Detail:

Abstract:
　　The maximum solar-to-electric power conversion efficiency of a conventional solar cell is determined by the Shockley-Queisser limit of ~33% [1]. In this lecture, I will discuss efforts in my group over the past a few years to explore photophysical mechanisms that may be used to exceed this limit [2]. The first approach is to create two electron-hole pairs from the absorption of one photon in a process called singlet fission. Experiments in my group on crystalline pentacene [3], tetracene [4], and hexacene [5] have provided first spectroscopic signatures in singlet fission of a critical intermediate known as the multiexciton state. We demonstrate the feasibility of harvesting the multiexciton state for multiple charge carriers or the triplets and the design/synthesis of new molecules for efficient singlet fission [6].
　　The second approach is based on the harvesting of excess electronic energy before it is lost to the thermal bath. We demonstrate the challenge of this process due to the efficient loss of excess electronic energy in most semiconductor systems [7]]. We show the discovery in my lab that energetic electrons in the most popular solar cell material today, hybrid organic-inorganic lead halide perovskite may be protected to give a remarkably long lifetime of ~100 ps [8].
[1] J. Appl. Phys. 1961, 32, 510. [2] Energy & Environmental Sci. 2013, 6, 3508.
[3] Science 2011, 334, 1541. [4] Nature Chem. 2012, 4, 840.
[5] Nature Chem. DOI:10.1038/NCHEM.2665. [6]Nature Mater. 2015, 14, 426.
[7] Science 2010, 328, 1543. [8] Science, 2016, 353, 1409.

Biosketch：
　Xiaoyang Zhu is a Professor of Chemistry at Columbia University. He received a BS degree from Fudan University in 1984 and a PhD from the University of Texas at Austin in 1989. After postdoctoral research with J. Mike White at UT-Austin and Gerhard Ertl at the Fritz-Haber-Institute, he joined the faculty at Southern Illinois University as an Assistant Professor in 1993. In 1997, he moved to the University of Minnesota as an Associate Professor, later a Full Professor. In 2009, he returned to Austin and joined the chemistry faculty. In 2013, he moved to Columbia University where he remains.
　　Zhu is known for his seminal contributions to the understanding of exciton and carrier dynamics in molecular, nano, and hybrid semiconductors and interface. He has been a leader in developing a mechanistic understanding of singlet exciton fission, a photophysical phenomena which may be utilized to increase the power conversion efficiency of solar cells beyond the Shockley-Queisser limit. Most recently, Zhu’s large polaron proposal is solving a major puzzle in hybrid perovskite research and shaping the mechanistic understanding in this very active research field.