The Photovoltaic Research Laboratory at Massachusetts Institute of Technology was founded by Prof. Tonio Buonassisi, associate professor of Mechanical Engineering, in 2007. As the name implies, the Photovoltaic Research Laboratory focusses on Photovoltaics, the field where semiconductor materials are used to produce electricity from sunlight.
Current projects in Photovoltaic Research Laboratory clearly demonstrate Prof. Buonassisi’s vision, ‘low cost / high efficiency’, which made him very successful not only in academia but also in solar energy industry.
The team introduces their projects under 3 topics, namely Crystalline Silicon, Thin Films, and Breakthrough Concepts.
Before going through these projects in detail, let us remember the most important challenges in today’s solar energy field. First and foremost, the cost of materials used in solar cells makes it impractical for many households to enjoy solar panels, even with the government incentives and tax credits. Moreover, the inefficiency in today’s solar energy systems makes it less desirable than energy solutions that are not considered Green. This is simply a lose-lose situation for the consumers as well as our environment. One of the great things about Prof. Buonassisi’s research team is that they are laser focused to resolve these important challenges with a strong vision, as we describe, ‘low cost / high efficiency’.
Prof. Buonassisi’s Ph.D. thesis was related to multi-crystalline silicon solar cell materials, therefore, it is not surprising to see Crystalline Silicon as one of the main research topics in Photovoltaic Research Laboratory.
The team’s work on Crystalline Silicon is also divided into 3 sub-categories.
• Increased Solar Conversion Efficiency
• Enabling High-Quality Thin Si Substrates
• Developing Cost-Effective Manufacturing Processes
Increased Solar Conversion Efficiency basically targets the efficiency gap mono crystalline solar modules and Shockley–Queisser limit & Thermodynamic efficiency limit. The average c-Si module efficiency is around 15%, with Sunpower modules being the most efficient with over 22% efficiency except for commercially unavailable module Prof. Martin Green’s team from UNSW created with 25% efficiency (click here to see top 10 most efficient c-Si modules). The Shockley–Queisser limit & Thermodynamic efficiency limit, on the other hand, have about 33% & 89% per PV Lab and 86% per Carnot Limit (click here to read more) efficiency respectively.
In order to close the first gap, with Shockley–Queisser limit, Prof. Buonassisi’s team focuses on iron impurities and dislocations, two defect types that have big impact on the efficiency of c-Si. Collaborating with Solar Energy Institute at Polytechnic University of Madrid (click here to visit their website) Prof. Buonassisi’s team created a simulation tool, Impurities to Efficiency (I2E), which helps estimate iron impurities during solar cell processing. Having access to such data, they were able to optimize throughput & efficiency. As a result, they were able to get multi-crystalline, which is a lot less expensive but also a lot less efficient than mono-crystalline, perform at efficiency levels comparable to mono-crystalline with a slight increase in cost. Their research continues with investigating the impact of mechanical stress on efficiency.
Prof. Buonassisi’s team is currently working on two methods to target the second & much larger gap, with Thermodynamic efficiency limit. The first method is splitting the sunlight into different colors and matching the best material for each color to increase overall efficiency. The second method is improving the optical absorption coefficient with laser hyperdoping in order to collect a larger part of the solar spectrum.
Enabling High-Quality Thin Si Substrates addresses the other part of Prof. Buonassisi’s vision, as we define it. The methods mentioned before are used to increase efficiency and as a part Enabling High-Quality Thin Si Substrates, Prof. Buonassisi’s team targets cost component of solar energy field. Specifically, the team calls out the fact that the 2/5 of Photovoltaic module’s cost stems from the silicon wafer used. Utilizing the methods mentioned before and some new approaches, Prof. Buonassisi’s team is working to cut the thickness of silicone used in wafers while keeping the same performance results. The goal is to cut the amount of silicone used in solar cells by >10x, hence decreasing the cost immensely.
