Interfacial Electron Transport in Oxide Thin Films for Solar Energy

Rafael Jaramillo, Harvard University

Friday, March 4, 2011, 3:30pm

This seminar is part of the Jones Seminars on Science, Technology, and Society series

Most concepts for advanced photovoltaic devices rely on the transfer of charge between light absorbing layers and transparent conducting oxide (TCO) thin films. Our incomplete understanding of the mechanisms that limit the efficiency of this charge transfer poses a problem for solar energy research across the board. I will present results obtained via scanning probe spectroscopic studies (Kelvin force microscopy and scanning tunneling microscopy) of one widely-used TCO, ZnO:Al, that reveal the role of grain boundaries in determining the efficiency of interfacial electron transport. The results suggest a path forward for several new device concepts, including a hot electron solar cell based on ballistic electron transport.

About the Speaker

Rafael Jaramillo is a solid state physicist who feels an imperative to work to develop sources of energy for our economy that are sufficient, safe, and renewable. As a physicist with an engineering background he also has deep interests in the science that it will take to achieve this goal. Rafael received a B.S. summa cum laude in engineering physics from Cornell University in 2002, an M.Eng. from the same department in 2003, and a Ph.D. in experimental physics from The University of Chicago in 2008. At Chicago he worked on several problems related to the emergence of magnetic correlations at quantum critical points, as well as studying the effects of antiferromagnetic domain structure on electron transport in bulk materials. He has held a NSF Graduate Research Fellowship and in 2007 received the Yodh Award for Excellence in Experimental Physics from The University of Chicago. As a Ziff Environmental Fellow, Rafael will work with Professor Shriram Ramanathan (SEAS) to understand and control electron transport across thin oxide barriers, a problem with broad relevance to future generations of solar cell technologies. As solar cells evolve beyond bulk silicon p-n junctions, the efficient extraction of useful electric charge becomes challenging due to the increased complexity of device materials and geometry. The use of thin oxides as tunnel barriers and as conducting electrodes is a promising route to improving the feasibility of several promising solar cell concepts, including those designed to harvest hot carriers or multiple excitons in nanometer-scale semiconductors. Rafael looks forward to applying his knowledge of solid state physics and electron transport together with the expertise of Professor Ramanathan on oxide thin films to meeting this technical challenge of great import for next generation solar cells.