Ruthenium Dyes, Charge Transfer, and the Sun

The performance of dye-sensitized solar cells (DSSC) and dye-sensitized photoelectrosynthesis cells (DSPEC)—and their constituent chromophores, catalysts, and substrates—is commonly evaluated by photocurrents, product fluxes, and time-resolved spectroscopies. Kinetic models of solar harvesting systems are often built from the data using phenomenological methods (i.e. sum-of-exponential or global fit analyses). Such models cannot be predictive, and therefore offer limited fundamental insights to the efficiencies of charge injection and photocatalysis. We describe an approach to modeling the molecular photophysics, interfacial electron transfer, and charge separation that yields a comprehensive kinetic framework for these processes. Simulations of femtosecond to steady-state dynamics using this framework provide a detailed picture of dye cycling under both pulsed-monochromatic and continuous broadband illumination at 1 sun intensity. The competition between molecular transitions and charge injection will be discussed, including the potential implications for the design of chromophore-catalyst assemblies.