Impact of ethynyl linkage on indoor photovoltaic performance of triphenylimidazole-phenothiazine dyes with dual-species copper electrolyte

Abstract

In this work, we have intended and synthesized two innovative dyes, LG-P7 and LG-P8, that significantly improve the efficiency of dye-sensitized solar cells (DSCs) under outdoor and indoor/ambient illuminations. These dyes (LG-P7 and LG-P8) are modified versions of our previously reported LG-P5 and LG-P6 dyes, with the addition of an ethynyl bridge to extend π-conjugation of the dye molecules, contributing to enhanced light harvesting behaviour. Using the asymmetric dual species copper (II/I) redox electrolyte ([Cu(II)(dmp)2Cl]+/[Cu(I)(dmp)2]+) and co-sensitization with the metal-free organic XY1b dye, both LG-P7/P8 devices delivered a PCE of ∼ 35 % under 1000 lx WW CFL illumination, comparable to typically used D35 co-sensitized devices. The impact of introduction of ethynyl linkage was more pronounced for the D-D-π-A dyes where moving from LG-P5:XY1b to LG-P7:XY1b, the PCE improved from 21.44 % to 35.14 % under 1000 lx CFL illumination. At a lower illumination intensity of 700 lx, the XY1b co-sensitized LG-P7/P8 devices even demonstrated superior performance compared to D35:XY1b (32.84 ± 0.37 %), with PCE of 33.95 ± 0.37 % (LG-P7:XY1b) and 33.03 ± 0.16 % (LG-P8:XY1b). The introduction of extended π-conjugation in the LG-P7 and LG-P8 dyes, compared to the parent triphenylimidazole-phenothiazine dyes (LG-P5 and LG-P6), contributed to enhanced light harvesting behaviour as well as improved photovoltaic performance further demonstrating the significance of systematic structural modifications in sensitizers to realize superior indoor photovoltaic performance in DSCs.