Provided are a composition and an organic light-emitting device including the same, wherein the composition includes a platinum-containing organometallic compound, a first compound, a second compound, and a third compound.
The “group represented by one of Formulae 9-1 to 9-66 in which at least one hydrogen is substituted with deuterium” may be a group represented by one of Formulae 9-501 to 9-552: