Organic light-emitting device

An organic light-emitting device comprising:

• a first electrode;
• a second electrode facing the first electrode;
• and
• an emission layer disposed between the first electrode and the second electrode,
• wherein
• the emission layer comprises a first material, a second material, and a light-emitting material,
• the light-emitting material comprises a transition metal-containing phosphorescent material that emits blue light having a maximum emission wavelength in a range of about 420 nanometers to about 480 nanometers,
• the emission layer emits blue phosphorescence generated when an exciton of the transition metal-containing phosphorescent material transits from a triplet excited state to a ground state,
• the first material and the second material are different from each other,
• the first material and the second material form an exciplex,
• at least one of an absolute value of a difference between triplet energy (expressed in electron volts) of the first material and singlet energy (expressed in electron volts) of the exciplex and an absolute value of a difference between triplet energy (expressed in electron volts) of the second material and the singlet energy (expressed in electron volts) of the exciplex is about 0.1 electron volts or less,
• the triplet energy of the first material is calculated from a peak wavelength of a phosphorescence spectrum measured at 77 Kelvins with respect to a mixture of the first material and 2-MeTHF,
• the triplet energy of the second material is calculated from a peak wavelength of a phosphorescence spectrum measured at 77 Kelvins with respect to a mixture of the second material and 2-MeTHF, and
• the singlet energy of the exciplex is calculated from a peak wavelength of a fluorescence spectrum measured at room temperature with respect to a 50-nanometer-thick thin film formed by co-depositing the first material and the second material at a weight ratio of 5:5.