Facile synthesis of a bulky BPTPA donor group suitable for cobalt electrolyte based dye sensitized solar cells

An efficient synthesis of N-(2 ',4 '-bis(hexyloxy)-[1,1 '-biphenyl]-4-yl)-N-(4-bromophenyl)-2 ',4 '-bis(hexyloxy)-[ 1,1 '-biphenyl]-4-amine (BPTPA donor, 5) was developed based on a new 4-step synthetic route. The BPTPA donor is used to quickly access two new sensitizers: NT35 and G220, which both exhibit greater IPCE response with cobalt-based redox shuttles, compared to the classical iodide/triiodide electrolyte. A reference sensitizer, G221, comprising only a TPA unit as the donor and cyanoacrylic acid as the acceptor/anchor unit, was also realized for comparative purposes. The devices consisting of the sensitizers bearing the BPTPA donor and cobalt-based redox shuttles showed the highest J(sc), V-oc and IPCE spectra response compared to G221. The BPTPA donor is shown to efficiently suppress the electron recombination between the TiO2 surface and the redox shuttle yielding high Voc values. Among these sensitizers, G220 showed the best photovoltaic performance having a short-circuit photocurrent density (J(sc)) of 14.8 mA cm(-2), an open-circuit photovoltage (V-oc) of 0.87 V, and a fill factor (FF) of 0.71, corresponding to an overall conversion efficiency of 9.06% under standard global AM 1.5 solar light conditions. These results demonstrate that organic sensitizers based on this bulky BPTPA donor are promising candidates for cobalt-based DSSCs.