Photovoltaic properties of octithiophene-based Schottky and p/n junction cells: Influence of molecular orientation

We report here on the photovoltaic properties of Schottky and p/n junction cells based on octithiophene (8T). In the solid state, 8T is an elongated planar molecule with efficient p-type transport properties. We investigate in particular the influence of molecular orientation of 8T films on light absorption, I/V characteristics and photocurrent spectra. We show that a substantial increase of the photocurrent density is obtained by aligning the 8T molecules horizontally and parallel to each other on the substrate by means of a simple rubbing technique. This improvement is attributed to a more efficient light absorption rather than to an improvement of the charge transport properties in the sandwich devices.