One of the most intensely studied systems for low-cost solar energy conversion is the dye-sensitized solar cell (DSSC), in which a dye molecule attached to a nanoparticulate semiconductor absorbs sunlight and injects an electron into the semiconductor. The electron can be extracted and used for electrical power, but before the dye can repeat the cycle, its electron must be replaced by reaction with a dissolved redox couple. One option for this redox couple combines iodide and triiodide ions, both of which are extremely cheap and abundant. The iodide/triiodide couple is nearly ideal for this purpose but for one problem: electrons lose a significant amount of energy while transferring from these ions to the dye. This project aims to reduce that energy loss by positioning a nano-sized catalyst precisely at the site where the dye reacts with the iodide/triiodide. The award is for a collaboration between Prof. Alexander G. Agrios at the University of Connecticut, providing expertise in nanoparticle synthesis and DSSC device fabrication and measurement, and Prof. Elena Galoppini at Rutgers University?Newark, for the synthesis expertise, and is derived from a previous EAGER award to the investigators. The work has the potential to increase the solar power conversion efficiency of the DSSC by as much as 50% while retaining the cheap redox couple. In addition, the concept of tethering catalytic metal nanoparticles directly to the site of an electrochemical reaction using molecular design can be applied to other kinds of renewable energy projects, such as photocatalytic systems. The research will be coupled to outreach efforts in which solar cells will be used as a teaching tool in K?12 education to explain concepts of chemistry, engineering and energy and to excite and inspire the next generation of STEM students and researchers. These activities will target underrepresented groups including high-school students from the Newark urban area, also through the ACS project SEED program.
This project makes use of specially made dye molecules with two different attachment groups on opposite sides of the molecule. One group (a carboxylic acid) attaches to the surface of metal oxides such as titanium dioxide (TiO2). The other group (a thiolane) attaches to certain metals, and will be used here to anchor platinum nanoparticles (Pt NPs). The project has three main intellectual components. First, fabricating the TiO2-dye-catalyst assembly will require (a) preparing the desired Pt NPs, (b) synthesizing the specialized dye molecule, and (c) assembling the components to give the desired structure. Second, groups capable of ?molecular rectification? will be incorporated into the dye at its point of connection to the Pt NP to ensure that electrons transfer from the Pt NP to the dye, as desired, and not in the reverse direction, which would short-circuit the device and reduce its solar power conversion efficiency. Third, electron energy levels in the dye molecule will be tuned by structural modification to the values that will give rapid electron transfer in the desired direction with minimal energy loss.
