The number of publications on perovskite solar cells (PSCs) continues to grow exponentially. Although the efficiency of PSCs has exceeded 25.5%, not every research laboratory can reproduce this result or even pass the border of 20%. Unfortunately, it is not always clear which dominating mechanism is responsible for the performance drop. Here, a simple method of light intensity analysis of the JV parameters is developed, allowing an understanding of what the mechanisms are that appear in the solar cell and limit device performance. The developed method is supported by the drift‐diffusion model and is aimed at helping in the explanation of parasitic losses from the interface or bulk recombination, series resistance, or shunt resistance in the perovskite solar cell. This method can help not only point toward the dominating of bulk or interface recombination in the devices but also determine which interface is more defective. A detailed and stepwise guidance for such a type of light intensity analysis of JV parameters is provided. The proposed method and the conclusions of this study are supported by a series of case studies, showing the effectiveness of the proposed method on real examples.

An experimental and theoretical study is reported to investigate the influence of bromine doping on CH₃NH₃Pb(I_1–xBr_x)₃ perovskite for Br compositions ranging from x = 0 to x = 0.1, in which the material remains in the tetragonal phase. The experimental band gap is deduced from UV–vis absorption spectroscopy and displays a linear behavior as a function of bromine concentration. Density functional theory calculations are performed for five different series of randomly doped structures in order to simulate the disorder in bromine doping sites. The computations predict a linear variation of the lattice parameters, supercell volume, density, band gap, and formation energy in the considered doping range. The calculated evolution of the band gap as the function of Br doping is in excellent agreement with the experimental data, provided that different Br doping configurations are included in the simulations. The analysis of the structural and electronic properties shows a correlation between the increase of the band gap and the increased distortion of the Pb(I_1–xBr_x)₆ octahedrons. Additionally, the simulations suggest that in CH₃NH₃Pb(I_1–xBr_x)₃ bromine doping is likely to occur at both the equatorial and apical positions of the octahedrons.