Vapour transport deposition of multi-dimensional tin-lead perovskite thin films'
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Date
2024
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University of the Western Cape
Abstract
Thin film solar technology offers a promising solution to address the escalating global demand for clean, affordable, and renewable energy. Despite significant advancements in traditional solar cell (SC) materials, the emergence of perovskite materials has sparked renewed innovation in the field. However, challenges related to lead (Pb) toxicity and the instability of Pb-based perovskites impede the widespread adoption of perovskite solar cells (PSCs). This study aims to overcome these challenges by integrating tin (Sn) atoms into Pb-based perovskite structures to mitigate Pb toxicity issues and environmental concerns. Employing a comprehensive approach centered on a multi-step chemical vapour deposition (MS-CVD) technique, the research endeavors to synthesize and characterize Pb-Sn perovskite thin films. Structural and electronic properties are meticulously analyzed utilizing state-of-the-art techniques such as Rutherford Backscattering Spectrometry (RBS), X-ray diffraction (XRD), and optical property measurements. Incorporating Sn into Pb-based perovskite films significantly alters the material energy bandgap (Eg) and the crystal structure. The utilization of a three-step sequential deposition method yields superior quality Pb-Sn perovskite films compared to the two-step approach, resulting in enhanced structural stability and reduced defect density. Synthesized Pb-Sn 3-dimensional (3D) perovskite films exhibit a tetragonal crystal structure (Space Group, SG: I4cm), with a reduced unit cell volume attributed to the smaller atomic radius of Sn compared to the Pb atom. The effect of Sn concentration on Pb-Sn perovskites was manifested by the decrease in the Eg with increasing Sn concentration, while the Urbach energy (EU) escalated, signifying an augmented defect density in the films. Investigation into the effect of conversion substrate temperature on the structural and electronic properties of Pb-Sn 2D perovskite films reveals an optimal conversion temperature of 100°C. This led to the synthesis of high-quality Pb-Sn 2D perovskite films with enhanced structural stability from -273.15°C to 87°C as confirmed by the temperature-dependent photoluminescence (PL) analysis.
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Keywords
Pb-Sn Perovskite Compositions, Multi-step Chemical Vapour Deposition, Structural and Electronic Properties, Defect Density Characterization, Perovskite Solar Cells.