Synthesis of Selenium Based DII-A-DI-A-DII Type Small Molecular e-Donors Employing Stille Coupling and Their Thermal, Electrochemical and Photovoltaic Properties

High power conversion efficiency (PCE) organic solar cells (OSC) with planar D-II-A-D-I-A-D-II structured organic molecule with alkylthiophene-bezodithiophene (SBDT) a midway donor unit D-I with varied number of fluorine atoms like benzoselenadiazole (SBTSe and SFBTSe) a acceptor unit and alkyl-bithiophene a end group and donor unit D-II, SFBTSe and SBTSe, were designed and synthesized for the appliance as donor moieties in OSC. It showed an intense absorption in visible expanse (582, 577 nm) and frontier orbital levels of HOMO (-5.49 and-5.50 eV), and LUMO level of (-3.57 and-3.59 eV), for SBTSe and SFBTSe respectively. The acceptor units were assigned using the results obtained from experiments and DFT/TD-DFT simulations. This study reveals that all the acceptors are not identical in influencing the energy levels. Besides acceptors, molecular framework also plays a significant role in this regard. In addition, we have found that the acceptor's performance depends on its electron withdrawing ability. This manuscript provides a better understanding about the acceptor's property relationship and vital insights on the design of novel terminal acceptor units with greater number of hetero-functionalities to developing the PCE of the OSC.