Efficiency enhancement in an inverted organic light-emitting device with a TiO2 electron injection layer through interfacial engineering

TiO2 is widely used in optoelectronic devices especially organic solar cells due to its excellent optical and electrical properties. However, its application in organic light-emitting devices (OLEDs) as an electron injection layer (EIL) usually suffers from insufficient electron injection and serious interfacial quenching, leading to low efficiency. In this work, efficiency enhancement of inverted OLEDs (IOLEDs) based on a TiO2 EIL by introducing various interlayers (ILs) is reported. Polyethylenimine (PEI), 10,10′-[5-(6-[1,1′-biphenyl]-4-yl-2-phenyl-4-pyrimidinyl)-1,3-phenylene] bis[9,10-dihydro-9,9-dimethyl-acridine] (DMAC-BPP) and 2,2′,2′′-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBI) are adopted as ILs to reduce quenching, improve electron injection by achieving stepped energy levels and achieve efficient exciton confinement. Compared with devices using PEI/TPBI interlayers, over 40% enhancement of the maximum external quantum efficiency (EQEmax) for TiO2-based IOLEDs by introducing DMAC-BPP interlayers is achieved. Furthermore, efficient carrier confinement and more balanced carrier injection are achieved by inserting a thin TPBI between DMAC-BPP and the emitting layer (EML), and then, the EQEmax is improved to 17.68%, which is the highest record for TiO2-based IOLEDs.