Mechanism for the separation of organic semiconductors via thermal gradient sublimation

Two common hole transporting materials, N,N'-di(1-naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine (NPD) and tris(4-carbazoyl-9-ylphenyl)amine (TCTA) are separated and purified using thermal gradient sublimation. Their sublimation rates are proportional to the tube diameter squared and inversely proportional to the distance from the source boat to the deposition region. The deposition of these materials exponentially decays with distance down the tube. A theory predicting these results is derived. This theory suggests that diffusion and surface capture are the dominant steps in this purification, not processes in the source boat. It provides a rationale for improving the separation between multiple components and suggests routes for producing larger quantities of these materials. (C) 2015 Elsevier B.V. All rights reserved.