UCLA

Metal-halide perovskite solar cells have attracted tremendous interest because of their compatibility with low-temperature processing, strong optical absorption, defect tolerance, and tunable electronic structures. Despite rapid improvements in power conversion efficiency, their practical deployment remains limited by insufficient operational stability. Interfaces are particularly important because they simultaneously govern charge extraction, non-radiative recombination, ionic redistribution, chemical reactions, and, at buried interfaces, the formation of the perovskite absorber itself. This dissertation investigates how molecularly engineered polymeric interfaces can regulate these coupled electronic, ionic, and structural processes to improve both the efficiency and long-term stability of perovskite solar cells.Chapter One introduces the fundamental properties and stability challenges of metal-halide perovskites, with particular emphasis on the multifunctional roles of interfaces. Electronic defect passivation, ionic and chemical stabilization, and buried-interface regulation of nucleation and crystal growth are established as complementary strategies for interface engineering. Chapter Two focuses on defect passivation at the exposed perovskite surface. hree polymeric modifiers, including poly(vinyl acetate), polyethylene glycol, and poly(9-vinylcarbazole), are systematically compared to establish a molecular design principle linking electronic structure and steric accessibility with defect-interaction strength. Stronger Lewis-base interactions with undercoordinated Pb species suppress non-radiative recombination, improve charge transport, and substantially enhance device efficiency and operational stability. Chapter Three extends the discussion from the exposed surface to the buried interface, highlighting its dual role as a dynamic ionic boundary during operation and as a template for perovskite formation during fabrication. Chapter Four identifies cross-interface Sn redistribution from SnO2 into the perovskite absorber as an important degradation pathway during prolonged operation. Sn migration is accompanied by chemical-state evolution, while ultrathin polymeric interlayers increase the energetic barrier for ionic transport and suppress Sn redistribution, leading to markedly improved long-term stability. Chapter Five demonstrates that the same buried interlayers also regulate perovskite formation by modifying wettability, interfacial contact, crystallization, phase quality, and defect formation. These changes reduce non-radiative recombination and enable high-efficiency small-area devices and modules. Together, these studies establish polymeric interface engineering as a strategy for simultaneously controlling defect chemistry, ionic transport, buried-interface evolution, and perovskite formation, providing design principles for efficient and durable perovskite photovoltaics.