Blocking Recombinations in DSCs Through MgO And PFTS Surface Treatments

High voltage dye-sensitized solar cells (DSCs) are becoming novel sources in the production of various fuel precursors, such as carbon monoxide and hydrogen, by powering carbon dioxide reduction, water oxidation, and proton reduction catalysts via sunlight. An important task in order to increase overall efficiency of DSC devices is to minimize recombination (electron flow in an undesirable direction) while increasing photovoltage. Surface treatment modifications can be applied to the TiO2 electrodes within DSC devices in an effort to block recombination without negatively effecting the other device performance metrics: fill factor (FF), short-circuit current density (Jsc), and open-circuit photovoltage (Voc). In this manuscript, PFTS (1H,1H,2H,2H-perfluorooctyltrimethoxysilane) for fluorinated self-assembled monolayer (F-SAM) as a post-sensitization treatment and a MgO (magnesium oxide) pre-sensitization treatment are explored as effective ways of slowing charge recombination, leading to more efficient devices. Devices employing the PFTS treatment for a ruthenium-based (Ru(II)) benchmark sensitizer, B11, and a Co(bpy)33+/2+ redox shuttle achieved an increased Voc of 779 mV with a power conversion efficiency (PCE) of 7.7% compared to the standard device preparation results of 724 mV and 5.9% PCE. Devices employing the MgO treatment showed a Voc of 773 mV with a PCE of 6.9%, while devices employing both the MgO and PFTS treatments showed a Voc of 809 mV with a PCE of 6.6%. The strategy for a successful surface treatment with PFTS is discussed herein for DSCs employing an Ru(II) sensitizer and a Co(bpy)33+/2+ redox shuttle, which are known to have adverse recombination losses when paired together