High performance p-type molecular electron donors for OPV applications via alkylthiophene catenation chromophore extension

The synthesis of key 4-alkyl-substituted 5-(trimethylsilyl)thiophene-2-boronic acid pinacol esters allowed a simplified alkylthiophene catenation process to access bis-, ter-, quater-, and quinquethiophene π-bridges for the synthesis of acceptor-π-bridge-donor- π-bridge-acceptor (A-π-D-π-A) electron donor molecules. Based on the known benzodithiophene-terthiophene-rhodanine ( ) material, the series of materials, (X = M, monothiophene), (X = B, bithiophene), known (X = T, terthiophene), (X = Q, quaterthiophene), and (X = P(penta), quinquethiophene) were synthesised to examine the influence of chromophore extension on the device performance and stability for OPV applications. The (x = 4, butyl, and x = 8, octyl) series of materials were synthesised by varying the oligothiophene π-bridge alkyl substituent to examine structure-property relationships in OPV device performance. The devices assembled using electron donors with an extended chromophore ( and ) are shown to be more thermally stable than the containing devices, with un-optimized efficiencies up to 9.0% PCE. has been incorporated as a secondary donor in ternary blend devices with resulting in high-performance OPV devices with up to 10.7% PCE.