Professor, Columbia University
B.S., Fudan University , 1984
Ph.D, University of Texas at Austin, 1989
Alexander-von-Humboldt Fellowship, Humboldt Foundation, 1992.
Camille and Henry Dreyfus New Faculty Award, Dreyfus Foundation, 1993.
Cottrell Scholar Award, Research Corporation, 1996.
Friedrich Wilhelm Bessel Award, Humboldt Foundation, 2006.
Fellow of the American Physical Society, 2011.
Solar energy conversion, photophysics, ultrafast spectroscopy
A main research thrust in my group is to establish new photophysical mechanisms that may be utilized to revolutionize solar energy conversion strategies. Our philosophy is to tackle fundamental scientific challenges of board technological impact. There is a “5% rule” in the group: we work on problems we know less than 5% about in the beginning. One of the key questions we are focusing on is at the heart of future photovoltaic technology: How can one extract electrons and holes from photo-generated excitons in organic semiconductors or inorganic quantum dots? To answer this question, we use model material systems and state-of-the-art laser spectroscopic techniques, including femtosecond time-resolved two-photon photoemission spectroscopy (2PPE) and time-resoved second harmonic generation (SHG). As examples, recent discoveries in our lab showed how an electron and a hole is bound by the Coulomb potential across an organic semiconductor interface, how one can extract hot electrons from a photoexcited quantum dot, and how an exciton can split into two to give two electron-hole pairs from the absorption of one photon. Answers to these questions are allowing us to formulate new solar energy conversion strategies with power conversion efficiency approaching or exceeding the so-called “Shockley-Queisser” limit, which is the fundamental limit of conventional solar cells. Our lab participates in two Energy Frontier Research Centers: one on Charge Separation and Transfer in Energy Materials (EFRC:CST) and the other on Redefining Photovoltaic Efficiency through Molecule Scale Control. In addition to solar energy conversion, we are interested in the general challenge of understanding many-body interactions in condensed matter, such as electron-nuclear interaction leading to polaron formation in organic semiconductors and electron-electron interaction responsible for new physical properties in molecular or nanomaterials. Another small thrust in the group is to understand fundamental physical principles underlying bio-material interactions.
W.-L. Chan, M. Ligges, A. Jailaubekov, L. Kaake, L. Miaja-Avila, X.-Y. Zhu, “Observing the Multi-Exciton State in Singlet Fission and Ensuing Ultrafast Multi-Electron Transfer,” Science 334 (2011) 1541-1545.
W. A. Tisdale, K. J. Williams, B. A. Timp, D. J. Norris, E. S. Aydil, X.-Y. Zhu, “Hot electron transfer from semiconductor nanocrystals,” Science 328 (2010) 1543-1547.
W.-L. Chan, J. Tritsch, A. Dolocan, M. Ligges, L. Miaja-Avila, X.-Y. Zhu, “Momentum resolved quantum interference in optically excited surface states,” J. Chem. Phys. 135 (2011) 031101.
M. Muntwiler, Q. Yang, W. A. Tisdale, X.-Y. Zhu, “Coulomb barrier for charge separation at an organic semiconductor interface,” Phys. Rev. Lett. 101 (2008) 196403.
L. Kaake, A. Jailaubekov, K. Williams, X.-Y. Zhu, “Probing ultrafast charge separation at organic donor/acceptor interfaces by a femtosecond electric field meter,” Appl. Phys. Lett. 99 (2011) 083307.
I. R. Gearba, J. Morris, T. Mills, D. Black, R. Pindak, X.-Y. Zhu, “Quantify interfacial electric fields and local crystallinity in polymer/fullerene bulk heterojunction solar cells,” Adv. Funct. Mater. 21 (2011) 2666-2673.
X.-Y. Zhu, B. Holtz, Y. Wang, Lai-Xi Wang, Paul E. Orndorff, Athena Guo, “Quantitative glycomics from fluidic glycan microarrays,” J. Am. Chem. Soc. 131 (2009) 13646-13650.