Revealing the Evolution Processes of Excitons on High Energy Level in Anthracene‐Based OLEDs

Abstract

It is well-known that the electrically generated excitons can perform the spin evolution between high-lying excited states, providing an efficient way to utilize triplet excitons in organic light-emitting diodes (OLEDs). Anthracene families offer an opportunity to deeply investigate the processes of triplet excitons on high-lying excited states in detail. Here, a simplified model is proposed to study the exciton dynamics in anthracene derivatives-based devices. The mechanism on the processes of high-energy level intersystem crossing in anthracene derivatives is well revealed by theoretical calculation, transient electroluminescence, transient photoluminescence, and transient absorption spectrum measurements. Besides, doping strategy is proposed to suppress the exciton loss channel for improving the efficiency of devices. The studies establish an in situ method to evaluate the apparent singlet exciton formation ratio in devices due to the exciton evolution between high-lying excited states and offer some clues to further utilize these triplet excitons, thus improving the efficiency of the resulting fluorescence OLEDs in the future.

Realizing Stable Narrowband Emission Blue Fluorescent Organic Light-Emitting Diodes with Dual-Channel Triplet Exciton Harvesting Host

“…At the same time, the first triplet state (T 1 ) of “hot exciton” materials is low, which can transfer the triplet excitons from the emitter. Some “hot exciton” fluorescent materials such as 2-(4-(10-(3-(9 H -carbazol-9-yl)phenyl)anthracen-9-yl)phenyl)-1-phenyl-1 H -phenanthro[9,10- d ]imidazole (PAC) , also exhibit a TTA process which can utilize triplet excitons dropped on the T 1 energy level. That is to say, the “hot exciton” fluorescent material PAC has dual channels to harvest and evacuate long-lived triplet excitons, which can reduce the exciton annihilation processes.…”

Hot‐Exciton Mechanism and AIE Effect Boost the Performance of Deep‐Red Emitters in Non‐Doped OLEDs

“…Interestingly, the hot-exciton path holds the potential for achieving a theoretical 100% internal quantum efficiency (IQE) and mitigating the issue of low-efficiency roll-off. [2][3][4][5][6][7][8][9][10][11][12][13] For instance, Ma et al have presented a highly efficient blue emitter PAC. This emitter features a small splitting energy between S 1 and T 2 (ΔE S 1 T 2 ) and a relatively large T 2 -T 1 energy gap (ΔE T 1 T 2 ), which effectively restricts internal conversion (IC) from T 2 to T 1 and promotes rapid reverse intersystem crossing from the high-lying triplet state (hRISC).…”

“…Interestingly, the hot‐exciton path holds the potential for achieving a theoretical 100% internal quantum efficiency (IQE) and mitigating the issue of low‐efficiency roll‐off. [ 2–13 ] For instance, Ma et al. have presented a highly efficient blue emitter PAC.…”

Pioneering research on blue “hot exciton” polymers and their application in solution-processed organic light-emitting diodes

“…17,18 In contrast with the TADF mechanism, fluorescent molecules with hybridized local and chargetransfer (HLCT) state characters inherently have a large overlap between ''particle'' and ''hole'' in excited states, which undoubtedly amplifies the oscillator strength of the S 1 state. [19][20][21] Currently, numerous HLCT small molecules comprising donor-acceptor-donor (D-A-D) molecular configurations have been designed and reported. 22,23 However, the task of achieving blue emission through the HLCT mechanism while incorporating long conjugated chains in polymers remains a formidable challenge that is yet to be addressed in the scientific community.…”