Abstract:

Nonequilibrium Electron and Phonon Dynamics in Advanced Photovoltaic Devices

The realization of advanced concept solar cells that circumvent the thermodynamic limitations of conventional devices [1] depends strongly on the competition between energy relaxation processes and high energy processes that do useful work.  Nanostructured systems offer advantages in terms of reduced channels for energy relaxation in reduced dimensional systems.  Here we use ensemble Monte Carlo simulation of electrons and holes to investigate the role of ultrafast carrier processes in the realization of advanced concept devices based on hot carrier capture and multi-exciton generation [2].  The particle-based simulation approach includes the electron-phonon scattering in quantum wells and quantum wires, intercarrier scattering including impact ionization, and nonequilibrium phonon effects.  For quantum well devices, we show how nonequilibrium phonon effects contribute to the slower energy relaxation rates and high carrier temperatures observed experimentally in InGaAs quantum well structures [3], including the impact of real and momentum space transfer. For nanowire systems, we show that energy relaxation is slowed due to bandstructure effects due to reduced dimensionality, resulting in a phonon bottleneck, and that impact ionization is enhanced above the threshold, leading to strong carrier multiplication, which is beneficial for multi-exciton generation solar cells.

[1] M. A. Green, 3rd Generation Photovoltaics (Springer, 2003).

[2] R. Hathwar et al., J. Phys. D. Appl. Phys. 52, 093001 (2019).

[3] H. Esmaielpour et al., Nat. Energy 5, 336–343 (2020).

Speaker Bio:  Stephen M. Goodnick is currently the David and Darleen Ferry Professor of Electrical Engineering at Arizona State University.  He received his Ph.D. degrees in electrical engineering from Colorado State University, Fort Collins, in 1983, respectively. He was an Alexander von Humboldt Fellow with the Technical University of Munich, Munich, Germany, and the University of Modena, Modena, Italy, in 1985 and 1986, respectively. He served as Chair and Professor of Electrical Engineering with Arizona State University, Tempe, from 1996 to 2005. He served as Associate Vice President for Research for Arizona State University from 2006-2008, and presently serves as Deputy Director of ASU Lightworks, as well as Deputy Director for the ULTRA Energy Frontier Research Center.  He was also a Hans Fischer Senior Fellow with the Institute for Advanced Studies at the Technical University of Munich.  Professionally, he served as President (2012-2013) of the IEEE Nanotechnology Council.  Some of his main research contributions include analysis of surface roughness at the Si/SiO2 interface, Monte Carlo simulation of ultrafast carrier relaxation in quantum confined systems, global modeling of high frequency and energy conversion devices, full-band simulation of semiconductor devices, transport in nanostructures, and fabrication and characterization of nanoscale semiconductor devices.  He has published over 450 journal articles, books, book chapters, and conference proceeding, and is a Fellow of IEEE (2004) for contributions to carrier transport fundamentals and semiconductor devices.