Efficient Stable Green Hybrid Light-Emitting Devices Using Cathode Interlayer

Abstract

Hybrid photoconductive materials of SnO2 doped organic materials (SnO2:PBA-PA and SnO2:PFN; PBA-PA, 2,9-bis(1-benzylpiperidinyl)-5,6,12,13-tetrachloroanthra[2,1,9-def:6,5,10-d′e′f′]diisoquinoline-1,3,8,10-(2H,9H)-tetraone; and PFN, 9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)) have been employed as the photoconductive interlayer in efficient hybrid organic light-emitting diodes (OLEDs). The absorption of the SnO2:PBA-PA interlayer reduced the emission intensity at 562 nm due to spectral overlap of the absorption of PBA-PA with the electroluminance (EL) of iridium(III) bis(4,5-dimethyl-1-(naphthalene-1-carbonitrile)-1H-imidazolato-N,C2′)(acetyl acetonate) (Ir(DNC)2(acac)). The fabricated OLEDs having the configuration of indium tin oxide (ITO)/cathode interlayers SnO2/SnO2:PBA-PA/SnO2:PFN/Ir(DNC)2(acac)/MoO3/Al show luminance (L) values of 4289/18056/23135 cd/m2, current efficiency (CE) values of 2.5/15.3/16.8 cd/A, power efficiency (PE) values of 1.1/7.4/8.6 lm/W, and external quantum efficiency (EQE) values of 7.3/14.3/17.0% at 4.6/3.0/2.9 V. The SnO2:PBA-PA based device exhibit increased luminance (ZL) of 22.0%, ZCE of 8.9%, ZPE of 14.0%, and ZEQE of 15.9% compared with SnO2:PFN based device. Compared with the SnO2 device, the SnO2:PBA-PA based device exhibited increased luminance (ZL) of 81.5%, ZCE of 85.1%, ZPE of 87.2%, and ZEQE of 57.1% with reduction in turn-on voltage from 4.6 to 2.9 V. These interlayers show increased conductivity due to effective electron mobility which enhances the electron–hole recombination efficiency in the emissive layer and leads to improvement of the performances of devices. The novel photoconductive interlayers (SnO2:PBA-PA and SnO2:PFN) decreased the energy barrier (cathode interlayer:light-emitting layer) results in the decrease of the turn-on voltage. Our research findings demonstrate that the insertion of a cathode interlayer opens up a new way to enhance the device efficiency.