Low-Temperature, Solution-Processed MoO_<i>x</i> for Efficient and Stable Organic Solar Cells

Sol–gel processed MoO_<i>x</i> (sMoO_<i>x</i>) 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 N₂ ambient is required to achieve sMoO_<i>x</i> layers with a high work-function of 5.3 eV. We demonstrate that in P3HT:PC₆₀BM organic solar cells (OSCs) our sMoO_<i>x</i> 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 MoO₃ layers (eMoO₃). 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>)_crit = 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>)_crit, we introduce additional compressively strained layers, e.g., metals or SiN_<i>x</i>. 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 Alq₃ 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 (Alq₃) is reported. The controlled formation of Alq₃ 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 Alq₃ 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