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

Abstract

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.