EECS500 Spring 2015 Department Colloquium

Tyler Grassman
Advances in the Development of Epitaxial III-V/Si Multijunction Solar Cells
Ohio State University
White 411
March 17, 2015

The marriage of high-performance III-V materials and devices with low-cost, high-availability Si substrates has been a ‘holy grail’ of photovoltaics materials research for decades. Further, III-V/Si multijunction solar cells utilizing active Si sub-cells, rather than merely cheap Si substrates – a “Si-plus” architecture – hold the potential for high conversion efficiencies on par with pure III-V multijunction structures, but at substantially lower costs. Detailed-balance modeling of such structures, even when significantly tempered for rational expectations, suggest practically achievable one-sun efficiencies for dual- and triple-junction III-V/Si series-connected devices well beyond 30%, and theoretical maxima over 50% with solar concentration. One of the most promising approaches to this end is via heteroepitaxial, heterovalent (polar/nonpolar) GaP/Si to provide the necessary integration route and metamorphic (lattice-mismatched), compositionally-graded GaAsyP1-y to accommodate the significant misfit between the Si substrate and target III-V junction materials. Nonetheless, only recently has sufficient progress actually been made in both of these endeavors – led by a small number of researchers, including our group at OSU – to provide realistic pathways for the development of high-performance epitaxial III-V/Si multijunction structures. Over the last few years, our group has made tremendous strides in GaP/Si epitaxial integration, GaAsyP1-y metamorphic grading and defect engineering, the development of integrable GaP/Si bottom junctions and novel, metamorphic GaAsyP1-y and Ga1-xIn­xP upper junctions, the development of new tunnel diodes to provide sub-cell electrical interconnection, and demonstrations of initial prototype multijunction structures.


Dr. Tyler Grassman is a research assistant professor at The Ohio State University since September 2012, with a joint appointment in the Departments of Materials Science & Engineering and Electrical & Computer Engineering. He earned his M.S. and Ph.D. in Materials Science & Engineering at the University of California, San Diego and his B.A. in Chemistry at the University of Oregon. Dr. Grassman’s research interests focus on the epitaxy and characterization of novel and integrated materials for optoelectronics applications, with a particular focus on photovoltaics and clean energy technologies.  Related efforts include III-V/Si integration, band gap and lattice constant engineering over the full gamut of III-V alloy systems, nanostructured materials, molecular beam epitaxy and metal-organic chemical vapor deposition, surface and interface science, defect engineering and mitigation strategies, and development of rapid characterization techniques.