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High Efficiency and Highly Saturated Red Emitting Inverted Quantum Dot Devices (QLEDs): Optimisation of Efficiency with Low Temperature Annealed Sol-Gel Derived ZnO as the Electron Transporter, a Novel High Mobility Hole Transporter and Thermal Annealing of the Devices

Abstract

Quantum dot light emitting diodes (QLEDs) are a promising candidate for high efficiency and high colour gamut displays with saturated colours. This paper reports a peak current efficiency of 46 cd/A and peak power efficiency 42 lm/W for red QLEDs with the CIE (x, y) of (0.695 and 0.305) which we believe to be the highest ever reported for a red QLED. Annealing the QLED devices at 40 0C for 120 hours makes such a dramatic increase in the peak efficiency by 207% (from 15 cd/A to 46 cd/A) and the power efficiency by 600% (from 6 lm/W to 42 lm/W). This paper also addresses three major issues confronting the development of QLEDs. First, the issue of nature of CdSe based QDs , whether Sulphur rich (Cdse(core)/CdS (shell)/ZnS (shell)) system or the Selenium rich (CdSe (core)/ZnSe(shell)/ZnS (shell)) gives higher efficiency. Secondly, how to balance the charge injection from the high electron mobility ZnO films by simply altering the annealing condition rather than the complicated application of thin insulating interfacial layers (2-5 nm). Thirdly, improving the hole injection by means of using high mobility hole transporters (electron blockers). In addition, the paper also investigates the effect of annealing the encapsulated devices (positive aging) on the device performance. The (CdSe/ZnSe/ZnS) QDs give higher efficiency (16 cdA-1 and 11 lmW-1 @ 1000 cdm-2) than the analogous (CdSe/CdS/ZnS) system (10 cd/A and 5.8 lm/W at 1000 cdm-2). Upon annealing at 40 0C for 120 hours, the latter system gives an enhanced efficiency of 26 cd/A and 12.5 lm/W at 1000 cdm-2. High mobility, high LUMO hole transporters/electron blockers are essential for the production of high efficiency QLEDs with saturated colour co-ordinates of CIE (0.708, 0.292).

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Publication details

The article was received on 25 Jul 2018, accepted on 11 Sep 2018 and first published on 12 Sep 2018


Article type: Paper
DOI: 10.1039/C8TC03676D
Citation: J. Mater. Chem. C, 2018, Accepted Manuscript
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    High Efficiency and Highly Saturated Red Emitting Inverted Quantum Dot Devices (QLEDs): Optimisation of Efficiency with Low Temperature Annealed Sol-Gel Derived ZnO as the Electron Transporter, a Novel High Mobility Hole Transporter and Thermal Annealing of the Devices

    P. Kathirgamanathan, M. Kumaraverl, N. Bramananthan and S. Ravichandran, J. Mater. Chem. C, 2018, Accepted Manuscript , DOI: 10.1039/C8TC03676D

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