Diameter-Dependent Excitation Energy Transfer for Enhanced Semiconducting Single-Walled Carbon Nanotube Solar Photoconversion

Wednesday, 31 May 2017: 10:40
Churchill C1 (Hilton New Orleans Riverside)
R. Ihly (National Renewable Energy Laboratory), S. van Bezouw (University of Antwerp), D. Arias (National Renewable Energy Lab), S. Cambre (University of Antwerp), J. Campo (National Insitute of Standards and Technology), A. J. Ferguson, J. C. Johnson (National Renewable Energy Laboratory), W. Wenseleers (University of Antwerp), and J. L. Blackburn (National Renewable Energy Laboratory)
Tremendous progress and innovation has ushered the incorporation of semiconducting single-walled carbon nanotubes (s-SWCNTs) as active components into organic/inorganic/hybrid solar cells and thermoelectrics. For solar photoconversion, strong and tunable absorption is necessitated, suggesting that s-SWCNTs can play a role as light-harvesting components, however the narrow and distinct excitonic optical transitions found in s-SWCNT systems limit broad-band absorption. As such, we introduce encapsulation of small molecules within the endohedral volume of s-SWCNTs as a route to increase and extend light absorption in regions outside s-SWCNT excitonic transitions. Creation of this self-assembled supra-molecular system can strongly modify the opto-electronic properties of both the s-SWCNT and encapsulated molecule.

We investigate excitation energy transfer occurring from encapsulated dye molecules to s-SWCNTs, which results in luminescent SWCNT excitons. We exploit the high-throughput and chiral selectivity of polyfluorene wrapping methods to generate dispersions of s-SWCNTs with dye encapsulation. We demonstrate that the selectivity of the polyfluorene polymer for semiconducting chiral distributions is not affected by the presence of encapsulated molecules. Tracking the excited state transient absorption signatures of excitation energy transfer provides detailed information regarding dynamics of both the encapsulated dye and s-SWCNTs. We observe sub-picosecond excitation energy transfer of excitons generated in dye molecules to the surrounding s-SWCNTs. Photoluminescence excitation maps reveal that the absorption of encapsulated dye molecules depends sensitively on the diameter of the s-SWCNT in which they are encapsulated. We consider a simple molecular exciton model to describe aggregate formation within the s-SWCNT endohedral volume, which reveals that the dye molecules adopt unique aggregate structures that are defined both by a competition between intermolecular interactions between the dye molecules and confinement effects due to the s-SWCNT diameter. Small molecule encapsulation in s-SWCNTs serves as a strong platform to control intermolecular interactions in small molecule systems through confinement, which opens up the possibility of enhancing photo-induced extraction of energy and charge in s-SWCNTs solar photoconversion systems.