4 research outputs found
Low-Temperature, Solution-Processed MoO<sub><i>x</i></sub> for Efficient and Stable Organic Solar Cells
Sol–gel processed MoO<sub><i>x</i></sub> (sMoO<sub><i>x</i></sub>) hole-extraction layers for organic
solar
cells are reported. A Bis(2,4-pentanedionato)molybdenum(VI)dioxide/isopropanol
solution is used and only a moderate thermal post deposition treatment
at 150 °C in N<sub>2</sub> ambient is required to achieve sMoO<sub><i>x</i></sub> layers with a high work-function of 5.3
eV. We demonstrate that in P3HT:PC<sub>60</sub>BM organic solar cells
(OSCs) our sMoO<sub><i>x</i></sub> layers lead to a high
filling factor of about 65% and an efficiency of 3.3% comparable to
that of reference devices with thermally evaporated MoO<sub>3</sub> layers (eMoO<sub>3</sub>). At the same time, a substantially improved
stability of the OSCs compared to devices using a PEDOT:PSS hole extraction
layer is evidenced
Stress Management in Thin-Film Gas-Permeation Barriers
Gas diffusion barriers (GDB) are
essential building blocks for the protection of sensitive materials
or devices against ambient gases, like oxygen and moisture. In this
work, we study the mechanics of GDBs processed by atomic layer deposition
(ALD). We demonstrate that a wide range of ALD grown barrier layers
carry intrinsic mechanical tensile stress in the range of 400–500
MPa. In the application of these GDBs on top of organic electronic
devices, we derive a critical membrane force (σ · <i>h</i>)<sub>crit</sub> = 1200 GPaÅ (corresponding to a layer
thickness of about 300 nm) for the onset of cracking and delamination.
At the same time, we evidence that thicker GDBs would be more favorable
for the efficient encapsulation of statistically occurring particle
defects. Thus, to reduce the overall membrane force in this case to
levels below (σ · <i>h</i>)<sub>crit</sub>, we
introduce additional compressively strained layers, e.g., metals or
SiN<sub><i>x</i></sub>. Thereby, highly robust GDBs are
prepared on top of organic light emitting diodes, which do not crack/delaminate
even under damp heat conditions 85 °C/85% rh
Conformal and Highly Luminescent Monolayers of Alq<sub>3</sub> Prepared by Gas-Phase Molecular Layer Deposition
The gas-phase molecular layer deposition
(MLD) of conformal and highly luminescent monolayers of tris(8-hydroxyquinolinato)aluminum
(Alq<sub>3</sub>) is reported. The controlled formation of Alq<sub>3</sub> monolayers is achieved for the first time by functionalization
of the substrate with amino groups, which serve as initial docking
sites for trimethyl aluminum (TMA) molecules binding datively to the
amine. Thereby, upon exposure to 8-hydroxyquinoline (8-HQ), the self-limiting
formation of highly luminescent Alq<sub>3</sub> monolayers is afforded.
The growth process and monolayer formation were studied and verified
by in situ quartz crystal monitoring, optical emission and absorption
spectroscopy, and X-ray photoelectron spectroscopy. The nature of
the MLD process provides an avenue to coat arbitrarily shaped 3D surfaces
and porous structures with high surface areas, as demonstrated in
this work for silica aerogels. The concept presented here paves the
way to highly sensitive luminescent sensors and dye-sensitized metal
oxides for future applications (e.g., in photocatalysis and solar
cells)
Adsorption Behavior of Lysozyme at Titanium Oxide–Water Interfaces
We
present an in situ X-ray reflectivity study of the adsorption
behavior of the protein lysozyme on titanium oxide layers under variation
of different thermodynamic parameters, such as temperature, hydrostatic
pressure, and pH value. Moreover, by varying the layer thickness of
the titanium oxide layer on a silicon wafer, changes in the adsorption
behavior of lysozyme were studied. In total, we determined less adsorption
on titanium oxide compared with silicon dioxide, while increasing
the titanium oxide layer thickness causes stronger adsorption. Furthermore,
the variation of temperature from 20 to 80 °C yields an increase
in the amount of adsorbed lysozyme at the interface. Additional measurements
with variation of the pH value of the system in a region between pH
2 and 12 show that the surface charge of both protein and titanium
oxide has a crucial role in the adsorption process. Further pressure-dependent
experiments between 50 and 5000 bar show a reduction of the amount
of adsorbed lysozyme with increasing pressure