Unravelling Structural, Optical, and Band Alignment Properties of Mixed Pb-Sn Metal-Halide Quasi-2D Ruddlesden-Popper...

Area of Science:

• Materials Science
• Solid State Physics
• Photovoltaics

Background:

• Lead-tin (Pb-Sn) mixed-halide perovskites offer tunable band gaps and enhanced stability for solar cells.
• Two-dimensional (2D) Ruddlesden-Popper (RP) perovskites present a promising avenue for improved photovoltaic performance.
• Understanding band alignment and charge carrier dynamics is crucial for optimizing perovskite solar cells.

Purpose of the Study:

• To synthesize and characterize lead-tin mixed-halide 2D RP perovskite thin films (BA₂FA(Pb_1-Sn)₂I₇).
• To investigate the effects of tin (Sn) substitution on the structural, optical, and electronic properties.
• To elucidate charge carrier dynamics and band alignment for enhanced optoelectronic applications.

Main Methods:

• Solution-based synthesis of 2D RP perovskite thin films.
• X-ray Diffraction (XRD) for structural phase analysis.
• UV-visible spectroscopy and cyclic voltammetry for optical and electrochemical characterization.
• Low-temperature photoluminescence (PL) spectroscopy for charge carrier dynamics.
• Density Functional Theory (DFT) calculations for electronic structure analysis.

Main Results:

• Formation of orthorhombic phases confirmed by XRD for both pristine and Pb-Sn-doped films.
• UV-vis analysis indicated the presence of different n phases in pristine samples, with a red-shift in Pb-Sn-doped samples.
• DFT calculations revealed reduced band gaps due to altered electrostatic interactions and charge distribution upon Sn substitution.
• Low-temperature PL analysis showed suppressed higher n phases and self-trapped excitons/carriers in mixed Pb-Sn perovskites.
• Band offsets between TiO₂ and SnO₂ layers were estimated.

Conclusions:

• Tin substitution in 2D RP perovskites leads to a reduced band gap and improved charge carrier dynamics.
• The study provides insights into electron transfer phenomena crucial for optoelectronic device fabrication.
• Mixed Pb-Sn 2D RP perovskites are promising for developing stable and efficient solar cells.