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MRS Advances © 2019 Materials Research Society DOI: 10.1557/adv.2019.300

Solution Process Feasible Highly Efficient Organic Light Emitting Diode with Hybrid Metal Oxide Based Hole Injection/Transport Layer Mangey Ram Nagar, Rohit Ashok Kumar Yadav, Deepak Kumar Dubey and Jwo-Huei Jou Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan

ABSTRACT

Organic light emitting diodes (OLEDs) have drawn great attention owing to their potential applications in high-quality flat display panels and smart solid-state lighting. Over the last three decades, numerous approaches have been made on material design and device physics to achieve high-efficiency and long-lifespan. Herein, we report a novel tactic to employ solution-processed hybrid metal oxide, molybdenum trioxide-tungsten trioxide (MoO3:WO3), as an efficient and stable hole injection/transport (HIL/HTL) and electron blocking layer for efficient OLEDs. By using phosphorescent orange-red emitter tris(2-phenylquinoline)iridium(III) Ir(2-phq)3, MoO3:WO3 HIL based OLED device exhibits a power efficiency of 27.7 lm W-1 and 22.9 lm W-1 at 100 and 1000 cd m-2, respectively, which are 89% and 157% higher than that of conventional OLED device consisting of poly(3,4ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) as an HIL. Moreover, the resulted device also displays 1.6 times lower turn-on voltage and 3.0 time higher brightness as compare to other counter part. The higher device performances of OLED device may be attributed to robust hole transporting ability, balanced charge carrier in the recombination zone and non-acidic nature of designed HIL. Our results demonstrate that a novel alternative approach based on transition metal oxide hybrid HIL/HTL as a substitute to PEDOT:PSS for high-efficiency solution process OLEDs.

INTRODUCTION Organic light emitting diodes (OLEDs) have become the most promising technology for next-generation high-quality flat-panel display and smart solid-state lighting owing to their amazing features such as low energy consumption, wide-vewing angle, ease scalability, light-weight, viability for flexible and transparent applications,

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roll-to-roll fabrication over large area, and potential to be low-cost [1-3]. Development of energy-efficient OLEDs have attracted enormous attention in the last two decades and become front-line research interest from academia as well as industries [4-5]. Numerous approaches have been reported in material chemistry and device engeenring physics to improve the OLEDs performance. Solution processed OLED devices are believed to have a significant cost advantage over conventional vacuum evaporated devices [6]. The carrier transporting materials with the fesibility of confinement of injected carriers within the emissive layer are