Figure 1.

Perovskite structure with the general chemical formula of ABX₃: (a) A and B represent positively charged metals and red spheres anion atoms; (b) the central A site filled with Methylammonium cation (${\mathrm{CH}}_3{\mathrm{NH}}_3^{+}$). Reproduced with permission from Reference [5]. Copyright 2015, Elsevier Ltd.