and remarkable efficiency are achieved and the designed tandem OLEDs exhibit a peak current efficiency of 135.74 cd/A (EQE = 36.85%) which is two times higher than 66.2 cd/A (EQE = 17.97%) of the device with a single emitter unit. This might be one of the highest efficiencies of OLEDs applying ultrathin emitters without light extraction. Moreover, with the proposed structure, the color gamut of the displays can be effectively increased from 76% to 82% NTSC if the same red and blue emissions as those in the NTSC are applied. A novel form of harmonious fusion among interface exciplex, UEML, and tandem structure is successfully realized, which sheds light on further development of ideal OLED structure with high efficiency, simplified fabrication, low power consumption, low cost, and improved color gamut, simultaneously.