Enhancement of Blue Doping-Free and Hyperfluorescent Organic Light Emitting Diode Performance through Triplet–Triplet Annihilation in the Derivatives of Anthracene and Carbazole

Abstract

Carbazoles with tert-butyl, methoxy, and methoxyethoxy groups are linked with anthracene-based moieties in a series of designed and synthesized compounds with the aim to obtain triplet levels lower than 2 eV and efficient triplet harvesting in electroluminescent devices. The upconversion of triplet excitons is studied theoretically and experimentally. The triplet fusion is responsible for the appearance of blue delayed emission with lifetimes up to 0.15 ms, which is detected for the methoxy-containing compound by photophysical investigation. The tert-butylated emitter shows good performance in organic light emitting diodes (OLEDs), reaching an external quantum efficiency of 5.9% with the 1931 Commission Internationale de l’Éclairage coordinates of (0.14, 0.12). The time-of-flight measurements demonstrate that the derivative of tert-butylcarbazolyl and anthracene is the most promising candidate for electronic devices due to its high hole mobility, reaching 7.6 × 10^–5 cm²/(V s) at an electric field of 8 × 10⁵ V/cm. Exploitation of a guest–host containing the tert-butylcarbazolyl and anthracene derivative as a host exhibiting triplet–triplet annihilation (TTA) and a fluorescent emitter resulted in an efficient hyperfluorescent OLED with a maximum external quantum efficiency of 7.1%. The OLED with such efficiency outperformed the theoretical limit of conventional fluorescence-based devices due to the utilization of triplet excitons in emission allocated to TTA upconverted excitons.