Mordechai Kot

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.

Metalloporphyrins based on open-shell transition metals, such as Ni(II), exhibit typically fast excited-state relaxation. In this work, we shed light into the nonradiative relaxation mechanism in a nanographene-Ni(II) porphyrin conjugate. Variable temperature transient absorption and global fit analysis are combined to produce a picture of the relaxation pathways. At room temperature, photoexcitation of the lowest π-π* transition is followed by vibrational cooling in 1.6 ps, setting a short 20 ps temporal window wherein a small fraction of relaxed singlets radiatively decay to the ground state before intersystem crossing proceeds. Following intersystem crossing, triplets relax rapidly to the ground state (S₀) in a few tens of picoseconds. By performing measurements at low temperature, we provide evidence for a competition between two terminal relaxation pathways from the lowest (metal-centered) triplet to the ground state: a slow ground state relaxation process proceeding in time scales beyond 1.6 ns and a faster pathway dictated by a sloped conical intersection, which is thermally accessible at room temperature from the triplet state. The overall triplet decay at a given temperature is dictated by the interplay of these two contributions. This observation bears significance in understanding the underlying fast relaxation processes in Ni-based molecules and related transition metal complexes, opening avenues for potential applications for energy harvesting and optoelectronics.

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.