Hybrid Heterojunction Nanorods for Nanoscale Controlled Morphology in Bulk Heterojunction Solar Cells

In this study, we report bulk heterojunction solar cells using hybrid heterojunction nanorods as photoactive material. The core–shell nanorods are obtained via self-assembly of low band gap p-type oligomers onto ZnO nanorod surfaces. This produces highly soluble donor–acceptor nanostructures that feature a grafted p-type semiconducting monolayer with a band gap of 2.1 eV. The solution processing of the coaxial nanorods into thin films leads to bulk heterojunctions of particularly large donor–acceptor interfaces. Importantly by simple processing donor domains smaller than typical exciton diffusion length of organic semiconductors are obtained which guaranties efficient exciton dissociation. The corresponding solar cells reveal that the hydrid nanorod layers form efficient interpenetrated networks which lead to external quantum efficiency of 20% at the absorption maximum λmax = 498 nm. Although the donor domains of these hybrid bulk heterojunction are constituted by monolayers, transient absorption spectroscopy could evidence long-lived photoinduced charge carrier generation of significant intensity. Thus the described hybrid heterojunction nanorods represent a promising strategy toward nanoscale controlled bulk heterojunction solar cells.