Two solution-processable star-shaped D–π–A organic molecules with triphenylamine (TPA) as donor unit, benzothiadiazole (BT) as acceptor unit and 4-hexyl-thienylenevinylene as pi conjugated bridge, S(TPA-TBTT) and S(TPA-TBTT-TPA), have been designed and synthesized for the application as donor materials in bulk-heterojunction organic solar cells (OSCs). The two molecules possess broader absorption from 350 to 700 nm benefitted from the longer pi-bridge in the molecules but weaker absorbance and poorer solubility in comparison with their corresponding organic molecules with shorter vinylene pi-bridge. The OSC based on S(TPA-TBTT): PC70BM (1:3, w/w) exhibited Jsc of 6.41 mA/cm2, Voc of 0.75 V, FF of 39.0% and power conversion efficiency of 1.90%, under the illumination of AM 1.5, 100 mW/cm2.Graphical abstractHighlights► We synthesized two new solution-processable star-shaped D–π–A organic molecules. ► The two molecules S(TPA-TBTT) and S(TPA-TBTT-TPA) possess broader absorption. ► We studied the photovoltaic properties of the molecules. ► The OSC based on S(TPA-TBTT): PC70BM exhibited power conversion efficiency of 1.90%.

A new solution-processable star-shaped D–π–A molecule with triphenylamine (TPA) as core and donor unit, dicyanovinyl (DCN) as end group and acceptor unit, and 3,6-dihexyl-thieno[3,2-b]thiophene (DHT) as π bridge, S(TPA–DHT–DCN) was synthesized for the application as donor material in solution-processed bulk-heterojunction organic solar cells (OSCs). The compound exhibits broad absorption in the visible region with suitable energy levels, which are desirable for application as a donor material in organic solar cells. The OSC devices based on S(TPA–DHT–DCN) as the donor and PC71BM as the acceptor (1:2, w/w) exhibited power conversion efficiency (PCE) of 2.87%, with high open circuit voltage (Voc) of 0.96 V, short circuit current density (Jsc) of 6.80 mA/cm2, and fill factor (FF) of 43.5%, under the illumination of AM.1.5, 100 mW/cm2. The Voc of 0.96 V for S(TPA–DHT–DCN) is among the top values for the solution-processed molecular-based OSCs reported so far.Graphical abstractHighlights► We synthesized a new solution-processable star-shaped organic molecule S(TPA–DHT–DCN). ► The molecule possesses a D–π–A structure with TPA as donor unit, dicyanovinyl (DCN) acceptor unit. ► The compound exhibits broad absorption in visible region with suitable energy levels. ► The organic solar cell based on S(TPA–DHT–DCN)/PC71BM showed power conversion efficiency of 2.87% with a high Voc of 0.96 V.