The use of a polarity matching and high-energy exciton generating host in fabricating efficient purplish-blue OLEDs from a sky-blue emitter

Abstract

We reveal in this communication a new finding regarding the use of a sky-blue emitter to generate purplish-blue emission from organic light emitting diodes (OLEDs) with a polarity matching and highenergy exciton generating host. The resulting device exhibits CIE xy coordinates of (0.155, 0.063) and a 3.5% external quantum efficiency, with a 1.2 lm W À1 power efficiency at 100 cd m À2 as a skyblue emitter, 1-((9,9-diethyl-9H-fluoren-2-yl)ethynyl)pyrene with CIE xy of (0.190, 0.241) is doped into a host of 4,4 0 -bis(9-carbazolyl)biphenyl, for example. The resulting purplish-blue emission enables a greater than 100% color saturation. The extraordinarily marked blue-shift may result from a low doping concentration to prevent bathochromic shift due to emitter segregation, a polarity matching host to further disperse the emitter, and an efficient host and guest energy level pairing that enables excitons to be generated on the host to trigger short wavelength emission. Furthermore, the host is capable of generating excitons with higher energy to facilitate the triggering of emission with a shorter wavelength. The high efficiency may be attributed to the low doping concentration preventing efficiency roll-off caused by concentration-quenching, the excitons generated on the host facilitating the occurrence of the effective host-to-guest energy transfer, and the employed host possessing an effective host-to-guest energy transfer effect. Notably, the new approach also works for other light-blue emitters in yielding a highly desirable deep-blue light, provided their molecular structure is free of steric hindrance.

Candle Light‐Style Organic Light‐Emitting Diodes

“…The efficacy roll‐off may be attributed to numerous factors, including concentration quenching,53, 54 exciton quenching,54, 55 imbalance carrier injection,56 and ineffective carrier confinement 57. To improve this, employing much diluted emitter,58 using multiple emission layers with step‐wise energy‐levels to extend exciton generation zone or enabling excitons to generate on both host and guest,59 improving the injection of minor carrier to balance the carriers,60 and incorporating effective electron and/or hole confinement layers21, 61 have been found to be effective. These approaches may be adopted to further improve the efficacy of the present devices.…”

Controllable molecular configuration for significant improvement of blue OLEDs based on novel twisted anthracene derivatives

“…The devices p1 and p2 showed pure blue emission with CIE coordinates of (0.15, 0.08) and (0.15, 0.09), which are close to the blue standards (0.14, 0.08) of NTSC. Curiously, a relatively rare blue-violet emission was found for the m-PABPI-doped devices with CIE coordinates (x, y) of (0.15, 0.04), which may owe to a low doping concentration to prevent red-shift and an effective host and guest energy level pairing that enables excitons to be generated on the host to trigger short wavelength emission [32]. More importantly, prior to p-PABPI, the CIE x,y (0.15, 0.04) of m-PABPI-doped devices is independent to dopant concentration.…”

Efficient fluorescent OLEDS based on assistant acceptor modulated HLCT emissive state for enhancing singlet exciton utilization

“…Diluting the emitter molecules in the host eliminates the effect of intermolecular close stacking and decreased medium polarity because m-MTDATA is generally used as a nonpolar host material. 86,87 The DDPPPA and DDPBA based OLEDs show improved device efficiencies of h ex of 4.72% (5 wt% DDPPPA) and 5.63% (5 wt% DDPBA). 88 The doped device m-MTDA-TA:DDPPPA/m-MTDATA:DDPBA show maximum efficiencies of h c À7.4/8.23 cd A À1 ; h p À5.8/6.13 lm W À1 ; h ex À4.72/5.63% The theoretically calculated maximum h EQE is of 5.61/5.20% DDPPPA (neat/20 wt% m-MDATA) and 5.55/5.10% DDPBA (neat/ 20 wt% m-MDATA) [h EQE ¼ h out  h rec  h g  F PL , 89 f PL :-DDPPPA (89/96%) and DDPBA (90/98%), h outout-coupling efficiency (20%), h recproduct of charge recombination efficiency (100%), h gradiative exciton-production (25%)] and the experimental h EQE is of 5.70/5.96% DDPPPA (neat/20 wt%) and 6.01/6.25%, DDPBA (neat/20 wt%) respectively.…”