Superior Phonon-Limited Exciton Mobility in Lead-Free Two-Dimensional Perovskites

Area of Science:

• Materials Science
• Solid State Physics
• Photovoltaics

Background:

• Tin-based two-dimensional (2D) perovskites offer a lead-free alternative in halide perovskites.
• Understanding exciton dynamics and transport in these materials is crucial but hindered by defect scattering.

Purpose of the Study:

• To investigate intrinsic exciton transport in tin- (Sn) and lead- (Pb) based 2D perovskites.
• To compare exciton mobility and scattering mechanisms between Sn- and Pb-based 2D perovskites.

Main Methods:

• Temperature-dependent transient photoluminescence (PL) microscopy was used to study exciton transport.
• High-quality 2D perovskite crystals with enhanced phase stability were synthesized using conjugated ligands.
• Molecular dynamics simulations supported the experimental findings.

Main Results:

• Phonon-limited exciton transport was observed in Sn-based perovskites, with diffusion constants increasing from 0.2 cm² s⁻¹ at room temperature to 0.6 cm² s⁻¹ at 40 K.
• Sn-based perovskites demonstrated higher exciton mobility than Pb-based equivalents, attributed to lighter effective masses.
• Thermally activated optical phonon scattering was present in Sn-based compounds but absent in Pb-based materials.

Conclusions:

• Exciton transport in Sn-based 2D perovskites is primarily limited by phonon scattering.
• Sn-based perovskites exhibit greater exciton mobility than their Pb counterparts due to distinct phonon scattering mechanisms.
• These findings contribute to the development of efficient lead-free halide perovskite materials.