Revealing the Effect of Triplet–Triplet Annihilation Up-Conversion and Improving the Operational Lifetime by Exciton Management in Anthracene- and Pyrene-Based Blue Fluorescent OLEDs

Abstract

Anthracene- and pyrene-based organic fluorescent molecules with hybridized local and charge-transfer (HLCT) process can achieve highly efficient exciton utilization through harvesting high-lying triplet (T_n, n ≥ 2) excitons via reverse intersystem crossing (hRISC) compared to conventional organic fluorescent molecules, but there exists a serious exciton loss caused by internal conversion (IC) from T_n to T₁.Nowadays, the stability difference between anthracene- and pyrene-based HLCT materials in OLEDs is rarely understood. In this article, the aging properties of anthracene derivated PAC and pyrene derivated CPPCN in the fabricated blue fluorescent OLEDs are systematically studied through exciton dynamics theory, and transient electroluminance and impedance spectroscopy measurements. It's experimentally found that the triplet exciton loss caused by IC is responsible for the device degradation. Through doping fluorescent emitter and introducing triplet-triplet annihilation upconversion layers in emissive layer, the IC process is efficiently suppressed and the operational lifetime is enhanced by ≈5.2 and 16 times under the luminance of 1000 cd m⁻² in PAC and CPPCN-based OLEDs, respectively. This work fully demonstrates the differences in the effects of anthracene and pyrene-based HLCT molecules on device stability, providing a basis for further improving the operational lifetime of blue fluorescent OLEDs based on HLCT molecules.