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The ability to robustly and with scalability detect single photons in the visible spectrum with wavelength resolution would transform many imaging applications. Theoretical studies propose an array of carbon nanotubes (CNTs) functionalized with semiconductor quantum dots (QDs) as a physical realization of such photon sensors. In this work, we report approaches to synthesize these CNT-QD nanostructures using DNA as a smart glue to connect CNTs to QDs.

Scanning tunneling spectroscopy (STS) has yielded significant insight into the electronic structure of graphene and other two-dimensional (2D) materials. STS directly measures a fundamental and directly calculable quantity: single particle density of states (SPDOS). Due to experimental setup limitations, however, STS has been unable to explore 2D materials in ultrahigh magnetic fields where electron-electron interactions can drastically change the SPDOS. Recent developments in the assembly of heterostructures composed of graphene and hexagonal boron nitride have enabled a device-based alternative to potentially overcome these roadblocks. Thus far, however, these nascent efforts are incomplete in analyzing and understanding tunneling spectra and havemore » yet to explore graphene at high magnetic fields. Here, we report an experiment at magnetic fields up to 18 T, which uses graphene tunneling field effect transistors (TFETs) to establish a clear benchmark for the measurement and analysis of graphene planar tunneling spectroscopy. We acquire gate tunable tunneling spectra of graphene and then use these data and electrostatic arguments to develop a systematic analysis scheme. This analysis reveals that TFET devices directly probe electronic structure features near and far from the Fermi level. In particular, our study yields identification of the Dirac point and numerous Landau levels as they fill and empty with charge via the application of a gate voltage. Our work demonstrates that TFET devices are a viable platform for directly probing the electronic structure of graphene and other 2D materials in high magnetic fields, where exotic electronic states emerge.« less

Here in this study we investigate the light and heat-induced degradation of methylammonium lead iodide (MAPbI₃) perovskite films in an inert atmosphere to exclude the effect of oxygen and humidity. Films aged under solar intensities started to degrade above 75 °C, while films in the dark degraded at 95 °C. To investigate the temperature-induced degradation mechanism, spectroscopic techniques such as Ultraviolet-Visible (UV–Vis) absorption spectroscopy, X-Ray Diffraction (XRD), Extended X-ray Absorption Fine Structure (EXAFS), and Fourier Transform Infrared (FT-IR) were used. Results show that the films aged under light at 75 °C degraded to a mixture of PbI₂ and metallic Pb.more » In contrast, films aged thermally in the dark, or with light and oxygen, degraded to PbI₂ only. MAPbI₃ solar cells were aged to show the effect of the metallic lead on the charge transfer mechanism« less

Organometal halide perovskites are highly promising materials for photovoltaic applications, yet their rapid degradation remains a significant challenge. Here, the light-induced structural degradation mechanism of methylammonium lead iodide (MAPbI₃) perovskite films and devices is studied in low humidity environment using X-Ray Diffraction, Ultraviolet-Visible (UV-Vis) absorption spectroscopy, Extended X-ray Absorption Fine Structure spectroscopy, Fourier Transform Infrared spectroscopy, and device measurements. Under dry conditions, the perovskite film degrades only in the presence of both light and oxygen, which together induce the formation of halide anions through donation of electrons to the surrounding oxygen. The halide anions generate free radicals that deprotonate themore » methylammonium cation and form the highly volatile CH₃NH₂ molecules that escape and leave pure PbI₂ behind. The device findings show that changes in the local structure at the TiO₂ mesoporous layer occur with light, even in the absence of oxygen, and yet such changes can be prevented by the application of UV blocking layer on the cells. Our results indicate that the stability of mp-TiO₂-MAPbI₃ photovoltaics can be dramatically improved with effective encapsulation that protects the device from UV light, oxygen, and moisture.« less

A Luminescent Solar Concentrator (LSC) greenhouse and an identical control greenhouse were constructed with photovoltaic (PV) cells attached to the roof panels of both structures. The placement and types of PV cells used in the LSC panels were varied for performance comparisons. Solar power generation was monitored continuously for one year, with leading LSC panels exhibiting a 37% increase in power production compared to the reference. The 22.3 m² greenhouse was projected to generate a total of 1342 kWh per year, or 57.4 kWh/m² if it were composed solely of the leading panel of Criss Cross panel design. The LSCmore » panels also showed no signs of degradation throughout the trial demonstrating the material's robustness in field conditions.« less