Suppressing Polaronic Defect-Photocarrier Interaction in Halide Perovskites by Pre-distorting Its Lattice.

Area of Science:

• Materials Science
• Solid-State Physics
• Photovoltaics

Background:

• Halide perovskites exhibit strong polaronic interactions between photocarriers and point defects.
• Iodide deficiency in methylammonium lead iodide (MAPbI3) leads to significant Fermi level shifts and deep electron trap formation upon illumination.

Purpose of the Study:

• To investigate the mechanism of light-induced effects in iodide-deficient MAPbI3.
• To explore the role of cation substitution in mitigating these effects.
• To understand how lattice predistortion influences defect behavior.

Main Methods:

• Experimental measurements of Fermi level shifts under illumination.
• Density functional theory (DFT) calculations.
• Investigation of Cs+ cation substitution in MAPbI3.

Main Results:

• Illumination of MAPbI3 causes a 0.6-0.7 eV Fermi level shift, linked to Pb-Pb dimer formation at iodide vacancies.
• Cesium (Cs+) doping suppresses these light-induced effects.
• DFT calculations show Cs-doping predistorts the lattice, mimicking the dimer formation and reducing defect activity.

Conclusions:

• Lattice predistortion via Cs-doping is a viable strategy to enhance the photostability of halide perovskites.
• This approach counterintuitively stabilizes the material by preemptively altering defect structures.
• Findings offer a new pathway for designing robust perovskite solar cells.