Titanium oxide:fullerene composite films as electron collector layer in organic solar cells and the use of an easy-deposition cathode

Abstract Here is reported the use of a titanium oxide:fullerene (TiO x :PC 71 BM) composite film as electron collector layer in organic photovoltaic devices (OPV cells). OPV cells were fabricated under the bulk heterojunction architecture: the active layer was a blend of either the photoconductor polymer MEH–PPV or P3HT with the fullerene derivative PC 71 BM. As cathode the eutectic alloy of Bi, In and Sn, known as Field’s metal, was used. The melting point of this alloy is above 62 °C, which makes it suitable for a vacuum-free deposition process and easy and fast device test. Cell fabrication and testing were carried out at normal room conditions. For OPV cells based on MEH–PPV, the composite thin electron collector layer improved the power conversion efficiency ( η ) from 1.12% to 2.07%, thus the η increase was about 85%. Meanwhile, for devices based on P3HT the use of the composite film improved the photocurrent in almost 1 mA/cm 2 and the efficiency slightly increase from 2.48% to 2.68%.