Photoinduced Absorption within Single-Walled Carbon Nanotube Systems

Abstract

We study the photoabsorption properties of photoactive bulk polymer/ fullerene/nanotube heterojunctions in the near-infrared region. By combining pump-probe spectroscopy and linear response time-dependent density functional theory within the random phase approximation (TDDFT-RPA) we elucidate the excited state dynamics of the $E_{11}$ transition within (6,5) and (7,5) single-walled carbon nanotubes (SWNTs) and combined with poly(3-hexylthiophene-2,5-diyl) (P3HT) and [6,6]-phenyl-C${}_{61}$-butyric acid methyl ester (PCBM) in P3HT/PCBM/SWNT blended samples. We find the presence of a photoinduced absorption (PA) peak is related mainly to the width of the photobleach (PB) peak and the charge carrier density of the SWNT system. For mixed SWNT samples, the PB peak is too broad to observe the PA peak, whereas within P3HT/PCBM/SWNT blended samples P3HT acts as a hole acceptor, narrowing the PB peak by exciton delocalization, which reveals a PA peak. Our results suggest that the PA peak originates from a widening of the band gap in the presence of excited electrons and holes. These results have important implications for the development of new organic photovoltaic heterojunctions including SWNTs.

9 pages, 10 figures

References in corpus (7)

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• Localized atomic basis set in the projector augmented wave method
• Linear density response function in the projector-augmented wave method: Applications to solids, surfaces, and interfaces
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Cited by in corpus (4)

• Optical Absorption Spectra and Excitons of Dye-Substrate Interfaces: Catechol on TiO${}_2$(110)
• Optical Absorption and Energy Loss Spectroscopy of Single-Walled Carbon Nanotubes
• LCAO-TDDFT-$k$-$\omega$: Spectroscopy in the Optical Limit
• Theoretical Insight into the Internal Quantum Efficiencies of Polymer/C${}_{60}$ and Polymer/SWNT Photovoltaic Devices