In situ monitoring of perovskite nanocrystal fluorescence lifetimes

A fully automated optofluidic platform that enables the measurement of fluorescence lifetimes of cesium lead halide nanocrystals

Lead halide perovskite nanocrystals (LHP NCs) keep on captivating the attention in the field of materials science due to their outstanding optical properties, making them promising materials for photovoltaics applications and next generation displays. In a new study lead by Dr. Stavros Stavrakis, in collaboration with Prof. Maksym Kovalenko, Dr Ioannis Lignos presents an automated microfluidic platform that monitors the influence of various reaction parameters on the fluorescence lifetime of cesium lead halide perovskite NCs.

Access to the fluorescence lifetime of LHPs can yield more information than just the brightness of the emission alone, and is hence useful for better engineering of nanocrystal properties. The optical characteristics of LHP NCs, including the observed fluorescence lifetime, are mainly influenced by the synthesis parameters (precursor ratios, ligands, reaction temperature, etc.) and post-synthetic modifications. Due to the vast parametric space of such reactions, high-throughput experimentation is highly desirable, and microfluidic platforms integrated with optical detection methods have proven extremely useful. In this work, a fully automated droplet microfluidic platform, as described previously by the deMello group, has been for the first time interfaced with a Time-Correlated Single Photon Counting module (TCSPC), enabling the tracking of fluorescence lifetime at the end-point of the reaction. TCSPC is a method of choice for fluorescence lifetime measurements as it enables high-resolution measurements with fast acquisitions times, and can be readily interfaced with the microfluidics components. With this new method, a wide range of reaction conditions can be scanned and their influence on the lifetime of the products investigated in situ. The setup enables the real-time extraction of the average lifetime using a multi-exponential fitting algorithm. Owing to the unparalleled time-efficiency of the microfluidic platform, the authors were able to perform 1000 lifetime measurements under various reaction conditions in just five hours. Specifically, the influence of the composition and ratios of reagents was investigated and the authors were able to demonstrate a strong dependency of the average lifetime on the Pb-to-Cs ratio.

This system makes valuable information on fluorescence lifetimes easily accessible in a highly time-efficient manner, and may be applied to a variety of optically active materials to boost their optimization.

Written by Julie Probst.

Read the full paper here.

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