Thin film solar cells based on Cu(In,Ga)Se2 (CIGS), where just the buffer layer is changed, were fabricated and studied. The effects of two different buffer layers, CdS and ZnxSn1-xOy (ZnSnO), are compared using several characterization techniques. We compared both devices and observe that the ZnSnO-based solar cells have similar values of power conversion efficiency as compared to the cells with CdS buffer layers. The ZnSnO-based devices have higher values in the short-circuit current (Jsc) that compensate for lower values in fill factor (FF) and open circuit voltage (Voc) than CdS based devices. Kelvin probe force microscopy (KPFM) results indicate that CdS provides junctions with slightly higher surface photovoltage (SPV) than ZnSnO, thus explaining the lower Voc potential for the ZnSnO sample. The TEM analysis shows a poly-crystalline ZnSnO layer and we have not detected any strong evidence of diffusion of Zn or Sn into the CIGS. From the photoluminescence measurements, we concluded that both samples are being affected by fluctuating potentials, although this effect is higher for the CdS sample.
The iridescent wings of the Chalcopterix rutilans damselfly (Rambur) (Odonata, Polythoridae) are investigated with focused ion beam/scanning electron microscopy, transmission electron microscopy, and time-of-flight secondary ion mass spectrometry. The electron microscopy images reveal a natural photonic crystal as the source of the varying colors. The photonic crystal has a consistent number and thickness (∼195 nm) of the repeat units on the ventral side of the wing, which is consistent with the red color visible from the bottom side of the wing in all regions. The dorsal side of the wing shows strong color variations ranging from red to blue depending on the region. In the electron microscopy images, the dorsal side of the wing exhibits varied number and thicknesses of the repeat units. The repeat unit spacings for the red, yellow/green, and blue regions are approximately 195, 180, and 145 nm, respectively. Three-dimensional analysis of the natural photonic crystals by time-of-flight secondary ion mass spectrometry reveals that changes in the relative levels of Na, K, and eumelanin are responsible for the varying dielectric constant needed to generate the photonic crystal. The photonic crystal also appears to be assembled with a chemical tricomponent layer structure due to the enhancement of the CHN species at every other interface between the high/low dielectric constant layers.
The aim of this work is to determine the varying dielectric constant of a biological nanostructured system via electrostatic force microscopy (EFM) and to show how this method is useful to study natural photonic crystals. We mapped the dielectric constant of the cross section of the posterior wing of the damselfly Chalcopteryx rutilans with nanometric resolution. We obtained structural information on its constitutive nanolayers and the absolute values of their dielectric constant. By relating the measured profile of the static dielectric constant to the profile of the refractive index in the visible range, combined with optical reflectance measurements and simulation, we were able to describe the origin of the strongly iridescent wing colors of this Amazonian rainforest damselfly. The method we demonstrate here should be useful for the study of other biological nanostructured systems.
In this work we attempt to directly observe anisotropic partial relaxation of epitaxial InAs islands using transmission electron microscopy (TEM) and synchrotron x-ray diffraction on a 15 nm thick InAs:GaAs nanomembrane. We show that under such conditions TEM provides improved real-space statistics, allowing the observation of partial relaxation processes that were not previously detected by other techniques or by usual TEM cross section images. Besides the fully coherent and fully relaxed islands that are known to exist above previously established critical thickness, we prove the existence of partially relaxed islands, where incomplete 60° half-loop misfit dislocations lead to a lattice relaxation along one of the 〈110〉 directions, keeping a strained lattice in the perpendicular direction. Although individual defects cannot be directly observed, their implications to the resulting island registry are identified and discussed within the frame of half-loops propagations.
High-quality CuInSe 2 (CISe) nanowires have been prepared by a one-step evaporation process. The presented growth process results in a composite material consisting of CISe NWs on top of a polycrystalline CISe base layer. The nanowires were extensively characterized by transmission electron microscopy, confirming their composition and atomic-scale crystal structure with a very low number of structural defects. From these analyses, we infer that the growth axis is along the [111] direction. The polycrystalline base layer has a tetragonal chalcopyrite structure and is optically active as confirmed by X-ray diffraction and photoluminescence (PL) analysis, respectively. Potential applications of this composite CISe NW/base-layer material for photovoltaic energy conversion are supported by the reduced reflectivity of the material and its strong PL intensity. The presented growth method is based on elemental evaporation under vacuum conditions, which makes the process compatible with the fabrication of photovoltaic devices.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.