A Breakthrough in Color-Tunable All-Fluorescent White OLEDs through the Cooperation Between a New Blue HLCT Fluorophore and a Long-Wavelength TADF Emitter

Abstract

It is a vitally important and challenging task to achieve high efficiency and wide color-tunable white organic light emitting diodes (CT-WOLEDs) meeting the needs of various decoration and lighting applications. Here, a high-performance single-cell all-fluorescent CT-WOLED with a single-doped single-emissive-layer structure has been developed employing a multi-functional hybrid local and charge transfer (HLCT) fluorophore 2-(4-(9H-carbazol-9-yl)−2′,5′-difluoro-[1,1′:4′,1′'-terphenyl]−4-yl)−1-phenyl-1H-phenanthro[9,10-d]imidazole (PICZ2F) as a deep-blue emitter as well as an effective host for a yellow thermally activated delayed fluorescence emitter. The record-breaking power efficiency of 89.50 lm W‒1 and correlated color temperature (CCT) span from 3749 to 18 279 K are achieved simultaneously, which is not only one of the state-of-the-art CT-WOLEDs reported so far, but also comparable to the best values from all-fluorescent white devices with a single-emissive-layer. Moreover, by using PICZ2F as an emitter, an external quantum efficiency (EQE) of 7.10% with the Commission Internationale de lEclairage (CIE) coordinates of (0.155, 0.068) is achieved in the doped device, and a low-efficiency roll-off even at a high luminance of 15 000 cd m−2 (EQE15000: 5.80%) is achieved in the non-doped device. Overall, the findings provide a promising strategy to develop simple but efficient CT-WOLEDs.