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.