In Situ kinetic analysis of perovskite halide exchange via laser trapping spectroscopy

Abstract

This study investigates the use of optical tweezers as a precise and non-invasive tool for probing chemical reaction kinetics, focusing specifically on halide exchange reactions in hybrid perovskite systems. A continuous-wave, tightly focused 1064 nm near-infrared laser beam was utilized to establish optical trapping conditions that precisely confine and manipulate the reaction interface between a methylammonium lead bromide (MAPbBr₃) microcrystal and a methylammonium iodide (MAI) solution. Upon laser irradiation, bromide ions within the perovskite lattice were progressively substituted by iodide ions, enabling controlled Br-to-I halide exchange. This compositional evolution was monitored in real time via optical spectroscopy by tracking the bandgap shift of the perovskite, which decreased from 2.29 eV (characteristic of pure MAPbBr₃) to 2.02 eV, confirming the formation of a mixed-halide phase, MAPb(Br_1−xI_x)₃ (0 ≤ x ≤ 1). Kinetic analysis of the bandgap evolution reveals a zero-order reaction behavior with a rate constant of 1.0 × 10⁻⁶ M min⁻¹ and a calculated half-life of approximately 55 minutes. These findings demonstrate that optical tweezers can serve not only as a micromanipulation tool but also as an effective platform for in situ kinetic studies in solution-phase reactions. The approach enables detailed investigation of microscale reaction dynamics, delivering high spatial accuracy and second-scale temporal resolution for continuous monitoring of slow-evolving processes.