Pyrene-Based Emitters with Ultrafast Upper-Level Triplet-Singlet Intersystem Crossing for High-Efficiency, Low Roll-Off Blue Organic Light-Emitting Diode

The reverse intersystem crossing (RISC) process from triplet to singlet manifold can efficiently improve the efficiencies of organic light-emitting diodes (OLEDs). The relevant RISC rate (k(RISC)) is one of the key factors that affect the efficiency roll-off and stability of devices. Here, a new blue hot exciton material, CPPCN, with pyrene as the core, is designed and synthesized. Photophysical studies indicate there are multiple high-lying triplet states near the lowest singlet excited state (S-1) of CPPCN, which facilitate the RISC from the high-lying triplet state (hRISC) to the S-1 state. The corresponding hRISC rate constant is determined to be as high as 2.86 x 10(8) s(-1), a value some two to three orders of magnitude higher than typical thermally activated delayed fluorescence materials emitters. Benefiting from this ultrafast hRISC process, non-doped blue OLED based on CPPCN reaches a high maximum external quantum efficiency (EQE) of 11.64% with suppressed efficiency roll-off (begin roll-off at a high brightness of 3732 cd m(-2) and retains EQE >8.5% at 10 000 cd m(-2)). The T-95 lifetime of the CPPCN-based device with a structure of commercial applications is evaluated to be approximate to 368 h at 1000 cd m(-2).

Automated summary

In this study, a new blue hot exciton material, CPPCN, was designed and synthesized, which has multiple high-lying triplet states near the lowest singlet excited state. The ultrafast RISC process facilitated by these high energy triplet states allows the non-doped blue OLED based on CPPCN to achieve high external quantum efficiency and suppressed efficiency roll-off.