Defect-Related Broadband Emission in Two-Dimensional Lead Bromide Perovskite Microsheets

Area of Science:

• Materials Science
• Solid-State Physics
• Optoelectronics

Background:

• Low-dimensional hybrid lead halide perovskites (LHPs) show promise for white-light-emitting diodes due to broadband emission (BE).
• The fundamental mechanisms driving BE in these materials remain unclear.
• Understanding BE is crucial for developing efficient single-source white-light emitters.

Purpose of the Study:

• To investigate the origin of broadband emission (BE) in [NH₃(CH₂)₈NH₃]PbBr₄ perovskite microsheets (PMSs).
• To elucidate the role of bromide vacancies (V_Br) in generating BE.
• To provide insights into controlling the optical properties of 2D perovskites.

Main Methods:

• Synthesis of dual-emissive [NH₃(CH₂)₈NH₃]PbBr₄ perovskite microsheets (PMSs).
• Optical characterization under varying conditions (e.g., Br-poor).
• Femtosecond transient absorption spectroscopy to study carrier dynamics.

Main Results:

• Broadband emission (BE) at ~522 nm was observed in PMSs under Br-poor conditions, distinct from narrowband emission (NE).
• Experimental evidence links BE to bromide vacancies (V_Br), showing quasisaturation behavior.
• Femtosecond spectroscopy revealed electron trapping by V_Br- occurs at ~15 ps, slower than surface defect trapping (<1 ps).

Conclusions:

• Broadband emission in these 2D perovskites is attributed to bromide vacancies (V_Br), not self-trapped excitons.
• This study offers a mechanism for BE and a method for tuning optical properties in perovskite materials.
• The findings advance the understanding of light emission in hybrid perovskites for optoelectronic applications.