Role of π-Spacer in Regulating the Photovoltaic Performance of Copper Electrolyte Dye-Sensitized Solar Cells using Triphenylimidazole Dyes

Abstract

In dye-sensitized solar cells (DSSCs), π-spacers play a critical role in regulating photovoltaic accomplishment. This is more pronounced when we use alternate redox mediators like cobalt and copper, which are mass transport limited. Previously we showed that triphenylimidazole dyes with non-planar donor units and phenyl spacers having D–A–π–A architecture are more suitable for [Cu(dmp)2]1+/2+ electrolytes for realizing improved power conversion efficiencies compared to the D–D–π–A counterpart. Interestingly when we changed the π-spacer from phenyl (LG-P1 and LG-P3 dyes) to thiophene (LG-P2 and LG-P4 dyes) we observed a reversal of the trend in photovoltaic performance. By attaining a more planar architecture and with properly placed energetics, the D–D–π–A dye LG-P2 with anthracene as an auxiliary donor having thiophene π-spacer outperformed the LG-P4 sensitizer having benzothiadiazole as an auxiliary acceptor in D–A–π–A architecture with thiophene π-spacer. Detailed studies carried out using electrochemical impedance spectroscopy (EIS), charge extraction (CE), open-circuit voltage decay (OCVD), and transient photovoltage and photocurrent decay measurements revealed interesting behaviour in photovoltaic performance when employing an alternate [Cu(dmp)2]1+/2+ electrolyte.