Precise microscale patterning is a prerequisite to incorporate the emerging colloidal metal halide perovskite nanocrystals into advanced, integrated optoelectronic platforms for widespread technological applications. Current patterning methods suffer from some combination of limitations in patterning quality, versatility, and compatibility with the workflows of device fabrication. This work introduces the direct optical patterning of perovskite nanocrystals with ligand cross-linkers or DOPPLCER. The underlying, nonspecific cross-linking chemistry involved in DOPPLCER supports high-resolution, multicolored patterning of a broad scope of perovskite nanocrystals with their native ligands. Patterned nanocrystal films show photoluminescence (after postpatterning surface treatment), electroluminescence, and photoconductivity on par with those of conventional nonpatterned films. Prototype, pixelated light-emitting diodes show peak external quantum efficiency of 6.8% and luminance over 20,000 cd m
−2
. Both are among the highest for patterned perovskite nanocrystal devices. These results create new possibilities in the system-level integration of perovskite nanomaterials and advance their applications in various optoelectronic and photonic platforms.
Precise patterning with microscale lateral resolution
and widely
tunable heights is critical for integrating colloidal nanocrystals
into advanced optoelectronic and photonic platforms. However, patterning
nanocrystal layers with thickness above 100 nm remains challenging
for both conventional and emerging direct photopatterning methods,
due to limited light penetration depths, complex mechanical and chemical
incompatibilities, and others. Here, we introduce a direct patterning
method based on a thermal mechanism, namely, the thermally activated
ligand chemistry (or TALC) of nanocrystals. The ligand cross-linking
or decomposition reactions readily occur under local thermal stimuli
triggered by near-infrared lasers, affording high-resolution and nondestructive
patterning of various nanocrystals under mild conditions. Patterned
quantum dots fully preserve their structural and photoluminescent
quantum yields. The thermal nature allows for TALC to pattern over
10 μm thick nanocrystal layers in a single step, far beyond
those achievable in other direct patterning techniques, and also supports
the concept of 2.5D patterning. The thermal chemistry-mediated TALC
creates more possibilities in integrating nanocrystal layers in uniform
arrays or complex hierarchical formats for advanced capabilities in
light emission, conversion, and modulation.
Epitaxial heterostructures of colloidal lead halide perovskite nanocrystals (NCs) with other semiconductors, especially the technologically important metal chalcogenides, can offer an unprecedented level of control in wavefunction design and exciton/charge carrier engineering. These NC heterostructures are ideal material platforms for efficient optoelectronics and other applications. Existing methods, however, can only yield heterostructures with random connections and distributions of the two components. The lack of epitaxial relation and uniform geometry hinders the structure-function correlation and impedes the electronic coupling at the heterointerface. This work reports the synthesis of uniform, epitaxially grown CsPbBr 3 /CdS Janus NC heterostructures with ultrafast charge separation across the electronically coupled interface. Each Janus NC contains a CdS domain that grows exclusively on a single {220} facet of CsPbBr 3 NCs. Varying reaction parameters allows for precise control in the sizes of each domain and readily modulates the optical properties of Janus NCs. Transient absorption measurements and modeling results reveal a type II band alignment, where photoexcited electrons rapidly transfer (within ≈9 picoseconds) from CsPbBr 3 to CdS. The promoted charge separation and extraction in epitaxial Janus NCs leads to photoconductors with drastically improved (approximately three orders of magnitude) responsivity and detectivity, which is promising for ultrasensitive photodetection.
The effectiveness of a highly sensitive sodium dodecyl benzenesulfonate (SDBS)–TiO2 thin film optical waveguide gas sensor assessed in detecting various organic gases. Gas sensing measurements indicated that the sensing element has good selectivity, high sensitivity, and a low detection limit of 1 ppb to xylene gas with fast response and short recovery times. Interference gas test results showed that the sensitive component can detect 1 ppm of xylene gas in a mixed system containing other interfering gases, thus demonstrating the effectiveness of the proposed sensor for organic gas detection.
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