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‐(9 H ‐carbazol‐9‐yl)−2′,5′‐difluoro‐[1,1′:4′,1′'‐terphenyl]−4‐yl)−1‐phenyl‐1 H ‐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 (EQE 15000 : 5.80%) is achieved in the non‐doped device. Overall, the findings provide a promising strategy to develop simple but efficient CT‐WOLEDs.