Directed Self-Assembly of Hybrid Oxide/Polymer Core/Shell Nanowires with Transport Optimized Morphology for Photovoltaics

Hybrid organic-inorganic solar cells are promising for the development of next generation low-cost, high efficiency photovoltaics (PVs). They combine the facile solution processability, large optical extinction coefficients, and good hole mobility of conjugated polymers with the high electron affinity and electron mobility of inorganic nanoparticles.[1] The most common configuration for effectively generating photocurrent with these materials is the bulk heterojunction (BHJ) device where intimate mixing of the polymer with inorganic nanoparticles generates a random bicontinuous morphology with nanometerscale dimensions. The morphology and ultimately the performance of this photoactive layer depend on a complex interplay of materials parameters and processing conditions such as temperature, polymer-solvent and particle-solvent interactions, solvent evaporation rate, solution composition (polymer volume fraction), and post-deposition treatments.[2] In particular, the role of polymer–particle miscibility has been well highlighted by recent reports.[3] Although there has been steady progress in improving device efficiency, the inherently disordered and kinetically-dictated structure of BHJ devices is suboptimal, particularly in terms of charge transport, but also in exciton utilization.[1a,4] An ideal hybrid device is one in which donor and acceptor materials are arranged in a densely packed vertical array. Nanometer-scale periodicity would minimize radiative decay of excitons, and the vertical alignment of the materials ensures a non-tortuous path for charge transport.[1a,4a,5] Such an ordered BHJ motif (OBHJ) has thus been the focus of recent interest,[6] but its realization, particularly in a manner compatible with low-cost fabrication of devices, remains elusive. A further refinement of the OBHJ entails atomic and molecularscale control of the donor and acceptor materials such that their