New-record efficiency in non-doped ultraviolet OLEDs: Hot-exciton emitters by a crossed long-short axis design boosting EQE up to 8.3% and emission peak close to 380 nm

Abstract

Organic light-emitting diodes (OLEDs) radiating ultraviolet (UV) emission are highly desirable for their unique applications in anti-counterfeit, healthcare, industry, etc. However, high-performance UV-OLEDs using a simplified non-doped process are rarely reported because organic emitters usually face the emission red-shift and quenching problems in aggregates. Herien, two new UV hot-exciton emitters with crossed long-short axis structures, abbreviated p-Cz and m-Cz, are designed by altering the para- and meta- patterns at the long-axis skeleton. Theoretical calculations combined with photophysical measurements indicate that the m-Cz can display a bluer emission because of its shorter π-conjugation and effectively alleviate the negative effects in aggregates. Consequently, a doped UV-OLED is realized based on m-Cz with an electroluminescence peak (λEL) at 382 nm and a maximum external quantum efficiency (EQEmax) of 10.6%. What's more, the non-doped UV-OLED based on m-Cz exhibits an λEL at 382 nm and an EQEmax up to 8.3% and maintains an EQE of 7.0% at 1000 cd m− 2, representing a new record of efficiency in the field. Furthermore, the device shows the longest reported operational lifetimes and can be successfully applied to an excitation light source.