An organic light emitting device (OLED, 100, 200, 300), comprising: an anode (115, 230, 315); a cathode (160, 215, 360); and an organic emissive layer (135, 220, 335) disposed between the anode and the cathode, the organic emissive layer comprising: a first host having a highest occupied molecular orbital (HOMO) energy, a lowest unoccupied molecular orbital (LUMO) energy, and a T 1 triplet energy; a second host having a highest occupied molecular orbital (HOMO) energy, a lowest unoccupied molecular orbital (LUMO) energy, and a T 1 triplet energy; a third host having a highest occupied molecular orbital (HOMO) energy, a lowest unoccupied molecular orbital (LUMO) energy, and a T 1 triplet energy; and an emitter having a highest occupied molecular orbital (HOMO) energy, a lowest unoccupied molecular orbital (LUMO) energy, and a T 1 triplet energy; wherein the emitter is a phosphorescent metal complex having E ET, T 1 triplet energy, of at least 2.50 eV, wherein the T 1 triplet energy is determined from the first emission peak of photoluminescence at 77K; wherein the LUMO energy of the first host is higher than the HOMO energy of the emitter; wherein the absolute value of the difference between the HOMO energy of the emitter and the LUMO energy of the first host is Δ E1; wherein the HOMO energy of the second host is lower than the HOMO energy of the emitter; wherein the absolute value of the difference between the HOMO energy of the emitter and the HOMO energy of the second host is Δ E4; wherein a ≤ ΔE1 - E ET ≤ b, wherein a ≥ 0.005 eV and b ≤ 0.60 eV; wherein ΔE4 ≤ d, wherein d is 1.2 eV; and wherein the HOMO energy of the third host is lower than the HOMO energy of the second host; and characterized in that the first host, second host, and third host are different from each other. an anode (115, 230, 315); a cathode (160, 215, 360); and an organic emissive layer (135, 220, 335) disposed between the anode and the cathode, the organic emissive layer comprising: a first host having a highest occupied molecular orbital (HOMO) energy, a lowest unoccupied molecular orbital (LUMO) energy, and a T 1 triplet energy; a second host having a highest occupied molecular orbital (HOMO) energy, a lowest unoccupied molecular orbital (LUMO) energy, and a T 1 triplet energy; a third host having a highest occupied molecular orbital (HOMO) energy, a lowest unoccupied molecular orbital (LUMO) energy, and a T 1 triplet energy; and an emitter having a highest occupied molecular orbital (HOMO) energy, a lowest unoccupied molecular orbital (LUMO) energy, and a T 1 triplet energy; a first host having a highest occupied molecular orbital (HOMO) energy, a lowest unoccupied molecular orbital (LUMO) energy, and a T 1 triplet energy; a second host having a highest occupied molecular orbital (HOMO) energy, a lowest unoccupied molecular orbital (LUMO) energy, and a T 1 triplet energy; a third host having a highest occupied molecular orbital (HOMO) energy, a lowest unoccupied molecular orbital (LUMO) energy, and a T 1 triplet energy; and an emitter having a highest occupied molecular orbital (HOMO) energy, a lowest unoccupied molecular orbital (LUMO) energy, and a T 1 triplet energy; wherein the emitter is a phosphorescent metal complex having E ET, T 1 triplet energy, of at least 2.50 eV, wherein the T 1 triplet energy is determined from the first emission peak of photoluminescence at 77K; wherein the LUMO energy of the first host is higher than the HOMO energy of the emitter; wherein the absolute value of the difference between the HOMO energy of the emitter and the LUMO energy of the first host is Δ E1; wherein the HOMO energy of the second host is lower than the HOMO energy of the emitter; wherein the absolute value of the difference between the HOMO energy of the emitter and the HOMO energy of the second host is Δ E4; wherein a ≤ ΔE1 - E ET ≤ b, wherein a ≥ 0.005 eV and b ≤ 0.60 eV; wherein ΔE4 ≤ d, wherein d is 1.2 eV; and wherein the HOMO energy of the third host is lower than the HOMO energy of the second host; and characterized in that the first host, second host, and third host are different from each other.