15 research outputs found
Correlating the Efficiency and Nanomorphology of Polymer Blend Solar Cells Utilizing Resonant Soft X-ray Scattering
Enhanced scattering contrast afforded by resonant soft X-ray scattering (R-SoXS) is used to probe the nanomorphology of all-polymer solar cells based on blends of the donor polymer poly(3-hexylthiophene) (P3HT) with either the acceptor polymer poly((9,9-dioctylfluorene)-2,7-diyl-<i>alt</i>-[4,7-bis(3-hexylthien-5-yl)-2,1,3-benzothiadiazole]-2′,2″-diyl) (F8TBT) or poly([<i>N</i>,<i>N</i>′-bis(2-octyldodecyl)-11-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-<i>alt</i>-5,5′-(2,2′-12-bithiophene)) (P(NDI2OD-T2)). Both P3HT:F8TBT and P3HT:P(NDI2OD-T2) blends processed from chloroform with subsequent annealing exhibit complicated morphologies with a hierarchy of phase separation. A bimodal distribution of domain sizes is observed for P3HT:P(NDI2OD-T2) blends with small domains of size ∼5–10 nm that evolve with annealing and larger domains of size ∼100 nm that are insensitive to annealing. P3HT:F8TBT blends in contrast show a broader distribution of domain size but with the majority of this blend structured on the 10 nm length scale. For both P3HT:P(NDI2OD-T2) and P3HT:F8TBT blends, an evolution in device performance is observed that is correlated with a coarsening and purification of domains on the 5–10 nm length scale. Grazing-incidence wide-angle X-ray scattering (GI-WAXS) is also employed to probe material crystallinity, revealing P(NDI2OD-T2) crystallites 25–40 nm in thickness that are embedded in the larger domains observed by R-SoXS. A higher degree of P3HT crystallinity is also observed in blends with P(NDI2OD-T2) compared to F8TBT with the propensity of the polymers to crystallize in P3HT:P(NDI2OD-T2) blends hindering the structuring of morphology on the sub-10 nm length scale. This work also underscores the complementarity of R-SoXS and GI-WAXS, with R-SoXS measuring the size of compositionally distinguishable domains and GI-WAXS providing information regarding crystallinity and crystallite thickness
Solution-Phase Conformation and Dynamics of Conjugated Isoindigo-Based Donor–Acceptor Polymer Single Chains
Conjugated polymers
are the key material in thin-film organic optoelectronic
devices due to the versatility of these molecules combined with their
semiconducting properties. A molecular-scale understanding of conjugated
polymers is important to the optimization of the thin-film morphology.
We examine the solution-phase behavior of conjugated isoindigo-based
donor–acceptor polymer single chains of various chain lengths
using atomistic molecular dynamics simulations. Our simulations elucidate
the transition from a rod-like to a coil-like conformation from an
analysis of normal modes and persistence length. In addition, we find
another transition based on the solvent environment, contrasting the
coil-like conformation in a good solvent with a globule-like conformation
in a poor solvent. Overall, our results provide valuable insights
into the transition between conformational regimes for conjugated
polymers as a function of both the chain length and the solvent environment,
which will help to accurately parametrize higher level models
Microstructural Evolution of the Thin Films of a Donor–Acceptor Semiconducting Polymer Deposited by Meniscus-Guided Coating
Crucial to the development
and refinement of organic electronics
is a fundamental understanding of how deposition processes affect
the active material’s resulting microstructure in the thin
film. Meniscus-guided coating (MGC) methods are attractive because
of their amenability to high-throughput, industrially relevant continuous
processes like roll-to-roll deposition, but the mechanism of solid
film formation has not been elucidated and is valuable for the precise
control of thin-film morphology and thus ultimate device performance.
In this work, we investigate the microstructural evolution of thin
films of a diketopyrrolopyrrole–terthiophene donor–acceptor
polymer semiconductor using both <i>in situ</i> and <i>ex situ</i> X-ray diffraction methods. On the basis of a comparison
of disorder between the film bulk and the top surface and a depth
profiling of the out-of-plane orientation of crystallites, we find
that faster coating speeds introduce more disorder into the resulting
films because the stochastic nucleation of disordered crystallites
at the meniscus air–liquid interface becomes more dominant
than substrate-mediated nucleation. Our results suggest that there
exist three separate deposition regimesnamely the shear-dominate,
disorder-dominate, and Landau–Levich–Derjaguin regimesrevealed
by observing both polymer alignment via dry film thickness and optical
dichroism, a property sensitive to the flow and shear fields. At low
coating speeds, the shear strain imparted upon the solution directly
induces polymer alignment, causing an increase in dichroism as a function
of coating speed. When solvent evaporation becomes too rapid as coating
speeds increase, a decrease in the dichroic ratio is observed before
the classical Landau–Levich–Derjaguin regime occurs
at the highest coating speeds, resulting in isotropic films. The preservation
of out-of-plane crystalline texture throughout the thickness of the
films is seen only for lower coating speeds, and a study of different
deposition temperatures similarly indicates that the lower overall
solvent evaporation is conducive to this process. Increased paracrystalline
disorder (i.e., peak broadening) is observed by grazing-incidence
wide-angle X-ray diffraction at the top interface of the dry films
and at higher coating speeds. Together, these results indicate that
more rapid solvent evaporation at higher coating speeds causes increased
disorder, which can cause the nucleation of misaligned crystallites,
affect the dichroic ratio, and may frustrate the alignment of polymer
molecules in the amorphous regions of the film. Because the polymer
studied and the deposition technique used are representative models,
these results are likely general for aggregating, semicrystalline
donor–acceptor polymers deposited with MGC
Solution-Phase Conformation and Dynamics of Conjugated Isoindigo-Based Donor–Acceptor Polymer Single Chains
Conjugated polymers
are the key material in thin-film organic optoelectronic
devices due to the versatility of these molecules combined with their
semiconducting properties. A molecular-scale understanding of conjugated
polymers is important to the optimization of the thin-film morphology.
