A Rice University study published in Science details a method for synthesizing formamidinium lead iodide (FAPbI3) into stable, high-quality photovoltaic films. The efficiency of these FAPbI3 solar cells declined by less than 3% over more than 1,000 hours of operation at 85 degrees Celsius (185 Fahrenheit).
"Right now, we think that this is state of the art in terms of stability," said Rice engineer Aditya Mohite. "Perovskite solar cells have the potential to revolutionize energy production, but achieving long-duration stability has been a significant challenge."
This breakthrough represents a major step towards making perovskite photovoltaics commercially viable. The researchers added specially designed two-dimensional (2D) perovskites to the FAPbI3 precursor solution, which served as a template to enhance the stability of the crystal lattice structure.
"Perovskite crystals get broken in two ways: chemically - destroying the molecules that make up the crystal - and structurally - reordering the molecules to form a different crystal," explained Isaac Metcalf, a Rice graduate student and a lead author on the study. "Of the various crystals that we use in solar cells, the most chemically stable are also the least structurally stable and vice versa. FAPbI3 is on the structurally unstable end of that spectrum."
The researchers found that while 2D perovskites are more stable, they are less effective at harvesting light. By using 2D perovskites as templates, they improved the stability and efficiency of FAPbI3 films. The addition of well-matched 2D crystals facilitated the formation of high-quality FAPbI3 films, showing less internal disorder and better illumination response.
The study showed that solar cells with 2D templates retained their efficiency and durability significantly better than those without. Encapsulation layers further enhanced the stability of these solar cells, extending their operational life to timescales relevant for commercial applications.
"Perovskites are soluble in solution, so you can take an ink of a perovskite precursor and spread it across a piece of glass, then heat it up and you have the absorber layer for a solar cell," Metcalf said. "Since you don't need very high temperatures - perovskite films can be processed at temperatures below 150 Celsius (302 Fahrenheit) - in theory that also means perovskite solar panels can be made on plastic or even flexible substrates, which could further reduce costs."
Silicon, the most commonly used semiconductor in photovoltaic cells, requires more resource-intensive manufacturing processes than perovskites, which have seen efficiency improvements from 3.9% in 2009 to over 26% currently.
"It should be much cheaper and less energy-intensive to make high-quality perovskite solar panels compared to high-quality silicon panels, because the processing is so much easier," Metcalf said.
"We need to urgently transition our global energy system to an emissions-free alternative," he added, referring to UN estimates that highlight the importance of solar energy in replacing fossil fuels.
Mohite emphasized that advancements in solar energy technologies are crucial for meeting the 2030 greenhouse gas emissions target and preventing a 1.5 degrees Celsius rise in global temperatures, essential for achieving net zero carbon emissions by 2050.
"If solar electricity doesn't happen, none of the other processes that rely on green electrons from the grid, such as thermochemical or electrochemical processes for chemical manufacturing, will happen," Mohite said. "Photovoltaics are absolutely critical."
Mohite holds the title of William M. Rice Trustee Professor at Rice, is a professor of chemical and biomolecular engineering, and directs the Rice Engineering Initiative for Energy Transition and Sustainability. The study's lead authors also include Siraj Sidhik, a Rice doctoral alumnus.
"I would like to give a lot of credit to Siraj, who started this project based on a theoretical idea by Professor Jacky Even at the University of Rennes," Mohite said. "I would also like to thank our collaborators at the national labs and at several universities in the U.S. and abroad whose help was instrumental to this work."
Research Report:Two-dimensional perovskite templates for durable, efficient formamidinium perovskite solar cells
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