CHEMICAL MODIFICATION APPROACHES IN ORGANOMETAL HALIDE PEROVSKITE MATERIALS AND SOLAR CELLS

Abstract

Metal halide perovskites are promising for future photovoltaics due to their optical absorption, carrier diffusion, and tunable bandgaps. Despite efficiency gains, instability and defects remain barriers. This thesis explores chemical modifications, additive engineering, and surface passivation to improve their optoelectronic properties and stability. First, the study examined how film formation and surface chemistry affect passivation by linking deposition techniques to the results. Oleic acid was used as a hydrophobic ligand for the surface passivation of MAPbI3 films prepared by different deposition techniques. Our findings showed that the success of surface treatments depends heavily on film morphology, and that customized passivation strategies notably improve resistance to humidity and stability. Next, we explored additive engineering through sulfur-based molecular engineering with thiazoline to boost crystallization, passivate halide vacancies, and enhance interfacial charge extraction. Strong Pb–S bonds lowered trap densities, increased carrier lifetimes, and led to high-performance devices with over 22% efficiency and better stability under humid and illuminated conditions. Finally, we synergistically combined additive engineering and surface passivation techniques by using carbamide-based additives to improve crystallization and reduce defect density in the bulk and 2D capping layer, passivating surface defects. These treatments resulted in significant improvements in charge-carrier lifetimes and recombination dynamics, emphasizing the importance of controlling defect formation during film growth. Overall, this research shows that incorporating specific chemical modifications into both the bulk and interfaces of perovskite films is an effective strategy to reduce recombination losses and improve environmental stability. By elucidating the connections between molecular design, film formation, and device physics, this thesis provides a detailed framework for creating high-efficiency, durable perovskite solar cells and supporting their development toward scalable, practical use.