The growing worldwide demand for energy due to a rapid growth of the world’s population and economy requires a change in the energy production. While fossil fuels are still the primary energy source used to meet the world’s growing demand for energy, there is an urgent request of exploiting the full potential of climate neutral alternatives (e.g. solar energy) to reduce greenhouse gas emissions and fight climate change. Lead-halide perovskite is a promising class of materials as active absorber in solar cells due to their excellent optoelectronic properties, low cost, and possibilities for large-scale fabrication. In addition, the versatility of these materials stems from the possibility to tune their properties by directly manipulating their chemical composition and structure. However, while sunlight supplies the energy necessary to produce electricity, it also impairs the stability and the performance of the perovskite solar cells over time, causing strain in the material. My work focuses on understanding the behaviour of perovskites under strain, paving the way for cheap and long-term stable perovskite solar cells. Unveiling the connection between the dynamically disordered perovskite lattice and the optoelectronic properties is quintessential to provide concrete guidelines for compositional engineering toward a rational design of mixed-halide devices, where targeted strain engineering strategies can be used as fabrication routes to obtain stable and bandgap-tunable materials.