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 E₁₁ 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-C₆₁-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

Encapsulation effect of π‐conjugated quaterthiophene on the radial breathing and tangential modes of semiconducting and metallic single‐walled carbon nanotubes

“…Several studies on blends of conjugated polymers and SWCNT suggest that efficient exciton quenching occurs at these interfaces and many studies have shown direct evidence for the generation of mobile carriers in polymer-SWCNT composites. [21][22][23][24] After exciton dissociation, ballistic carrier transport in single tubes and extremely high conductivity in networks suggest that SWCNT may yield higher mobilities and form more conductive percolation networks than fullerenes. OPV cells based on CNTs as acceptor on the concept of BHJ is one of the most promising.…”

Broadband pump-probe spectroscopy at 20-MHz modulation frequency

“…We measured T/T dynamics on a spin-coated sample of semiconducting single-walled carbon nanotubes (SWNTs) starting from a highly concentrated dispersion in orthodichlorobenzene [20]. The resulting sample presents a large number of bundles and aggregates, with a predominance of the (6,5) and the (7,5) chiralities, resulting in a broad absorption band of the first excitonic transition (S11) centered at 1060 nm.…”

Theoretical Insight into the Internal Quantum Efficiencies of Polymer/C60and Polymer/SWNT Photovoltaic Devices

“…We included two thirds of the number of electrons ( 2 ⁄3N e ) many bands within the calculations. This has been shown to be sufficient to converge the first π → π * transitions of graphene 46 and SWNT/polymer hybrid systems, 47 and the optical spectra of polymers and oligomers 48 in the random phase approximation (RPA). Structural optimization was performed within the atomic simulation environment (ASE), 49 until a maximum force below 0.05 eV/Å was obtained.…”