The efficiency of charge generation and recombination at a donor/acceptor (D/A) interface of organic photovoltaic (OPV) strongly depends on the interfacial molecular orientation of donor and acceptor materials. Edge-on (i.e. the main chain is parallel and the π-plane is perpendicular to D/A interface) and face-on (i.e. both the main chain and π-plane are parallel to D/A interface) orientations was obtained for the same π-conjugated semiconducting material at D/A interface by proper solvent selection.1 Several studies have been performed to clarify the effects of these orientation difference on OPV performance. Recently, we reported the formation of end-on orientation (i.e. The main chain is aligned vertical to the surface).2-3 This is based on the formation of surface segregated monolayer (SSM) of P3BT-F17 on P3HT film (Fig. 1a). For the end-on orientation, strong electronic and optical anisotropy and unique photophysical behavior were observed. 2-3
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