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Photolithography is an important manufacturing process that relies on using photoresists, typically polymer formulations, that change solubility when illuminated with ultraviolet light. Here, we introduce a general chemical approach for photoresist-free, direct optical lithography of functional inorganic nanomaterials. The patterned materials can be metals, semiconductors, oxides, magnetic, or rare earth compositions. No organic impurities are present in the patterned layers, which helps achieve good electronic and optical properties. The conductivity, carrier mobility, dielectric, and luminescence properties of optically patterned layers are on par with the properties of state-of-the-art solution-processed materials. The ability to directly pattern all-inorganic layers by using a light exposure dose comparable with that of organic photoresists provides an alternate route for thin-film device manufacturing.

A wide range of materials can now be synthesized into semiconducting quantum dots. Because these materials grow from solutions, there is scope to combine quantum dots into devices by using simple, low-cost manufacturing processes. Kagan et al. review recent progress in tailoring and combining quantum dots to build electronic and optoelectronic devices. Because it is possible to tune the size, shape, and connectivity of each of the quantum dots, there is potential for fabricating electronic materials with properties that are not available in traditional bulk semiconductors. Science , this issue p. 885 The continued growth of mobile and interactive computing requires devices manufactured with low-cost processes, compatible with large-area and flexible form factors, and with additional functionality. We review recent advances in the design of electronic and optoelectronic devices that use colloidal semiconductor quantum dots (QDs). The properties of materials assembled of QDs may be tailored not only by the atomic composition but also by the size, shape, and surface functionalization of the individual QDs and by the communication among these QDs. The chemical and physical properties of QD surfaces and the interfaces in QD devices are of particular importance, and these enable the solution-based fabrication of low-cost, large-area, flexible, and functional devices. We discuss challenges that must be addressed in the move to solution-processed functional optoelectronic nanomaterials.

Improving charge mobility in quantum dot (QD) films is important for the performance of photodetectors, solar cells and light-emitting diodes. However, these applications also require preservation of well defined QD electronic states and optical transitions. Here, we present HgTe QD films that show high mobility for charges transported through discrete QD states. A hybrid surface passivation process efficiently eliminates surface states, provides tunable air-stable n and p doping and enables hysteresis-free filling of QD states evidenced by strong conductance modulation. QD films dried at room temperature without any post-treatments exhibit mobility up to μ  ~ 8 cm 2  V −1  s −1 at a low carrier density of less than one electron per QD, band-like behaviour down to 77 K, and similar drift and Hall mobilities at all temperatures. This unprecedented set of electronic properties raises important questions about the delocalization and hopping mechanisms for transport in QD solids, and introduces opportunities for improving QD technologies. High charge mobility while retaining signatures of quantum-confined states is obtained in films of surface-passivated HgTe quantum dots.

The field of self-assembly has moved far beyond early work, where the focus was primarily the resultant beautiful two- and three-dimensional structures, to a focus on forming materials and devices with important properties either otherwise not available, or only available at great cost. Over the last few years, materials with unprecedented electronic, photonic, energy-storage, and chemical separation functionalities were created with self-assembly, while at the same time, the ability to form even more complex structures in two and three dimensions has only continued to advance. Self-assembly crosscuts all areas of materials. Functional structures have now been realized in polymer, ceramic, metallic, and semiconducting systems, as well as composites containing multiple classes of materials. As the field of self-assembly continues to advance, the number of highly functional systems will only continue to grow and make increasingly greater impacts in both the consumer and industrial space.

Colloidal semiconductor nanocrystals, also known as “quantum dots” (QDs), represent an example of a disruptive technology for display and lighting applications. The QDs’ high luminescence efficiency and precisely tunable, narrow emission are nearly ideal for achieving saturated colors and enriching the display or TV color gamut. Quantum dot light-emitting diodes (QLEDs) can provide saturated emission colors and allow inexpensive solution-based device fabrication on almost any substrate. The first incorporation of QDs into the consumer market is using them as optical down-converters. Blue light from an efficient high energy light source (e.g., GaN blue LED) is absorbed and reemitted at any desired lower energy wavelength. Alternatively, electric current can be used for direct excitation of QDs. QLEDs are an exciting technical challenge and commercial opportunity for display and solid-state lighting applications. Recent developments in the field show that efficiency and brightness of QLEDs can match those of organic LEDs.

