The Quantum Efficiency Roll-Off Effect in Near-Infrared Organic Electroluminescent Devices with Iridium Complexes Emitters
Wojciech Mróz,
Sagar Kesarkar,
Alberto Bossi,
Daniel Pelczarski,
Piotr Grygiel,
Waldemar Stampor
Affiliations
Wojciech Mróz
Institute of Macromolecules’ Study (ISMAC), National Research Council (CNR), Via E. Bassini 15, 20133 Milan, Italy
Sagar Kesarkar
Istituto di Scienze e Tecnologie Chimiche “G. Natta”, Consiglio Nazionale delle Ricerche (CNR-SCITEC), Via Fantoli 16/15, 20138 Milano and SmartMatLab Center, Via C. Golgi 19, 20133 Milano, Italy
Alberto Bossi
Istituto di Scienze e Tecnologie Chimiche “G. Natta”, Consiglio Nazionale delle Ricerche (CNR-SCITEC), Via Fantoli 16/15, 20138 Milano and SmartMatLab Center, Via C. Golgi 19, 20133 Milano, Italy
Daniel Pelczarski
Department of Physics of Electronic Phenomena, Faculty of Applied Physics and Mathematics, Gdańsk University of Technology, Narutowicza 11/12, 80–233 Gdańsk, Poland
Piotr Grygiel
Department of Physics of Electronic Phenomena, Faculty of Applied Physics and Mathematics, Gdańsk University of Technology, Narutowicza 11/12, 80–233 Gdańsk, Poland
Waldemar Stampor
Department of Physics of Electronic Phenomena, Faculty of Applied Physics and Mathematics, Gdańsk University of Technology, Narutowicza 11/12, 80–233 Gdańsk, Poland
The electroluminescence quantum efficiency roll-off in iridium(III)-based complexes, namely Ir(iqbt)2(dpm) and Ir(iqbt)3 (iqbt = 1 (benzo[b]thiophen-2-yl)-isoquinolinate, dpm = 2,2,6,6-tetramethyl-3,5-heptanedionate) utilized as near-infrared emitters in organic light emitting diodes with remarkable external quantum efficiencies, up to circa 3%, 1.5% and 1%, are measured and analyzed. With a 5–6 weight% of emitters embedded in a host matrix, the double-layer solution-processed structure as well as analogous three-layer one extended by a hole-conducting film are investigated. The triplet-polaron, the Onsager electron-hole pair dissociation and the triplet-triplet annihilation approaches were used to reproduce the experimental data. The mutual annihilation of triplets in iridium emitters was identified as prevailingly controlling the moderate roll-off, with the interaction between those of iridium emitters and host matrixes found as being less probable. Following the fitting procedure, the relevant rate constant was estimated to be ( 0.5 − 12 ) × 10 − 12 cm3/s, values considered to be rather too high for disordered organic systems, which was assigned to the simplicity of the applied model. A coexistence of some other mechanisms is therefore inferred, ones, however, with a less significant contribution to the overall emission quenching.
