Charge recombination at the NiO/electrolyte interface is one of the performance‐limiting factors that prevent p‐type dye‐sensitized solar cells (p‐DSCs) from matching the efficiency of conventional TiO2 devices. This article describes the role of redox mediator species I−, I3−, and I2 in the charge‐transfer processes at the NiO/electrolyte interface. NiO appears to catalyze the oxidation of iodide but the addition of guanidinium thiocyanate inhibits recombination by forming a complex with I2. This increases the voltage but decreases the current so the efficiency is only slightly improved. These results suggest that new redox electrolytes will be needed if tandem DSCs are to exceed the efficiency of state‐of‐the‐art TiO2 devices.

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