On the unipolarity of charge transport in methanofullerene diodes

Abstract

Optoelectronics: Unipolar electron transport in fullerene diodes Fullerenes are commonly used in organic solar cells to attract and trap negatively charged electrons, whilst being able to block positively charged holes in photodiodes applications. Then the question is whether or not fullerenes conduct only one type of charge carriers, namely being unipolar, or are bipolar depending on the setups. A team led by Paul Meredith at Australia's University of Queensland evaluated the electron and hole transport mobility in neat PC70BM and PC60BM films using metal-insulator-semiconductor diodes, which are sensitive to the intrinsic transport properties of the samples. Their data showed that the hole mobility in bulk fullerenes is orders of magnitude lower than that of electrons and below the limits of their measurement, 10–9 cm2/Vs, indicating fullerenes are predominately unipolar. This research may help us better design fullerene-based optoelectronics and solar cells with high charge injection and extraction capability.