A composition formed of a first mixture of a first compound and a second compound wherein the first compound has different chemical structure than the second compound; the first compound is capable of functioning as a hole transporting material in an organic light emitting device at room temperature; the first compound comprises at least one carbazole group; the first compound has a evaporation temperature T1 of 150 to 350 °C; the second compound has evaporation temperature T2 of 150 to 350 °C; the absolute value of T1-T2 is less than 20 °C; the first compound having a concentration C1 in said first mixture, and the first compound having a concentration C2 in a film formed by evaporating the first mixture in a vacuum deposition tool at a constant pressure between 1x10 -6 Torr to 1x10 -9 Torr, at a 2Å/sec deposition rate on a surface positioned at a predefined distance away from the mixture being evaporated; and wherein the absolute value of (C1-C2)/C1 is less than 5%.