Achieving pure-fluorescent color-tunable WOLED through long-range coupling of spatially separated electron-hole pairs

Abstract The color-tunable white organic light-emitting diode (CT-WOLED) with a wide correlated color temperature (CCT) offers numerous advantages in meeting human daily needs related to circadian rhythm. The study of CCT variation trends and the rules governing the expansion of the CCT range will help further improve the performance of such devices. This study proposes an effective strategy for achieving high-efficiency fluorescent CT-WOLEDs through long-range radiative coupling of spatially separated electron-hole pairs. After inserting a 5 nm thick DMAC-DPS layer between the donor (TAPC) and the acceptor (PO-T2T), the charge transfer (CT) excitons between TAPC and PO-T2T still exist. As the voltage increases, holes selectively undergo different photophysical processes, resulting in a wide CCT range. This demonstrates the extraordinary potential of spatially separated electron-hole pairs in regulating luminescent properties. By further introducing a bulk exciplex and the conventional red fluorescent dye DCJTB, the device's efficiency, brightness, and CCT range have been further optimized. Additionally, significant highest occupied molecular orbital (HOMO) energy level difference between the hole transport layer (HTL) TAPC and the spacer layer facilitates hole accumulation at the TAPC/spacer interface, thereby enhancing the long-range coupling effect. In device E, we achieved a wide CCT range of 2774K along with a high external quantum efficiency (EQE) of 9.2%. The results indicate that our proposed long-range coupling strategy not only enables a wide CCT range but also ensures broad spectral emission and high electroluminescence (EL) efficiency, providing new possibilities for the field of intelligent lighting.