Photovoltaic devices fabricated with a p-type conjugated multi-branched molecules

New multi-branched crystalline molecules were synthesized through Horner(Emmons reactions using hexyl-substituted thiophene-based carbaldehydes as dendrons and [1,2,4,5-tetra-(diethoxy-phosphorylmethyl)-benzyl]-phosphonic acid diethyl ester as the core unit. 1,2,4,5-Tetrakis((E)-2-(5′-hexyl-2,2′-bithiophen-5-yl)vinyl)benzene (HPBT) and 1,2,4,5-tetrakis((E)-2-(5′-dodecyl-2,2′-bithiophen-5-yl)vinyl)benzene (DPBT) have different alkylene peripheral moities such as the hexyl and dodecyl group. The molecules were employed to fabricate organic photovoltaic (OPV) cells with methanofullerene [6,6]-phenyl C61-butyric acid methyl ester (PCBM). As a result, HPBT-based bulk heterojunction with PCBM exhibited higher short-circuit current density and open circuit voltage, resulting in a higher power conversion efficiency of around 0.944%.