Han Wang

III‐V group colloidal quantum dots (CQDs) are promising semiconductors for short‐wavelength infrared optoelectronic devices because of their narrow bandgaps and size tunability. Furthermore, their composition complies with the ‘Restriction of Hazardous Substances’ directive of the European Union, making them attractive for consumer electronics, including photodetectors and light‐emitting diodes. However, achieving surface passivation comparable to that of well‐studied Pb chalcogenides demonstrated to be challenging. Currently, the device performance of InAs CQDs with InBr ₃ ‐based ligands obtained via solution‐phase ligand exchange is limited, indicating insufficient surface passivation. In this study, we introduce for InAs CQDs with excitonic peak centered at approximately 1200 nm, a novel AlBr ₃ ‐ligand with methylammonium acetate (MAAc) as co‐ligand. The resulting CQDs show enhanced photoluminescence intensity indicating better surface passivation, attributed to the reduced steric hindrance of Al cations. The transport properties of the films obtained from inks yield a maximum field‐effect mobility of 0.26 cm ² V ^{− 1} s ^{− 1} with ion gel gating. The CQD films obtained with the new inks also maintain stable optoelectronic properties at temperatures up to 200°C. This enhanced thermal stability represents a crucial step toward Pb‐free CQD‐based optoelectronics for consumer applications.

Incorporating tin (Sn) and lead (Pb) into metal halide perovskites is an effective strategy for reducing bandgap energy, enabling applications in the near‐infrared (NIR) spectral region. Recently, we demonstrated light‐emitting diodes (LEDs) with long‐wavelength emission peaks exceeding 900 nm. However, non‐radiative recombination at the perovskite/transport layer interface remains a key limitation to device efficiency. In this work, we introduce carbazole ammonium iodide as an interfacial modifier, forming a hydrophilic thin layer atop the PEDOT:PSS hole transport layer. This interlayer enhances surface wettability, promotes improved perovskite crystallization, and facilitates better interface contact. The resulting perovskite films exhibit extended carrier lifetimes, and the corresponding NIR LEDs show reduced leakage current densities. Additionally, we systematically investigate the influence of annealing temperature on Sn–Pb‐based perovskite film formation. X‐ray diffraction (XRD) analysis reveals that high‐temperature annealing accelerates crystallization but promotes PbI ₂ formation, leading to rougher surfaces and increased crystal defects. By combining surface modification of the hole transport layer with optimized annealing conditions, we achieve a significant performance enhancement. The NIR LED with an emission peak at 988 nm exhibits a twofold increase in external quantum efficiency (EQE), improving from 0.6% to 1.3%, compared to devices using unmodified PEDOT:PSS.

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.

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.