Additive Conformational Engineering To Improve the PbI₂ Framework for Efficient and Stable Perovskite Solar Cells

Area of Science:

• Materials Science
• Renewable Energy
• Solid-State Chemistry

Background:

• The lead iodide (PbI2) framework is crucial for fabricating efficient two-step perovskite solar cells.
• Understanding additive effects on PbI2 precursor solutions is key to enhancing perovskite thin-film quality and device performance.

Purpose of the Study:

• To investigate the impact of incorporating two urea-based molecules, biuret (BU) and dithiobiuret (DTBU), into PbI2 precursor solutions.
• To correlate molecular structure with effects on PbI2 crystallization, perovskite film quality, and solar cell performance.

Main Methods:

• Synthesis and characterization of PbI2 precursor solutions with BU and DTBU additives.
• Fabrication and testing of perovskite solar cells using treated PbI2 layers.
• Analysis of structural properties, defect density, and carrier lifetime of perovskite films.
• Long-term stability testing under controlled humidity and temperature conditions.

Main Results:

• Biuret (BU), with its symmetrical structure and C=O bond, enhanced PbI2 crystallization, leading to reduced defect density and extended carrier lifetime in perovskite films.
• Devices incorporating BU achieved a maximum power conversion efficiency (PCE) of 23.50% and retained 93% of their initial efficiency after 1300 hours of storage under ambient conditions (30-40% humidity).
• Dithiobiuret (DTBU), with a twisted molecular structure and C=S bond, resulted in inferior PbI2 crystallization, lower perovskite film quality, and significantly reduced device performance (PCE < 10%) and stability.

Conclusions:

• The molecular structure and functional groups of additives play a critical role in the performance of perovskite solar cells.
• Symmetrical molecules like BU can facilitate improved PbI2 crystallization, leading to enhanced perovskite thin-film quality and superior device efficiency and stability.
• DTBU's non-planar structure hinders crystallization, negatively impacting device performance and long-term operational stability, highlighting the importance of molecular design in perovskite solar cell development.