Teams around the world are developing perovskite solar cells that can use light in the green and blue parts of the spectrum, boosting the efficiency. Research usually focuses on organometallic hybrid perovskites whose crystal structure consists of inorganic elements such as lead and iodine as well as an organic molecule.
Fully inorganic perovskite semiconductors such as CsPbI3 have the same crystalline architecture 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 a production step at a very high temperature of several hundred degrees Celsius. For this reason, inorganic perovskite semiconductors are difficult to integrate into thin-film solar cells that do not tolerate high temperatures.
A team led by Dr. Thomas Unold from the Helmholtz Research Center Berlin has now succeeded in producing inorganic perovskite semiconductors at moderate temperatures so that they could also be used in various thin-film cells in the future.
Next: Inorganic perovskite production
The physicists designed an innovative experiment with which they could synthesize and analyze many material combinations within a single sample. By co-evaporation of cesium iodide and lead iodide, along with systematically varying the excess of elements in the atmosphere, they produced thin layers of CsPbI3. The substrate temperature was below 60 degrees Celsius. “Such a combinatorial research approach allows optimal production parameters for new material systems to be found much faster than in the conventional approach, which typically requires 100 samples to be produced for 100 compositions,” explains Unold.
Their measurements show that both the structural and important optoelectronic material properties are sensitive to the relationship between cesium and lead. For example, an excess of cesium enables a stable perovskite phase with good mobility and lifetime of the charge carriers.
In cooperation with the junior research group of Prof. Steve Albrecht at the HZB, these optimized CsPbI3 layers were used to demonstrate perovskite solar cells with an efficiency of more than 12% and a stability of 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 manufactured accordingly. We are currently working on the assumption that such components can still be very strongly optimized,” says Unold.
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