Organo-metal halide perovskites (MHPs) have emerged as a promising group of materials with excellent optoelectronic properties. Consequently, film-based perovskite devices have undergone rapid development. Currently, the most commonly used methods for preparing MHP films include spin-coating, spray-coating, slot-die coating, blade coating, and ink-jet coating. While the specific techniques for depositing the precursor solutions onto the substrate might differ, all typically involve a subsequent thermal annealing step. This crucial annealing step aims at eliminating any residual solvents or additives present in the film and at fully crystallizing the black perovskite phase. Consequently, achieving a comprehensive understanding of the annealing process is paramount.