Abstarct: In this thesis, the electronic, mechanical and optical properties of bulk and nano-laxyer structures of organic-mineral hybrid perovskites MAPbX3 (X=Cl, Br, I) have been investigated. In recent years, these compounds have been widely considered as adsorbent materials of a new generation of solar cells. Bulk phase of these materials at temperatures higher than room temperature which equals to work temperature of the solar cells is cubic. Hence, at the first step cubic phase of bulk MAPbX3 (X=Cl, Br, I) and then two dimensional single and multi-laxyer of their nano-structures have been investigated. The results obtained with the help of PBEsol, SOC and HSE06 approximations showed that the electronic properties of these materials are directly depend on the type of halogen (X = Cl, Br, I) in the compound. As the halogen radius increases (RCl<RBr<RI), the direct band gap of bulk phases beside single and multi-laxyer nanostructures decreases. The reason for this behavior is the increase in the overlapping of p and s orbitals of the halogens, and the increase of intense anti-adhesion interactions and displacement of the edge of the valence band towards larger energies. The results obtained with the GGA-PBEsol approximation were very consistent with experimental results. Additionally, in order to investigate relativistic effects of heavy Pb atom inside these compounds, electronic properties of the bulk structures were investigated considering spin-orbit coupling but the results were not consistent well with the experimental reports. Also, mechanical properties of these structures have been studied using energy-strain approach. In this approach, by applying the strain and structures’ deformations baxsed on deformation matrices, and using obtained energy-strain curves, elastic constants of these structures were calculated. After that, utilizing relations of these constants with mechanical parameters such as Young’s module, Bulk and shear modules and also Poisson ratio, the elastic behavior of considered structures have been studied. The results showed that, with increasing of the halogens radius and decreasing of the strength of X-Pb-X bonds, the elastic coefficients and, consequently, the mechanical parameters have decreasing trend. However, significant point in bulk and nano structures are the high formability power of these materials which are very flexible compared with the silicon solar cells Since for the optical applications it is very important to know the optical parameters of the structures, by computing the real and imaginary parts of the dielectric function, some coefficients like, refractive index, extinction coefficient, absorption and reflectivity coefficients were investigated. The important result was the high order of the absorption coefficient (at a rate of 105 cm-1), which is important for absorber laxyers using in the solar cells. The mineral component of these materials is the main factor of this high absorption coefficient. Also, the presence of organic cations in these compounds cause a significant reduction of their static dielectric constants compared to the CsPbI3 perovskites.