Near-ultraviolet emitters based on carbazole-imidazole for highly efficient solution-processed organic light-emitting diodes

Abstract

Solution-processable near-ultraviolet (NUV) and deep-blue organic emitters are crucial for the development of organic light-emitting diodes (OLEDs) in large-area production. However, such wide band gap materials with high photoluminescence quantum yield (PLQY) and stable electroluminescence are sparse. Here, three NUV and deep-blue solution-processable emitters, carbazole-imidazole derivatives, BuCzI, BuCzI-CN and BuCzI-BCN, are synthesized by employing 3,6-di-tert-butyl-carbazole at N1 position of imidazole as electron donor to construct a twisted and rigid structure of donor-linker-acceptor. The combination of carbazole and imidazole fulfills saturated NUV and deep-blue emission in solution and film, accompanied with excellent solubility in non-chlorinated solvents. Furthermore, the bulky donor of 3,6-di-tert-butyl-carbazole not only enhances localized excited and keeps high PLQY in different solvents, but also suppresses emission red-shift which results from intramolecular charge transfer (ICT) to realize NUV emission. The solution-processed undoped OLEDs fabricated with BuCzI, BuCzI-CN and BuCzI-BCN as emitters achieve external quantum efficiency (EQE) up to 3.30 %, 2.20 % and 2.63 % with the Commission Internationale de L’Eclairage (CIE) coordinates of (0.15, 0.04), (0.15, 0.06) and (0.15, 0.09), respectively. All devices retain stable NUV and deep-blue emission at varied applying voltages. The results of this work have provided a novel design strategy for NUV solution-processable organic emitters with high efficiency and stability.