Design of new benzothiadiazole-based linear and star molecules with different functional groups as solar cells materials: A theoretical approach

The novel linear and star molecules based on benzothiadiazole as a central core, TPA as end groups and different functional groups as pi-spacers were theoretically examined in the OSC applications. The geometry structures in ground and excited state, ionization potentials (IPs), electron affinities (EM) and reorganization energy (E-lambda(+) and E-lambda(-)) of linear and star molecules were studied by DFT methods. The absorption and the emission spectra were calculated by TD-BHandHLYP method. Star molecules based on ethynyl groups as pi-spacer exhibit ameliorative IPs, EAs, E-lambda(+) and E-lambda(-), indicating they are more suitable for the formation and transfer of holes than the others. Moreover, the diethynyl groups improve the charge transfer character and extend the absorption wavelength towards the range with the maximum photon flux. (C) 2011 Elsevier B.V. All rights reserved.