Prof. Buonassisi’s projects are extremely exciting and the results will directly impact solar energy industry as well as consumers. The ‘low cost / high efficiency’ is a vision that can be adapted at a very high academic level and yet it allows keeping a close bond with the consumers.
Developing Cost-Effective Manufacturing Processes comes into play after targeting both efficiency and cost issues associated with today’s silicon solar cells. The team is developing methods to improve the remaining component, manufacturing of silicon solar cells. We will be closely following Photovoltaic Research Laboratory website (click here to visit) to get more updates regarding these methods.
An important point here is the fact that Prof. Buonassisi’s projects mentioned here aim to improve the whole silicone solar cell process from A to Z. The team starts at the molecular level, works through sunlight spectrum, investigates defects at the solid matter, tackles the amount of matter required in solar cells, and improves the manufacturing technologies. This is truly an impressive way to approach to a topic. A significant number of researchers target the specific area of a topic that they are very strong with. Prof. Buonassisi‘s team covers the whole spectrum of challenges associated with silicone solar cells.
There are two materials that Prof. Buonassisi’s team is especially interested in as a part of ‘Thin Films’ category, namely Tin Sulfide (SnS) and Cuprous Oxide (Cu2O).
Prof. Buonassisi’s team defines ideal material for Photovoltaics having strong optical absorption and long carrier lifetime properties. Indicating that the current materials used carry only one of the two properties optimally, the team identifies Tin Sulfide (SnS) as the material that optimizes both properties. Moreover, the team points out the fact that Tin Sulfide (SnS) is found in large amounts in our environment, making it a very cost-effective material. Once again, the ‘low cost / high efficiency’ vision seems to be the main goal behind the team’s efforts.
Cuprous Oxide (Cu2O) is not a new material, on the contrary, it was used as paint / pigment in as early as 1920s. Moreover, it’s one of the first materials used in Photovoltaics. However, Prof. Buonassisi’s team developed a method to achieve performance from multi-crystalline film comparable to single-crystalline. As we mentioned before, multi-crystalline materials are a lot less expensive but also a lot less efficient than mono-crystalline materials. With this method, once again, the group aims to achieve ‘low cost / high efficiency’.
The projects under Crystalline Silicone and Thin Films utilize new technologies to achieve radically improved performance results. These technologies; Hyperdoped Silicon, Spectral Splitting, and Solar Fuels are explained in detail under Breakthrough Concepts category. To read more about these technologies, click on this link.
Prof. Buonassisi is an associate professor of Mechanical Engineering at MIT. He joined MIT in 2007 and founded Photovoltaic Research Laboratory. Prof. Buonassisi earned his Ph.D. degree under Prof. Eicke Weber’s supervision from U.C. Berkeley in 2006. His dissertation topic was ‘Transition Metals in Multicrystalline Silicon Solar Cells: Understanding the Nature, Origins, and Impacts of Metal Contamination to Minimize its Influence on Solar Cell Performance’. Before joining MIT, Prof. Buonassisi worked at Evergreen Solar Inc. and later, while at MIT, co-founded Fraunhofer Center for Sustainable Energy Systems.
Prof. Buonassisi has over 120 published papers and he has received many awards from prestigious organizations world-wide. For more visual learners, we suggest the following program offered at MIT. Prof. Buonassisi is one of the instructors in this program.
Short video clips that involve Prof. Buonassisi are also available online:
What we find so impressive about Prof. Buonassisi’s research is the fact that he tackles the silicone solar cells topic from A to Z. He works on the materials at the molecular level, followed by physical properties and how they react to environmental changes as matter, and then improves the processes & technologies used in manufacturing, all with ‘low cost / high efficiency’ in mind. Most researchers only focus on one aspect of silicone solar cells whereas Prof. Buonassisi delivers solutions to the whole spectrum of challenges in this field. More information about Prof. Buonassisi’s academic biography can be found in this link.