Efficient doped and non-doped OLEDs based on a deep-blue HLCT material and all-HLCT WOLEDs with standard white-light emission

Abstract

Hybrid local and charge-transfer (HLCT) materials are attracting considerable interest in organic light-emitting diodes (OLEDs) owing to their advantages such as 100% theoretical internal quantum efficiency and low efficiency roll-off, particularly for blue HLCT materials. Although progress has been made toward high-efficiency HLCT materials and even HLCT-based white OLEDs (WOLEDs), all-HLCT WOLEDs remain rarely reported. In this work, we report two novel HLCT molecules: blue CzPyPPI based on phenanthroimidazole (PPI) and orange BTPA4 based on benzothiadiazole, and their HLCT characteristics were revealed through theoretical calculations and photophysical studies. The CzPyPPI and BTPA4 neat films exhibited photoluminescence quantum yields as high as 72.0% and 89.8%, respectively, contributing to high device performances. The doped device based on CzPyPPI delivered a maximum external quantum efficiency (EQE_max) of 7.37% with deep-blue emission (CIE_y = 0.063), while the doped device based on BTPA4 showed an EQE_max of 5.13%. Importantly, WOLEDs with a simple emissive layer consisting of the blue CzPyPPI host and orange BTPA4 dopant were fabricated. The optimized WOLED presented an EQE_max of 6.86% with low efficiency roll-off, together with near-standard white-light emission with CIE coordinates of (0.335, 0.334). This work provides new insights for the development of high-performance blue HLCT materials and all-HLCT WOLEDs.