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-((3r,5r,7r)-adamantan-1-yl)-9-(dibenzo[b,d]thiophen-2-yl)-9H-carbazole (AdCz-DBT) and 9-(dibenzo[b,d]thiophen-2-yl)-9H-carbazole (Cz-DBT) as p-type hosts for the exciplex host implementation, and 7-(4-(tert-butyl)phenyl)-5,9-dioxa-13b-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.