57 research outputs found
X-ray Spectroscopy of a Rare-Earth Molecular System Measured at the Single Atom Limit in Room Temperature
We investigate the limit of X-ray detection at room temperature on rare-earth
molecular films using lanthanum and a pyridine-based dicarboxamide organic
linker as a model system. Synchrotron X-ray scanning tunneling microscopy is
used to probe the molecules with different coverages on a HOPG substrate.
X-ray-induced photocurrent intensities are measured as a function of molecular
coverage on the sample allowing a correlation of the amount of La ions with the
photocurrent signal strength. X-ray absorption spectroscopy shows cogent M4,5
absorption edges of the lanthanum ion originated by the transitions from the
3d3/2 and 3d5/2 to 4f orbitals. X-ray absorption spectra measured in the
tunneling regime further reveal an X-ray excited tunneling current produced at
the M4,5 absorption edge of La ion down to the ultimate atomic limit at room
temperature.Comment: 19 pages, 4 figure
Triplet-sensitization by lead halide perovskite thin films for near-infrared-to-visible upconversion
Lead halide-based perovskite thin films have attracted great attention due to
the explosive increase in perovskite solar cell efficiencies. The same
optoelectronic properties that make perovskites ideal absorber materials in
solar cells are also beneficial in other light-harvesting applications and make
them prime candidates as triplet sensitizers in upconversion via
triplet-triplet annihilation in rubrene. In this contribution, we take
advantage of long carrier lifetimes and carrier diffusion lengths in perovskite
thin films, their high absorption cross sections throughout the visible
spectrum, as well as the strong spin-orbit coupling owing to the abundance of
heavy atoms to sensitize the upconverter rubrene. Employing bulk perovskite
thin films as the absorber layer and spin-mixer in inorganic/organic
heterojunction upconversion devices allows us to forego the additional
tunneling barrier owing from the passivating ligands required for colloidal
sensitizers. Our bilayer device exhibits an upconversion efficiency in excess
of 3% under 785 nm illumination
Homogenization of Halide Distribution and Carrier Dynamics in Alloyed Organic-Inorganic Perovskites
Perovskite solar cells have shown remarkable efficiencies beyond 22%, through
organic and inorganic cation alloying. However, the role of alkali-metal
cations is not well-understood. By using synchrotron-based nano-X-ray
fluorescence and complementary measurements, we show that when adding RbI
and/or CsI the halide distribution becomes homogenous. This homogenization
translates into long-lived charge carrier decays, spatially homogenous carrier
dynamics visualized by ultrafast microscopy, as well as improved photovoltaic
device performance. We find that Rb and K phase-segregate in highly
concentrated aggregates. Synchrotron-based X-ray-beam-induced current and
electron-beam-induced current of solar cells show that Rb clusters do not
contribute to the current and are recombination active. Our findings bring
light to the beneficial effects of alkali metal halides in perovskites, and
point at areas of weakness in the elemental composition of these complex
perovskites, paving the way to improved performance in this rapidly growing
family of materials for solar cell applications.Comment: updated author metadat
Photoresponse of supramolecular self-assembled networks on graphene–diamond interfaces
Nature employs self-assembly to fabricate the most complex molecularly precise machinery known to man. Heteromolecular, two-dimensional self-assembled networks provide a route to spatially organize different building blocks relative to each other, enabling synthetic molecularly precise fabrication. Here we demonstrate optoelectronic function in a near-to-monolayer molecular architecture approaching atomically defined spatial disposition of all components. The active layer consists of a self-assembled terrylene-based dye, forming a bicomponent supramolecular network with melamine. The assembly at the graphene-diamond interface shows an absorption maximum at 740 nm whereby the photoresponse can be measured with a gallium counter electrode. We find photocurrents of 0.5 nA and open-circuit voltages of 270 mV employing 19 mW cm−2 irradiation intensities at 710 nm. With an ex situ calculated contact area of 9.9 × 102 μm2, an incident photon to current efficiency of 0.6% at 710 nm is estimated, opening up intriguing possibilities in bottom-up optoelectronic device fabrication with molecular resolution
Graphene directed architecture of fine engineered nanostructures with electrochemical applications
Correction:Â Engineering 3D perovskites for photon interconversion applications.
[This corrects the article DOI: 10.1371/journal.pone.0230299.]
Precharging Photon Upconversion: Interfacial Interactions in Solution-Processed Perovskite Upconversion Devices
Recent advances in perovskite-sensitized photon upconversion via triplet-triplet annihilation (TTA) in rubrene have yielded several unanswered questions about the underlying mechanism and processes occurring at the interface. In particular, the near-infrared perovskite emission is not significantly quenched and a rapid reversible photobleach of the upconverted emission can be observed under fairly low excitation densities of 3.2 mW/cm2. In this contribution, we investigate the perovskite/organic interface in more detail and conclude that non-covalent interactions between the organic layer and perovskite result in surface trap passivation. In addition, band bending results in a charge space region at the perovskite/rubrene interface, which precharges the rubrene interface with holes. Upon initial illumination, electrons can rapidly transfer to the excited triplet state of rubrene, followed by efficient TTA upconversion. As the device is continuously illuminated, the precharged holes are consumed and a new equilibrium is reached, resulting in the previously investigated steady-state upconversion efficiency.</p
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