O rganic-based photovoltaic cells (OPVs) are of great interest owing to their potential for low-cost solar energy conversion. 1 An important breakthrough for OPVs was the use of a heterojunction (HJ) structure, in which the difference of the energy levels of two materials (donor and acceptor) can lead to efficient dissociation of photogenerated excitons at the HJ interfaces. 1 Since then, tremendous efforts have been taken to optimize the carrier donor/acceptor (DA) interface morphology to improve the photogenerated exciton dissociation and consequently the overall power conversion efficiency. 2 One successful approach is to use a bulk heterojunction (BHJ) structure that can create dissociation centers everywhere within the active layer. 2 Typically, the formation of a BHJ structure can be achieved via self-assembly of nanostructured soft materials by spontaneous phase separation in a number of solution processed polymer/ fullerene systems, yet efficiency in these structures might be significantly reduced through unpredicted shunt paths and isolated islands of materials. 3 Nanoimprint lithography (NIL) offers a potential solution for producing well-defined interpenetrating networks at the DA interface and is compatible with roll-to-roll manufacturing for lowcost and high-throughput nanopatterning. 4,5 To efficiently harvest photogenerated excitons, densely packed nanoimprinted OPV structures with halfpitch smaller than 2 times that of the exciton diffusion length are needed (typically sub-20 nm regime). 6 Recent efforts in this field have been mainly focusing on polymeric PV materials. However, OPVs with small-molecular weight materials could also benefit from similar morphologies. In addition, small-molecular weight OPV materials provide additional advantages over polymers, such as higher chemical/thermal stability and higher material purity. 7 Previous work has shown relatively poor stability of imprinted nanostructures in smallmolecular compounds. 8Ϫ10 Problems arise due to pronounced surface diffusion and self-faceting and are exacerbated when features head toward the sub-20 nm regime. 11,12 These instabilities must be understood and overcome to achieve efficient nanostructured OPVs.Boron subphthalocyanines (SubPcs) are a class of photoactive small-molecularweight materials with unique physical properties. 13 A typical SubPc has a nonplanar pyramid-shaped structure, in which the boron atom is surrounded by three coupled

Resist adhesion to the mold is one of the challenges for nanoimprint lithography. The main approach to overcoming it is to apply a self-assembled monolayer of an organosilane release agent to the mold surface, either in the solution phase or vapor phase. We compared the atomic force microscopy, ellipsometry, reflection-absorption infrared spectroscopy, and contact angle results collected from substrates treated by two different application processes and found that the vapor-phase process was superior. The vapor-treated substrates had fewer aggregates of the silane molecules on the surface, because the lower density of the agent in the vapor phase was not conducive to aggregation formation, and received a superior coating of the releasing agent, because the vapor was more effective than the solution in penetrating into the nanoscale gaps of the mold. A pattern transfer of 20 parallel nanowires with a line width of 40 nm at 100 nm pitch-size was performed faithfully with the vapor-treated mold without any resist adhesion.

Nanoscale molecular-electronic devices comprising a single molecular monolayer of bistable [2]rotaxanes sandwiched between two 40-nm metal electrodes were fabricated using imprint lithography. Bistable current–voltage characteristics with high on–off ratios and reversible switching properties were observed. Such devices may function as basic elements for future ultradense electronic circuitry.