Year: 2026
Type: dissertation
Abstract: This thesis presents a systematic bilayer engineering strategy to simultaneously improve the efficiency and long-term stability of perovskite solar cells. The study focuses on the controlled formation of a quasi-two-dimensional (2D) perovskite capping layer on a three-dimensional (3D) chloride–iodide perovskite absorber. The quasi-2D layer passivates bulk and surface defects through halide diffusion and surface trap reduction while also acting as a moisture-resistant capping layer. Device performance is shown to depend strongly on the quality of the quasi-2D layer. Chapter 1 introduces photovoltaic technology and the research objectives. Chapter 2 reviews recent advances and challenges in 3D/2D bilayer chloride–iodide perovskite solar cells. Chapter 3 describes the fabrication and characterization methods. Chapter 4 optimizes the electron transport layer and perovskite absorber, identifying 7.5% SnO₂ and FA₀.₆MA₀.₄PbI₂.₇Cl₀.₃ as the optimum composition. Surface passivation promotes quasi-2D layer formation, while a self-formed SnCl₂ interfacial layer passivates the buried interface. The champion device achieves a PCE of 20.81% and retains over 85% of its initial efficiency after 650 h under ambient conditions. Chapter 5 employs mixed chlorobenzylammonium chloride/bromide passivation, increasing the PCE to 21.00%, reducing trap density by half, and limiting efficiency loss to only 12% after 672 h. Chapter 6 introduces fluorinated mixed-halide passivation using 4-fluorobenzylammonium chloride/bromide, improving surface coverage and energy-level alignment. The champion device reaches 21.10% PCE and retains 80% efficiency after 56 days. Chapter 7 optimizes quasi-2D layer formation by combining aliphatic and aromatic organic cations. The optimal composition delivers approximately 22% PCE and retains 96% of its initial efficiency after 1000 h without encapsulation. Chapter 8 summarizes the major findings and future directions. Overall, this thesis demonstrates that rational bilayer engineering through controlled halide migration, mixed-halide passivation, and optimized quasi-2D capping-layer formation provides an effective pathway toward highly efficient and stable chloride–iodide perovskite solar cells.
Author: Howlader, Ashraful Hossain
Language: English
Subfield: Electrical and Electronic Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7214934884