Despite the well-known implications in the field of III–V semiconductors, lattice strain in halide perovskite materials has been largely overlooked until recently. Here, we review the effect of lattice strain on the structural, chemical, and optoelectronic properties of metal halide perovskites to understand how strain engineering can be applied to improve device performance. We start by arguing that perovskites, like any other semiconducting material, are not immune to the negative effects of mismanaged strain. We analyze the originand detrimental consequencesof lattice strain in perovskite crystals and heterostructures. We then discuss how strain management addresses the polymorphism issue of some of the most desirable perovskite compositions, and how it prevents the harmful migration of ions in perovskites. We conclude by offering our perspective on the unexplored potential of strain engineering and argue that its controlled management can lead to untapped territories, including perovskite large-area single-crystalline thin films and electrically pumped lasers.

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Hierarchical block copolymer self-assembly is used to produce "polyplex-in-hydrophobic-core" (PIHC) micelles for gene delivery. The unique PIHC micelle structure provides nuclease protection and controlled release by embedding nucleic acids in the micelle core surrounded by condensed hydrophobic polymer chains. PIHC micelles are generated through a simple, two-step process using commercially available polymers: (1) electrostatic binding between the nucleic acid cargo and poly(ε-caprolactone)block-poly(2-vinyl pyridine) (PCL-b-P2VP) (SA1), followed by (2) microprecipitation of the polyplex with poly(ε-caprolactone)block-poly(ethylene glycol) (SA2). The resulting vectors possess poly(ethylene glycol) (PEG) coronae and nucleic acid−P2VP polyplexes embedded within condensed PCL hydrophobic cores. Using a two-phase microfluidic reactor for the SA2 step, we produce mainly spherical PIHC micelles with ∼30 nm PCL cores and ∼15 nm PEG shells. Plasmids encapsulated in PIHC micelles show resistance to DNase I degradation compared to plasmids located outside the micelle cores. PIHC micelles containing pUC18 show enhanced transformation efficiencies in competent Escherichia coli with a linear time dependence over 8 h associated with slow plasmid release via hydrolytic degradation of PCL cores. Finally, we show that PIHC micelles are readily taken into the cytosol of MDA-MB-231 (human breast cancer) cells.

Ambient air processing is desirable for the industrial fabrication of perovskite solar cells. Here, we show that perovskite ink containing methylammonium and formamidinium in Nmethyl-2-pyrrolidone and N,N-dimethylformamide, a cosolvent composition that satisfies prerequisites for upscaling solar cell fabrication, degrades within a day in ambient air. From 1 H NMR spectroscopic analysis, we find that water proton exchange with methylammonium and formamidinium facilitates the aminolysis of formamidinium by methylamine. The addition of elemental sulfur inhibits this proton exchange process via sulfur−amine reactions, resulting in a stable perovskite ink with an extrapolated half-life of 6300 h. The control ink aged for 1 day does not form perovskite films for solar cell fabrication, while the sulfur-stabilized ink is reproducibly used to make devices with efficiencies >15% when aged for over 1 month. The stabilized ink is suitable for upscaling perovskite solar cell fabrication, with efficiencies up to 17% for blade-coated devices.

We describe a basic theoretical treatment of how film–substrate and substrate–environment (air, water, and solution) interfaces can be selectively probed by controlling the film thickness and beam angles in a visible-infrared sum frequency generation experiment. In this model, we also account for the unique interfacial environment that may have optical properties that differ from the adjacent bulk phases. We see that this affects components of the electric field that are perpendicular to the surface such as when p-polarized light is used. We then provide an example using the glass–polydimethylsiloxane–air system and model the fields at both surfaces of the polymer. This is followed by some practical considerations for setting up such experiments and some typical experimental results.