A new and versatile template towards vertically oriented nanopillars and nanotubes.

Vertically oriented nanostructures bring unparalleled high surface area, light trapping capability, and high device density to electronic, optoelectronic, and energy storage devices. However, general methods to prepare such structures remain sparse and are typically based on anodized metal oxide templates. Here, we demonstrate a new approach: using vertically oriented tetraaniline nanopillar arrays as templates for creating nanopillars and nanotubes of other materials. The tetraaniline templates are scalable and easy to prepare. Vertical arrays of a variety of materials can be created by directly coating them onto the tetraaniline nanopillars via vapor, solution, or electrodeposition. Since the tetraaniline template is encased within the target material, it does not require post-deposition removal, thus enabling vertical structure formation of sensitive materials. Conversely, removal of the encased tetraaniline template provides vertically oriented nanotube arrays in a lost-wax-type operation. The resulting vertical structures exhibit a high degree of orientation and height uniformity, with tunable feature size, spacing, and array density. Furthermore, the deposition location and shape of the vertical arrays can be patterned at a resolution of 3 μm. Collectively, these attributes should broaden the material repertoire for vertically oriented structures, and lead to advancements in energy storage, electronics, and optoelectronics

Understanding local and macroscopic electron mobilities in the fullerene network of conjugated polymer-based solar cells : time-resolved microwave conductivity and theory

The efficiency of bulk heterojunction (BHJ) organic photovoltaics is sensitive to the morphology of the fullerene network that transports electrons through the device. This sensitivity makes it difficult to distinguish the contrasting roles of local electron mobility (how easily electrons can transfer between neighboring fullerene molecules) and macroscopic electron mobility (how well-connected is the fullerene network on device length scales) in solar cell performance. In this work, a combination of density functional theory (DFT) calculations, flash-photolysis time-resolved microwave conductivity (TRMC) experiments, and space-charge-limit current (SCLC) mobility estimates are used to examine the roles of local and macroscopic electron mobility in conjugated polymer/fullerene BHJ photovoltaics. The local mobility of different pentaaryl fullerene derivatives (so-called ‘shuttlecock’ molecules) is similar, so that differences in solar cell efficiency and SCLC mobilities result directly from the different propensities of these molecules to self-assemble on macroscopic length scales. These experiments and calculations also demonstrate that the local mobility of phenyl-C₆₀ butyl methyl ester (PCBM) is an order of magnitude higher than that of other fullerene derivatives, explaining why PCBM has been the acceptor of choice for conjugated polymer BHJ devices even though it does not form an optimal macroscopic network. The DFT calculations indicate that PCBM's superior local mobility comes from the near-spherical nature of its molecular orbitals, which allow strong electronic coupling between adjacent molecules. In combination, DFT and TRMC techniques provide a tool for screening new fullerene derivatives for good local mobility when designing new molecules that can improve on the macroscopic electron mobility offered by PCBM.9 page(s