Developing perovskite solar cells, with Dr. Marina Leite

Conventional solar panels are usually heavy and expensive to install. Perovskites are a class of materials that have the potential to create lighter weight and cheaper solar cells that still convert the sun to electricity at a high efficiency. Perovskite solar cells could potentially make solar energy more affordable, accessible, and environmentally friendly.

Perovskites are a group of materials in which hydrogens and carbons bind to a metal, such as lead, and a halogen, such as chlorine, and form a three dimensional crystal lattice. Thousands of different chemical compositions are possible, which allows perovskite solar cells to absorb many different colors of the solar spectrum, depending on which composition is used. This ability makes it possible for the perovskite solar cells to be used in tandem with or on top of other kinds of solar cells, such as traditional silicon solar cells, because each type of cell absorbs different parts of the solar spectrum. Together with the silicon cells, the total power conversion efficiency, or the efficiency of converting solar energy into electricity, increases to over 33 percent. 

To make a perovskite solar cell, a thin layer of perovskite ink solution is deposited onto a base and then heated to set it into a film. The thin perovskite layer absorbs light, exciting a type of charged particle called electrons. These electrons are then extracted to generate electricity. Additional layers of material help direct the flow of electrons and laser scribed channels separate the film into individual cells. Separating the film into individual cells helps lower the current and raise the voltage, making a higher voltage solar device.

When compared to traditional silicon solar panels, perovskites solar cells are cheaper and create fewer emissions. Silicon is rarely found in its pure form, which is the form it is needed in for conventional solar panels. Silicon is mostly found in beach sand as silicon dioxide. To get rid of the excess oxygen, the silicon dioxide is heated in a furnace to a very high temperature of about 1500 to 2000 degrees celsius. The energy required to run these furnaces not only increases the production cost of the silicon solar panels, but also creates additional greenhouse gas emissions. By comparison, perovskite solutions are made and set at lower temperatures, therefore resulting in fewer emissions and potentially costing less to produce. 

Conventional solar panels are rigid, flat, and heavy, so they are mostly installed on top of roofs or as solar farms. Perovskite solution can be deposited on bases of many different shapes, and it weighs very little. This gives perovskite solar cells more flexibility in the ways they can be used. Perovskite also appears to be more resilient to imperfections in its crystal lattice structure than other materials typically used in solar panels, which improves its performance. These features of the perovskite solar cells, as well as their high power conversion efficiency, that matches that of traditional solar panels at over 26 percent, gives perovskites solar cells the potential to improve accessibility of solar panels.

According to the Integrated Energy Systems Office of the US Department of Energy, there are four primary challenges to the commercialization of perovskite technology: durability, power conversion efficiency at scale, manufacturing, and technology validation and bankability. 

The durability of perovskite cells is limited when compared to other solar cells. Perovskites can decompose when exposed to stressors like moisture, oxygen, light for extended periods of time, heat, and applied voltage. Early perovskite devices degraded within a matter of minutes or hours, but now they can last for several months. Still, devices that cannot operate for more than 20 years, or ideally 30, are not likely to be commercially successful.

Perovskites have shown high power conversion efficiency as small devices, but maintaining these high efficiencies in larger devices still needs to be achieved. Methods used in labs for producing perovskite devices are not easily scalable, making uniform and high-performing perovskite material difficult to produce in a large-scale manufacturing facility. This can lead to significant differences between the efficiency of small devices and larger devices. 

The US Department of Energy has created several funding programs for perovskite cells, but getting investment from other financial institutions is still a challenge. The testing protocols for perovskite devices are not standardized and there is a lack of field data on their long-term operational behavior. To increase investment in their production, confidence in the technology needs to be increased through standardized testing protocols that can accurately demonstrate how perovskite technologies fare in real-world circumstances.

Marina Leite believes that perovskite solar cells have great potential. Perovskite solar cells could reduce the cost of solar panels by at least 30 percent while being better for the environment to produce. Perovskite solar cells can also be placed on top of existing solar panels, increasing overall efficiency. 

Leite’s lab is working on discovering the best perovskite materials to use in the solar cells by utilizing machine learning models that help predict the efficiency and durability of each material. The materials are tested under different conditions of light, temperature, oxygen, and humidity to see how they degrade, then machine learning models help extrapolate those results to other environmental conditions and predict the behavior of the material under such conditions days and weeks into the future.

Marina Leite began her work with solar cells as a post-doctoral scholar at the California Institute of Technology between 2008 and 2011. Currently, Leite is an associate professor at the University of California, Davis, in the Department of Materials Science and Engineering, conducting scientific research that helps our society mitigate climate change. Leite is also a UC Davis Chancellor’s Fellow.

• US Department of Energy, Perovskite Solar Cells
• National Laboratory of the Rockies, Photovoltaic Research
• Journal of Manufacturing Science and Engineering, Laser Scribing of Solar Cells
• US Department of Energy, Perovskite Research Challenges
• World Economic Forum, Solar power has big limitations, but Perovskites could change that
• UC Davis Material Science and Engineering, Faculty Spotlight: Marine Leite
• Leite Lab, Materials for Energy Harvesting

For a transcript of this episode, visit https://climatebreak.org/developing-perovskite-solar-cells-with-dr-marina-leite/