EAGER:TDM Solar Cells: Collaborative Research: 30%-Efficient, Stable Perovskite/Silicon Monolithic Tandem Solar Cells

Stanford University, Stanford CA

Investigators

Abstract

Abstract Nontechnical Description Solar cells, which harvest energy from the sun and generate electricity, are diversifying our energy portfolio and will be an important part of reducing our dependence on fossil fuels and preventing undesirable climate change. It is important to make solar panels as efficient as possible so that the number of panels needed to obtain a certain amount of power can be reduced in order to save on installation costs. Tandem cells, comprised of a top cell that harvests the visible portion of the spectrum and a bottom cell that harvests the infrared portion, are the most promising way to achieve higher efficiencies. Silicon, which is used in approximately 92% of the solar panels that are manufactured each year, is ideal for the bottom cell and typically has 16-21 % efficiency by itself. Perovskite semiconductors are highly attractive for the top cell because they can be tuned to have the right bandgap and have efficiency as high as 22%. The objective of this project is to demonstrate the first 30%-efficient perovskite/silicon tandem solar cell. Technical Description This project describes plans for a perovskite expert, Professor Michael McGehee, to partner with a silicon expert, Professor Zachary Holman, to make perovskites/silicon tandem solar cells. This team has made a prototype two-terminal monolithic device with a power conversion efficiency of 25.3 %. They hold the world record for this type of device and are in a very strong position to increase the efficiency to 30% over the next two years. This development is especially exciting because their packaged perovskite solar cells have already passed the PV industry standard damp heat and temperature cycling tests and it is likely that panels with these cells could be manufactured at a cost of < $100/m2. The bandgap of perovskites can be tuned from 1.2 eV to 2.3 eV using the materials set ABX3, where A is a mixture of methylammonium, formamidinium or cesium, B is a mixture of tin and lead, and X is a mixture of bromine or iodine. The most important research goal of this project is to find the optimal combination of these components for making a stable and high-quality semiconductor with a bandgap of 1.8 eV. The team will thoroughly characterize the semiconductors it makes to guide the process of optimizing the properties. Additional research goals of this project are to develop high-mobility TCO layers for the front of the tandem solar cells, improve the infrared response of the silicon bottom cell while decreasing its cost via a porous dielectric/metal rear reflector, and fabricate PDMS layers with scattering textures to be used at the front of the tandem to reduce reflectance. This project has the potential to change our future energy landscape through the development of efficient yet inexpensive PV technologies. The project will also train a diverse pool of students and the results will be disseminated broadly. Holman is the PI of an NSF REU site into which the proposed project will be integrated. Approximately once every 18 months McGehee gives a lecture that is intended to be easy to understand even for people who are not yet scientists and posts it on YouTube. These lectures are typically viewed more than 20,000 times by a wide variety of people.