A Paradigm Shift Inspired by Nature: Robust Frenkel Excitons Despite Extreme Heat Stress
Dorthe M. Eisele
Center for Discovery and Innovation, CCNY
The future of sustainable energy technologies requires not only highly efficient but also robust light-harvesting (LH) materials, especially as rising global temperatures (i.e. increase of extreme weather events such as excessively high temperatures) threaten the efficiency of existing photovoltaic installations. Unlike current solar energy conversion technologies, natural photosynthetic organisms1 have clearly evolved beyond these challenges, capturing and transporting solar energy robustly and efficiently even under extreme environmental stress. Within photosynthetic organisms, delocalized Frenkel excitons — coherently-shared excitations among chromophores — are responsible for the remarkable efficiency of supramolecular LH assemblies. Clearly, supramolecular assemblies are Nature’s most successful material system for solar energy harvesting. However, the persistent limitations in translating nature’s design principles for applications in optoelectronic devices have been (1) the supramolecular structures’ fragility, and the Frenkel excitons’ delicate nature, especially (2) under elevated temperatures and (3) upon deposition onto solid substrates.
In my talk, I will present proof-of-concept that the intrinsic barriers towards functionalization of supramolecular assemblies can finally be overcome; through in situ cage-like scaffolding of individual supramolecular LH nan- otubes2 (as illustrated in the figure), we designed highly stable supramolecular nanocomposites3 with discretely tunable (~4.7-5.0 nm), uniform (±0.3 nm), cage-like scaffolds. High-resolution cryo-TEM, spectroscopy, and near- field scanning optical microscopy (NSOM) revealed supramolecular excitons within cage-like scaffolds are robust, even under extreme heat-stress. Complementary substrate studies on prototype dye-sensitized solar cells showed that our nanocomposites’ precise scaffold tunability in-solution was also maintained upon immobilization onto a solid substrate. Together, these results indicate that our novel supramolecular nanocomposite system is a successful, critical first step towards the development of practical bio-inspired LH materials for solar- energy conversion technologies as well as a basis for future fundamental investigations that were previously not possible, such as dilution of supramolecular assemblies required for single-molecule imaging or precise tunability of scaffold dimensions for controlled functionalization of hybrid model systems, i.e., plexcitonic systems.