Physico-Chemical nanomaterials science

The influence of direct electric current on the properties of CsPbCl3 and CsPbBr3 perovskites
Lys R.M.1, Gamernyk R.V.2, Pavlyk B.V.1
1 Department of Sensor and Semiconductor Electronics, Ivan Franko National University of Lviv. Str. Tarnavskoho, 107, Lviv-79017, Ukraine. 
E-mail: lys_r@ukr.net 
2 Department of Experimental Physics, Ivan Franko National University of Lviv. Str. Kyrylo and Methodiy, 8, Lviv-79005, Ukraine.

Nowadays silicon-based solar cells are mainly used in solar power. The efficiency of cells does not reach 0.25. Therefore, the search for effective and inexpensive materials for solar cells remains relevant. Recently, the attention of researchers was drawn to organo-inorganic perovskites with the general formula MPbX3. A factor of conversion of solar energy into electrical at the level of 0.22 was obtained for these crystals in the laboratory. However, these elements degrade very quickly. Therefore, the attention of the researchers was drawn to completely inorganic perovskites, where cations are cesium ions.
CsPbCl3 and CsPbBr3 single crystals grown by the Bridgman method were used for the studies. The samples obtained were characterized by fairly high transparency in the visible region of the spectrum and had a clear edge of their absorption. It was observed that their transparency in the visible region of the spectrum decreases (crystals are colored) after the passage of direct electric current through the samples. To identify the crystal structure and to change it as a result of coloring the crystals, X-diffraction studies of the original and colored samples were performed.
As the current passes as a result of moving the anions, the crystal is not colored uniformly throughout the volume but becomes darker (more colored) near the negative contact. This means that from this area the anions move to the positive contact, and a region of the crystal emerges, which is depleted by the anions. After the effect of direct electric current, the lead caused strong absorption in the visible region of the spectrum, which was observed on the optical transmission spectra.