Precise Regulation of Excited-State Intramolecular Proton-Transfer Materials for High-Efficiency Monochromatic and White-emitting OLEDs

Abstract

Conventional fluorescent WOLEDs generate white light by incomplete energy transfer but face challenges in precisely controlling energy transfer and improving device efficiency due to the maximal utilization of 25% singlet excitons. In this study, two newly developed excited-state intramolecular proton transfer (ESIPT) fluorophores emit orange and white light. These fluorophores utilize excitons efficiently (70–88%) via high-level reverse intersystem crossing (hRISC) exclusively in the keto form and in both isomers (enol/keto), respectively. The white emitter, with comparable dual emissions, enables the fabrication of color-stable cold-white single-emitter OLED with a CRI of 74 and maximum external quantum efficiency (EQE) of up to 5.60%. The orange emitter, when combined with a sky-blue TADF fluorophore, creates non-energy-transferred single-emitting-layer (SML) high-performance cold- and pure-white WOLEDs with CIE coordinates of (0.26, 0.35) and (0.32, 0.32), and maximum EQEs of 13.34% and 9.66%, respectively. Importantly, these complementary-color WOLEDs demonstrate high reproducibility, offering advantages for industrial batch fabrication. Thus, this research presents a route to achieve cost-effective mass production of simple-structured and high-efficiency WOLEDs.