Role of carbon nanotubes as an acceptor to enhance the photovoltaic performances of organic solar cells based on π ‐conjugated thiophene as a donor materials

Abstract

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.