We examine the solution-phase behavior of conjugated isoindigo-based
donor–acceptor polymer single chains of various chain lengths
using atomistic molecular dynamics simulations. Our simulations elucidate
the transition from a rod-like to a coil-like conformation from an
analysis of normal modes and persistence length. In addition, we find
another transition based on the solvent environment, contrasting the
coil-like conformation in a good solvent with a globule-like conformation
in a poor solvent. Overall, our results provide valuable insights
into the transition between conformational regimes for conjugated
polymers as a function of both the chain length and the solvent environment,
which will help to accurately parametrize higher level models
Solution-Phase Conformation and Dynamics of Conjugated Isoindigo-Based Donor–Acceptor Polymer Single Chains
Conjugated polymers
are the key material in thin-film organic optoelectronic
devices due to the versatility of these molecules combined with their
semiconducting properties. A molecular-scale understanding of conjugated
polymers is important to the optimization of the thin-film morphology.
We examine the solution-phase behavior of conjugated isoindigo-based
donor–acceptor polymer single chains of various chain lengths
using atomistic molecular dynamics simulations. Our simulations elucidate
the transition from a rod-like to a coil-like conformation from an
analysis of normal modes and persistence length. In addition, we find
another transition based on the solvent environment, contrasting the
coil-like conformation in a good solvent with a globule-like conformation
in a poor solvent. Overall, our results provide valuable insights
into the transition between conformational regimes for conjugated
polymers as a function of both the chain length and the solvent environment,
which will help to accurately parametrize higher level models
A Wide Band Gap Polymer with a Deep Highest Occupied Molecular Orbital Level Enables 14.2% Efficiency in Polymer Solar Cells
To simultaneously
achieve low photon energy loss (<i>E</i><sub>loss</sub>)
and broad spectral response, the molecular design
of the wide band gap (WBG) donor polymer with a deep HOMO level is
of critical importance in fullerene-free polymer solar cells (PSCs).
Herein, we developed a new benzodithiophene unit, i.e., DTBDT-EF,
and conducted systematic investigations on a WBG DTBDT-EF-based donor
polymer, namely, PDTB-EF-T. Due to the synergistic electron-withdrawing
effect of the fluorine atom and ester group, PDTB-EF-T exhibits a
higher oxidation potential, i.e., a deeper HOMO level (ca. −5.5
eV) than most well-known donor polymers. Hence, a high open-circuit
voltage of 0.90 V was obtained when paired with a fluorinated small
molecule acceptor (IT-4F), corresponding to a low <i>E</i><sub>loss</sub> of 0.62 eV. Furthermore, side-chain engineering demonstrated
that subtle side-chain modulation of the ester greatly influences
the aggregation effects and molecular packing of polymer PDTB-EF-T.
With the benefits of the stronger interchain π–π
interaction, the improved ordering structure, and thus the highest
hole mobility, the most symmetric charge transport and reduced recombination
are achieved for the linear decyl-substituted PDTB-EF-T (P2)-based
PSCs, leading to the highest short-circuit current density and fill
factor (FF). Due to the high Flory–Huggins interaction parameter
(χ), surface-directed phase separation occurs in the P2:IT-4F
blend, which is supported by X-ray photoemission spectroscopy results
and cross-sectional transmission electron microscope images. By taking
advantage of the vertical phase distribution of the P2:IT-4F blend,
a high power conversion efficiency (PCE) of 14.2% with an outstanding
FF of 0.76 was recorded for inverted devices. These results demonstrate
the great potential of the DTBDT-EF unit for future organic photovoltaic
applications
Compact Roll-to-Roll Coater for in Situ X‑ray Diffraction Characterization of Organic Electronics Printing
We describe a compact roll-to-roll
(R2R) coater that is capable of tracking the crystallization process
of semiconducting polymers during solution printing using X-ray scattering
at synchrotron beamlines. An improved understanding of the morphology
evolution during the solution-processing of organic semiconductor
materials during R2R coating processes is necessary to bridge the
gap between “lab” and “fab”. The instrument
consists of a vacuum chuck to hold the flexible plastic substrate
uniformly flat for grazing incidence X-ray scattering. The time resolution
of the drying process that is achievable can be tuned by controlling
two independent motor speeds, namely, the speed of the moving flexible
substrate and the speed of the printer head moving in the opposite
direction. With this novel design, we are able to achieve a wide range
of drying time resolutions, from tens of milliseconds to seconds.
