An efficient perovkite light-emitting diode (PeLED) is fabricated by incorporating 1,3,5-tri (m-pyrid-3-yl-phenyl)benzene (TmPyPB) between the emitting layer (EML) and the electron transporting layer (ETL), where TmPyPB plays an indispensable blocking effect on both excitons and holes. It shows a maximum current efficiency of 9.37 cd/A, and the corresponding external quantum efficiency (EQE) of 2.42% with a saturated green color Commission International de I'Eclairage (CIE1993) coordinated of (0.1279, 0.7951) under a driving voltage of 6 V. Meanwhile, the operational lifetime of the TmPyPB-based PeLED is improved to about 2.6-fold to that of the one with only the traditional ETL of aluminum 8-hydroxyquinolinate (Alq 3 ). The enhancements of electroluminescence (EL) performance are mainly attributed to better confinement of both the holes and the excitons in the EML, and more balanced carrier transportation in the TmPyPB-based PeLED. This work offers a feasible strategy to develop high performance optoelectronic devices.
Yongfang Yuan,Xiaowen Zhang,Dongliang Li,Xiuyun Zhang,Lihui Wang,Zongliu Lu,Liming Liu,Feng Chi
Hole injection governs the efficiency of ultraviolet organic light-emitting diodes (UV OLEDs) due to the deep highest occupied molecular orbital level of the emissive molecule. Tungsten oxides (WOx), transition metal oxides with high work functions and good stability, cast light on solving this problem. By a low-cost, scalable and high-throughput manufacturing process, herein the facile synthesis of a WOx solution and its doping in poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS + WOx) is systematically investigated for assembling efficient UV OLEDs. X-ray diffraction, atomic force microscopy, scanning electron microscopy and X-ray photoelectron spectroscopy measurements confirm that WOx and PEDOT:PSS + WOx have good film morphology and exceptional electronic properties, such as the oxygen deficiency dominated non-stoichiometry of WOx. With PEDOT:PSS + WOx tailoring hole injection and 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole as the emitter, the UV OLEDs show outstanding electro-optic performance, with a radiance of 3.98 mW cm−2, external quantum efficiency of 2.30%, electroluminescence peak at 400 nm and full width at half maximum of 47 nm, which is superior to the performance of the corresponding reference materials. The mechanism of charge transfer from the PEDOT polycation to WOx, enhancing conductivity, is responsible for the robust hole injection/transport and is further elucidated by ultraviolet photoelectron spectroscopy and impedance spectroscopy, contributing to the optimization of the carrier balance and recombination zone. Our results illustrate an alternative approach for boosting UV OLED performance and advancing organic electronics.
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