Organic light-emitting device and apparatus including the same

An organic light-emitting device comprising:

• a first electrode,
• a second electrode, and
• an organic layer between the first electrode and the second electrode,
• wherein the organic layer comprises an emission layer,
• the organic layer comprises an electron transport region between the emission layer and the second electrode,
• the electron transport region comprises a hole blocking layer,
• the emission layer comprises a first compound, a second compound, a third compound, and a fourth compound,
• the first compound, the second compound, the third compound, and the fourth compound are different from each other,
• the third compound comprises a metal element having an atomic number of 40 or more,
• the fourth compound comprises boron (B),
• the hole blocking layer comprises a hole blocking material, and
• each of the first compound, the second compound, and the hole blocking material satisfies Conditions 4 and 5:
• T1(HB)≥T1(C1) Condition 4
• T1(HB)≥T1(C2) Condition 5
• wherein, in Conditions 4 and 5,
• T1(C1) is a lowest excitation triplet energy level of the first compound;
• T1(C2) is a lowest excitation triplet energy level of the second compound;
• T1(HB) is a lowest excitation triplet energy level of the hole blocking material;
• and
• each of T1(C1), T1(C2), and T1(HB) is an onset value which is a measured value.