Synthesis of Perovskite Quantum Dots


Posted on Thu, Dec 19, 2019 by Thomas Fallows

During the original development of all-inorganic perovskite quantum dots, several synthetic routes were attempted in order to find a process that can reliably produce stable and defect resistant dots. Two major routes to the synthesis have now been developed: room temperate synthesis and synthesis by hot injection.

Perovskite quantum dot ink synthesis
Figure 2: Injection of Cs-oleate into lead precursor during hot injection synthesis of perovskite QD

Synthesis at Room Temperature


The first route can be undertaken at room temperature and in air.

First, stoichiometric amounts of cesium halide (CsX) and lead halide (CsX2) are dissolved in a good solvent such as dimethyl sulfoxide (DMSO) or N,N-dimethylformamide (DMF). Capping ligands such as oleic acid and oleylamine are then added, and the mixture is stirred vigorously.

An aliquot of this mixture is then added to vigorously stirring flask of a poorer solvent (such as toluene). This causes the perovskite quantum dots to precipitate within seconds. The resultant crude reaction mixture can then be separated by centrifuge and the pellet washed to give quantum dots in good yield and with high photoluminescent quantum yields (PLQYs).

This method is good for preparing CsPbBr3 quantum dots but is less reliable at producing QDs containing either chloride or iodide.

Synthesis by Hot Injection


The second, so-called ‘hot injection’, synthesis firstly requires the preparation of cesium oleate by stirring cesium carbonate and oleic acid in 1-octadecene (ODE) under argon at 150 °C. Separately, lead halide is dried in ODE by heating in vacuo. Capping ligands such as oleic acid and oleylamine are added under argon to fully dissolve the lead halide and the temperature is raised to 140-200 °C depending on the desired emission wavelength of the quantum dot.

The cesium oleate solution at 150 °C is then swiftly injected and the mixture stirred for 5-10 seconds before quenching the reaction in an ice water bath.

Video by Ossila

Quenching the reaction in an ice-water bath

Separation by centrifuge and washing of the pellet is able to afford the QDs in good yields and with PLQY values approaching unity.

Synthesis of quantum dots containing chloride requires the extra step of adding trioctylphosphine (TOP) to ensure full dissolution of PbCl2 prior to the injection of cesium oleate.

Perovskite QDs can be synthesised from PbCl2, PbBr2, PbI2 or any mixture of PbCl2/PbBr2 or PbBr2/PbI2 to form mixed halide QDs. Alternatively, CsPbBr3 quantum dots can be transformed post-synthesis via ion exchange reaction with chloride or iodide salts.

The entire spectrum of visible light can be emitted by perovskite quantum dots by tuning the reaction temperature and the proportion of halides in the product.

Conclusion


Unlike metal chalcogenide quantum dots, pervoskite quantum dots do not use toxic materials like cadmium metal and do not require surface passivation. They are therefore considerably less prone to defects. The available synthetic processes of perovskite quantum dots mean that they can be reliably mass-produced with photoluminescent yields of up to 100%.

We synthesis our new range of pervoskite quantum dots using the hot injection method. Caesium lead perovskite quantum dots of chloride/bromide (450 nm, blue), bromide (515 nm, green) and iodide (685 nm, red) are now available.

Author: Thomas Fallows


Tom graduated from the University of Manchester in 2012 with a first-class honours degree in Chemistry. After spending a year teaching English in China, Tom returned to Manchester to complete an interdisciplinary PhD in Nanoscience, submitting his thesis on iron oxide nanoparticles in 2018. He stayed at the University of Manchester as a postdoctoral researcher, collaborating with industrial partners to produce polydiacetylene compounds. Tom brought his strong background in chemical synthesis and materials science to Ossila in 2019, taking up the post of Perovskite Quantum Dot Synthetic Chemist and quickly established a new range of quantum dot products.