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

Abstract

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 V_oc 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.