High-efficiency non-doped near-ultraviolet OLEDs achieved by regulating excited-state spatial distribution through molecular optimization to realize hybridized local and charge-transfer (HLCT) characteristics

Abstract

The development of high-performance near-ultraviolet organic light-emitting diodes (NUV-OLEDs) remains challenging due to their intrinsic wide-bandgap characteristics. Therefore, this study fully exploits the weak electron-accepting characteristics of the PPI group, combined with its high photoluminescence quantum yield (PLQY) and excellent thermal stability. Through a precise molecular structure modulation strategy involving direct introduction of electron-donating diphenylamine groups into the side phenyl ring and systematic integration of donor/acceptor units with tailored electronic properties into the main backbone, effective control of excited-state characteristics and their spatial distribution was successfully achieved. Based on this molecular design concept, four near-ultraviolet luminescent molecules (TPA-PPI, DTPA-PPI, TPAAd-PPI, and TPA-POPPI) with hot-exciton properties were successfully developed, significantly improving the material's PLQY and electroluminescence (EL) performance. Notably, compared to analogous structures, the TPAAd-PPI derivatives demonstrate significantly enhanced PLQY and EL performance. Specifically, the external quantum efficiency (EQE) was substantially improved from 4.0% for DMP to 12.1%, while the CIEy coordinates decreased from 0.053 to 0.048, achieving near-ultraviolet emission. Remarkably, the non-doped device based on TPA-POPPI achieved a record-high EQE of 13.8%. These outstanding results underscore the significant potential of this innovative molecular design strategy for developing high-performance NUV-OLEDs.