Organic electroluminescent materials and devices

Abstract

A premixed co-evaporation source that is a mixture of a first compound and a second compound is disclosed. The co-evaporation source is for vacuum deposition process. The first compound has a different chemical structure than the second compound. The first compound and the second compound are both organic compounds. At least one of the first compound and the second compound contains at least one less abundant stable isotope atom. At least one of the first compound and the second compound is a fluorescent or delayed fluorescent emitter. The first compound has an evaporation temperature T1 of 100 to 400° C.; the second compound has an evaporation temperature T2 of 100 to 400° C.; the absolute value of T1−T2 is less than 20° C. The first compound has a concentration C1 in said mixture and a concentration C2 in a film formed by evaporating the mixture in a high vacuum deposition tool with a chamber base pressure between 1×10Torr to 1×10Torr, at a 2 Å/sec deposition rate on a surface positioned at a predefined distance away from the mixture being evaporated. The absolute value of (C1−C2)/C1 is less than 5%.