Advancing light detecting next-generation optoelectronic devices with quantum dots
Aug 29, 2025
Colloidal quantum dots (CQDs) are attractive for next-generation optoelectronics due to their size-tuneable properties and low-cost processing. However, harnessing their capacities is typically hindered by disordered assemblies and surface traps, especially in three-dimensional superlattices. Achieving ordered structures with minimized trap densities is key to unlocking their potential. Researchers from the University of Groningen aimed to address this challenge by developing highly ordered quantum dots superlattices and improving their electronic quality through post-synthetic surface treatments. The study employed GISAXS and GIWAXS measurements performed at Diamond's I07 beamline that were crucial to investigate the structural order and crystallographic orientation of the superlattices. The results were published in ACS Nano.
Enabling efficient Quantum Dot optoelectronic metamaterials
Quantum dots (QD) are semiconductor nanocrystals that can emit light when they are excited by UV light. Their optical properties will vary depending on the size or the shape of the quantum dots. There are many ways to produce QDs, but an efficient way is to synthetise QDs directly from solution, by adjusting the temperature to optimise the nanocrystal growth. This technique is called colloidal synthesis and will result in the production of colloidal quantum dots (CQDs). To be used, these QDs are usually deposited on a substrate to form thin films. Scientists are searching for ways to create ordered lattices that will retain the optical and electronic properties of the QDs. Indeed, disordered layers of QDs will results in poor electrical conductivity.
- Figure: Grazing-incidence X-ray scattering measurements. (a) GISAXS pattern of the 220 nm thick OA sample. The inset scale bar is logarithmic; (b) corresponding wedge-corrected GIWAXS pattern for the sample in panel (a). The scale bar is linear for ease of visualisation.
In this publication, researchers created CQDs superlattices of PbS (lead sulfide) with tuneable thickness up to 200 nm and high coherent ordering, both in-plane and along the thickness. They previously developed a protocol that allowed them to produce these ordered lattices of quantum dots, but they add an extra step at the end: they immersed the thin films in lead iodide (PbI2). This process called passivation removed electron traps at the surface of the films, which improved the conductivity of the material.
Diamond's I07 beamline was used for GISAXS/GIWAXS experiments to probe the structural integrity and crystallinity of the QD superlattices at both the nano- and atomic scale. The GISAXS pattern of the 220 nm-thick sample reveals up to three orders of sharp diffraction spots. This number of reflections and their clear spot-like shape clearly prove the high level of long rage order and the low structural disorder of the sample. The arc-like nature of the GIWAXS signal suggests the collective alignment of the CQDs and, consequently, of their atomic planes.
The researchers demonstrated that post-deposition PbI2 treatment dramatically improved the electronic performance of the superlattices, achieving field-effect electron mobilities among the highest for PbS quantum dot films. The high absorption in the short-wavelength infrared combined with the very high mobility and the superior stability of the PbS make these metamaterials ideal candidates for the next generation of optoelectronic devices to detect light.
Pinna, J. et al. PbI2 passivation of three-dimensional PbS quantum dot superlattices toward optoelectronic metamaterials. ACS Nano (2024). DOI: 10.1021/acsnano.4c04076
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