Designing and Theoretical study of fluorinated small molecule donor materials for organic solar cells

Abstract

A recently synthesized photoactive donor named fluorinated thienyl substituted benzodithiophene (DRTB-FT), modified with four novel end capped acceptor molecules, have been investigated through different electrical, quantum and spectrochemical techniques for their enhanced electro-optical and photovoltaic properties. DRTB-FT was connected to 2-methylenemalononitrile (D-1), 2-methylene-3-oxobutanenitrile (D-2), 2-(2-methylene-3-oxo-2,3-dihydro-1H-inden-1-ylidene) malonitrile (D-3) and 3-methyl-5methylene-2-thioxothiazolidin-4-one (D-4) as terminal acceptor moieties. The architectural D-1 and D-3 molecules owe reduced optical band gap of 2.45 and 2.28 eV benefited from A-D-A configuration and have broaden maximum absorption band (λmax) at 617 and 602 nm in polar organic solvent (chloroform). Reduced optical band gap set the ease for enhanced absorption. Reorganization energy of electron (λe) of D-3 molecule (0.00397 eV) was smaller amongst all which disclosed its greater mobility of conducting electrons (ICT). Larger values of dipole moment (µ) of D-1(5.939 Debye) and D-3 (3.661 Debye) molecules in comparison to R indicated greater solubilities of the targeted molecules. Among the tailored molecules, D-3 showed lowest binding energy of 0.25 eV in solvent phase and 0.08 eV in gaseous phase. The voltaic strength of designed molecules was examined with respect to fullerene derivative (PC61BM) which exposed that D-1 is the best choice for achieving higher PCE. TDM (transition density matrix), DOS (density of states) analysis and binding energies all were estimated at MPW1PW91/6-31G (d, p) level of DFT (density functional theory).