7 research outputs found
Water as Origin of Hysteresis in Zinc Tin Oxide Thin-Film Transistors
The hysteresis behavior of transparent zinc tin oxide
(ZTO) thin
film transistors (TFTs) is identified to be a result of short-term
bias stress induced by the measurement. The related density of shallow
defect states can be adjusted by the amount of water in the ambient.
Time-resolved studies of the TFTs under varied ambient demonstrate
that hysteresis can be immediately switched on and off by the adsorption
and desorption of water, respectively. These findings are expected
to be of general importance also for other oxide-based TFTs
Polyanionic, Alkylthiosulfate-Based Thiol Precursors for Conjugated Polymer Self-Assembly onto Gold and Silver
Anionic, conjugated thiophene- and
fluorene-based polyelectrolytes with alkylthiosulfate side chains
undergo hydrolysis under formation of alkylthiol and dialkyldisulfide
functions. The hydrolysis products can be deposited onto gold or silver
surfaces by self-assembly from solutions of the anionic conjugated
polyelectrolyte (CPE) precursors in polar solvents such as methanol.
This procedure allows solution-based surface modifications of gold
and silver electrodes using environmentally friendly solvents and
enables the formation of conjugated polymer bilayers. The herein presented
alkylĀthiosulfate-substituted CPEs are promising candidates for
increasing the work function of gold and silver electrodes thus improving
hole injection from such electrode assemblies into organic semiconductors
Spatial Atmospheric Pressure Atomic Layer Deposition of Tin Oxide as an Impermeable Electron Extraction Layer for Perovskite Solar Cells with Enhanced Thermal Stability
Despite
the notable success of hybrid halide perovskite-based solar cells,
their long-term stability is still a key-issue. Aside from optimizing
the photoactive perovskite, the cell design states a powerful lever
to improve stability under various stress conditions. Dedicated electrically
conductive diffusion barriers inside the cell stack, that counteract
the ingress of moisture and prevent the migration of corrosive halogen
species, can substantially improve ambient and thermal stability.
Although atomic layer deposition (ALD) is excellently suited to prepare
such functional layers, ALD suffers from the requirement of vacuum
and only allows for a very limited throughput. Here, we demonstrate
for the first time spatial ALD-grown SnO<i><sub>x</sub></i> at atmospheric pressure as impermeable electron extraction layers
for perovskite solar cells. We achieve optical transmittance and electrical
conductivity similar to those in SnO<i><sub>x</sub></i> grown
by conventional vacuum-based ALD. A low deposition temperature of
80 Ā°C and a high substrate speed of 2.4 m min<sup>ā1</sup> yield SnO<i><sub>x</sub></i> layers with a low water vapor
transmission rate of ā¼10<sup>ā4</sup> gm<sup>ā2</sup> day<sup>ā1</sup> (at 60 Ā°C/60% RH). Thereby, in perovskite
solar cells, dense hybrid Al:ZnO/SnO<i><sub>x</sub></i> electron
extraction layers are created that are the key for stable cell characteristics
beyond 1000 h in ambient air and over 3000 h at 60 Ā°C. Most notably,
our work of introducing spatial ALD at atmospheric pressure paves
the way to the future roll-to-roll manufacturing of stable perovskite
solar cells
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 trisĀ(8-hydroxyquinolinato)Āaluminum
(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)