Professor Shane Ardo of the University of California-Irvine is supported by the Chemical Catalysis program in the Division of Chemistry to investigate dye-sensitized solar cells (DSSCs). DSSCs are an inexpensive alternative to commercial solar cells but have exhibited low solar-energy-conversion efficiencies that hamper their commercialization. This project is investigating an alternative reaction to dramatically increase the efficiency of iodide-containing DSSCs, from their current world-record efficiency of ~12% to over 20%. The project promotes the progress of science and facilitates environmental stewardship. Outreach workshops accompany this research program with the aim of increasing the participation and interest of female middle-school students in research related to solar energy conversion.
The research is motivated by a new mechanism of operation for DSSCs and dye-sensitized functional assemblies for solar fuels where multiple-electron-transfer redox-shuttle chemistry is driven at molecular electrocatalysts co-anchored to dye-sensitized nanocrystalline TiO2. Fundamental studies include (i) surface-confined electrocatalysis of multiple-electron-transfer redox-shuttle oxidation, (ii) self-exchange electron transfer between molecules anchored to the TiO2 surface, and (iii) (slow) recombination of electrons in TiO2 with oxidized surface-anchored molecules. Several series of polymeric materials and Pt and Pd organometallic coordination compounds are synthesized and investigated for their ability to facilitate inner-sphere iodide oxidation electrocatalysis. The molecular structure of dyes is varied to identify those with the most rapid self-exchange electron transfer and slowest recombination. TiO2-bound electrocatalysts and dyes are studied simultaneously in order to interrogate the effects of several interacting functions and with the aim of realizing efficient light-driven iodide electrocatalysis. The electrocatalysis work is performed using a rotating ring-disk electrode setup and/or cyclic voltammetry to assess the catalytic competency of the molecules. Dye phenomena are interrogated using spectroelectrochemistry and nanosecond pump-probe transient-absorption and time-resolved photoluminescence (polarization) spectroscopies. In addition to spectrally modeling transient spectra and polarization kinetics, numerical models and Monte Carlo simulations helps clarify what controls the rate of (desired) self-exchange electron transfer and (undesired) recombination.
