Horizontally oriented molecular thin films for application in organic solar cells

• Influence of molecular orientation on organic solar cell performance is investigated.
• A rubbing technique induces double horizontal orientations of α-6T and PTCBI.
• The horizontal orientations enhance efficiency and operation stability of the cell.
• The improved cell performance is discussed in terms of molecular orientation.

The authors investigate the influence of molecular orientation of p-type molecules of alpha-sexithiophene (α-6T) and n-type molecules of 3,4,9,10-perylene tetracarboxylic bisbenzimidazole (PTCBI) on organic solar cell (OSC) performance. Deposition of α-6T and subsequently PTCBI on an α-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.

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