An ITO glass substrate was cut to a size of 50 mm×50 mm×0.5 mm and then, sonicated in acetone isopropyl alcohol and pure water, each for 15 minutes, and then, washed by exposure to UV ozone for 30 minutes.
Subsequently, F6-TCNNQ was deposited on the ITO electrode (i.e., an anode) of the substrate to form a hole injection layer having a thickness of 100 ?, HT1 was deposited on the hole injection layer to form a first hole transport layer having a thickness of 1,260 ?, and F6-TCNNQ and HT1 were co-deposited at a weight ratio of 5:95 on the first hole transport layer to form a second hole transport layer having a thickness of 100 ?, thereby forming a hole transport region.
By using Compounds H2-1, H3-78, and H1-63 (at a weight ratio of 3.5:3:3.5) as hosts and Compound 3-337 as a dopant, the hosts and the dopant were deposited at a weight ratio of 85:15 on the hole transport region to form an emission layer having a thickness of 380 ?.