Stable blue phosphorescent organic light emitting devices

An organic light emitting device, comprising:

• an anode;
• a cathode;
• an emissive layer disposed between the anode and the cathode, the emissive layer including a host and a phosphorescent emissive dopant having a peak emissive wavelength less than 500 nm;
• wherein
• the phosphorescent emissive dopant is deposited from a source that has a purity in excess of 99.5% as determined by high pressure liquid chromatography, the source further having a combined concentration of halide and metal impurities below 100 ppm;
• the phosphorescent emissive dopant leaves a residue corresponding to less than 5 wt % of the original charge in the sublimation crucible;
• and
• the phosphorescent emissive dopant has a sublimation temperature less than 350° C. and is deposited via sublimation;
• the phosphorescent emissive dopant is deposited in an environment having less than 10 ppm oxygen, and in the near absence of light having a wavelength <600 nm;
• the phosphorescent emissive dopant comprises a cyclometallated N,C-donor imidazophenanthridine ligand comprising at least one 2,2,2-trialkylethyl substituent.