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.

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We developed a hybrid approach, combining the density functional theory, molecular mechanics, bond polarizability model and the spectral moment's method to compute the nonresonant Raman spectra of a single quaterthiophene (4T) molecule encapsulated into a single-walled carbon nanotube (metallic or semiconducting). We reported the optimal tube diameter allowing the 4T encapsulation. The influence of the encapsulation on the Raman modes of the 4T molecule and those of the nanotube (radial breathing modes and tangential modes) are analyzed. An eventual charge transfer between the 4T oligomer and the nanotube is discussed.

Summary Filled semiconducting single‐walled carbon nanotubes (SWNTs), with π‐conjugated polymer as a light harvester and charge transporter in the active layer, could play a key role in the development of more qualified organic solar cells (OSCs) in the sense of high energy conversion efficiency and long‐term stability. In this paper,we used three computational approaches to investigate a series of oligothiophene (nT) (n = 2, 4 or 6) encapsulated inside SWNTs. The first approach is based on a combination of the density functional theory (DFT), molecular mechanics, bond polarizability model and the spectral moment's method (SMM) to compute the nonresonant Raman spectra of the encapsulated systems. We reported the optimal tube diameter allowing the nT encapsulation. The influence of the encapsulation on the radial breathing mode and G‐band modes of the selected semiconducting SWNTs zigzag (11,0), labeled (NT11), is testified to the presence of the charge transfer (CT) in the nT@NT11 hybrid systems without specifying their direction. The second approach is based on the electronic and optical properties with DFT at the generalized gradient approximation. The CT and its direction in nT@NT11 hybrid systems is identified by electronic and optical calculations. The third approach is based on electronic transport properties with DFT in combination to nonequilibrium Green's function formalism. We have investigated the transmission spectra and current‐voltage characteristics of nT@NT11 hybrid. It was observed that a strong correlation between transmission spectra and DOS near the Fermi level due to delocalization of electronic states, and the I‐V characteristic exhibits interesting electronic transport properties. The results illustrate that the filled semiconducting SWNTs exhibiting type II heterojunctions are expected to be a good candidate as a light harvester and charge transporter in the active layer, which can contribute to developing highly efficient filled SWNT‐based OSCs.

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