Dissertation Defense Committee Members

• Committee Chair: Prof. Xiaohang Li
• Ph.D. Advisor: Prof. Thomas Anthopoulos
• Committee Member: Prof. Shadi Fatayer
• External Examiner: Prof. Yabing Qi

 

Zoom link: https://kaust.zoom.us/j/97580655824

Abstract

Organic–inorganic metal halide perovskite solar cells (PSCs) have achieved power conversion efficiencies (PCEs) exceeding 27%, yet poor long-term stability—caused primarily by interfacial defects and ion migration in three-dimensional (3D) perovskites—remains a key obstacle to commercialization. Integrating low-dimensional (LD) perovskite layers at the surface has emerged as a promising approach to suppress defects and improve stability. However, conventional methods often result in phase-mixed and disordered LD layers, hindering charge transport and limiting ferroelectric behavior. Furthermore, the absence of systematic ligand design principles has hampered the development of phase-pure, well-ordered 3D/LD interfaces.

This dissertation addresses these challenges by engineering low-dimensional ligands to control interfacial dimensionality and optimize heterojunction performance. In Chapter 3, we introduce a post-deposition isopropanol rinsing strategy for meta-amidinopyridine (m-APY)-treated perovskite films. This process reorganizes disordered 2D domains into a well-aligned, phase-pure n = 1 structure, significantly enhancing interfacial passivation and ferroelectric properties. Devices fabricated with this approach reached a certified PCE of 25.44% and maintained over 80% of their efficiency after 1000 hours under damp heat and outdoor exposure.

In Chapter 4, we compare six ligands—BZAM, BZA, o-APY, m-APY, p-APY, and m-AMPY—revealing that π–π stacking and hydrogen bonding are critical for 2D phase formation. m-APY, despite being amidinium-based, uniquely forms stable 2D perovskites due to its molecular conformation.

Chapter 5 applies these ligands in 3D/LD heterostructures. m-APY and m-APMY produce uniform 2D layers with efficient defect passivation, while BZA, o-APY, and p-APY generate disordered 1D caps. Devices incorporating m-APY achieve a PCE of 25.8% (1 cm²) and retain over 95% efficiency after 1100 hours of aging, confirming the robustness of m-APY-driven interface design.

Together, these findings establish a molecular-level framework for building stable and efficient 3D/2D perovskite interfaces and provide strategies to advance the practical viability of PSC technologies.