The perovskite (CH₃NH₃MX₃) solar cells are the newest class of photovoltaics showing an unprecedentedly fast development in terms of power conversion efficiency (PCE), reaching values of 20% in as prepared samples. This type of solar cells have a great commercial potential for large scale applications due to their potential low fabrication cost. While the high PCE values and potentially low production costs are important assets there are several challenges to be addressed and open questions to be answered. Among them, stability in time and reliability, understanding the measured properties of the cells (hysteresis, dependence on the voltage rate and range) and the involved phenomena, are critical issues in the search for reliable performance enhancement paths.The talk is addressing these issues based on the work performed on photovoltaic devices with CH₃NH₃PbI₃ or CH₃NH₃PbI_3-xCl_x as active materials and TiO₂ film (thin and mesoporous) and spiro-OMeTAD as electron and hole transporter materials. The perovskites used here are synthesized by several chemical routes using as solvents either only dimethylformamide or also dimethylsulfoxide. The influence of the spiro-OMeTAD, metallic top contact (Mo/Ag and Au) or chemical route for the perovskite fabrication is unveiled, and their effect on aging and device performance is discussed.The stability of the cells is monitored over time, with periodic measurements of the current-voltage characteristic under 1 Sun illumination, XRD and XPS. The anomalous dependence of the determined PCE (from current-voltage response) on the bias scan direction, rate and range is analyzed and discussed. The origin of the dynamic hysteresis is still under debate and has been attributed to different phenomena, such as ferroelectric effects, trapping and de-trapping of the charges and ion migration. A dynamic electrical model, accounting the pre-poling effects, able to reproduce qualitatively and quantitatively detailed features of the measured I-V characteristics is presented, pointing out the differences between initially over- and under-polarized samples. Furthermore, the dynamic hysteresis is measured and analyzed with respect to changing the bias scan rate, the obtained results matching also other experimental reported data. The role of chlorine in achieving enhanced solar cell power conversion efficiencies is discussed based on the results of ab initio density functional theory calculations. In particular, we discuss the effects introduced in the electronic band structure and show the role of chlorine in the enhanced electron injection into the rutile-TiO₂ layer.