Study shows thermal instability of solar cells but offers a bright path ahead

Research reveals thermal instability of solar cells but offers a bright path ahead

Surface stoichiometry changes in CsFAMA films treated with PEAI and OAI N1 (left) and Pb4f (right) peaks of PEAI (top) and OAI (bottom) treated films. Credit: Advanced Materials (2022). DOI: 10.1002/adma.202204726

A new type of solar technology has looked promising in recent years. Perovskite halide solar cells are both high-efficiency and low-cost to produce electrical energy—two components required for any successful solar technology in the future. But the new solar cell materials must also match the stability of silicon-based solar cells, which have a reliability of more than 25 years.

In newly published research, a team led by Juan-Pablo Correa-Baena, an assistant professor in the School of Materials Science and Engineering at Georgia Tech, shows that perovskite halogen solar cells are less stable than those of a perovskite halogen solar cell. with previous thinking. Their work shows that thermal instability occurs in the interface layers of cells, but also offers a path towards reliability and efficiency for perovskite halide solar technology.

Their research, published as a cover story for the journal Advanced Materials in December 2022, has immediate implications for both academics and industry professionals working with perovskites in photovoltaics, a field that deals with electric currents generated by sunlight.

Lead-halogen perovskite solar cells promise remarkable conversion of sunlight into electrical energy. Currently, the most common strategy to obtain high conversion efficiency from these cells is to treat their surfaces with large positively charged ions called cations.

These cations are too large to fit in the perovskite atomic-scale lattice, and when they fall on the perovskite crystal, they change the structure of the material at the interface where they are deposited. As a result, defects at the atomic scale limit the efficiency of solar cell current extraction. Despite being aware of these structural changes, research on whether cations are stable after deposition is still limited, leaving gaps in the understanding of the process that could affect the ability to longevity of perovskite halide solar cells.

“Our concern is that over the long run of the solar cell, the process of reinventing the interfaces will continue,” Correa-Baena said. “So we sought to understand and demonstrate how this process plays out over time.”

To perform the experiment, the team created a prototype solar device using typical perovskite membranes. The device has eight independent solar cells, allowing researchers to experiment and generate data based on individual cell performance. They studied how the cells would behave, both with and without cationic surface treatment, and studied the cationic-modified interfaces of individual cells before and after prolonged thermal stress using the technique. Synchrotron-based X-ray characterization.

The researchers first exposed the pre-treated samples to a temperature of 100 degrees Celsius for 40 minutes, then measured the change in their chemical composition using X-ray photoelectron spectroscopy. uses a different type of X-ray technology to investigate exactly what kind of crystal structure forms on the surface of the film. Combining information from the two tools, the researchers were able to visualize how the cations diffuse into the lattice and how the interface structure changes when exposed to heat.

Next, to understand how cation-induced structural changes affect solar cell performance, the researchers used excitation-correlation spectroscopy in collaboration with Carlos Silva, professor physics and chemistry at Georgia Tech. This technique exposes solar cell samples to very fast pulses of light and detects the intensity of light emitted by the film after each pulse to understand how energy from the light is lost. The measurements allowed the researchers to understand what types of surface defects were detrimental to performance.

Finally, the team compared changes in the structure and optoelectronic properties with differences in solar cell performance. They also studied the high temperature-induced changes in two of the most used cations and observed differences in the dynamics at their interfaces.

“Our work reveals that there is instability associated with dealing with a particular type of drug,” said Carlo Perini, a research scientist in the Correa-Baena lab and first author of the paper. certain number of cations”. “But the good news is, with proper engineering of the interface layer, we should see enhanced stability of this technology in the future.”

Researchers have learned that the surface of metal halide perovskite Membranes treated with organic cations continued to grow in structure and composition under thermal stress. They found that the resulting atomic-scale changes at display can cause significant losses in energy conversion efficiency in solar battery. In addition, they found that the rate of these changes depends on the type cationic used, suggesting that stable interfaces may be within reach with full molecular engineering.

“We hope this work will force researchers to test these interfaces at high temperatures and look for solutions to the instability problem,” Correa-Baena said. “This work will point scientists in the right direction, to an area where they can focus on building more efficient and stable solar technologies.”

More information:
Carlo Andrea Riccardo Perini et al, Ruddlesden–Popper interface reconstruction impacts stability in lead-Halide Perovskite solar cells, Advanced Materials (2022). DOI: 10.1002/adma.202204726

quote: Study showing thermal instability of solar cells but offering a bright path ahead (2023, Feb. 9) retrieved Feb. 9, 2023 from news/2023-02-reveals-thermal-instability-solar-cells.html

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