Effect of different topological structures (D-π-D and D-π-A-π-D) on the optoelectronic properties of benzo[2,1-B:3,4-B́]dithiophene based donor molecules toward organic solar cells.

Simulated absorption spectra of twelve donors based on D-π-D (a) and D-π-A-π-D (b) topologies with the Solar Flux for AM 1.5G. • A comparative analysis of different shapes (star, π, H and X) and different topologies (D-π-D and D-π-A-πD) molecules is done. • DFT and TD-DFT calculations has been carried out to know their optical and charge transfer properties. • On the basis of results, we suggest best performing donor materials for organic solar cells. As substantial building units, different shapes and topologies enhance optical and electronic properties. Hence, in this paper, twelve anisotropic molecules of different shapes (star or S, π and H) based on D-π-D and D-π-A-π-D topologies have been designed and investigated theoretically applying a double overlapping wave band strategy for organic photovoltaic applications. This analysis indicates that stronger electron withdrawing A1 fragment, D-π-A-π-D topology, star and π shaped molecules impart toward lower LUMO and smaller Eg values than those of D-π-D type and X or H- shaped molecules. According to TD-DFT calculations, start-shaped molecules show broader spectra with intense peaks in both topologies covering not only visible region but also IR region of spectrum. Furthermore, the optical analysis also demonstrates that π-π* absorptions in short and middle wavelength region are because of central anisotropic multibranched donor (Bi)n-2DF-(Bi)n moiety, where A components exhibit absorptions in the ML wavelength region of spectrum. In General, smaller λ e and λ h values are exhibited for star and π-shaped molecules because of better dimensionality, whereas H and X-shaped (D1b) display more or less similar values. The predicted electron and hole mobility values for DAD1-S are as; µ e = 2.46 (cm2/Vs) and µ h = 0.0540 (cm2/Vs), respectively. Thus, results of these calculation prove that our theoretical studies provide a deep insights to confirm that investigated donor compounds would be appropriate vs PDIs acceptors for OSCs. [ABSTRACT FROM AUTHOR]