An Interhalogen-Based Binary Redox Couple for the Efficiency Enhancement of Type-II Dye-Sensitized Solar Cells

Abstract

In this work, the photovoltaic (PV) performance of dye-sensitized solar cells (DSSCs), sensitized with salicylic acid (SA) and indole-3-acetic (IAA) and mediated by iodide (I−)/tri-iodide (I3−), binary-redox system (I−, Br−)/(I3−, I2Br−), and bromide (Br−)/tri-bromide (Br3−), were investigated. The (I−, Br−)/(I3−, I2Br−) redox electrolyte induced the highest recombination resistance at the TiO2/dye/electrolyte interface for both SA and IAA-sensitized DSSCs. Concurrently, additive-free binary electrolyte-based cells showed enhanced dye regeneration capability and decreased rate of back reaction compared to the cells prepared with additive-free I−/I3− and Br−/Br3− electrolytes. Energy band alignment of SA and IAA and the optical analyses revealed the direct one-step electron injection into the conduction band of TiO2 upon photoexcitation. Further, additive-containing electrolytes showed decreased PV performance compared to the additive-free electrolytes in both molecules sensitized DSSCs, conceivably due to the increased rate of back reaction with decreased charge collection efficiency. Thus, a maximum power conversion efficiency (PCE) of 0.57 % was attained for SA-sensitized DSSCs based on additive-free binary redox mediator, while the PCE values for additive-free I−/I3− and Br−/Br3− electrolytes-based identical cells were 0.19 and 0.54 %, respectively. This research suggests that the binary redox couple is a potential candidate for the PCE improvement of type-II DSSCs. © 2023 Wiley-VCH GmbH.