MgF2 as an interlayer to enhance the stability of thermally activated delayed fluorescence based organic electroluminescence devices
Author:
Gaur Nrita1ORCID,
Banappanavar Gangadhar S.1ORCID,
Kabra Dinesh1ORCID
Affiliation:
1. Department of Physics, Indian Institute of Technology Bombay , Powai, Mumbai 400076, India
Abstract
Stability is one of the major challenges in organic semiconductor based optoelectronic devices. A comparative study of thermally activated delayed fluorescence (TADF) based organic light emitting diodes (OLEDs) with alkali-halide lithium fluoride (LiF) vs alkaline halide magnesium fluoride (MgF2) inorganic electron injection interlayers is presented. A TADF emitter 4CzIPN doped in CBP is used as an active layer (thickness = 15 nm @6wt. % doping) in an OLED structure: Glass/ITO/PEDOT:PSS/NPD/CBP/CBP:4CzIPN/TPBi/interlayer/Al. Prior to this comparative study, a separate exercise is carried out to obtain an optimal thickness of an MgF2 interlayer on the basis of leakage current and efficiency in the TADF-OLEDs. OLEDs with an LiF interlayer showed an external quantum efficiency (EQE) of 19.7% in comparison with an MgF2 interlayer-based OLED showed slightly lower average EQE ∼19.1% at a luminance level of 100 cd/m2; these efficiency numbers are averaged over ∼60 OLEDs. These slight changes in EQE are supported by the relative photoluminescence quantum yield measurements with a whole device stack. However, alkaline halide MgF2 based TADF-OLEDs showed approximately seven-fold enhancement in the stability (LT60) under identical operating conditions. In situ photoluminescence monitoring of operational TADF-OLEDs confirmed that the probable cause of reduced lifetime is degradation of an LiF/TPBi interface.
Funder
Department of Science & Technology New Delhi
Ministry of Education, New Delhi- India
University Grant Commission Forbes & Marshall Chair Professor
Subject
General Physics and Astronomy
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