Revealing thermal stability dynamics of an inorganic metal halide perovskite at high temperatures

Inorganic metal halide perovskites have garnered notable interest in recent years as a promising material for high-performance solar cells, lasers, LEDs and photodetectors that operate from room temperature to high temperatures. Their dense crystalline structure can absorb the entire visible light spectrum, and they are cheap and easy to manufacture.

Still, crystal degradation of these materials under high temperatures is not well understood, which is further complicated by perovskite sensitivity to moisture, oxygen, pressure and other variables.

Using transmission electron microscopy (TEM) and videoing the process, Zhang et al. show in real time the thermal stability dynamics of one such perovskite, cesium lead bromide, in both high vacuum and pressurized environments. Among other findings, they observed that the perovskite could withstand noticeably higher temperatures in the pressurized environment.

The perovskite thin film was arranged on a microelectromechanical chip and studied in a high-vacuum TEM environment with low humidity and no illumination. The film maintained its stability until reaching its melting point of 690 K. At this temperature, the material surface began to evaporate but maintained a single-crystalline structure while the interior part of the crystal became amorphous. Evaporation eventually extended to the whole particle. Recrystallization was not observed due to high vacuum conditions and cold trapping of the microscope.

To confirm the melting point at a meaningful pressure, the researchers used a TEM technique to sandwich the nanocrystal material between layers of amorphous carbon, which pressurized and sealed the perovskite. The melting point in this case was much higher, at 840 K, with the material recrystallizing at 838 K.

The researchers expect to extend their TEM method to study similar inorganic perovskites and show understand and improve perovskite stability.

Source: “Thermal stability of CsPbBr₃ perovskite as revealed by in situ transmission electron microscopy,” by Chao Zhang, Joseph F. S. Fernando, Konstantin L. Firestein, Joel E. von Treifeldt, Dumindu Siriwardena, Xiaosheng Fang, and Dmitri Golberg, APL Materials (2019). The article can be accessed at https://doi.org/10.1063/1.5108849 .