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Evidence for I2 loss from the perovskite-gas interface upon light-induced halide segregation.
Michael Lee1, Julian A Vigil1,2, Zhiqiao Jiang1,3
1Department of Chemistry, Stanford University Stanford California 94305 USA hemamala@stanford.edu.
Chemical Science
|May 19, 2025
Summary
Sunlight causes halide segregation in perovskite solar cells, leading to voltage loss. This study reveals that light also triggers irreversible iodine loss, degrading device stability even in bromide-rich materials.
Area of Science:
- Materials Science
- Photovoltaics
- Chemical Engineering
Background:
- Mixed-halide perovskites (CH3NH3)Pb(BrxI1-x)3 are promising for solar cells.
- Sunlight can induce halide segregation, negatively impacting device performance.
- Understanding degradation pathways is crucial for long-term perovskite stability.
Purpose of the Study:
- To investigate the effect of sustained illumination on halide-segregated perovskite films.
- To identify and confirm the mechanism of irreversible iodine loss under light.
- To assess the intrinsic nature of this decomposition pathway in perovskite materials.
Main Methods:
- Synthesized (CH3NH3)Pb(Br0.75I0.25)3 and CsPb(Br0.75I0.25)3 films.
- Exposed films to sustained illumination (ca. 1 sun) in an open system under nitrogen.
- Trapped gaseous iodine (I2) and monitored electronic conductivity changes.
- Characterized the perovskite-air solid-gas interface reactions.
Main Results:
- Sunlight induces irreversible iodine (I2) loss from halide-segregated perovskite films.
- Increased electronic conductivity confirms electron doping via iodide oxidation to I2.
- I2 off-gassing occurs at the perovskite-air interface, independent of solvents or vacuum.
- This light-induced I2 loss is intrinsic to both methylammonium and cesium-based perovskite frameworks.
Conclusions:
- Light-induced halide segregation in perovskites can lead to irreversible I2 loss and decomposition.
- This process can be mistaken for light-induced healing but results in permanent degradation.
- Even bromide-rich mixed-halide perovskites are susceptible due to light-induced segregation.
- I2-impermeable encapsulation is recommended for enhancing the long-term stability of perovskite solar cells.
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