Effect of host polarity on efficiency of thermally activated delayed fluorescent and hyperfluorescent organic light emitting devices

Molecular interaction between 10-phenyl-10H, 10′H-spiro[acridine-9,9′-anthracen]-10′-one (ACRSA), a sensitizer exhibiting thermally-activated delayed fluorescence (TADF) properties, and host materials with different polarity was analyzed. Interestingly, the OLED devices fabricated with ACRSA as a final dopant and bis[2-(diphenylphosphino)phenyl] ether oxide (DPEPO), as a high polarity host material showed higher efficiency (by ∼ 1.7 times) than that obtained from ACRSA as a final dopant and N,N′-dicarbazolyl-3,5-benzene (mCP), as a low polarity host material. Similarly, the hyperfluorescent OLED fabricated with ACRSA as a TADF sensitizer and 10-(2-benzothiazolyl)-2,3,6,7-tetrahydro-1,1,7,7-tetramethyl-1H,5H,11H -[1]benzopyropyrano[6,7,8-i,j]quinolizine-11-one (C545T), as a final green fluorescent dopant gave higher efficiencies (by up to 1.4 times) when more polar host materials were used. A comprehensive analysis of this trend was carried out, and we found that the host polarity caused strong or weak interactions with a certain state of the TADF materials, and these interactions are responsible for the corresponding high or low efficiency. This result suggests that it is possible to increase the efficiency of hyperfluorescent devices by appropriately selecting the host materials with right polarity.