High-Efficiency White Organic Light-Emitting Diodes Integrating Gradient Exciplex Allocation System and Novel D-Spiro-A Materials

How to maintain high power efficiency (PE) and color stability under operating brightness is critical for the white organic light-emitting diodes (WOLEDs). To this end, two novel spiro-type materials STPy3 and STPy4 were designed. These materials could act as a single host and achieve a remarkable external quantum efficiency of 27.5% at 1000 cd m–2; to further optimize the PEs of OLEDs, STPy3/4 and PO-T2T were used as co-host-induced exciplexes, which enhanced the PE of green OLED to over 148.0 lm W–1. Unfortunately, the lower triplet energy level of exciplexes than blue emitters implied it is commonly unsuitable to fabricate WOLEDs. Herein, a new allocation of gradient exciplex (AGE) strategy was developed in which the formed excitons could be rationally allocated in a consequently doped nonuniform profile. The AGE incorporated the advantages of the exciplex with an ultralow turn-on voltage of 2.3 V and efficiency stability of spiro materials. The PE at 1000 cd m–2 was enhanced to 72.7 lm W–1, representing the first exciplex WOLED with the performance exceeding that of conventional fluorescent tubes.