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1. Iron Redox Shuttles with Wide Optical Gap Dyes for High‐Voltage Dye‐Sensitized Solar Cells

   https://doi.org/10.1002/cssc.202100884  

   Curiac, Christine ; Rodrigues, Roberta R. ; Watson, Jonathon ; Hunt, Leigh Anna ; Devdass, Anthony ; Jurss, Jonah W. ; Hammer, Nathan I. ; Fortenberry, Ryan C. ; Delcamp, Jared H. ( June 2021 , ChemSusChem)

   A series of iron polypyridyl redox shuttles were synthesized in the 2+ and 3+ oxidation states and paired with a series of wide optical gap organic dyes with weak aryl ether electron‐donating groups. High voltage dye‐sensitized solar cell (HV‐DSC) devices were obtained through controlling the redox shuttle energetics and dye donor structure. The use of aryl ether donor groups, in place of commonly used aryl amines, allowed for the lowering of the dye ground‐state oxidation potential which enabled challenging to oxidize redox shuttles based on Fe²⁺polypyridyl structures to be used in functional devices. By carefully designing a dye series that varies the number of alkyl chains for TiO₂surface protection, the recombination of electrons in TiO₂to the oxidized redox shuttle could be controlled, leading to HV‐DSC devices of up to 1.4 V.

    

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2. A High‐Voltage Molecular‐Engineered Organic Sensitizer–Iron Redox Shuttle Pair: 1.4 V DSSC and 3.3 V SSM‐DSSC Devices

   https://doi.org/10.1002/anie.201712894  

   Rodrigues, Roberta R. ; Cheema, Hammad ; Delcamp, Jared H. ( April 2018 , Angewandte Chemie International Edition)

   The development of high voltage solar cells is an attractive way to use sunlight for solar‐to‐fuel devices, multijunction solar‐to‐electric systems, and to power limited‐area consumer electronics. By designing a low‐oxidation‐potential organic dye (RR9)/redox shuttle (Fe(bpy)₃^3+/2+) pair for dye‐sensitized solar‐cell (DSSC) devices, the highest single device photovoltage (1.42 V) has been realized for a DSSC not relying on doped TiO₂. Additionally, Fe(bpy)₃^3+/2+offers a robust, readily tunable ligand platform for redox potential tuning.RR9can be regenerated with a low driving force (190 mV), and by utilizing theRR9/Fe(bpy)₃^3+/2+redox shuttle pair in a subcell for a sequential series multijunction (SSM)‐DSSC system, one of the highest known three subcell photovoltage was attained for any solar‐cell technology (3.34 V, >1.0 V per subcell).

    

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3. Minimizing the Reorganization Energy of Cobalt Redox Mediators Maximizes Charge Transfer Rates from Quantum Dots

   https://doi.org/10.1002/anie.202202322  

   Fort, Madeleine J. ; Click, Sophia M. ; Robinson, Evan H. ; He, Felix M. C. ; Bernhardt, Paul V. ; Rosenthal, Sandra J. ; Macdonald, Janet E. ( May 2022 , Angewandte Chemie International Edition)

   Light‐induced charge separation is at the very heart of many solar harvesting technologies. The reduction of energetic barriers to charge separation and transfer increases the rate of separation and the overall efficiency of these technologies. Here we report that the internal reorganization energy of the redox acceptor, the movement of the atoms with changing charge, has a profound effect on the charge transfer rates from donor quantum dots. We experimentally studied and modelled with Marcus Theory charge transfer to cobalt complexes that have similar redox potentials covering 350 mV, but vastly different reorganization energies spanning 2 eV. While the driving force does influence the electron transfer rates, the reorganization energies had a far more profound effect, increasing charge transfer rates by several orders of magnitude. Our studies suggest that careful design of redox mediators to minimize reorganization energy is an untapped route to drastically increase the efficiency of quantum dot applications that feature charge transfer.

    

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4. Minimizing the Reorganization Energy of Cobalt Redox Mediators Maximizes Charge Transfer Rates from Quantum Dots

   https://doi.org/10.1002/ange.202202322  

   Fort, Madeleine J. ; Click, Sophia M. ; Robinson, Evan H. ; He, Felix M. C. ; Bernhardt, Paul V. ; Rosenthal, Sandra J. ; Macdonald, Janet E. ( May 2022 , Angewandte Chemie)

   Light‐induced charge separation is at the very heart of many solar harvesting technologies. The reduction of energetic barriers to charge separation and transfer increases the rate of separation and the overall efficiency of these technologies. Here we report that the internal reorganization energy of the redox acceptor, the movement of the atoms with changing charge, has a profound effect on the charge transfer rates from donor quantum dots. We experimentally studied and modelled with Marcus Theory charge transfer to cobalt complexes that have similar redox potentials covering 350 mV, but vastly different reorganization energies spanning 2 eV. While the driving force does influence the electron transfer rates, the reorganization energies had a far more profound effect, increasing charge transfer rates by several orders of magnitude. Our studies suggest that careful design of redox mediators to minimize reorganization energy is an untapped route to drastically increase the efficiency of quantum dot applications that feature charge transfer.

    

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5. Eliminating nonradiative decay in Cu(I) emitters: >99% quantum efficiency and microsecond lifetime

   https://doi.org/10.1126/science.aav2865  

   Hamze, Rasha ; Peltier, Jesse L. ; Sylvinson, Daniel ; Jung, Moonchul ; Cardenas, Jose ; Haiges, Ralf ; Soleilhavoup, Michele ; Jazzar, Rodolphe ; Djurovich, Peter I. ; Bertrand, Guy ; et al ( February 2019 , Science)

   Luminescent complexes of heavy metals such as iridium, platinum, and ruthenium play an important role in photocatalysis and energy conversion applications as well as organic light-emitting diodes (OLEDs). Achieving comparable performance from more–earth-abundant copper requires overcoming the weak spin-orbit coupling of the light metal as well as limiting the high reorganization energies typical in copper(I) [Cu(I)] complexes. Here we report that two-coordinate Cu(I) complexes with redox active ligands in coplanar conformation manifest suppressed nonradiative decay, reduced structural reorganization, and sufficient orbital overlap for efficient charge transfer. We achieve photoluminescence efficiencies >99% and microsecond lifetimes, which lead to an efficient blue-emitting OLED. Photophysical analysis and simulations reveal a temperature-dependent interplay between emissive singlet and triplet charge-transfer states and amide-localized triplet states. 

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