Interfacial Topochemical Fluoridation of MAPbI₃ by Fluoropolymers

Area of Science:

• Materials Science
• Solid-State Chemistry
• Photovoltaics

Background:

• Halide perovskites are promising photovoltaic materials.
• Interface engineering is crucial for optimizing perovskite device performance.
• Fluoropolymer encapsulation is a common technique in perovskite device fabrication.

Purpose of the Study:

• To investigate the interfacial chemical reactions between halide perovskites and fluoropolymers during synthesis.
• To understand the impact of fluoride transfer on the electronic properties of perovskites.
• To correlate processing conditions with the formation of interfacial species and their effect on charge carrier dynamics.

Main Methods:

• Topochemical reaction analysis at the perovskite-fluoropolymer interface.
• Temperature- and time-dependent studies of interfacial reactions.
• Measurement of photoinduced charge carrier lifetime.
• Photoluminescence spectroscopy to assess electronic structure changes.

Main Results:

• Fluoride transfer from fluoropolymers to halide perovskites occurs above 140 °C in air.
• Moderate fluoride transfer enhances carrier lifetimes up to threefold by passivating surface defects.
• Excessive fluoridation leads to PbF2 formation, shortening carrier lifetimes and quenching photoluminescence.
• PbF2 acts as an electron acceptor, negatively impacting MAPbI3 (methylammonium lead iodide) perovskite performance.

Conclusions:

• The study reveals a critical interplay between fluoropolymer processing and perovskite electronic properties.
• Optimizing fluoride transfer is key to leveraging defect passivation for improved perovskite solar cells.
• Understanding and controlling PbF2 formation is essential to prevent performance degradation.