This work seeks to understand the role of structural defects in the polymer chain on the crystallization and crystal lattice of π-conjugated polymers, which is crucial for being able to predict morphology and performance of πconjugated polymer active layers in optoelectronic devices. Such a predictive understanding of device performance has been difficult to establish; however, in this work self-assembled nanowires of poly(3-hexylthiophene) (P3HT) are used to reduce analytical contributions from amorphous domains, allowing a more direct path to probe the effect of regio-defects and chain end-groups on the crystal lattice. By use of P3HT synthesized to have precisely varied defect concentrations, it was demonstrated that these defects can be incorporated into the crystal lattice, particularly regio-defects. However, this incorporation comes with a decrease in electronic properties as a result of diminished short-range order and lattice distortions. Bulky end-groups can be incorporated into the lattice, although there is a preference for their exclusion. However, the use of π−π interacting end-groups, such as toluene, is shown to mitigate disruption to the crystal lattice that results from the endgroup incorporation. In fact, π−π interacting end-groups seem to promote long-range order and crystal growth. Additionally, it was found that tuning the molecular weight of the polymer to an integer multiple of the observed width of the crystal lamellae, l c , can increase the enthalpy of fusion, ΔH f , for the crystal by as much as 20% by facilitating the exclusion of end-groups from the crystal lattice. These results demonstrate that π-conjugated polymer crystal lattices have a high tolerance for disruptions to short-range order so that long-range order can be preserved. In addition, this study underscores the need to consider structural defects in polymer chains and their consequences on the crystal lattice during the design and implementation of π-conjugated polymers.
We
describe an open-source and widely adaptable Python library
that recognizes morphological features and domains in images collected
via scanning probe microscopy. π-Conjugated polymers (CPs) are
ideal for evaluating the Materials Morphology Python (m2py) library
because of their wide range of morphologies and feature sizes. Using
thin films of nanostructured CPs, we demonstrate the functionality
of a general m2py workflow. We apply numerical methods to enhance
the signals collected by the scanning probe, followed by Principal
Component Analysis (PCA) to reduce the dimensionality of the data.
Then, a Gaussian Mixture Model segments every pixel in the image into
phases, which have similar material-property signals. Finally, the
phase-labeled pixels are grouped and labeled as morphological domains
using either connected components labeling or persistence watershed
segmentation. These tools are adaptable to any scanning probe measurement,
so the labels that m2py generates will allow researchers to individually
address and analyze the identified domains in the image. This level
of control, allows one to describe the morphology of the system using
quantitative and statistical descriptors such as the size, distribution,
and shape of the domains. Such descriptors will enable researchers
to quantitatively track and compare differences within and between
samples.
Mass transport is performance‐defining across energy storage devices, often causing limitations at high current rates. To optimize and balance the device‐scale energy and power density for a given energy storage demand, tailored electrode architectures with precisely controllable phase dimensions are needed in combination with low‐tortuosity channels that maximize the geometric component of diffusion and species flux. A material‐agnostic nonequilibrium soft‐matter process is reported to fabricate free‐standing inorganic composite electrodes with adjustable thicknesses of 100s of µm, featuring straight and accessible channels ranging in diameter from 5–30 µm, coupled with tunable material‐to‐pore ratios. Such architected anode and cathode electrodes exhibit electrochemical and architectural stability over extended cycling in a full‐cell battery. Further, mass‐transport constraints appear at high current densities, and the lithiation step is identified as rate‐performance limiting, a result of insufficient lithium‐ion supply and concentration polarization. The results demonstrate the need for and feasibility of tailored electrode architectures where dimensional ratios between low‐tortuosity channels, the charge‐storing matrix, and electrode thickness are tunable to meet coupled power and energy‐storage requirements.
Functional thin films and interphases are omnipresent in modern technology and often determine the performance and life-time of devices. However, existing coating strategies are incompatible with emerging mesoscaled 3D architected...
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