Horizontally oriented molecular thin films for application in organic solar cells

The authors investigate the influence of molecular orientation of p-type molecules of alpha-sexithiophene (alpha-6T) and n-type molecules of 3,4,9,10-perylene tetracarboxylic bisbenzimidazole (PTCBI) on organic solar cell (OSC) performance. Deposition of alpha-6T and subsequently PTCBI on an alpha-6T buffer surface rubbed with a nylon cloth allows their horizontal orientations to be formed in separate layers. Power conversion efficiency and operation stability of a rubbed OSC are markedly improved when compared with an unrubbed OSC. The improved OSC performance is confirmed to be due to increases in light absorption, exciton diffusion length, energy difference between the p-type and n-type layers, and carrier collection by electrodes, which are caused by the rubbing-induced double horizontal orientations. (C) 2014 Elsevier B.V. All rights reserved.