Presenter: Sang M. Han

Description: Energy savings can come in many different forms. In my research group, we focus on materials engineering solutions to extend the solar module lifetime as a way of reducing the cost of solar electricity. We are also developing solar-rejection coating materials for radiative cooling, which can be used for buildings, transportation systems, clothing, and even space vehicles. These solutions represent our approach to use increased durability as well as energy conservation for cost savings.

One of the ways to reduce the cost of solar electricity is to reduce the degradation rate of solar modules and extend their lifetime well beyond 30 years. The extended module lifetime in turn can positively influence the financial model and the bankability of utility-scale PV projects. Today, one of the highest-risk-priority solar module degradation mechanisms is what is known as hot spots, often induced by cell cracks. In order to address this degradation mechanism, we make use of low-cost carbon nanotubes embedded in commercial screen-printable silver pastes. When the carbon nanotubes are properly functionalized and appropriately incorporated into commercial silver pastes, the resulting metal contacts on solar cells, after screen-printing and firing, show exceptional fracture toughness. These composite metal contacts possess increased ductility, electrical gap-bridging capability >50 µm, and “self-healing” to regain electrical continuity after cycles of complete electrical failure. I will present our work ranging from materials engineering to module-level testing to demonstrate the utility of carbon-nanotube-reinforced metallization.

The practice of radiative cooling has been around since 400 BC, but recaptured people’s imagination in recent years. Coatings for radiative cooling can reduce the temperature of coated objects, often well below the ambient temperature, without having to expend any electricity or energy. The asymmetry in heat transfer rate in summer vs. winter, combined with the low cost of natural gas, makes the radiative cooling an economically attractive option for the building envelope. In my group, we make use of low-cost, bulk-quantity, commercial ingredients (e.g., silica microspheres, paint binder, and silicone) to develop the coating material. Our technology eliminates the need for complex fabrications and expensive materials, such as silver. I will demonstrate that when the coatings consist of properly sized and randomly packed microspheres (also known as photonic glass) in a paint format, the temperature of the “painted” object can reach as much as 12 ºC below the ambient temperature and 5 ºC below the best performing commercial solar rejection paint under intense summer solar radiation.

Bio: Dr. Han is a Regents Professor in the Departments of Chemical & Biological Engineering and Electrical & Computer Engineering at the University of New Mexico (UNM). He earned his Ph.D. in chemical engineering from the University of California at Santa Barbara and his B.S. in chemical engineering with honors from the University of California at Berkeley. Dr. Han has over 25 years of experience in electronic and photonic materials engineering and fabrication. His current research topics include (1) instability-driven, patternable quantum structure formation in epitaxial compound semiconductors; (2) low-cost, crack-tolerant, advanced metallization for improved solar cell durability; (3) microsphere-based manufacturable coatings for radiative cooling; and (4) precision plasma-delayering of microchips for defect analysis. He has 82 publications in peer-reviewed journals and over 200 invited/contributed papers at academic institutions, national laboratories, and conferences. For his excellence in both research and teaching, Dr. Han received a Regents Professor title at UNM in 2015, a UNM Junior Faculty Research Excellence Award in 2005, and an NSF CAREER Award in 2001. Dr. Han holds 21 UNM-affiliated U.S. patents and 17 pending U.S. and PCT patent applications. He was elected as the UNM Rainforest 2018 Innovation Fellow and inducted into the National Academy of Inventors in 2023. From 2022 to 2024, Dr. Han served as Department Chair, and he currently serves as Chief Technology Officer of Osazda Energy, a startup company based on his intellectual property generated at UNM. Prior to his entrepreneurial venture, Dr. Han served as the main campus faculty member of the UNM Rainforest Innovations Board of Directors from 2015 to 2016.

Hosted by: Professor Hao Ye & UC Santa Cruz ECE Department

Zoom link: https://ucsc.zoom.us/j/99916319246?pwd=wlipSeBqozlxwWF9KkqutaHnVy8gN9.1