Laterally Ordered Bulk Heterojunction of Conjugated Polymers: Nanoskiving a Jelly Roll

This paperdescribes the fabricationof ananostructuredheterojunctionof twoconjugatedpolymersbya three-stepprocess: i) spincoating a multilayered film of the two polymers, ii) rolling the film into a cylinder (a ‘‘jelly roll’’) and iii) sectioning the film perpendicular to the axis of the roll with an ultramicrotome (nanoskiving). The conjugated polymers are poly(benzimidazobenzophenanthroline ladder) (BBL, n-type) and poly(2-methoxy-5-(20-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV, p-type). Theprocedureproduces sectionswithan interdigitated junctionof the twopolymers.Thespacingbetween thephases isdetermined by spin-coating ( 15 nm to 100 nm) and the thickness of each section is determined by the ultramicrotome (100 to 1000 nm). The minimumwidthof theMEH-PPVlayersaccessiblewith this technique( 15 nm)isclose toreportedexcitondiffusion lengths for the polymer.Whenplaced ina junctionbetween twoelectrodeswithasymmetricwork functions (tin-doped indiumoxide (ITO)coated with poly(3,4-ethylenedioxythiophene:poly(styrenesulfonate) (PEDOT:PSS), and eutectic gallium-indium, EGaIn) the heterostructures exhibit a photovoltaic response under white light, although the efficiency of conversion of optical to electrical energy is low. Selective excitation of BBL with red light confirms that the photovoltaic effect is the result of photoinduced charge transfer between BBL and MEH-PPV.