The dye-sensitized solar cell (DSSC) is a promising technology for low-cost solar energy conversion in which a dye molecule adsorbed on a semiconductor absorbs light, injects a photoinjected electron into the semiconductor (becoming oxidized), and is reduced (regenerated) by dissolved iodide, giving the neutral dye and triiodide. The electron is collected from the semiconductor, travels through an external circuit, and is returned to a counterelectrode where it reduces triiodide to iodide, completing the circuit. The reduction of oxidized dyes by iodide requires a large overpotential (at least 0.5 V), constituting a significant energy loss in the DSSC. Alternative redox couples that can reduce oxidized dyes with much smaller overpotentials tend to remove electrons from the semiconductor at high rates, replacing one loss process with another. Surmounting this latter problem (recombination) requires increasing the speed of electron transport in the semiconductor, in order that the electron may be extracted before it is lost to recombination. This exploratory project will generate preliminary data to demonstrate the potential for new composite semiconductor nanostructures to solve this problem.
Intellectual Merit The design paradigm that governs this work is the paring of two semiconducting materials: an active layer on which dye molecules adsorb and inject electrons, and a transport layer that extracts charges from the active layer and rapidly transports them to the conducting substrate for collection. The active layer must have a high surface area to allow a large dye loading per geometric area for strong absorption of incident sunlight. Two instances of this paradigm will be produced in this work. One consists of titania nanoparticles coated over zinc oxide nanorods; the nanorods provide fast transport while the nanoparticles greatly increase the total surface area. The other is a conformal layer of titania over a fluorine-doped tin oxide (FTO) aerogel. The aerogel is inherently a high-surface area structure, allowing a conformal coating of the active layer. This project focuses on preliminary data regarding blocking layers to retard recombination, analysis of fluorine dopant levels in FTO aerogel samples, and optoelectronic measurements of solar cell devices made with the novel composite semiconductor films.
Broader Impacts This research will significantly advance the technology of low-cost solar energy conversion, for which there is an increasingly urgent need in the face of sharply increasing energy usage among a large population together with impending climate change and other environmental impacts from fossil fuel combustion. The project will provide education and training to involved graduate students including the writing of research articles and travel to domestic and international conferences for dissemination of the results. The PI actively engages K-12 students and teachers using the DSSC as a teaching tool for topics related to energy, the environment, chemistry and engineering.
