Photovoltaic devices based on hybrid perovskite materials have exceeded 22% e ciency due to high charge-carrier mobilities and lifetimes. Properties such as photocurrent generation and open-circuit voltage are influenced by the microscopic structure and orientation of the perovskite crystals, but are di cult to quantify on the intra-grain length scale and are often treated as homogeneous within the active layer. Here, we map the local short-circuit photocurrent, open-circuit photovoltage, and dark drift current in state-of-the-art methylammonium lead iodide solar cells using photoconductive atomic force microscopy. We find, within individual grains, spatially correlated heterogeneity in short-circuit current and open-circuit voltage up to 0.6 V. These variations are related to di erent crystal facets and have a direct impact on the macroscopic power conversion e ciency. We attribute this heterogeneity to a facet-dependent density of trap states. These results imply that controlling crystal grain and facet orientation will enable a systematic optimization of polycrystalline and single-crystal devices for photovoltaic and lighting applications. Photocurrent microscopy to probe local e ciency We used two sets of methylammonium lead iodide chloride (MAPbI 3−x Cl x) thin films, which were processed in parallel. One set was used to fabricate planar solar cells by depositing a hole transport layer (HTL, spiro-OMeTAD) and a gold top contact, resulting in an

Mind the Gap Near-field microscopy has benefited from subwavelength near-field plasmonic probes that make use of the field-concentrating properties of gaps. These probes achieve maximum enhancement only in the tip-substrate gap mode, which can yield large near-field signals, but only for a metallic substrate and for very small tip-substrate gap distances. Bao et al. (p. 1317 ) designed a probe that unites broadband field enhancement and confinement with bidirectional coupling between far-field and near-field electromagnetic energy. Their tips primarily rely on the internal gap modes of the tip itself, thereby enabling it to image nonmetallic samples.

Optical antenna structures have revolutionized the field of nano-optics by confining light to deep subwavelength dimensions for spectroscopy and sensing. In this work, we fabricated coaxial optical antennae with sub-10-nanometer critical dimensions using helium ion lithography (HIL). Wavelength dependent transmission measurements were used to determine the wavelength-dependent optical response. The quality factor of 11 achieved with our HIL fabricated structures matched the theoretically predicted quality factor for the idealized flawless gold resonators calculated by finite-difference time-domain (FDTD). For comparison, coaxial antennae with 30 nm critical dimensions were fabricated using both HIL and the more common Ga focus ion beam lithography (Ga-FIB). The quality factor of the Ga-FIB resonators was 60% of the ideal HIL results for the same design geometry due to limitations in the Ga-FIB fabrication process.

Metasurfaces have facilitated the replacement of conventional optical elements with ultrathin and planar photonic structures. Previous designs of metasurfaces were limited to small deflection angles and small ranges of the angle of incidence. Here, we have created two types of Si-based metasurfaces to steer visible light to a large deflection angle. These structures exhibit high diffraction efficiencies over a broad range of angles of incidence. We have demonstrated metasurfaces working both in transmission and reflection modes based on conventional thin film silicon processes that are suitable for the large-scale fabrication of high-performance devices.

We have developed a micromechanical sensor based on vertically oriented oscillating beams, in which contrary to what is normally done (for example with oscillating cantilevers) the sensitive area is located at the free end of the oscillator. In the micropillar geometry used here, analyte adsorption is confined only to the tip of the micropillar, thus reducing the volume from which the analyte molecules must diffuse to saturate the surface to a sphere of radius more than 2 orders of magnitude smaller than the corresponding linear distance valid for adsorption on a macroscopic surface. Hence the absorption rate is 3 orders of magnitude faster than on a typical 200 × 20 square micrometer cantilever. Pillar oscillations are detected by means of an optical lever method, but the geometry is suitable for multiplexing with compact integrated detection. We demonstrate our technology by investigating the formation of a single-strand DNA self-assembled monolayer (SAM) consisting of less than 10(6) DNA molecules and by measuring their hybridization efficiency. We show that the binding rate is 1000 times faster than on a "macroscopic" surface. We also show that the hybridization of a SAM of maximum density DNA is 40% or 4 times the value reported in the literature. These results suggest that the lower values previously reported in the literature can be attributed to incomplete saturation of the surface due to the slower adsorption rate on the "macroscopic" surfaces used.