Perovskite halides are well-suited to monolithic multijunction photovoltaics, promising low-cost solar-to-electrical power conversion. Critical to all-perovskite multijunction fabrication is the deposition of a low-bandgap absorber without damaging other device layers. Vapor deposition is thus an attractive method, obviating the need for optically lossy protective interlayers, but is challenging for multicomponent perovskites. Here, we demonstrate a method to dual-source coevaporate low-bandgap perovskite films and devices. We used mixtures formed by melting of metal halides as a single-crucible source of Cs, Pb, and Sn cations. Surprisingly, when this melt was coevaporated with formamidinium iodide (FAI), uniform and dense perovskite films in the family FA1–xCsxSn1–yPbyI3 were formed. Inclusion of SnF2 in the melt helped to regulate the perovskite’s optoelectronic quality, leading to a steady-state power conversion efficiency of ∼10% in a solar cell. This represents a new processing paradigm for evaporated perovskite alloys, which is an important step toward all-perovskite multijunction photovoltaics.

This Review discusses the electronic structure of plasmonic resonances in metal nanostructures, clarifying existing misconceptions on the topic. Here we underscore the key property of the plasmonic response in metal nanocrystals: the plasmon and its wave function are mostly composed of a large number of low-energy excitations, which involve electrons near the Fermi level. Simultaneously, some number of high-energy hot electrons are excited in a nanocrystal due to the scattering of electrons by surfaces and in hot spots. It is an established fact that plasmon excitations are well described by classical frameworks, considering the collective oscillation of low-energy carriers moving as the result of classical acceleration. This classical motion is intrinsically dissipative and leads to heating. On the other hand, the generation of hot electrons in nanocrystals is a quantum surface effect. The energy efficiency of such hot-electron processes is always limited. However, there are interesting possibilities for the hot-electron enhancement, which we discuss here in the context of applications for plasmonic photodetectors, photocatalysis, and ultrafast spectroscopy.