**Abstract**

Perovskite solar cells were fabricated and characterized. X-ray diffraction analysis and transmission electron microscopy were used for investigation of the devices. The structure analysis by them showed structural transformation of the crystal structure of the perovskite, which indicated that a cubic-tetragonal crystal system depended on the annealing condition. The photovoltaic properties of the cells also depended on the structures. Metal doping and halogen doping to the perovskite and TiO2 were also investigated. The results showed an increase in the efficiencies of the devices, due to the structural change of the perovskite compound layers.

**Keywords:** perovskite, solar cell, doping, structure, CH3NH3PbI3, Sb, Cl, TiO2, Nb, Ge, Cs
