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Perovskites are very interesting for applications such as optoelectronic devices emitting light, such as OLEDs and lasers. On
the other hand, one can consider using these perovskites in a very special architecture: the tandem cells. The principle of
these tandem cells is to put in series two types of absorbers to optimize the absorption of the solar spectrum and thus increase
the efficiency of the cells: the perovskites could make it possible collection to increase the UV part of the solar spectrum. Many
perovskite crystals (ABX3) have been discovered to present second order properties for NLO, they undergo phase transitions
in which they transform into slightly disordered original crystals. Perovskite crystal CsSnBr3 undergoes three successive
phase transitions at T=19.1 and 26°C respectively. The crystal symmetry is sequentially transformed from rhombohedral to
monoclinic then to cubic with a decreasing temperature, and this phase transition influences the structural properties and
consequently the electronic and optical properties of this material. The results found for the perovskite cubic structure has
been compared with experimental values and other theoretical works and they are in good agreement, but concerning the
monoclinic structure, our results consist of a prediction. The calculation of the electronic properties shows the semi-conductor
character of this material since there is a small spacing of the valence electron (Br-4p5) and conduction (Sn- 5p2) bands which
is estimated at Eg=0.5375 eV in the cubic structure. This gap energy plays a key role in evaluating the use and yield of this
material in solar cells.
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properties. J. Phys.: Condens. Matter. 17(46):7275.
2. P Ren, J Qin and C Chen (2003) A novel nonlinear optical crystal for the IR region: noncentrosymetrically crystalline
CsCdBr3 and its properties. Inorg. Chem. 42:(1)8-10.
3. U Schwarz et al. (1996) Effect of pressure on the optical-absorption edges of CsGeBr3 and CsGeCl3 Phys. Rev. B
4. D K Seo et al. (1998) Pressure-induced changes in the structure and band gap of CsGeX3 (X=Cl, Br) studied by electronic
band structure calculations. Inorg. Chem. 37(3):407-410.
5. M Mori and H Saito (1986) An X-ray study of succesive phase transitions in CsSnBr3. J. Phys. C 19(14):2391-2401.
Karima Benyahia pursued her PhD from the University of Sidi Bel Abbes, Algeria and postdoctoral studies in the Department of Physics at the Galileo Gallile University of Padova, Italy and in the Chemistry Department, SINTEF, Oslo. Norway. She is mainlly interested in materials for solar cells.