Jacopo Pinna

PbS colloidal quantum dots (CQDs) hold strong promise for short‐wave infrared (SWIR) optoelectronics. However, current photodetectors rely on p ‐type CQD layers fabricated via a laborious, defect‐prone layer‐by‐layer process. While robust n ‐type CQD inks have been realized, p ‐type inks remain challenging due to the absence of suitable ligands and solvents. An ideal solvent must ensure colloidal stability and be orthogonal to underlying layers. Here, we report a thiolate‐capped p ‐type PbS CQD ink using mercapto‐2‐propanol as the ligand and hexafluoro‐2‐propanol as the solvent. Stabilization arises from ligand–solvent hydrogen bonding, providing a shelf‐life exceeding six days. The solvent does not compromise pre‐deposited layers, enabling fully blade‐coated photodiodes in both n–p and p–n architectures. Devices fabricated with this ink exhibit a twofold increase in specific detectivity (2.55 × 10 ¹² Jones) and a 70% enhancement in bandwidth (155 kHz) compared to layer‐by‐layer controls, attributed to improved film morphology and charge transport.

Two-dimensional (2D) metal halide perovskite-like quantum wells can be obtained by slicing the inorganic perovskite lattices with large organic molecules, where the number of consecutive inorganic slabs (n) determines the quantum confinement. Synthesizing large-area and ultrathin 2D perovskite sheets is crucial to achieving heterostructures for future thin-sheet optoelectronic devices. In this work, we demonstrate a synthesis method in which perovskite precursor solutions are introduced on an antisolvent liquid surface. Well-defined n = 1 sheets with sub-10 nm thickness and up to 50 μm lateral size are obtained in a scalable manner. This is achieved through careful engineering of subphase and spreading phase compositions to encourage controlled perovskite crystallization at the antisolvent–air interface. Structural and spectroscopic characterizations reveal a high phase purity and a clean excitonic emission, with their overall optical properties comparable to those of the highly crystalline films fabricated by blade coating, highlighting the clear potential of this liquid surface synthesis strategy.

Metal halide perovskites have emerged as a highly promising class of materials, garnering immense scientific and technological interest in recent years. Their exceptional properties make them particularly attractive for a wide range of optoelectronic applications, most notably in high‐efficiency solar cells and advanced photodetectors. Beyond these uses, hybrid perovskite materials have also demonstrated potential as sensitive platforms for detecting volatile organic compounds, further expanding their technological relevance. It has been demonstrated that the adsorption of these organic molecules can passivate surface defects, which improves the conductance of the perovskite layer. Here, we show that methylammonium lead bromide (MAPbBr ₃ ) and 2‐phenylethylammonium lead bromide ((PEA) ₂ PbBr ₄ ) are highly effective in sensing 1‐propanol, which has been identified as biomarker for lung cancer. Both systems exhibit a response time of 1 s, and a recovery time of 1.7 and 14 s for MAPbBr ₃ and (PEA) ₂ PbBr ₄ , respectively. Going from a 3D to a 2D structure allows us to tailor electronic properties and trap density states, thereby greatly enhancing gas sensitivity. Both systems show a remarkable maximum response of 10 ⁶ and 10 ⁷ at 6000 and 7000 ppm, respectively, and a low detection limit of 90 ppm.

Superlattices of lead chalcogenide colloidal quantum dots hold promise to revolutionise the field of infrared optoelectronics due to their unique combination of optical and transport properties. However, the main challenge remains to form a homogeneous thin-film with long-range order avoiding cracking upon ligand exchange. To overcome these issues, we introduce an approach where external lateral pressure is applied during the self-assembly and ligand exchange, thus avoiding the formation of cracks due to volume shrinking. The formed monolayer superlattices are crack-free over several millimetres square. Transport measurements in an ionic gel-gated field-effect transistor reveal that increasing the external pressure during the superlattice formation leads to higher electron mobilities above 25 cm²V⁻¹s⁻¹ thanks to better compactness, high ordering, and a higher number of nearest neighbours. These results demonstrate that colloidal quantum dot superlattices with high charge mobility can be fabricated over large areas with important implications for technological applications.

Superlattices of lead chalcogenide colloidal quantum dots hold promise to revolutionise the field of infrared optoelectronics due to their unique combination of optical and transport properties. However, the main challenge remains to form a homogeneous thin-film with long-range order avoiding cracking upon ligand exchange. This problem is particularly evident in 2D superlattices where the interactions driving the self-assembly are limited to a single plane yielding very defective films. To overcome these issues, we introduce a novel approach where external lateral pressure is applied during the self-assembly and ligand exchange, forcing the quantum dots toward each other thus avoiding the formation of cracks due to the volume shrinking. Such films consist of a hexagonal monolayer superlattice with long-range order that are crack-free over several millimetres square. The mechanism beyond the formation and ordering of the samples under external pressure is elucidated by atomistic molecular dynamic simulations. Transport measurements in an ionic gel-gated field-effect transistor reveal that increasing the external pressure during the superlattice formation leads to higher electron mobilities above 25 cm²/Vs thanks to better compactness, high ordering, and a higher number of nearest neighbours. These results demonstrate that colloidal quantum dot superlattices with high charge mobility can be fabricated over large areas with important implications for technological applications.

