Abstract: Perovskite solar cells (PSCs) are among the most promising photovoltaic technologies. Although PSCs offer numerous advantages, their commercialization still faces significant challenges, particularly related to stability and defects. To address these issues, novel passivation materials are emerging, and self-polymerizing functional materials have proven highly effective in optimizing PSCs. Self-polymerizing materials can spontaneously undergo polymerization reactions under specific conditions to form stable polymers or network structures. They can interact with defect sites on the perovskite surface, filling the defects and reducing carrier recombination. The passivation layer formed by these materials also acts as a physical barrier, protecting the perovskite from external environmental factors. Introducing self-polymerizing functional materials into PSCs significantly enhances the photoelectric conversion efficiency and environmental stability of the devices through defect passivation and interfacial optimization. Based on their application in PSCs, this review classifies self-polymerizing materials according to their active functional groups—including acrylates, acrylamides, vinyl aromatic/heterocyclic groups, sulfur-containing groups, and ionic liquids. It systematically reviews the categories, mechanisms of action, and research progress of these materials, with a focus on their key roles in defect passivation, interface optimization, and stability enhancement. The review explores the mechanisms of self-polymerizing materials from multiple perspectives, including regulation of perovskite film crystallization, improvement of interfacial performance, enhancement of device stability, and synergistic effects, providing theoretical support and technical guidance for the commercialization of PSCs. The results show that self-polymerizing materials offer significant advantages in perovskite solar cell research, achieving important progress in defect passivation, stability enhancement, and interface optimization. These materials effectively reduce defect state density in perovskites, inhibit non-radiative recombination, and improve perovskite film crystallization. By reducing grain boundary defects, they weaken the trapping of charge carriers and enhance carrier transport efficiency. For example, forming a passivation layer at the perovskite surface via self-polymerization blocks defect sites, minimizing energy loss from carrier recombination. Self-polymerizing materials also improve PSC stability by forming hydrophobic protective layers and suppressing ion migration. Hydrophobic layers act as physical barriers against moisture and oxygen, while the inhibition of ion migration (e.g., Pb²⁺ or organic cation diffusion) prevents structural degradation under operational conditions. This dual effect prolongs device lifespan and increases resistance to environmental fluctuations. Moreover, these materials can regulate energy level alignment between perovskites and electron transport layers by introducing functional groups or molecular structures with specific energy levels. This optimization reduces energy loss during charge transport, leading to higher open-circuit voltage and photoelectric conversion efficiency. For instance, precise control of interfacial energy levels ensures efficient electron/hole extraction while minimizing charge accumulation at interfaces. Current research still faces challenges, such as large-scale fabrication of devices using self-polymerizing materials, long-term stability, and adaptability to complex environments. Continuous innovation in self-polymerizing materials is expected to accelerate the commercialization of PSCs and promote the development of photovoltaic technology.