The driving voltage of an organic light-emitting diode（OLED） is lowered by employing molybdenum trioxide（MoO3）/N,N＇-bis（naphthalene-1-yl）-N,N＇-bis（phe-nyl）-benzidine（NPB） multiple quantum well（MQW） structure in the hole transport layer.For the device with double quantum well（DQW） structure of ITO/[MoO3（2.5 nm）/NPB（20 nm）]2/Alq3（50 nm）/LiF（0.8 nm）/Al（120 nm）],the turn-on voltage is reduced to 2.8 V,which is lowered by 0.4 V compared with that of the control device（without MQW structures）,and the driving voltage is 5.6 V,which is reduced by 1 V compared with that of the control device at the 1000 cd/m2.In this work,the enhancement of the injection and transport ability for holes could reduce the driving voltage for the device with MQW structure,which is attributed not only to the reduced energy barrier between ITO and NPB,but also to the forming charge transfer complex between MoO3 and NPB induced by the interfacial doping effect of MoO3.
We fabricate a kind of novel efficient blue fluorescent organic light emitting device（OLED） based on p-n heterojunctions composed of hole transporting layer（HTL） N,N ＇-bis（naphthalen-1-yl）-N,N ＇-bis（phenyl）-benzidine（NPB） and electron transporting layer（ETL） 4,7-diphnenyl-1,10-phenanthroline（BPhen）,into which a new blue material,DNCA（a derivation of N 6,N 6,N 12,N 12-tetrap-tolylchrysene-6,12-diamine）,is partially doped simultaneously,and double emitting layers are configured.With a turn-on voltage of 2.6 V at 1 cd/m 2,this type of OLED presents a maximum luminance efficiency（η max） of 8.83 cd/A at 5.818 mA/cm 2 and a maximum luminance of over 40000 cd/m 2.Meanwhile,the Commission Internationale De L＇Eclairage（CIE） coordinates of this device change slightly from（0.13,0.27） to（0.13,0.23） as the driving voltage increases from 3 V to 11 V.This improvement in the electroluminescent characteristics is attributed mainly to the ideal p-n heterojunction which can confine and distribute excitons evenly on two sides of the heterojunction interface so as to improve the carrier combination rate and expand the light-emitting region.
The efficiency of organic light-emitting devices （OLEDs） based on N,N＇-bis（1-naphthyl）-N,N＇-diphenyl-N,1＇- biphenyl-4,4＇-diamine （NPB） （the hole transport layer） and tris（8-hydroxyquinoline） aluminum （Alq3） （both emission and electron transport layers） is improved remarkably by inserting a LiF interlayer into the hole transport layer. This thin LiF interlayer can effectively influence electrical performance and significantly improve the current efficiency of the device. A device with an optimum LiF layer thickness at the optimum position in NPB exhibits a maximum current efficiency of 5.96 cd/A at 215.79 mA/cm2, which is about 86% higher than that of an ordinary device （without a LiF interlayer, 3.2 cd/A）. An explanation can be put forward that LiF in the NPB layer can block holes and balance the recombination of holes and electrons. The results may provide some valuable references for improving OLED current efficiency.
In this study the performance of organic light-emitting diodes （OLEDs） are enhanced significantly, which is based on dual electron transporting layers （13phen/CuPc）. By adjusting the thicknesses of Bphen and CuPc, the maximal luminescence, the maximal current efficiency, and the maximal power efficiency of the device reach 17570 cd/m^2 at 11 V, and 5.39 cd/A and 3.39 lm/W at 3.37 mA/cm^2 respectively, which are enhanced approximately by 33.4%, 39.3%, and 68.9%, respectively, compared with those of the device using Bphen only for an electron transporting layer. These results may provide some valuable references for improving the electron injection and the transportation of OLED.
We demonstrate high current efficiency of a blue fluorescent organic light-emitting diode （OLED） by using the charge control layers （CCLs） based on Alq3 . The CCLs that are inserted into the emitting layers （EMLs） could impede the hole injection and facilitate the electron transport, which can improve the carrier balance and further expand the exciton generation region. The maximal current efficiency of the optimal device is 5.89 cd/A at 1.81 mA/cm2 , which is about 2.19 times higher than that of the control device （CD） without the CCL, and the maximal luminance is 19.660 cd/m2 at 12V. The device shows a good color stability though the green light emitting material Alq3 is introduced as the CCL in the EML, but it has a poor lifetime due to the formation of cationic Alq3 species.
