Control of molecular orientation of organic p-i-n structures by using molecular templating effect at heterointerfaces

Structural control of the organic intrinsic layer (i-layer), which consists of a mixture of p- and n-type organic semiconductor materials, and the organic p-i-n triple-layer structure has been investigated. Significant modification of these structures, which used metal-free phthalocyanine (H2Pc) and 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) as the p- and n-type materials, respectively, was observed by introducing a modification layer deposited on a glass substrate. The orientation of the molecular planes of both H2Pc and PTCDA in the i-layer (H2Pc:PTCDA mixture) and p-i-n structure (H2Pc/i-layer/PTCDA) formed onto a PTCDA modification layer was parallel to the substrate surface. On the other hand, when H2Pc was used as the modification layer, the orientation of the molecular planes in the i-layer was found to be random. These results indicate that the internal structure of the organic mixed-layer is strongly affected by the organic layer-substrate interface. The enhancement in optical absorption observed for the orientation controlled p-i-n structure suggests the importance of the control of molecular orientation for improving the optical properties in organic device structures. (c) 2007 Elsevier B.V. All rights reserved.