Solution processable small molecule based TADF exciplex OLEDs

In this work we report the optimisation of the solution processable TADF exciplex emitter in OLED devices formed by the small molecules 9-[2,8]-9-carbazole-[dibenzothiophene-S,S-dioxide]-carbazole (DCz-DBTO2) and 4,4′-cyclohexylidenebis[N,N-bis(4-methylphenyl)benzenamine] (TAPC). This exciplex, previously reported by Jankus et al. [1], has gave vacuum deposited devices having respectively current efficiency, power efficiency and EQE of 32.3 cd/A, 26.7 lm/W and 10.3 % obtained for with DCz-DBTO2:TAPC wt% ratio of 30:70. In this work we optimised the thickness and ratio of the exciplex layer using two different solvents, chlorobenzene and chloroform. The best results were achieved when the two solvents were mixed, adding 5 vol% of chlorobenzene to chloroform. With this solvent mixture comparable results to evaporated devices were achieved, 27.5 ± 3.5 cd/A, 16.5 ± 2.0 lm/W and EQE of 8.9 ± 0.6 % at the same DCz-DBTO2:TAPC wt% ratio of 30:70, demonstrating the suitability of small molecule TADF exciplexes as solution processable emissive layer for OLEDs.