Electron Transport in a Methanofullerene

The current–voltage characteristics of methanofullerene [6,6]‐phenyl C61‐butyric acid methyl ester (PCBM)‐based devices are investigated as a function of temperature. The occurrence of space–charge limited current enables a direct determination of the electron mobility. At room temperature, an electron mobility of μe = 2 × 10–7 m2 V–1 s–1 has been obtained. This electron mobility is more than three orders of magnitude larger than the hole mobility of donor‐type conjugated polymer poly(2‐methoxy‐5‐(3′,7′‐dimethyloctyloxy)‐p‐phenylene vinylene) (OC1C10‐PPV). As a result, the dark current in PCBM/OC1C10‐PPV based devices is completely dominated by electrons. The observed field and temperature‐dependence of the electron mobility of PCBM can be described with a Gaussian disorder model. This provides information about the energetic disorder and average transport‐site separation in PCBM. The transport properties of electrons in C60 based molecules (see Figure), as used in conjugated polymer based solar cells have been investigated. At room temperature, the electrons in the C60 based molecules are a factor of four thousand more mobile than the holes in the conjugated polymer. These results are of fundamental importance to further the understanding of polymer/C60 solar cells.