Abstract
Although organic light emitting diodes (OLEDs) can find important applications in display-related fields, it still remains a challenge to fabricate high-efficiency ultraviolet (UV) OLEDs with tunable wavelength. In this work, we demonstrate a facile method to adjust the electroluminescence (EL) peak from an inverted UV-OLED device that has zinc oxide nanowires (ZnO NWs) as an electron injection layer. The organic–inorganic interface between ZnO NWs and the 3-(4-biphenyl)-4-phenyl-5-tert-butylphenyl-1,2,4-triazole (TAZ) emission layer employed in this work allows a reduction of the diffusion length of excitons, which further results in a hampered relaxation process of higher energy states as well as a blue shift of the EL spectrum. As a result, the emission peaks of the UV-OLED can be easily adjusted from 383 nm to 374 nm by tuning both the length of the ZnO NWs and the thickness of the TAZ emission layer. Our work reveals an important correlation between emission peaks and exciton diffusion, and presents a novel approach to fabricate high-performance UV-OLEDs with the capability of facilely modifying the emission wavelength.
Highlights
IntroductionZinc oxide (ZnO) NWs have been well known for their properties of lower temperature sensitivity and enhanced con nement of charge carriers in one dimensional nanostructures,[21,22,23,24] which enables the material to be implemented in optoelectronics and energy harvesting.[25,26,27,28] A plethora of efforts have been dedicated to the reduction of the electroluminescence (EL) wavelength from zinc oxide nanowires (ZnO NWs) based organic light emitting diodes (OLEDs)
Organic light emitting diodes (OLEDs) have been extensively studied for their various advantages such as solution-processability, cost-effectiveness, and room temperature processing.[1,2,3,4,5,6] In particular, due to their capability of emitting high-energy ultraviolet (UV) light, high-efficiency UVOLEDs demonstrate great signi cance for IT storage, photocuring, aerospace, medical and military applications.[7,8] In addition, UV-organic light emitting diodes (OLEDs) can be potentially implemented in RGB screens
We report the fabrication of an inverted UVOLED device with vertically-aligned, self-assembled zinc oxide nanowires (ZnO NWs) employed as an electron transport layer
Summary
Zinc oxide (ZnO) NWs have been well known for their properties of lower temperature sensitivity and enhanced con nement of charge carriers in one dimensional nanostructures,[21,22,23,24] which enables the material to be implemented in optoelectronics and energy harvesting.[25,26,27,28] A plethora of efforts have been dedicated to the reduction of the electroluminescence (EL) wavelength from ZnO NWs based OLEDs. We report the fabrication of an inverted UVOLED device with vertically-aligned, self-assembled ZnO NWs employed as an electron transport layer. A erwards, molybdenum oxide (MoO3) and aluminum (Al) materials were sequentially deposited via thermal evaporation at a pressure of 4 Â 10À4 Pa. The evaporation rate is 0.2–0.4 A sÀ1 for MoO3, and 5 A sÀ1 for Al. The as-fabricated UV-OLED device exhibits an inverted structure of ITO (100 nm)/ZnO NWs/PEI (4 nm)/TAZ (15 nm)/CBP (20 nm)/MoO3 (5 nm)/Al (100 nm), as shown in the schematic of Fig. 2(a). A 10 nm ZnO seed layer was sputtered onto the pre-cleaned ITO glass followed by growing ZnO NWs using a hydrothermal method.[33,34,35] The polyethylenimine (PEI) material was spin-coated from a 0.4 wt% 2-methoxyethanol solution
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