Organic
bulk heterojunction (BHJ) solar cells are a promising alternative
for future clean-energy applications. However, to become attractive
for consumer applications, such as wearable, flexible, or semitransparent
power-generating electronics, they need to be manufactured by high-throughput,
low-cost, large-area-capable printing techniques. However, most research
reported on BHJ solar cells is conducted using spin coating, a single
batch fabrication method, thus limiting the reported results to the
research lab. In this work, we investigate the morphology of solution-sheared
films for BHJ solar cell applications, using the widely studied model
blend P3HT:PCBM. Solution shearing is a coating technique that is
upscalable to industrial manufacturing processes and has demonstrated
to yield record performance organic field-effect transistors. Using
grazing incident small-angle X-ray scattering, grazing incident wide-angle
X-ray scattering, and UV–vis spectroscopy, we investigate the
influence of solvent, film drying time, and substrate temperature
on P3HT aggregation, conjugation length, crystallite orientation,
and PCBM domain size. One important finding of this study is that,
in contrast to spin-coated films, the P3HT molecular orientation can
be controlled by the substrate chemistry, with PEDOT:PSS substrates
yielding face-on orientation at the substrate–film interface,
an orientation highly favorable for organic solar cells.
The supramolecular structure essentially determines the properties of organic thin films. Therefore, it is of utmost importance to understand the influence of molecular structure modifications on supramolecular structure formation. In this article, we demonstrate how to tune molecular orientations of amphiphilic 4-hydroxy thiazole derivatives by means of the Langmuir-Blodgett (LB) technique and how this depends on the length of an alkylic spacer between the thiazole chromophore and the polar anchor group. Therefore, we characterize their corresponding supramolecular structures, thermodynamic, absorption, and fluorescence properties. Particularly, the polarization-dependence of the fluorescence is analyzed to deduce molecular orientations and their possible changes after annealing, i.e., to characterize the thermodynamic stability of the individual solid state phases. Because the investigated thiazoles are amphiphilic, the different solid state phases can be formed and be controlled by means of the Langmuir-Blodgett (LB) technique. This technique also allows to deduce atomistic supramolecular structure motives of the individual solid phases and to characterize their thermodynamic stabilities. Utilizing the LB technique, we demonstrate that subtle molecular changes, like the variation in spacer length, can yield entirely different solid state phases with distinct supramolecular structures and properties.
Processing of 4-alkoxythiazole sulfonamidesviathe Langmuir–Blodgett technique gave an insight into the influence of aggregation on the electro-optical properties of thin films.
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