Tuning the driving force for exciton dissociation in single-walled carbon nanotube heterojunctions

Abstract

Understanding the kinetics and energetics of interfacial electron transfer in molecular systems is crucial for the development of a broad array of technologies, including photovoltaics, solar fuel systems and energy storage. The Marcus formulation for electron transfer relates the thermodynamic driving force and reorganization energy for charge transfer between a given donor/acceptor pair to the kinetics and yield of electron transfer. Here we investigated the influence of the thermodynamic driving force for photoinduced electron transfer (PET) between single-walled carbon nanotubes (SWCNTs) and fullerene derivatives by employing time-resolved microwave conductivity as a sensitive probe of interfacial exciton dissociation. For the first time, we observed the Marcus inverted region (in which driving force exceeds reorganization energy) and quantified the reorganization energy for PET for a model SWCNT/acceptor system. The small reorganization energies (about 130 meV, most of which probably arises from the fullerene acceptors) are beneficial in minimizing energy loss in photoconversion schemes.

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Figure 1: Probing SWCNT exciton dissociation as a function of thermodynamic driving force using TRMC.
Figure 2: TRMC photoconductance transients at I0FA = 2 × 1012 cm−2 for the SWCNT bilayers (with C60 and C60(CF3)4) and neat films ((7,5) SWCNTs and LV SWCNTs).
Figure 3: Yield-mobility product versus absorbed flux.
Figure 4: Relative yield versus ΔGPET for (7,5) and LV bilayers with fullerene derivatives.

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Acknowledgements

We especially thank N. Kopidakis and R. Larsen for helpful discussions. R.I., K.S.M., A.J.F, G.R. and J.L.B. were funded by the Solar Photochemistry Program, Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences, US Department of Energy (Grant DE-AC3608GO28308). T.T.C., B.W.L., O.V.B. and S.H.S. acknowledge funding from the National Science Foundation (Grants CHE-1012468 and CHE-1362302).

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G.R., J.L.B. and A.J.F. conceived and designed the experiments. R.I. and K.S.M. prepared the bilayer samples and performed the experiments. T.T.C. and B.W.L. synthesized, purified and characterized the fullerene acceptors. A.J.F. and O.R. developed the kinetic analysis and facilitated the data fitting of the TRMC transients and Marcus curves. R.I., K.S.M., A.J.F. and J.L.B. wrote the paper. G.R., J.L.B., O.V.B. and S.H.S. supervised the overall project. All the authors discussed the results and commented on the manuscript.

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Correspondence to Jeffrey L. Blackburn.

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Ihly, R., Mistry, K., Ferguson, A. et al. Tuning the driving force for exciton dissociation in single-walled carbon nanotube heterojunctions. Nature Chem 8, 603–609 (2016). https://doi.org/10.1038/nchem.2496

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