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Three copper redox shuttles ([Cu( 1 )] 2+/1+ , [Cu( 2 )] 2+/1+ , and [Cu( 3 )] 2+/1+ ) featuring tetradentate ligands were synthesized and evaluated computationally, electrochemically, and in dye-sensitized solar cell (DSC) devices using a benchmark organic dye, Y123 . Neutral polyaromatic ligands with limited flexibility were targeted as a strategy to improve solar-to-electrical energy conversion by reducing voltage losses associated with redox shuttle electron transfer events. Inner-sphere electron transfer reorganization energies ( λ ) were computed quantum chemically and compared to the commonly used [Co(bpy) 3 ] 3+/2+ redox shuttle which has a reported λ value of 0.61 eV. The geometrically constrained biphenyl-based Cu redox shuttles investigated here have lower reorganization energies (0.34–0.53 eV) and thus can potentially operate with lower driving forces for dye regeneration (Δ G reg ) in DSC devices when compared to [Co(bpy) 3 ] 3+/2+ -based devices. The rigid tetradentate ligand design promotes more efficient electron transfer reactions leading to an improved J SC (14.1 mA cm −2 ), higher stability due to the chelate effect, and a decrease in V lossOC for one of the copper redox shuttle-based devices. 

Four organic sensitizers incorporating a cross-conjugated cyclopenta[2,1- b :3,4- b ′]dithiophene (CPDT) π-bridge have been synthesized. As a result of molecular engineering, broad high energy bands and red shifted absorption maxima and onset is observed relative to a benchmark analogue ( C218 ) using a non-cross-conjugated CPDT π-bridge. The use of a cross-conjugated bridge allows a new strategy for tuning dye energetics and introduction of increased absorption uniformity by adding additional high-energy absorption bands. These dyes show solar-to-electric conversion up to 800 nm with one derivative exceeding the performance of C218 under identical conditions. 

Sequential series multijunction dye‐sensitized solar cells (SSM‐DSCs) can power solar‐to‐fuel processes with a single illuminated area device. Dye selection and strategies limiting photon losses are critical in SSM‐DSC devices for higher performance systems. Herein, an efficient and readily applicable spin coating protocol on glass surfaces with an antireflective fluoropolymer (CYTOP) is applied to an SSM‐DSC architecture. Combining CYTOP with the use of an immersion oil between glass spacers in a three subcell SSM‐DSC with judiciously selected TiO₂photoanode sensitizers and thicknesses, an overall power conversion efficiency (PCE) of 10.1% is obtained with an output of 2.3 V. Without external bias, this SSM‐DSC configuration shows an impressive overall solar‐to‐fuel conversion efficiency of 6% when powering IrO₂and Au₂O₃electrocatalysts for CO₂and H₂O to CO and H₂conversion in aqueous solution. The role of CYTOP, immersion oil, sensitizer selection, and film thickness on SSM‐DSC devices is discussed along with the stability of this system.