Common Defects Accelerate Charge Carrier Recombination in CsSnI₃ without Creating Mid-Gap States

Area of Science:

• Materials Science
• Solid-State Physics
• Photovoltaics

Background:

• Lead-free metal halide perovskites offer environmental benefits and good optoelectronic properties.
• Current efficiencies of these materials lag behind theoretical limits, hindering widespread adoption.
• Understanding defect behavior is crucial for improving perovskite solar cell performance.

Purpose of the Study:

• To investigate the atomistic origins of nonradiative charge recombination in CsSnI3 perovskites.
• To elucidate the role of intrinsic defects in limiting photovoltaic efficiency.
• To provide a comparative analysis of defect impacts in lead-free versus lead-based perovskites.

Main Methods:

• Utilized *ab initio* nonadiabatic molecular dynamics simulations.
• Analyzed the influence of intrinsic point defects on electronic and vibrational properties.
• Quantified electron-vibrational coupling and carrier interactions with defects.

Main Results:

• Intrinsic defects in CsSnI3 accelerate nonradiative charge recombination without forming midgap traps.
• Tin (Sn)-related defects, specifically Sn vacancies and Sn-Cs replacement, are highly detrimental.
• Iodine (I)-related defects have a less pronounced negative impact on carrier lifetimes.

Conclusions:

• Tin-related defects significantly perturb the Sn-I lattice, increasing electron-vibrational coupling and hindering carrier transport.
• CsSnI3 synthesis should prioritize tin-rich conditions to minimize efficiency losses.
• This work offers an atomistic explanation for the lower photovoltaic performance of CsSnI3 compared to lead-based perovskites.