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 (I 3 − ), binary‐redox system (I − , Br − )/(I 3 − , I 2 Br − ), and bromide (Br − )/tri‐bromide (Br 3 − ), were investigated. The (I − , Br − )/(I 3 − , I 2 Br − ) redox electrolyte induced the highest recombination resistance at the TiO 2 /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 − /I 3 − and Br − /Br 3 − electrolytes. Energy band alignment of SA and IAA and the optical analyses revealed the direct one‐step electron injection into the conduction band of TiO 2 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 − /I 3 − and Br − /Br 3 − 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.