Device fabrication

Device configuration: ITO/NPB (40 nm)/TCTA (15 nm)/mCP (15 nm)/host materials: 2% ν-DABNA (20 nm)/TmPyPB (40 nm)/LiF(1 nm)/Al (200 nm). N,N’-Bis(naphthalen-1-yl)-N,N’-bis(phenyl)-benzidine (NPB), 4,4’,4-Tris(carbazol-9-yl)triphenylamine (TCTA) used as an injection layer. 1,3-Bis(carbazol-9-yl)benzene (mCP) was used as both a hole transporting layer and an electron blocking layer. 1,3,5-Tris(3-pyridyl-3-phenyl)benzene (TmPyPB) was used as both an electron transporting layer and a hole blocking layer. As a dopant for the emitting layer, ν-DABNA, a multiple resonance TADF material reported by Hatakeyama et al. was used. As the host material, synthesized TDBA-based host materials were applied to confirm the relationship between host and dopant. For the EL devices, all organic layers were deposited under 10⁻⁶ torr, with a rate of deposition of 1 Å/s to give an emitting area of 4 mm². The LiF and aluminum layers were continuously deposited under the same vacuum conditions. The current-voltage-luminance (I-V-L) characteristics of the fabricated EL devices were obtained with a Keithley 2400 electrometer. Light intensities were obtained with a Minolta CS-1000A. To calibrate the EQE values considering the angular dependence, emission angular distributions were also measured. The operational stabilities of the devices were measured under encapsulation in a glovebox.