Solventless deposition of oligo- and polythiophenes for bulk heterojunction solar cells

• Preparation of a methoxyhexyl-substituted octithiophene for OPV cells.
• One-shot deposition of the photoactive layer using vacuum thermal evaporation.
• Chemical and structural analysis of the evaporated oligomer.
• Efficiency with evaporated oligomer higher than with conventional P3HT.
• Efficiency with VTE higher than using the conventional deposition technique.

In this paper we report on the vacuum thermal evaporation (VTE) of poly(3-hexyl)thiophene (P3HT) and a thiophene derivative octamer (OCT) on glassy substrates. The films obtained have been characterized using FT-IR and NMR techniques and, for OCT, UV–vis, XRD and cyclic voltammetry. Solar cells, obtained by simultaneous evaporation of the electron–donor (P3HT or OCT) and electron-acceptor (C60-fullerene) components, were examined by AFM and their efficiency was evaluated under simulated solar illumination. With the oligomeric sample a power conversion efficiency of 1.21% was obtained: a value higher than that obtained with a device prepared with the same oligomer adopting the conventional coating systems used for building-up polymeric BHJ solar cells.

Optical microscopy image with cross polarizers showing the crystalline morphology of a thin film of octithiophene (OCT) obtained by vacuum thermal evaporation (50×).Figure optionsDownload as PowerPoint slide