Controlling Intermolecular Interactions at Interfaces: Case of Supramolecular Tuning of Fullerene’s Electronic Structure
in: Advanced Energy Materials (2018)
It is demonstrated that systematic and designated control of supramolecular nanostructures via interfacial engineering enables (opto)electronic C60-materialproperties to be widely adjusted. Interestingly, the lowest unoccupied molecular orbital (LUMO) energies of the same amphiphilic fullerene species are tuned up to 120 meV using supramolecular assembly, competitive to complete molecular change; cf. PC61BM to PC71BM causes a change of 200 meV. Morphology control is achieved through different thin-film production techniques involving molecular assembly at interfaces, including liquid–liquid interfacial precipitation (LLIP), and Langmuir–Blodgett technique at air–water interface. LLIP enables supramolecularly ordered extended surfaces, yielding the least electronically stable LUMO (ELUMO = −4.28 eV). After qualitatively explaining the observed electrochemical LUMO energy variation for these assemblies with varied molecular packing and aggregate dimensions, an analytical equation is proposed, connecting morphological parameters with LUMO energies with prospects in supramolecular chemistry. To demonstrate the applicability of supramolecular structure–electronic property relations and of supramolecular structure fabrication protocols established in this work to tailor device properties, amorphous-Si/fullerene hybrid solar cells are built and characterized. It is found that the supramolecular structure variation can be successfully translated to the solar cells, giving rise to a prototype linear relation between LUMO energy and open-circuit voltage.