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Researchers are investigating material properties for more durable, more efficient solar cells



FSU researchers are investigating material properties for more durable, more efficient solar cells

Former Florida State University postdoctoral fellow Sarah Wieghold, left, and FSU assistant professor of chemistry and biochemistry Lea Nienhaus. Their research helps to understand the basic processes in a material called perovskites, work that can lead to more efficient solar cells that also do a better job of resisting degradation. Credit: FSU

The designers of solar cells know that their creations must be able to withstand a wide range of temperatures and all kinds of weather conditions – conditions that can affect their efficiency and useful life.


Florida State University Assistant Professor of Chemistry and Biochemistry Lea Nienhaus and former FSU postdoctoral researcher Sarah Wieghold help understand the basic processes in a material called perovskites, work that can lead to more efficient solar cells that also do a better job of resisting degradation . They found that small adjustments to the chemical composition of the materials as well as the size of the electric field to which they are exposed can affect the overall material stability.

Their latest work is published in a couple of studies in Journal of Materials Chemistry C and Journal of Applied Physics.

Their research focuses on improving the potential of perovskites, a material with a crystal structure based on positively charged lead ions called cations and negatively charged halogen ions. In a cubic perovskite crystal structure, octahedra formed by lead and halide ions are surrounded by additional positively charged cations.

The first solar cells from perovskite, which were developed in 2006, had a conversion efficiency for solar energy of about 3 percent, but cells developed in 2020 have a power conversion efficiency of more than 25 percent. The rapid increase in efficiency makes them a promising material for further research, but they have disadvantages with commercial profitability, such as a tendency to degrade rapidly.

“How can we make perovskites more stable under real conditions where they will be used?” In Nienhaus. “What causes the degradation? That’s what we’re trying to understand. Perovskites that do not degrade quickly can be a valuable tool for getting more energy from solar cells.”

Perovskites are a so-called “soft material” despite the ionic bonds of the crystal lattice that make up their structure. The halides or cations in the material can move through that lattice, which can increase their degradation rate, resulting in a lack of long-term stability.

IN Journal of Materials Chemistry C paper, the researchers investigated the combined influence of light and elevated temperature on the performance of mixed cation mixed halide perovskites.

They found that the addition of a small amount of the element cesium to the perovskite film increases the stability of the material under light and elevated temperatures. Addition of rubidium, on the other hand, led to poorer performance.

“We found that depending on the choice of cation, two degradation pathways can be observed in these materials, which we then correlated to a decrease in performance,” said Wieghold, now an assistant researcher at the Center for Nanoscale Materials and the Advanced Photon Source at Argonne National Laboratory. “We also showed that the addition of cesium increased the film stability under our test conditions, which is a very promising result.”

They also found that a decrease in film performance of the less stable perovskite mixtures was correlated with the formation of the lead bromide / iodide compound and an increase in electron-phonon interactions. The formation of lead bromide / iodide is due to the undesirable degradation mechanism, which must be avoided in order to achieve long-term stability and performance of these perovskite solar cells.

In the Journal of Applied Physics, they examined the link between voltage and performance of perovskite materials. This showed that the ionic motion in the material changes the underlying electrical response, which will be a critical factor in solar cell performance.

“Perovskites are a great opportunity for the future of solar cells, and it’s exciting to help advance this science,” said Nienhaus.


Chemical innovation stabilizes the best-performing formulation of perovskite


More information:
Sarah Wieghold et al., Understanding the effect of light and temperature on the optical properties and stability of mixed ion halide perovskites, Journal of Materials Chemistry C (2020). DOI: 10.1039 / D0TC02103B

Provided by Florida State University

Quote: Researchers examine material properties for long-lasting, more efficient solar cells (2020, 26 October) retrieved 26 October 2020 from https://phys.org/news/2020-10-material-properties-longer-lasting-efficient-solar .html

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