Synthesis and Characterization of Benzothiadiazole and Dicyanovinylindandione Based Small-Molecular Conjugated Materials and Their Photovoltaic Properties

A series of non-fullerene small molecules ( BT-T-IDC and BT-T-tB-IDC ) with the architecture of A1- π -A2- π -A1 (acceptor 1- π -acceptor 2- π -acceptor 1), electron-deficient benzothiadiazole (BT) used as the core (A2), electron-rich thiophene used as the π -bridge ( π ), and electron-deficient dicyanovinylindandione (IDC) or t-butyl substituted IDC used as end groups (A1), have been synthesized. IDC groups are widely used as the acceptor unit due to the strong electron-withdrawing property that can lead to deep LUMO energy levels. Materials showed good thermal stability with the onset decomposition temperature ( T d ) upon 310 °C at 5 wt% loss. BT-T-tB-IDC showed better solubility in chloroform and chlorobenzene than that of BT-T-IDC due to t -butyl groups on the IDC . The HOMO/LUMO energy levels of BT-T-IDC and BT-T-tB-IDC were −5.60/−3.90 and −5.71/−3.87 eV, respectively. Organic solar cell based on PBDBT-T (poly[(2,6-(4,8-bis (5-(2-ethylhexyl) thiophen-2-yl)-benzo [1,2-b:4,5-b′] dithiophene))-alt-(5,5-(1′,3′-di-2-thienyl-5′,7′-bis(2-ethylhexyl) benzo[1′,2′-c:4′,5′-c′] dithiophene-4,8-dione))])) as the donor and BT-T-IDC as the acceptor showed low power conversion efficiency (PCE) of 0.06% due to poor solubility. However, the PCE of the device based on BT-T-tB-IDC showed a better PCE of 1.55%.