Molecular Engineering of Emitters Toward Synergistic Hot-Exciton Harvesting and Light Outcoupling for High-Efficiency OLEDs.

Simultaneously realizing high internal quantum efficiency (IQE) and light outcoupling efficiency (LOE) in OLEDs solely depending on molecular engineering has never been achieved. Here, we design three OLED emitters (DCzPDO, DPhCzPDO, and DPAPDO), all comprising 3-hydroxypropenone and β-diketone tautomers. One prominent feature of them is hot-exciton emission enabled by high-lying reverse intersystem crossing (hRISC), hence significantly improving material electroluminescence. Interestingly, in DPAPDO, both isomers exhibit hot-exciton fluorescence, while in the other two materials, only the β-diketone tautomer demonstrates this feature. On the other hand, these materials possess different degrees of preferential transition-dipole-moment alignment, promoting light extraction in OLEDs. Furthermore, their molecules tend to self-assemble along 1D directions, inducing a quasi-parallel V-shaped nanogroove, significantly enhancing light outcoupling in devices. Among them, DPAPDO achieves the highest device performance, reaching a maximum external quantum efficiency (EQE) of 23.7%. DPAPDO comprises the highest concentration of β-diketone isomer, with both isomers facilitating effective hRISC transitions, leading to a near unity IQE of luminescence. Additionally, DPAPDO displays the highest-quality film nanostructure and moderate horizontal dipole ratio, thereby achieving a high LOE of 57%. All these factors account for its high OLED performance. The synergistic interplay between electroluminescence and molecular/supramolecular structures paves the way for cost-effective, scalable, high-efficiency OLEDs.