Germanium endometallo fullerene was synthesized by arcing Ge-impregnated graphite rod as anode and pure graphite rod as cathode. Photoluminescence (PL) and resistance measurements suggest that there are effective interactions at the interface of Ge endometallo fullerene and poly 3-hexyl thiophene (P3HT). Four-fold enhancement of conductance has been found by adding just one weight percentage of Ge endometallo fullerene in the P3HT matrix at room temperature. However, at lower and higher temperatures, the enhancement in conductivity is low compared with room temperature, indicating the efficient charge transfer across the interface at the temperature range of 300-350 K. Atomic force microscopy (AFM) images also confirm the fact that temperature makes the more ordered heterojunctions between P3HT and Ge endohedral metallofullerene, which, in turn, trigger charge separation across interfaces. A sharp quenching in PL intensity of P3HT at room temperature by adding Ge endometallo fullerene indicates a strong interaction between the two and this composite material can be useful in photovoltaic cell. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 114: 491-495, 2009