Molecular dynamics study of pair interactions, interfacial microstructure, and nanomorphology of C₆₀/MEH-PPV hybrids

Atomistic molecular dynamics (AMD) simulations are utilized to simultaneously explore the detailed pair interactions, interfacial microstructure, and nanoscale (phase-separated) morphology of a series of thermally annealed C₆₀-MEH-PPV (monomer and oligomer) (poly(2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene)) hybrids. The present study provides essential details for understanding fundamental particle interactions that regulate the microscopic (structural and morphological) features of a standard polymer-fullerene material, paving the way to the eventual goal of capturing the photovoltaic physics of similar hybrid systems widely viewed as a potential alternative to the conventional (inorganic) semiconducting materials. Specifically, we show that two dominant interfacial pair C₆₀-MEH-PPV-mer configurations—denoted as “face-on” or “side-on” motif—can thus be identified. These two motifs seem to be rather universal, and are shown to be dictated by many-body energetic forces in a condensed phase, as they display clear independence on the effects of system temperature, blending ratio, and chain connectivity. Importantly, the pair configurations (which should embed precise information on separation distance and mutual alignment) so unraveled provide an unambiguous first step toward resolving quantum-mechanic properties relevant to the photovoltaic performance of a hybrid material. Although the simulation length scale is limited for one to unequivocally reveal bulk phase behavior, the results on nanoscale phase morphologies are in accord with recent experimental trends regarding the effects of polymer molecular weight and blending ratio. Future outlooks of utilizing the established molecular system for predicting light adsorption and interfacial charge behavior are remarked.