Strain-activated light-induced halide segregation in mixed-halide perovskite solids

Area of Science:

• Materials Science
• Solid-State Physics
• Photovoltaics

Background:

• Mixed-halide perovskites offer tunable bandgaps crucial for advanced solar cells.
• Light-induced halide segregation is a known issue that hinders device performance and stability.

Purpose of the Study:

• To investigate the role of strain in light-induced halide segregation in mixed-halide perovskites.
• To determine the critical bromine concentration threshold for strain-activated versus intrinsic segregation.
• To explore methods for suppressing strain-activated halide segregation.

Main Methods:

• Synthesis and characterization of single crystals and polycrystalline thin films of methylammonium lead (iodide, bromide) perovskites (MAPb(I_1-xBr_x)₃).
• Application of uniaxial pressure to single crystals to study strain effects.
• Growth of perovskite films on lattice-mismatched and ideal substrates.
• Utilized scanning probe microscopy to analyze halide segregation in films.

Main Results:

• Light-induced halide segregation is strain-activated in MAPb(I_1-xBr_x)₃ for Br concentrations below ~50%.
• For Br concentrations above ~50%, halide segregation is intrinsic and occurs regardless of strain.
• Strain at grain boundaries in polycrystalline films leads to selective segregation.
• Strain release using additives (e.g., potassium iodide) or suitable substrates (e.g., silicon dioxide) suppresses strain-activated segregation.

Conclusions:

• Strain plays a critical role in light-induced halide segregation in mixed-halide perovskites, particularly at lower bromine concentrations.
• Understanding and controlling strain is essential for improving the stability and performance of perovskite-based tandem photovoltaics.
• Strategies for strain management offer a pathway to mitigate halide segregation and enhance device longevity.