Effects of Phase Separation on Charge Mobility in Active Layer of Polymer Solar Cells
Malyutin, Andrey G.
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One of the limiting factors in polymer solar cell performance is charge carrier mobility through the cell. Recently, it has been reported that the hole mobility in certain blends can be enhanced by additional electron transport material. Our hypothesis is that the phase segregation process induces local ordering which increases hole mobility. We study how the hole mobility changes as a function of blend composition and domain size in solar cells with active layers consisting of various mixtures of [6,6]-phenyl C61- butyric acid methyl ester (PCBM) (electron acceptor) and poly[2-methoxy-5-(3,7- dimethyloctyloxy)-p-phenylene vinylene] (MDMO-PPV) (electron donor). We show that charge carrier mobility increases as the ratio of PCBM to PPV in the active layer increases. We present AFM images of each blend, and show that phase separation between the two molecules and increase in feature size of PCBM are correlated with the increase in hole mobility.