Solution-processed hybrid organic−inorganic perovskites (HOIPs) from organoammonium halide and lead halide precursors form efficacious active layers for photovoltaics, light-emitting diodes, and flexible electronics. Though solvent−solute coordination plays a critical role in HOIP crystallization, the influence of solvent choice on such interactions is poorly understood. We demonstrate Gutmann's donor number, D N , as a parameter that indicates the coordinating ability of the processing solvent with the Pb 2+ center of the lead halide precursor. Low D N solvents interact weakly with the Pb 2+ center, favoring instead complexation between Pb 2+ and iodide and subsequent crystallization of perovskite. High D N solvents coordinate more strongly with the Pb 2+ center, which in turn inhibits iodide coordination and stalls perovskite crystallization. Varying the concentration of high-D N additives in precursor solutions tunes the strength of lead− solvent interactions, allowing finer control over the crystallization and the resulting morphology of HOIP active layers.

We describe a patterning technique that uses self-assembled monolayers and other surface chemistries for guiding the transfer of material from relief features on a stamp to a substrate. This purely additive contact printing technique is capable of nanometer resolution. Pattern transfer is fast and it occurs at ambient conditions. We illustrate the versatility of this method by printing single-layer metal patterns with feature sizes from a few tens of microns to a few tens of nanometers. We also demonstrate its use for patterning, in a single step, metal/dielectric/metal multilayers for functional thin film capacitors on plastic substrates.

Crystallization within the discrete spheres of a block copolymer mesophase was studied by time-resolved x-ray scattering. The cubic packing of microdomains, established by self-assembly in the melt, is preserved throughout crystallization by strong interblock segregation even though the amorphous matrix block is well above its glass transition temperature. Homogeneous nucleation within each sphere yields isothermal crystallizations which follow first-order kinetics, contrasting with the sigmoidal kinetics normally exhibited in the quiescent crystallization of bulk polymers.

We examine the crystallization behavior of polyethylene-b-poly(vinylcyclohexane) diblock copolymers, E/VCH, using a combination of transmission electron microscopy (TEM), dilatometry, and time-resolved small-angle X-ray scattering (SAXS). The glassy VCH matrix effectively restricts E crystallization to within the spheres, cylinders, gyroid channels, or lamellae formed by microphase separation in the melt. The VCH matrix can contract in response to crystallization of the E microdomains, so crystallization proceeds without cavitation. The crystallization kinetics strongly reflect the connectivity of the E microdomains: homogeneous nucleation and first-order crystallization kinetics for spheres or cylinders of E; conventional sigmoidal kinetics for the highly interconnected gyroid structure. Lamellar materials show an interesting two-step crystallization behavior: at higher temperature, heterogeneous nucleation permits the crystallization of lamellae interconnected through grain boundaries or defects, and then at lower temperature homogeneous nucleation permits the crystallization of the remaining isolated lamellae.

The conclusions reached by a diverse group of scientists who attended an intense 2-day workshop on hybrid organic-inorganic perovskites are presented, including their thoughts on the most burning fundamental and practical questions regarding this unique class of materials, and their suggestions on various approaches to resolve these issues.

We describe a method for contact printing metal patterns with nanometer features over large areas. This nanotransfer printing ͑nTP͒ technique relies on tailored surface chemistries to transfer metal films from the raised regions of a stamp to a substrate when these two elements are brought into intimate physical contact. The printing is purely additive, fast ͑Ͻ15 s contact time͒, and it occurs in a single processing step at ambient conditions. Features of varying dimensions, including sizes down to ϳ100 nm, can be printed with edge resolution better than 15 nm. Electrical contacts and interconnects for high-performance organic transistors and complementary inverter circuits have been successfully fabricated using nTP.Advanced techniques for nanofabrication are in widespread use for research in biology, physics, chemistry and materials science. They are also essential manufacturing tools for electronics, photonics and many other existing and emerging areas of technology. Established nanolithographic methods ͑e.g., electron-beam lithography, deep ultraviolet photolithography, etc.͒ require elaborate, expensive systems that are capable of only patterning a narrow range of specialized materials over small areas on ultraflat surfaces of rigid inorganic substrates. These limitations have created substantial interest in alternative techniques, such as those based on forms of contact printing, molding, embossing, and writing. 1,2 Although the basic operating principles of these techniques are conceptually old, recent research has demonstrated that their resolution can be extended into the micron and nanometer regimes by combining them with advanced materials and processing approaches. For example, elastomeric stamps and self-assembled monolayer inks 3 form the basis of a relatively new high-resolution printing technique. 4,5 This method, known as microcontact printing ͑CP͒, is rapidly becoming important for a range of applications in biotechnology, 6 plastic electronics, 7,8 and fiber optics 9 where the relevant patterning requirements cannot be satisfied easily with conventional methods. Although the resolution of CP is only ϳ0.25 m, this method and other emerging printing techniques, such as those that rely on imprinted polymer resists 10 and cold-welded metals, 11 offer fast and low-cost approaches for patterning flat or curved surfaces over large areas in a single processing step. While these methods appear to be useful for many patterning tasks, they are all generally subtractive in operation, i.e., they typically require the use of sacrificial resists, etching procedures or postpatterning deposition steps.In this letter we describe a purely additive printing tech-nique that has nanometer resolution. The method, which we refer to as nanotransfer printing ͑nTP͒, allows us to transfer metal films from the raised regions of a stamp onto various oxide surfaces. Using nTP, we have been able to transfer metal patterns from elastomeric ͓e.g., poly͑dimethylsiloxane͒ ͑PDMS͔͒ as well as hard ͑e.g., GaAs͒ stamps onto both conf...

We introduce a novel approach, nanotransfer printing (nTP), to fabricate top-contact electrodes in Au/1,8-octanedithiol/GaAs junctions. Current− voltage and photoresponse experiments were conducted to evaluate the nature of electrical contact. Results show that the nTP method produces superior devices in which the electrical transport in nTP devices occurs through the 1,8-octanedithiol molecules. By contrast, conventional evaporation of Au onto the molecules results in direct Au/GaAs contacts. Thus, nTP is potentially useful for making electrical contacts in molecular electronics.

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