Effective exciplex host for solution-processed narrowband blue TADF-OLEDs using a 9-(dibenzo[b,d]thiophen-2-yl)-9H-carbazole analogue with an adamantane substituent.

Implementing an exciplex host system in the emitting layer is crucial for achieving highly efficient thermally activated delayed fluorescence (TADF) and phosphorescent organic light-emitting diodes (OLEDs). In this study, we successfully designed and synthesized 3-((3 r ,5 r ,7 r)-adamantan-1-yl)-9-(dibenzo[ b,d ]thiophen-2-yl)-9 H -carbazole (AdCz-DBT) and 9-(dibenzo[ b,d ]thiophen-2-yl)-9 H -carbazole (Cz-DBT) as p -type hosts for the exciplex host implementation, and 7-(4-(tert -butyl)phenyl)-5,9-dioxa-13 b -boranaphtho[3,2,1- de ]anthracene (tPDBA) as an n -type host. The AdCz-DBT host incorporates a large and robust adamantane group into Cz-DBT, increasing molecular weight, film-forming properties and thermal stability. Additionally, AdCz-DBT maintains energy levels and photophysical properties similar to those of adamantane-free Cz-DBT. Efficient exciplex emission was observed in the blend film due to well-matched energy levels of the synthesized p - and n -type hosts. The introduction of adamantane into Cz-DBT did not hinder exciplex formation, resulting in a relatively high photoluminescence quantum yield and improved charge balance in the mixed host with tPDBA. Ultimately, the solution-processed blue TADF-OLED with the AdCz-DBT:tPDBA blend host demonstrated a relatively high external quantum efficiency of 8.00% and a long operational lifetime, exhibiting excellent performance compared to devices using the Cz-DBT:tPDBA blend host. [Display omitted] • AdCz-DBT was successfully synthesized, demonstrating a high glass transition temperature. • AdCz-DBT:tPDBA blend film exhibited promising exciplex emission behavior. • AdCz-DBT-based OLEDs displayed a highly improved external quantum efficiency. • AdCz-DBT based OLEDs showcased significantly improved operational stability. [ABSTRACT FROM AUTHOR]