Engineering of metal oxide nanostructures and interfaces for applications in perovskite solar cells

Abstract

Continued growth of the global population has driven electricity usage to unprecedented heights, placing pressure on conventional energy sources and accelerating the transition to renewable technologies. Among these, solar energy is especially attractive due to advances in materials science and scalable photovoltaic fabrication. Although silicon-based photovoltaic cells dominate the market, their high-temperature and energy-intensive manufacturing underscores the demand for alternative technologies. Consequently, solution-processable perovskite solar cells (PSCs) have emerged as promising candidates, characterized by low-temperature fabrication, rapid power conversion efficiency (PCE) gains reaching 27% in just 17 years, and tunable bandgaps suitable for single-junction and tandem devices. However, persistent stability issues hinder the broader application of PSCs. Central to this investigation is the electron transport layer (ETL)/perovskite interface, as it significantly impacts charge transport, recombination dynamics, and device stability. Accordingly, two distinct interfacial engineering techniques were investigated for different PSC architectures: hybrid organic-inorganic and all-inorganic perovskite-based solar cells. The first approach focused on nanostructured ETLs, offering a large surface area, tunable geometric characteristics, and enhanced charge transport pathways for effective interfacial engineering. Considering that the solvothermal growth of SnO2 nanorod arrays is highly sensitive to the synthesis conditions, every critical parameter was systematically optimized to establish a reliable and reproducible fabrication protocol. Several parameters are involved: reactor pressure, substrate orientation, solvent ratio, seed-layer configuration, acetic acid concentration, and growth duration. The findings emphasize the importance of precisely controlling growth parameters for effective interfacial engineering and provide a practical framework for future customization of specific nanorod shapes by adjusting the identified synthesis parameters. In the second approach, an ultrathin MgO interlayer was incorporated between the ETL and the CsPbI2Br. The influence of the MgO interlayer was evaluated through a comprehensive set of investigations, revealing that MgO-incorporated PSCs significantly improved the photovoltaic performance and stability. Following 7 weeks of storage, the MgO-incorporated devices maintained 70% of their initial PCE, whereas the unmodified counterparts dropped to 55%. The devices were further tested for their resilience against proton irradiation to assess their performance in harsh environments. The MgO-optimized devices exhibited high durability and demonstrated a slight improvement in photovoltaic parameters. In contrast, the unmodified devices showed a significant reduction, retaining only 47% of their initial performance after 11 weeks. This thesis underscores the critical role of interfacial engineering in PSCs, demonstrating how innovative strategies enable the development of stable and efficient perovskite solar technologies.