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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]

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]