Spiro[fluorene-9,9′-phenanthren]-10′-one as auxiliary acceptor of D-A-π-A dyes for dye-sensitized solar cells under one sun and indoor light

Six novel organic dyes (RY1 similar to RY6) containing spim Ifluorene-9,9'-phenanthren1-10'-one as an auxiliary acceptor were synthesised and effectively used for the fabrication of D-A-pi-A type dye-sensitized solar cells (DSSCs). The molecular structures were modified by introducing a novel spiro Ifluorene-9,9'-phenanthren1-10'-one auxiliary acceptor group between the donor and the pi-bridge. The molecular rigidity can be enhanced by depressing intermolecular aggregation and carbonyl group can trapping the Li+ or I(3)(-)( )ions to retard the charge recombination. The sensitizer RY3 was found to perform remarkable light-harvesting efficiency of 6.30% at AM1.5 solar condition and 21.67% at TL84 (2500 lux) illuminations without DCA co-deposition. For further improvement, a higher efficiency can be achieved through a suitable co-sensitization of N719 and RY3, which displayed an efficiency of 8.55% under one sun (AM 1.5). While operated under indoor light, the efficiency was boosted to 25.57% and 27.04% at 1000 & 2500 lux illuminations, respectively. The high performance of co-sensitization of N719 and RY3 can be ascribed to a high surface coverage and a broader range of absorption wavelength. Stability test of the device co-sensitized with N719 and RY3 showed a mild decay of PCE 3.74% after 96 h, while it retained 84.49% of its original PCE after 336 h in ambient atmosphere without encapsulation.