Inorganic perovskite absorbers for use in thin-film solar cells

A team from the Helmholtz-Zentrum Berlin has succeeded in producing a thin layer of inorganic perovskite at moderate temperatures using coevaporation – making post-tempering at high temperatures unnecessary. This process greatly facilitates the production of thin-film solar cells from this material. Compared to metal-organic hybrid perovskites, inorganic perovskites are more thermally stable. The work was published in Advanced energy materials.

Teams around the world are working intensively on the development of perovskite solar cells. The focus is on what is called the metal-organic hybrid perovskites whose crystalline structure is composed of inorganic elements such as lead and iodine, as well as other substances. an organic molecule.

Fully inorganic perovskite-based semiconductors such as CsPbI₃ have the same crystalline structure as hybrid perovskites, but contain an alkali metal such as cesium instead of an organic molecule. This makes them much more stable than hybrid perovskites, but usually requires an extra production step at very high temperatures – several hundred degrees Celsius. For this reason, perovskite-based inorganic semiconductors have so far been difficult to integrate into thin-film solar cells that can not withstand high temperatures. A team led by Dr. Thomas Unold has succeeded in producing perovskite-based inorganic semiconductors at moderate temperatures, so that they can also be used in thin-film cells in the future.

Physicists designed an innovative experiment in which they synthesized and analyzed many combinations of materials within a single sample. Using the co-evaporation of cesium iodide and lead iodide, they produced thin layers of CsPbI₃, by systematically varying the quantities of these elements, while the temperature of the substrate was below 60 degrees Celsius.

"Such a combinatorial research approach allows us to find the optimal production parameters for new material systems much faster than with the conventional approach that typically requires the production of 100 samples for 100 different compositions", explains Unold. Through careful analysis during the synthesis and subsequent measurements of the optoelectronic properties, they were able to determine the effect of the thin film composition on the properties of the material.

Their measurements show that the structural and important optoelectronic properties of the material are sensitive to the ratio of cesium to lead. Thus, an excess of cesium promotes a stable perovskite phase with good mobility and a good lifespan of the charge carriers.

In collaboration with Professor Steve Albrecht's group of young HZB researchers, these optimized CsPbI tools₃ Layers were used to present perovskite solar cells with an initial efficiency of more than 12% and stable performance close to 11% for more than 1200 hours. "We have shown that inorganic perovskite absorbers could also be suitable for use in thin-film solar cells if they can be adequately manufactured, and we believe that much more needs to be done to improve," says Unold.