Characterization of Interfacial Electronic Structure and Dynamics in Quantum Dot-Sensitized Solar Cells

William Tisdale (CEMS)
Advisors: Eray Aydil (CEMS), David Norris (CEMS), Xiaoyang Zhu (Chem)

More energy from sunlight strikes the earth's surface in one hour (4.3 · 10²⁰ J) than the world currently consumes in one year (4.1 · 10²⁰ J)¹. Yet, in 2001, solar energy provided less than 0.1% of the world's energy. While steady progress has been made in solar cells based on the p-n junction diode, the cost of producing electricity from sunlight is still four to five times more expensive than competitive technologies. Alternative photovoltaic devices are needed that achieve higher conversion efficiencies while employing lower-cost manufacturing methods.

E. Aydil has proposed a new device architecture (see Fig. 1), based on Gratzel's “dye-sensitized solar cell” (DSSC)², in which wide band gap semiconductor nanowires (e.g. ZnO) are sensitized by semiconductor quantum dots (e.g., CdSe, CdS, or Si). In these

“quantum dot-sensitized solar cells” (QDSSCs), the quantum dots are attached to the ZnO nanowires by molecular bridges that function as directional charge separators. Choosing the correct linker for optimum charge injection requires fundamental understanding of the electronic structure and charge transfer rates at the molecule-semiconductor interfaces. The quantum dot composition, structure, and size; degree of π-conjugation or the presence of electron donating or withdrawing groups in the molecular linker; and chemical identity of the anchor define energetics and electron transfer rates at the molecule-semiconductor interfaces. I will use static ultra-violet photoemission spectroscopy (UPS) and time-resolved pump-probe spectroscopy techniques to investigate the role that these variables play in determining interfacial electronic structure and dynamics.