A comprehensive experimental study of five fundamental phenothiazine geometries increasing the diversity of the phenothiazine dye class for dye-sensitized solar cells

Phenothiazine is a versatile scaffold frequently used in both pharmaceutical and photovoltaic applications. Still, the structural diversity within the class of phenothiazine sensitizers for dye-sensitized solar cells is minute. Substituents are found in 3, 7 and 10-positions, often all three. In this work, we report the synthesis and evaluation of sensitizers illuminating five geometries for the phenothiazine dye class, of which three are novel geometries. Eleven sensitizers were prepared, investigating auxiliary donor contributions, effect of pi-spacer and also the position of the anchoring group. We have established that the pi-spacer has to be connected para to the 10H nitrogen atom of phenothiazine, the 3-position. Also, thiophene is a far superior pi-spacer than phenyl, but we were unable to find any significant photovoltaic performance differences between the 3,7 and 3,8 geometries. A higher dye loading for the 3,8 geometry indicates there is hidden potential in this geometry which could be harvested by further optimization. The best device of the study was fabricated with AFB-27 of the 3,8 geometry delivering a PCE of 5.88% (J(SC) = 10.28 mA cm(-2), V-OC = 773 mV, FF = 0.75) under 1 sun AM 1.5G illumination.