The efficiency of organic solar cells has raised drastically in the past years. However, there is an undeniable lack of hole transport layers that can provide high carrier selectivity, low defect density, and high processing robustness, simultaneously. In this work, this issue is addressed by studying defect generation and surface passivation of nickel oxide (NiO _x ). It is revealed that the generation of high oxidation state species on NiO _x surface lowers contact resistance but hinders charge extraction when employed as transport layer in organic solar cells. By using them as coordination centers, a straightforward surface modification strategy is implemented using (2‐(9H‐carbazol‐9‐yl)ethyl)phosphonic acid (2PACz) that enhances charge extraction and increases the solar cell efficiency from 11.46% to 17.12%. Additionally, the robustness of this modification across different deposition methods of the carbazole molecule is demonstrated. Finally, by fine‐tuning the Fermi level using various carbazole‐based molecules, and in particular with ((4‐(7H‐dibenzo[c,g]carbazol‐7‐yl)butyl)phosphonic acid (4PADCB), a power conversion efficiency of 17.29% is achieved, with an outstanding combination of a V _OC of 0.888 V and a fill factor of 80%.

Lead chalcogenide colloidal quantum dots are one of the most promising materials to revolutionize the field of short-wavelength infrared optoelectronics due to their bandgap tunability and strong absorption. By self-assembling these quantum dots into ordered superlattices, mobilities approaching those of the bulk counterparts can be achieved while still retaining their original optical properties. The recent literature focused mostly on PbSe-based superlattices, but PbS quantum dots have several advantages, including higher stability. In this work, we demonstrate highly ordered 3D superlattices of PbS quantum dots with tunable thickness up to 200 nm and high coherent ordering, both in-plane and along the thickness. We show that we can successfully exchange the ligands throughout the film without compromising the ordering. The superlattices as the active material of an ion gel-gated field-effect transistor achieve electron mobilities up to 220 cm² V^-1 s^-1. To further improve the device performance, we performed a postdeposition passivation with PbI₂, which noticeably reduced the subthreshold swing making it reach the Boltzmann limit. We believe this is an important proof of concept showing that it is possible to overcome the problem of high trap densities in quantum dot superlattices enabling their application in optoelectronic devices.

Slow hot-carrier cooling may potentially allow overcoming the maximum achievable power conversion efficiency of single-junction solar cells. For formamidinium tin triiodide, an exceptional slow cooling time of a few nanoseconds was reported. However, a systematic study of the cation influence, as is present for lead compounds, is lacking. Here, we report the first comparative study on formamidinium, methylammonium, and cesium tin triiodide thin films. By investigating their photoluminescence, we observe a considerable shift of the emission peak to high energy with the increase of the excited-state population, which is more prominent in the case of the two hybrid organic-inorganic perovskites (∼45 meV vs ∼15 meV at 9 × 10¹⁷ cm^-3 carrier density). The hot-carrier photoluminescence of the three tin compositions decays with a 0.6-2.8 ns time constant with slower cooling observed for the two hybrids, further indicating their importance.

The phase‐transfer ligand exchange of PbS quantum dots (QDs) has substantially simplified device fabrication giving hope for future industrial exploitation. However, this technique when applied to QDs of large size (>4 nm) gives rise to inks with poor colloidal stability, thus hindering the development of QDs photodetectors in short‐wavelength infrared range. Here, it is demonstrated that methylammonium lead iodide ligands can provide sufficient passivation of PbS QDs of size up to 6.7 nm, enabling inks with a minimum of ten‐week shelf‐life time, as proven by optical absorption and solution‐small angle X‐ray scattering. Furthermore, the maximum linear electron mobility of 4.7 × 10⁻² cm² V⁻¹ s⁻¹ is measured in field‐effect transistors fabricated with fresh inks, while transistors fabricated with the same solution after ten‐week storage retain 74% of the average starting electron mobility, demonstrating the outstanding quality both of the fresh and aged inks. Finally, photodetectors fabricated via blade‐coating exhibit 76% external quantum efficiency at 1300 nm and 1.8 × 10¹² Jones specific detectivity, values comparable with devices fabricated using ink with lower stability and wasteful methods such as spin‐coating.

3D superlattices made of colloidal quantum dots are a promising candidate for the next generation of optoelectronic devices as they are expected to exhibit a unique combination of tunable optical properties and coherent electrical transport through minibands. While most of the previous work was performed on 2D arrays, the control over the formation of these systems is lacking, where limited long‐range order and energetical disorder have so far hindered the potential of these metamaterials, giving rise to disappointing transport properties. Here, it is reported that nanoscale‐level controlled ordering of colloidal quantum dots in 3D and over large areas allows the achievement of outstanding transport properties. The measured electron mobilities are the highest ever reported for a self‐assembled solid of fully quantum‐confined objects. This ultimately demonstrates that optoelectronic metamaterials with highly tunable optical properties (in this case in the short‐wavelength infrared spectral range) and charge mobilities approaching that of bulk semiconductor can be obtained. This finding paves the way toward a new generation of optoelectronic devices.