Perovskite materials play an important role as absorber in the field of photovoltaic applications due to their remarkable light absorption and charge transport properties. The defects generation in perovskite absorbers for fabrication of solar cells is a major research topic. However, the defects generated in these materials significantly impact their efficiency, stability, and performance. This chapter provides the detailed mechanisms of underlying defect generation in perovskite absorbers, emphasizing on types of defects and their formation processes. The defects have been categorized into—vacancies, interstitials, and grain boundaries. Their formation mechanisms including synthesis conditions, thermal processing, and environmental conditions will be described thoroughly. These defects impact the electronic properties, charge transport, and recombination processes. By employing advanced synthesis techniques, proper material selection, and defect control strategies, researchers can improve the performance and stability of perovskite-based photovoltaic devices. This chapter will highlight the in-depth understanding of optimizing perovskite materials for next-generation solar energy technologies and emphasizes the importance of computational approaches in understanding and mitigating defect-related challenges in perovskite absorbers. Numerical analysis such as density functional theory (DFT), machine learning (ML), SCAPS (solar cell capacitance simulator), and SILVACO ATLAS play as significant tools in simulation and help to understand the defect dynamics.