Ultra-fast co-sensitization and tri-sensitization of dye-sensitized solar cells with N719, SQ1 and triarylamine dyes

This paper describes the synthesis of a new, yellow triphenylamine dye, 4-[2-(4-diphenylaminophenyl) vinyl] benzoic acid] (6), with a sorption maximum at 380 nm in solution for which EQE data show shifts to 420 nm on sorption to TiO2. The performance of this dye has been measured in dye-sensitized solar cell (DSC) devices, showing eta = 2.6% for 1 cm(2) devices. Light soaking of (6) shows excellent long-term stability with <10% variation in device performance over 1800 h. Full characterization data are reported for (6) and the intermediates used in its synthesis including single-crystal X-ray structural analysis of all compounds. The paper also describes the ultra-fast dye sensitization and co-sensitization of TiO2 photo-electrodes in 5 minutes using one or two dyes and the first example of ultra-fast tri-sensitization. The dyes tested include the ruthenium dye N719, the squaraine dye SQ1, the red triphenylamine dye 2-cyano-3-{4-[2-(4-diphenylaminophenyl)vinyl]phenyl} acrylic acid (5) and (6). DSC efficiencies of 7.5% have been achieved for 1 cm(2) devices co-sensitized using (6) and N719. These efficiencies exceed those recorded for single dye devices and EQE measurements confirm efficient photon capture from two or more dyes in a single photo-electrode. Photo-acoustic calorimetry (PAC) has also been used to measure the energy of the charge separation states formed for (6) and N719, showing a larger value (1.47 eV) for (6) compared to N719 (1.08 eV), whilst a TiO2 film co-sensitized with both (6) and N719 gave an intermediate value (1.28 eV). These data have been used to calculate dye HOMO, LUMO and lambda(max) levels for (6) and N719 leading to important insights for future successful co-sensitization.