Determining the Free-Carrier Fraction in 2D Perovskites Using Power Dependent Photoluminescence

Area of Science:

• Materials Science
• Solid State Physics
• Optoelectronics

Background:

• Distinguishing between excitons and free carriers in nanostructured materials is vital for designing efficient optoelectronic and photovoltaic devices.
• Traditional power-law analysis of photoluminescence can oversimplify the physics of excited states, especially in materials with intermediate exciton binding energies.

Purpose of the Study:

• To develop a direct and quantitative method for analyzing the free-carrier fraction in semiconductors.
• To validate the proposed method using Ruddlesden-Popper perovskites with varying thicknesses as a model system.
• To provide a reliable tool for probing the nature of optically excited states and spatial variations in charge carrier fractions.

Main Methods:

• Utilizing power-dependent peak photoluminescence measurements.
• Applying the Saha equation for quantitative analysis of the free-carrier fraction.
• Investigating Ruddlesden-Popper perovskites with controlled thickness variations.

Main Results:

• The developed method provides a quantitative analysis of the free-carrier fraction, consistent with known exciton binding energies in perovskites.
• The approach successfully probes spatial variations in free charge fractions at micrometer resolution, particularly near grain boundaries.
• The study highlights the impact of excitation density on excited-state interpretation, emphasizing the need for realistic operating conditions.

Conclusions:

• The presented photoluminescence analysis offers a simple, effective, and reliable tool for determining excited-state dynamics in semiconductors.
• This method is crucial for optimizing materials for optoelectronic and photovoltaic applications by accurately characterizing charge carrier behavior.
• Accurate characterization under relevant excitation densities is essential to avoid misinterpretation of excited-state properties.