An organic light emitting device includes a substrate, an anode and a cathode disposed over the substrate, and a luminescent layer disposed between the anode and the cathode wherein the luminescent layer includes a host and at least one dopant. The host of the luminescent layer is selected to include a solid organic material comprising a mixture of at least two components, one of which contains at least one perylene carbocyclic ring structure or at least one mono-aza-perylene or poly-aza-perylene ring structure and is capable of forming both monomer state and an aggregate state.