An extension of electron acceptor sites around Thiazolothiazole unit for evaluation of large power conversion efficiency: A theoretical insight

• Extended conjugated acceptor sites around thiazolothiazole unit. • Effect of basis sets size on optoelectronic properties. • Estimated short circuit current density ( J s c ) based on PCE. • Large power conversion efficiencies at constant. J s c . • Improved fill factor (FF) with large voltages ( V O C ) . • Fast electron transport rate for efficient non-fullerene acceptors. Small organic solar cells containing thiazolothiazole unit as an electron acceptor for solution processed bulk heterojunction (BHJ) small donor-acceptor-donor (D-A-D) type materials have been designed and studied theoretically with state-of-the-art density functional theory and time-dependent density functional theory (TD-DFT) for reliable estimation of their excited state and charge transfer photophysical characteristics for estimating their power conversion efficiencies. The suggested possible synthetic routes with complete reaction information have been also provided for synthesis. The electron acceptor sites around the thiazolothiazole unit have been enlarged by introducing different strong electron withdrawing groups and checked their effects on the voltages ( V O C ) and fill factor (FF) which are the two main parameters directly influences on power conversion efficiencies. Out of five theoretically studied molecules, the experimental reported data of TT-TTPA (Thiazolothiazole-thiaophene triphenyl amine) has been compared with four designed molecules and concluded that extension of acceptor sites significantly contributed towards the better charge transport properties of electron and hole.