Solution processable star-shaped molecules with a triazine core and branching thienylenevinylenes for bulk heterojunction solar cells

Abstract

Two new star-shaped A–π–D molecules with triazine as a core and an acceptor unit, thienylenevinylene as the π bridge, and tert-butyl-substituted triphenylamine (tTPA)- or carbazole (tCz) as the end group and donor units of TTVTPA and TTVCz were synthesized for their application as donor materials in solution processed bulk heterojunction organic solar cells (OSCs). The charge transfer was convergent from peripheral groups to the central core along the conjugated branches in these star-shaped molecules (SSMs). TTVTPA and TTVCz are soluble in common organic solvents. Excellent thermal stability was observed for TTVTPA and TTVCz. OSCs were fabricated by spin-coating a blend of each SSM with the fullerene derivatives (PC₆₁BM or PC₇₁BM) as a composite film-type photoactive layer. The PV properties of the TTVTPA/fullerene derivative based OSCs were considerably better than those of the TTVCz/fullerene derivative blend based OSCs. A power conversion efficiency of 2.48%, a short-circuit current density of 10.57 mA cm⁻², an open-circuit voltage of 0.69 V, and a fill factor of 0.34 were observed for the OSC based on the active layer of TTVTPA/PC₇₁BM (1 : 7, w/w).