Flexible, thin-film electronic and optoelectronic devices typically involve a trade-off between performance and fabrication cost 1 , 2 , 3 . For example, solution-based deposition allows semiconductors to be patterned onto large-area substrates to make solar cells and displays, but the electron mobility in solution-deposited semiconductor layers is much lower than in semiconductors grown at high temperatures from the gas phase 4 . Here, we report band-like electron transport in arrays of colloidal cadmium selenide nanocrystals capped with the molecular metal chalcogenide complex 5 , 6 In 2 Se 4 2− , and measure electron mobilities as high as 16 cm 2  V −1  s −1 , which is about an order of magnitude higher than in the best solution-processed organic 7 and nanocrystal 8 devices so far. We also use CdSe/CdS core–shell nanoparticles with In 2 Se 4 2− ligands to build photodetectors with normalized detectivity D * > 1 × 10 13 Jones (I Jones = 1 cm Hz 1/2  W −1 ), which is a record for II – VI nanocrystals. Our approach does not require high processing temperatures, and can be extended to different nanocrystals and inorganic surface ligands. Arrays of cadmium selenide nanocrystals capped with molecular metal chalcogenide complexes exhibit high values of electron mobility and photoconductivity.

Conducting organic materials, such as doped organic polymers 1 , molecular conductors 2 , 3 and emerging coordination polymers 4 , underpin technologies ranging from displays to flexible electronics 5 . Realizing high electrical conductivity in traditionally insulating organic materials necessitates tuning their electronic structure through chemical doping 6 . Furthermore, even organic materials that are intrinsically conductive, such as single-component molecular conductors 7 , 8 , require crystallinity for metallic behaviour. However, conducting polymers are often amorphous to aid durability and processability 9 . Using molecular design to produce high conductivity in undoped amorphous materials would enable tunable and robust conductivity in many applications 10 , but there are no intrinsically conducting organic materials that maintain high conductivity when disordered. Here we report an amorphous coordination polymer, Ni tetrathiafulvalene tetrathiolate, which displays markedly high electronic conductivity (up to 1,200 S cm −1 ) and intrinsic glassy-metallic behaviour. Theory shows that these properties are enabled by molecular overlap that is robust to structural perturbations. This unusual set of features results in high conductivity that is stable to humid air for weeks, pH 0–14 and temperatures up to 140 °C. These findings demonstrate that molecular design can enable metallic conductivity even in heavily disordered materials, raising fundamental questions about how metallic transport can exist without periodic structure and indicating exciting new applications for these materials. An unusual new material, NiTTFtt, is reported that is structurally amorphous, precluding a classical band structure, but detailed characterization reveals high conductivity and a metallic character.

Initially poorly conducting PbSe nanocrystal solids (quantum dot arrays or superlattices) can be chemically \"activated\" to fabricate n- and p-channel field effect transistors with electron and hole mobilities of 0.9 and 0.2 square centimeters per volt-second, respectively; with current modulations of about 10³ to 10⁴; and with current density approaching 3 x 10⁴ amperes per square centimeter. Chemical treatments engineer the interparticle spacing, electronic coupling, and doping while passivating electronic traps. These nanocrystal field-effect transistors allow reversible switching between n- and p-transport, providing options for complementary metal oxide semiconductor circuits and enabling a range of low-cost, large-area electronic, optoelectronic, thermoelectric, and sensing applications.

