Solvent dependent iodide oxidation in metal-halide perovskite precursor solutions

Area of Science:

• Materials Science
• Photovoltaics
• Solution Chemistry

Background:

• Metal-halide perovskites (MHPs) are promising for solar cells, with solution processing being a key research area.
• Understanding MHP solution chemistry is crucial for controlling thin-film properties and synthesis reproducibility.
• Triiodide (I3-) concentration is a known factor influencing MHP solution particle size and film defect concentration.

Purpose of the Study:

• To identify and characterize an underestimated source of triiodide (I3-) in metal-halide perovskite (MHP) precursor solutions.
• To investigate how iodide salt counter-cations and solvents affect the formation of I3- and its impact on MHP synthesis stoichiometry.
• To elucidate the role of this hidden reaction in the overall processing quality of MHP thin films.

Main Methods:

• Analysis of iodide salt solutions used in MHP synthesis.
• Investigation of triiodide (I3-) formation over time.
• Comparative study of different iodide salt counter-cations (K+, CH3NH3+) and solvents (e.g., γ-butyrolactone).

Main Results:

• Iodide salts, commonly used in MHP synthesis, are a significant source of triiodide (I3-).
• The formation of I3- consumes iodide ions (I-), leading to under-stoichiometric MHP precursor solutions.
• The extent of I- oxidation to I3- varies with the counter-cation and solvent, with higher oxidation observed in γ-butyrolactone (GBL).

Conclusions:

• An overlooked reaction involving iodide salt oxidation to triiodide (I3-) impacts MHP precursor solutions.
• This reaction affects the stoichiometry and potentially the quality of MHP thin films.
• Controlling I3- formation is essential for reproducible and high-quality MHP solar cell fabrication.