One of the key issues with improving the efficiency of conjugated polymer-based phovoltaics is controlling the nm-scale morphology of the two active components. Typically, efficiency is optimized by trial-and-error: component weight ratios, solvent additives, post-processing thermal annealing, etc. are all used to attempt to obtain the desired bulk heterojunction (BHJ) interpenetrating network. In this talk, we discuss some of our recent work aimed at using alternate, more reproducible methods for controlling BHJ morphology. We present results showing new amphiphilic semiconducting polymers and fullerenes that spontaneously selfassembly into co-axial cylindrical micelles in solution, and thus provide a built-in connected network when cast into gels that form thin films. Photoexcitation of the polymer in these systems produces separated charges on sub-ps time scales, and the separated charges are stable for weeks to months in air-free environments. The stability of the charge-separated pair can be controlled by changing the gel morphology. We also show that sequential processing of the polymer and fullerene components can provide an exquisite degree of control of the nm-scale morphology of a BHJ, and that the degree of crystallinity of the polymer controls both the amount of intercalated fullerene and the geometry of the interpenetrating network.

Avoiding kinetic control over the nm-scale morphology of conjugated polymer-based bulk heterojunction solar cells

248th National Meeting (2014)

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