Synthesis process increases performance of perovskite solar cells to near commercialization standards

Solar energy is not only the fastest growing energy technology in recent history, but also one of the cheapest and most efficient sources of energy in terms of reducing greenhouse gas emissions. Greenhouse.

A Rice University study featured on the cover of Science describes a way to synthesize formamidinium lead iodide (FAPbI₃) – the type of crystal currently used to make the most efficient perovskite solar cells – into ultra-stable, high-quality photovoltaic films. The overall effectiveness of the resulting FAPbI₃solar cells shrunk by less than 3% over more than 1,000 hours of operation at temperatures of 85 degrees Celsius (185 Fahrenheit).

“Right now, we think it's the state of the art in terms of stability,” said Aditya Mohite, an engineer at Rice, whose lab has gradually improved the durability and performance of perovskites over the course of of recent years. “Perovskite solar cells have the potential to revolutionize energy production, but achieving long-term stability is a significant challenge.”

With this most recent breakthrough, Mohite and his collaborators have taken a crucial step toward commercializing perovskite-based photovoltaics. The key was to “season” the FAPbI₃precursor solution with a pinch of specially designed two-dimensional (2D) perovskites. These served as a template guiding the growth of the bulk/3D perovskite, providing additional compression and stability to the crystal lattice structure.

“Perovskite crystals break in two ways: chemically, by destroying the molecules that make up the crystal, and structurally, by rearranging the molecules to form a different crystal,” said Isaac Metcalf, graduate student in materials science and nano. -Rice engineering and lead author of the work. the study.

“Among the different crystals we use in solar cells, the most chemically stable are also the least structurally stable and vice versa. FAPbI ₃ lies on the structurally unstable side of this spectrum. »

Although more stable than FAPbI₃Both chemically and structurally, 2D perovskites are generally not very effective at capturing light, making them a poor choice of material for solar cells.

However, the researchers hypothesized that 2D perovskites would be used as templates for FAPbI growth. ₃ the films could give the latter their stability. To test this idea, they developed four different types of 2D perovskites, including two with a surface structure almost indistinguishable from that of FAPbI. ₃ and two less well matched – and used them to create different FAPbI₃film formulations.

“The addition of well-matched 2D crystals made the task of FAPbI easier ₃ “Crystals to form, while mismatched 2D crystals made formation more difficult, thus validating our hypothesis,” Metcalf said.

“FAPbI ₃ Films modeled with 2D crystals were of higher quality, showing less internal disorder and exhibiting a stronger response to illumination, resulting in higher efficiency.

2D crystal models not only improved FAPbI efficiency ₃ solar cells but also their durability. While solar cells without 2D crystals degraded significantly after two days of generating electricity from sunlight in the air, solar cells with 2D models did not begin to degrade even after 20 days. By adding an encapsulation layer to the 2D modeled solar cells, stability was further improved at time scales close to commercial relevance.

These discoveries could have a transformative impact on light harvesting or photovoltaic technologies, further reducing manufacturing costs and enabling the construction of solar panels with a simplified structure that is lighter and more flexible than their silicon-based counterparts. .

“Perovskites are soluble in solution, so you can take the ink of a perovskite precursor and spread it on a piece of glass, then heat it and you get the absorbent layer for a solar cell,” Metcalf said.

“Since you don't need very high temperatures – perovskite films can be processed at temperatures below 150 degrees Celsius (302 Fahrenheit) – in theory this also means that perovskite solar panels can be made on plastic or even flexible substrates, which could further reduce costs.

Although it is the most widely used semiconductor in photovoltaic cells, silicon requires more resource-intensive manufacturing processes than those of emerging alternatives. Among these, halide perovskites stand out for their dazzling efficiencies, which have increased from 3.9% in 2009 to more than 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 much easier,” Metcalf said.

“We urgently need to evolve our global energy system towards an emissions-free alternative,” he added, highlighting estimates from the United Nations Intergovernmental Panel on Climate Change which “constitute solid arguments for solar energy as an alternative to fossil fuels.

Mohite stressed that advancements in solar energy technologies and infrastructure are key to meeting the 2030 greenhouse gas emissions target and preventing a 1.5 degree Celsius increase in global temperatures. , which would then “put us on track to achieve net zero carbon emissions by 2050”. “

“If solar electricity does not occur, none of the other processes that depend on green electrons in the lattice, such as thermochemical or electrochemical processes for making chemicals, will occur,” Mohite said. “Photovoltaics are absolutely crucial.”

Mohite is Rice's William M. Rice Trustee Professor, professor of chemical and biomolecular engineering, and educational director of the Rice Engineering Initiative for Energy Transition and Sustainability. In addition to Metcalf, Rice PhD alumnus Siraj Sidhik is one of the study's lead authors.

“I would like to give a lot of credit to Siraj, who started this project based on a theoretical idea from Professor Jacky Even of the University of Rennes,” Mohite said. “I would also like to thank our collaborators at the national laboratories and several universities in the United States and abroad whose assistance was instrumental in this work.”