Fast fluorescence resonance energy transfer between CdSe nanoplatelets on a picosecond timescale is measured. This process is faster than Auger recombination and leads to the observation of multiexcitonic energy transfer in these materials. Fluorescence resonance energy transfer (FRET) enables photosynthetic light harvesting 1 , wavelength downconversion in light-emitting diodes 2 (LEDs), and optical biosensing schemes 3 . The rate and efficiency of this donor to acceptor transfer of excitation between chromophores dictates the utility of FRET and can unlock new device operation motifs including quantum-funnel solar cells 4 , non-contact chromophore pumping from a proximal LED 5 , and markedly reduced gain thresholds 6 . However, the fastest reported FRET time constants involving spherical quantum dots (0.12–1 ns; refs  7 , 8 , 9 ) do not outpace biexciton Auger recombination (0.01–0.1 ns; ref.  10 ), which impedes multiexciton-driven applications including electrically pumped lasers 11  and carrier-multiplication-enhanced photovoltaics 12 , 13 . Few-monolayer-thick semiconductor nanoplatelets (NPLs) with tens-of-nanometre lateral dimensions 14 exhibit intense optical transitions 14 and hundreds-of-picosecond Auger recombination 15 , 16 , but heretofore lack FRET characterizations. We examine binary CdSe NPL solids and show that interplate FRET (∼6–23 ps, presumably for co-facial arrangements) can occur 15–50 times faster than Auger recombination 15 , 16 and demonstrate multiexcitonic FRET, making such materials ideal candidates for advanced technologies.

Well-connected quasicrystals Quasicrystals are unique materials combining long-range order with 'impossible' packing symmetries like fivefold rotation, forbidden in periodic structures. Until now, they have been found only in specific systems such as intermetallic compounds, block copolymers, or colloidal particles under the action of a laser standing-wave pattern. Now Talapin et al . have self-assembled colloidal nanoparticles into aperiodic quasicrystalline lattices by carefully tailoring their sizes and using a novel packing motif. They can obtain quasicrystals with nanoparticles made of several different combinations of materials, pointing to the fact that only sphere packing and simple inter-particle potentials are important for their formation, and not specific interactions between the components These quasicrystals can also connect to the ordinary (crystalline) world through a thin 'wetting' layer with structures resembling the classic Archimedean tiling pattern. Quasicrystals are ordered structures that lack any translational symmetry, challenging the classic conception of ordered solids as periodic structures. So far, they have been reported in certain systems and can, for example, form from intermetallic compounds and organic dendrimers. Here it is shown that colloidal inorganic nanoparticles from several materials can self-assemble into binary aperiodic superlattices with quasicrystalline order. The discovery of quasicrystals in 1984 changed our view of ordered solids as periodic structures 1 , 2 and introduced new long-range-ordered phases lacking any translational symmetry 3 , 4 , 5 . Quasicrystals permit symmetry operations forbidden in classical crystallography, for example five-, eight-, ten- and 12-fold rotations, yet have sharp diffraction peaks. Intermetallic compounds have been observed to form both metastable and energetically stabilized quasicrystals 1 , 3 , 5 ; quasicrystalline order has also been reported for the tantalum telluride phase with an approximate Ta 1.6 Te composition 6 . Later, quasicrystals were discovered in soft matter, namely supramolecular structures of organic dendrimers 7 and tri-block copolymers 8 , and micrometre-sized colloidal spheres have been arranged into quasicrystalline arrays by using intense laser beams that create quasi-periodic optical standing-wave patterns 9 . Here we show that colloidal inorganic nanoparticles can self-assemble into binary aperiodic superlattices. We observe formation of assemblies with dodecagonal quasicrystalline order in different binary nanoparticle systems: 13.4-nm Fe 2 O 3 and 5-nm Au nanocrystals, 12.6-nm Fe 3 O 4 and 4.7-nm Au nanocrystals, and 9-nm PbS and 3-nm Pd nanocrystals. Such compositional flexibility indicates that the formation of quasicrystalline nanoparticle assemblies does not require a unique combination of interparticle interactions, but is a general sphere-packing phenomenon governed by the entropy and simple interparticle potentials. We also find that dodecagonal quasicrystalline superlattices can form low-defect interfaces with ordinary crystalline binary superlattices, using fragments of (3 3 .4 2 ) Archimedean tiling as the ‘wetting layer’ between the periodic and aperiodic phases.