Defect-Limited Efficiency of Pnictogen Chalcohalide Solar Cells

Area of Science:

• Materials Science
• Solid-State Physics
• Photovoltaics

Background:

• Pnictogen chalcohalides (MChX) are promising nontoxic photovoltaic absorbers.
• They offer strong light absorption and low-temperature synthesis.
• Current device efficiencies are below 10%, hindering commercial viability.

Purpose of the Study:

• Investigate defect chemistry in Bi-based chalcohalides.
• Identify the origin of performance losses in MChX solar cells.
• Determine strategies to improve MChX photovoltaic performance.

Main Methods:

• First-principles calculations.
• Systematic defect chemistry investigation.
• Analysis of defect formation energies and charge-carrier capture coefficients.

Main Results:

• Chalcogen vacancies are dominant defects with low formation energies.
• These vacancies act as deep nonradiative recombination centers.
• Sulfur vacancies in BiSI and BiSBr are less detrimental than selenium vacancies in BiSeI and BiSeBr.

Conclusions:

• Defect chemistry, particularly chalcogen vacancies, is a critical bottleneck for MChX solar cells.
• Chalcogen-rich synthesis and anion substitutions can mitigate detrimental vacancies.
• BiSeI shows the best efficiency due to its optimal bandgap, despite high recombination rates.