Charge transfer evidence in donor–acceptor single‐walled carbon nanotubes filled with sexithiophene oligomers: Nanotube diameter dependence

Abstract

Encapsulation of photoactive organic molecules inside single‐walled carbon nanotubes (SWNTs) appears to be of great interest in terms of high power conversion efficiency and long‐term stability for a commercial application of organic solar cells (OSCs). In this paper, we report a charge transfer (CT) evidence in donor–acceptor SWNTs filled with Sexithiophene oligomers (6T) by Raman spectroscopy. To compute the optimal diameter and demonstrate the most stable structure of the hybrid systems with either a single 6T molecule encapsulated into SWNTs (6T@SWNTs), or two 6T chains encapsulated (6T‐6T@SWNTs), we have performed structural geometry optimization on the hybrid encapsulated systems using a convenient Lennard–Jones (LJ) expression of the van der Waals (vdW) intermolecular potential. Combining the density functional theory (DFT), molecular mechanics, bond polarizability model, and the spectral moment method (SMM), we computed the polarized nonresonant Raman spectra of 6T molecule and SWNTs (metallic and semiconducting) before and after encapsulation. The influence of the encapsulation on the Raman‐active modes of the 6T molecule and those of the nanotube (radial breathing modes and tangential modes) are analyzed. In particular, significant changes observed in the G‐band wavenumber. The possibility (or not) of an eventual CT between the 6T oligomer and the nanotube in both hybrid systems (6T@SWNTs and 6T‐6T@SWNTs) is discussed. We show that there is a dependence of the CT with respect to the diameter of SWNTs, the CT vanish with increasing diameter of the nanotubes. Our finding of CT behavior in the filled SWNTs with respect to SWNT diameter will provide a useful guidance for enhancing the performance of OSCs by SWNTs.

High-Performance Broadband Photodetectors Based on Asymmetric All-Carbon Nano-Heterostructures

“…In Figure e, an enhanced blue shift of the 2D – band can be observed with increasing C 60 thickness, indicating the electron transfer from SWCNTs to C 60 . The 2D – band of graphene/SWCNT heterostructures is increased by ∼2.1 cm –1 compared to that of pure SWCNTs, indicating that graphene plays a p-doping role in SWCNTs and the holes transfer from SWCNTs to graphene. , Likewise, graphene is responsible for the 2D + band of the C 60 /graphene/SWCNT heterostructures. As shown in Figure f, the 2D + band blue shift increases with the increase of C 60 thickness on graphene, which indicates p-doping and the holes transfer from C 60 to graphene. , The 2D + band of graphene/SWCNT heterostructures is decreased by ∼0.9 cm –1 compared to that of pure SWCNTs, and this indicates that SWCNTs provide n-doping to graphene and the electrons transfer from SWCNTs to graphene. , Regardless of whether it is hole or electron doping, the Raman shifts of G bands are decreased, but the 2D – and 2D+ bands shift differently for each type of doping resulting in the two trends in Figure e,f.…”

“…However, when the C 60 thickness increases from 35 to 56 nm, the red shift is attenuated significantly. The red shift of the G band, 2D – band, and 2D + band indicates the electron doping effect induced by the charge transfer (holes) from C 60 to graphene/SWCNT in the heterostructures. , This indicates that the electron doping of the graphene/SWCNT heterojunction increases with the C 60 thickness from 0 to 35 nm, and then the electron doping weakens slightly with the further increase of C 60 thickness from 35 to 56 nm.…”

“…The 2D − band of graphene/SWCNT heterostructures is increased by ∼2.1 cm −1 compared to that of pure SWCNTs, indicating that graphene plays a p-doping role in SWCNTs and the holes transfer from SWCNTs to graphene. 43,44 Likewise, graphene is responsible for the 2D + band of the C 60 /graphene/SWCNT heterostructures. As shown in Figure 4f, the 2D + band blue shift increases with the increase of C 60 thickness on graphene, which indicates p-doping and the holes transfer from C 60 to graphene.…”

“…To minimize the influence of any inhomogeneity on the interfacial charge transfer, Raman shifts statistics have been 42,43 This indicates that the electron doping of the graphene/SWCNT heterojunction increases with the C 60 thickness from 0 to 35 nm, and then the electron doping weakens slightly with the further increase of C 60 thickness from 35 to 56 nm.…”

Hole Doping in Polythiophenes Encapsulated in Semiconducting and Metallic Single-Walled Carbon Nanotubes: Impact of the Electronic Structure

“…The PT backbone was chemically oxidized by iodine. Another route is the condensation of thiophene molecules in nanocylinders such as zeolites , and single-walled carbon nanotubes (SWNTs). − It is known that SWNTs can encapsulate oligothiophene molecules, − and several papers reported condensation of the molecules in the SWNTs. − Sasaki et al used dibromo-terthiophenes (Br 2 -3T) as precursors. In this study, oligothiophene with the number of thiophene rings ( n ) is denoted by n T. They succeeded in the synthesis and spontaneous oxidization (hole doping) of PT molecules .…”