My work in the Dauskardt group focuses primarily on building new understandings of the reliability and degradation of materials for multijunction photovoltaic systems, as part of the Sunshot's PREDICTS program, and in collaboration with major multijunction PV companies including Solar Junction and Boeing’s Spectrolab. Solar power generation with high-efficiency multijunction photovoltaic (PV) cells has been an area of significant interest in recent years, as improved concentrator systems have enabled cost effective terrestrial deployment. While these systems have held a clear advantage in conversion efficiency over their traditional silicon counterparts, with efficiencies that have long exceeded 40% and even recently reaching as high as 46%, questions regarding long term reliability remain as availability of in-field exposure data is limited. Furthermore, environmental degradation is of greater concern as cells are subjected to higher incident flux of ultraviolet light and larger temperature cycles.
We have worked to leverage the Dauskardt group’s expertise in fracture and degradation of multilayer thin film structures to develop the necessary testing methods to evaluate multijunction PV structures, from the antireflective layers, to the frontside- and backside-metal contacts, to the semiconductors themselves. This includes the new composite dual cantilever beam (cDCB) testing method, in which strong reinforcing beams are adhered to fragile semiconductor substrates in order to enable the first ever reliable quantitative measurement of adhesion within multijunction cells.
Previous work in the group has also included collaborations with Nissan ARC on Proton Exchange Membrane materials for fuel cells, and with the Iacopi group at Griffiths University on mechanical characterization of 3C-SiC films grown on silicon.
Following the theme of mechanical characterization of fragile thin film materials, SiC membranes have been an area of significant interest. Measurement of the residual stress and biaxial modulus of thin films can be difficult to measure via traditional testing methods due to sample geometries. However, characterization via a spherical bulge test can give a direct measurement of both of these quantities. Given a sufficiently reflective film, the small deflections caused by pressurizing a film can be measured using an interferometer and CCD camera. We performed modelling on the shape of a bulging SiC membrane and ultimately found that fracture stress measured by this method is highly dependent upon stress concentration at the edges of a bulging membrane.
- R. Brock, R. Rewari, P. Hebert, J. Ermer, D. Miller, R. Dauskardt, “Quantitative Adhesion Characterization of Antireflective Coatings in Multijunction Photovoltaics”, In preparation, 2015.
- R. Brock, F. Iacopi, A. Iacopi, L. Hold, R. Dauskardt, “Highly Compressed Nano-Layers in Epitaxial Silicon Carbide Membranes for MEMs Sensors", Proceedings of the IEEE IITC/AMC, 2014, p241.
- F. Iacopi, R. Brock, A. Iacopi, L. Hold, R. Dauskardt, “Evidence of a highly compressed nanolayer at the epitaxial silicon carbide interface with silicon”, Acta Mat., 2013, 61 (17), p6533.
- A. Antaris, J. Seo, R. Brock, M. Hersam, “Probing and tailoring pH-dependent interactions between block copolymers and single-walled carbon nanotubes for density gradient sorting” , J. Phys. Chem. C, 2012, 116 (37), p20103.
- R. Brock*, et al, “Electronically monodisperse single-walled carbon nanotube thin films as transparent conducting anodes in organic photovoltaic devices”, Adv. Energy Mater., 2011, 1, p785. (Cover Article)
- C. Tester, R. Brock, C. Wu, M. Krejci, S. Weigand, D. Joester, “In vitro synthesis and stabilization of amorphous calcium carbonate (ACC) nanoparticles within liposomes”, CrystEngComm, 2011, 13, p3975.
Conference Proceedings and Presentations
- R. Brock, P. Hebert, H. Cotal, J. Ermer, R. Dauskardt, “Adhesion and Reliability of Complex Multijunction Photovoltaic Structures", MRS Spring Meeting, 2015.
- R. Brock, F. Iacopi, A. Iacopi, L. Hold, R. Dauskardt, “Residual stress and fracture behavior of pressurized epitaxial SiC membranes", MRS Spring Meeting, 2014.
- R. Brock, C. Cai, T. Hasegawa, J. Ye, K. Yoneda, R. Dauskardt, “Size-dependent tearing resistance of polymer membranes”, MRS Spring Meeting, 2013.
- President, Materials Research Society, Stanford Chapter (2014-2015)
- Volunteer, GRID Alternatives Bay Area (2013-)
- Undergraduate Research Mentor, Dauskardt group (2013-2015)
- Atomic Force Microscope Trainer, Stanford Nano Shared Facilities (2013-2015)
- Baron & Ladewick Scholarship (2007-2011)
- Gotaas Award for Best Undergraduate Research in School of Engineering (2011)
- Hilliard Award for Leadership, Scholarship, and Service (2011)
- Yang and Yamazaki Engineering Fellowship (2011)
- National Science Foundation GRFP Honorable Mention (2012)
- Department of Energy SCGF Finalist (2012)