5 research outputs found
Semitransparent Organic Light Emitting Diodes with Bidirectionally Controlled Emission
Semitransparent OLEDs
are a candidate for large-area eco-friendly light sources that can
be integrated into building facades, suggesting colorful windows that
become luminescent if the OLED is switched on. However, since the
light is emitted in two directions, smart light engineering has to
be implemented to direct the light into a preferred direction and
to prevent for instance huge energetic losses to the outside of a
building. We introduce an unprecedented device architecture, composed
of a dielectric mirror attached to a semitransparent OLED. Such a
system features a dual functionality that depends on the viewing direction:
changing the color perception and/or enhancing the light directionality
while still preserving a high overall device transparency. First,
we motivate the potential of this concept with a theoretical study,
showing that broad modifications in the color range can be realized
via device optimization and that the maximum possible emission enhancement
of the OLED is limited only by the transparency of the interfacial
layers and the electrodes. Then, experimental investigations with
a semitransparent yellow OLED (transparency = 58.2%) in combination
with six different dielectric mirrors validate the theoretical results.
Retaining the same color perception, up to 80% of the total emitted
light can be directed toward one side while the color is modified
at the other side of the device stack. Here, modifications from yellow
to purple to dark or light blue can be realized
Graphene-Supported Pd Nanoclusters Probed by Carbon Monoxide Adsorption
The
adsorption of CO on graphene-supported Pd nanoparticles was studied
in situ with high-resolution synchrotron-based X-ray photoelectron
spectroscopy. At 150 K, CO adsorbs mainly in bridge and 3-fold-hollow
sites. The nanoparticles are considered as a mixture of low-index
facets. The variation of the amount of deposited Pd revealed identical
CO adsorption behavior for all investigated cases, confirming a similar
average cluster size over a wide range of Pd coverages. The desorption
characteristics were studied with temperature-programmed XPS. The
observed desorption maxima at 230 and 430 K are in good agreement
with temperature-programmed desorption data on stepped Pd single crystals.
At 500 K, CO is completely desorbed from the Pd clusters. The adsorption
and desorption of CO are found to be not fully reversible as the Pd
particles undergo restructuring upon heating
Coloring Semitransparent Perovskite Solar Cells <i>via</i> Dielectric Mirrors
While
perovskite-based semitransparent solar cells for window applications
show competitive levels of transparency and efficiency compared to
organic photovoltaics, the color perception of the perovskite films
is highly restricted because band gap engineering results in losses
in power conversion efficiencies. To overcome the limitation in visual
aesthetics, we combined semitransparent perovskite solar cells with
dielectric mirrors. This approach enables one to tailor the device
appearance to almost any desired color and simultaneously offers additional
light harvesting for the solar cell. In the present work, opto-electrical
effects are investigated through quantum efficiency and UV-to-visible
spectroscopic measurements. Likewise, a detailed chromaticity analysis,
featuring the transmissive and reflective color perception of the
device including the mirror, from both sides and in different illumination
conditions, is presented and analyzed. Photocurrent density enhancement
of up to 21% along with overall device transparency values of up to
31% (4.2% efficiency) is demonstrated for cells showing a colored
aesthetic appeal. Finally, a series of simulations emulating the device
chromaticity, transparency, and increased photocurrent density as
a function of the photoactive layer thickness and the design wavelength
of the dielectric mirror are presented. Our simulations and their
experimental validation enabled us to establish the design rules that
consider the color efficiency/transparency interplay for real applications
Graphene-Templated Growth of Pd Nanoclusters
Graphene grown on Rh(111) was used
as a template for the growth
of Pd nanoclusters. Using high-resolution synchrotron radiation-based
X-ray photoelectron spectroscopy, we studied the deposition of Pd
on corrugated graphene in situ. From the XP spectra, we deduce a cluster-by-cluster
growth mode. The formation of clusters with 3 nm diameter was confirmed
by low-temperature scanning tunneling microscopy measurements. The
investigation of the thermal stability of the Pd particles showed
three characteristic temperature regimes: Up to 550 K restructuring
of the particles takes place, between 550 and 750 K the clusters coalesce
into larger agglomerates, and finally between 750 and 900 K Pd intercalates
between the graphene layer and the Rh surface
Interface Engineering of Perovskite Hybrid Solar Cells with Solution-Processed Perylene–Diimide Heterojunctions toward High Performance
Perovskite hybrid solar cells (pero-HSCs)
were demonstrated to
be among the most promising candidates within the emerging photovoltaic
materials with respect to their power conversion efficiency (PCE)
and inexpensive fabrication. Further PCE enhancement mainly relies
on minimizing the interface losses via interface engineering and the
quality of the perovskite film. Here, we demonstrate that the PCEs
of pero-HSCs are significantly increased to 14.0% by incorporation
of a solution-processed perylene–diimide (PDINO) as cathode
interface layer between the [6,6]-phenyl-C61 butyric acid methyl ester
(PCBM) layer and the top Ag electrode. Notably, for PDINO-based devices,
prominent PCEs over 13% are achieved within a wide range of the PDINO
thicknesses (5–24 nm). Without the PDINO layer, the best PCE
of the reference PCBM/Ag device was only 10.0%. The PCBM/PDINO/Ag
devices also outperformed the PCBM/ZnO/Ag devices (11.3%) with the
well-established zinc oxide (ZnO) cathode interface layer. This enhanced
performance is due to the formation of a highly qualitative contact
between PDINO and the top Ag electrode, leading to reduced series
resistance (<i>R</i><sub>s</sub>) and enhanced shunt resistance
(<i>R</i><sub>sh</sub>) values. This study opens the door
for the integration of a new class of easily-accessible, solution-processed
high-performance interfacial materials for pero-HSCs