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(Br1−xIx)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.