Constructing Multifunctional Virus-Templated Nanoporous Composites for Thin Film Solar Cells: Contributions of Morphology and Optics to Photocurrent Generation

Biotemplates, such as the high aspect ratio M13 bacteriophage, can be used to nucleate noble metal nanoparticles and photoactive materials such as metal oxides, as well as organize them into continuous structures. Such attributes make them attractive scaffolds for solar applications requiring precise organization at the nanoscale. For instance, thin film solar cells benefit from nanostructured morphologies that aid light absorption and carrier transport. Here, we present a biotemplating strategy for assembling nanostructured thin film solar cells that enhance the generated photocurrent through two features: (1) a nanoporous and continuous M13 bacteriophage-templated titania network that improves charge collection and (2) the incorporation of metal nanoparticles within the active layer of the device to improve light harvesting. We demonstrate our ability to construct virus-templated solar cells by applying this strategy to depleted titania–lead sulfide quantum dot (PbS QD) bulk heterojunctions. The titania morphology produced by our biotemplate allows charges to be efficiently collected from the bulk of the active material and light that is otherwise poorly absorbed by the QDs to be harvested using metal nanoparticles that exhibit plasmon resonances in the visible range. We show that high aspect ratio bacteriophages provide a structural template for synthesizing titania networks with tunable porosity, into which PbS QDs are infiltrated to create photoactive nanocomposites suitable for photovoltaics. Upon optimization, the generated photocurrent and power conversion efficiency of the bacteriophage-templated devices demonstrate a 2-fold improvement over those of control devices made with randomly organized titania nanoparticles. When the virus is complexed with gold nanoparticles (Au NPs), silver nanoparticles (Ag NPs), or silver nanoplates (Ag NPLs) during assembly, the device performance is further improved, with Ag NPLs enhancing the short-circuit current density and power conversion efficiency by 16% and 36.5%, respectively, over those of virus-based devices without NPs. The observed trends in photocurrent enhancement match well with numerical predictions, and the role of the nanostructured morphology on the device optics was computationally explored. The challenges overcome in this work could be extended to other heterojunction devices, such as hybrid systems involving conducting polymers, as well as other biologically templated electronics.