Carrier Mobilities in Amorphous Organic Semiconductor Films Prepared at Various Film Formation Processes

The hole mobility of an organic semiconductor film that consists of N,N’-di (1-naphthyl)-N,N’-diphenyl-benzidine (α-NPD) is evaluated at various film formation processes, such as vacuum deposition and capillary injection. The mobility varies with the film formation process. From the temperature dependence of mobility, the Poole−Frenkel model and disorder model are discussed. From the analysis based on the Poole−Frenkel model, activation energies of the vacuum-deposited film, the slowly cooled-melted film, and the rapidly cooled-melted film are 0.28, 0.20, and 0.40 eV, respectively. This result suggests that organic semiconductor thin films formed by different film formation methods have different molecular aggregation states.