Ligand removal and photo-activation of CsPbBr₃ quantum dots for enhanced optoelectronic devices

Abstract

Perovskite quantum dots have recently emerged as a promising light source for optoelectronic applications. However, integrating them into devices while preserving their outstanding optical properties remains challenging. Due to their ionic nature, perovskite quantum dots are extremely sensitive and degrade on applying the simplest processes. To maintain their colloidal stability, they are surrounded by organic ligands; these prevent efficient charge carrier injection in devices and have to be removed. Here we report on a simple method, where a moderate thermal process followed by exposure to UV in air can efficiently remove ligands and increase the photo-luminescence of the room temperature synthesized perovskite quantum dot thin films. Annealing is accompanied by a red shift of the emission wavelength, usually attributed to the coalescence and irreversible degradation of the quantum dots. We show that it is actually related to the relaxation of the quantum dots upon the ligand removal, without the creation of non-radiative recombining defects. The quantum dot surface, as devoid of ligands, is subsequently photo-oxidized and smoothened upon exposure to UV in air, which drastically enhances their photo-luminescence. This adequate combination of treatments improves by more than an order of magnitude the performances of perovskite quantum dot light emitting diodes.

Photo-Induced Black Phase Stabilization of CsPbI3 QDs Films

“…Nevertheless, excessive washing causes Cs + vacancies and strong aggregation or degradation [16,24]. On the other hand, UV/O 3 has proven to remove ligands from CsPbBr 3 QDs and simultaneously increase the PL emission, by a photoactivation mechanism [25]. The QDs surface is reduced of ligands, and subsequently photo-oxidized and smoothened upon exposure to UV in air, with positive consequences, for instance, on the light emitting diodes performances [25].…”

Lead Halide Perovskite Nanocrystals: Room Temperature Syntheses toward Commercial Viability

“…Moyen et al took a different approach to improving the yield of CsPbBr 3 NC syntheses. [66] They separated the ligands into different precursor solutions (oleylamine in DMF and oleic acid in toluene) to obtain greater control over the ratio between the two ligands on the NC surface. As a result, the reaction yield was increased by ≈300%.…”

Doping and Photon Induced Defect Healing of Hybrid Perovskite Thin Films: An Approach Towards Efficient Light Emitting Diodes

“…[34][35][36][37] These studies speculate that oxygen, which can act as a catalyst in the presence of photo-generated electrons, can diffuse into crystals resulting in photoluminescence (PL) enhancement by tens of magnitude in commonly used MAPbI 3 and MAPbBr 3 thin films. [34][35][36][37][38] These works can be extended to show the impact of photon healing on a mixed halide system to enhance the performances of PeLEDs, which, to the best of our knowledge, has not been done so far.…”