Regular Article

Enhancement in electron transport and exciton confinement in OLEDs: role of n-type doping and electron blocking layers^★

¹ Photosciences and Photonics Section, Chemical Sciences and Technology Division, CSIR-National Institute for Interdisciplinary Science and Technology, Thiruvananthapuram, Kerala 695019, India
² Academy of Scientific and Innovative Research, Ghaziabad-201002, India

^* e-mail: unni@niist.res.in

Received: 29 January 2019
Received in final form: 16 March 2019
Accepted: 27 March 2019
Published online: 29 May 2019

Abstract

Doped transport layers are essential for achieving high efficiency in organic light emitting diodes (OLEDs). We have studied the effect of doping the electron transport layer (ETL), tris-(8-hydroxyquinoline) aluminum (Alq₃) with different percentages of lithium fluoride (LiF). We have also studied the effect of different electron blocking layers (EBLs) such as Tris (4-carbazoyl-9-ylphenyl)amine (TCTA), N,N'-Bis (naphthalen-1-yl)-N,N'-bis(phenyl)-benzidine(NPB), and Di-[4-(N,N-di-p-tolyl-amino)-phenyl]cyclohexane (TAPC) in an Alq₃:2,3,6,7-Tetrahydro-1,1,7,7,-tetramethyl-1H, 5H, 11H −10-(2-benzothiazolyl)quinolizino[9,9a, 1gh] coumarin (C545T) based organic light emitting diode (OLED) with optimized ETL doping. TCTA was found to effectively block the electrons and influence the recombination region in the process. At a brightness of 1000 cd/m², an improvement of 27.8% was observed in external quantum efficiency (EQE) for the device with TCTA as the EBL and doped Alq₃ as the ETL, compared to the one with just NPB as both EBL and HTL.