This allows examination of the crystallization process over either
fast or slow drying processes depending on coating conditions. Using
regioregular poly(3-hexylthiophene-2,5-diyl) (P3HT) and phenyl-C61-butyric
acid methyl ester (PCBM) inks based on two different solvents as a
model system, we demonstrate the capability of our in situ R2R printing
tool by observing two distinct crystallization processes for inks
drying from the solvents with different boiling points (evaporation
rates). We also observed delayed on-set point for the crystallization
of P3HT polymer in the 1:1 P3HT/PCBM BHJ blend, and the inhibited
crystallization of the P3HT during the late stage of the drying process
Quadruple H‑Bonding Cross-Linked Supramolecular Polymeric Materials as Substrates for Stretchable, Antitearing, and Self-Healable Thin Film Electrodes
Herein,
we report a de novo chemical design of supramolecular polymer materials
(SPMs-<b>1</b>–<b>3</b>) by condensation polymerization,
consisting of (i) soft polymeric chains (polytetramethylene glycol
and tetraethylene glycol) and (ii) strong and reversible quadruple
H-bonding cross-linkers (from 0 to 30 mol %). The former contributes
to the formation of the soft domain of the SPMs, and the latter furnishes
the SPMs with desirable mechanical properties, thereby producing soft,
stretchable, yet tough elastomers. The resulting SPM-<b>2</b> was observed to be highly stretchable (up to 17 000% strain),
tough (fracture energy ∼30 000 J/m<sup>2</sup>), and
self-healing, which are highly desirable properties and are superior
to previously reported elastomers and tough hydrogels. Furthermore,
a gold, thin film electrode deposited on this SPM substrate retains
its conductivity and combines high stretchability (∼400%),
fracture/notch insensitivity, self-healing, and good interfacial adhesion
with the gold film. Again, these properties are all highly complementary
to commonly used polydimethylsiloxane-based thin film metal electrodes.
Last, we proceed to demonstrate the practical utility of our fabricated
electrode via both in vivo and in vitro measurements of electromyography
signals. This fundamental understanding obtained from the investigation
of these SPMs will facilitate the progress of intelligent soft materials
and flexible electronics
Quadruple H‑Bonding Cross-Linked Supramolecular Polymeric Materials as Substrates for Stretchable, Antitearing, and Self-Healable Thin Film Electrodes
Herein,
we report a de novo chemical design of supramolecular polymer materials
(SPMs-<b>1</b>–<b>3</b>) by condensation polymerization,
consisting of (i) soft polymeric chains (polytetramethylene glycol
and tetraethylene glycol) and (ii) strong and reversible quadruple
H-bonding cross-linkers (from 0 to 30 mol %). The former contributes
to the formation of the soft domain of the SPMs, and the latter furnishes
the SPMs with desirable mechanical properties, thereby producing soft,
stretchable, yet tough elastomers. The resulting SPM-<b>2</b> was observed to be highly stretchable (up to 17 000% strain),
tough (fracture energy ∼30 000 J/m<sup>2</sup>), and
self-healing, which are highly desirable properties and are superior
to previously reported elastomers and tough hydrogels. Furthermore,
a gold, thin film electrode deposited on this SPM substrate retains
its conductivity and combines high stretchability (∼400%),
fracture/notch insensitivity, self-healing, and good interfacial adhesion
with the gold film. Again, these properties are all highly complementary
to commonly used polydimethylsiloxane-based thin film metal electrodes.
Last, we proceed to demonstrate the practical utility of our fabricated
electrode via both in vivo and in vitro measurements of electromyography
signals. This fundamental understanding obtained from the investigation
of these SPMs will facilitate the progress of intelligent soft materials
and flexible electronics
Quadruple H‑Bonding Cross-Linked Supramolecular Polymeric Materials as Substrates for Stretchable, Antitearing, and Self-Healable Thin Film Electrodes
Herein,
we report a de novo chemical design of supramolecular polymer materials
(SPMs-<b>1</b>–<b>3</b>) by condensation polymerization,
consisting of (i) soft polymeric chains (polytetramethylene glycol
and tetraethylene glycol) and (ii) strong and reversible quadruple
H-bonding cross-linkers (from 0 to 30 mol %). The former contributes
to the formation of the soft domain of the SPMs, and the latter furnishes
the SPMs with desirable mechanical properties, thereby producing soft,
stretchable, yet tough elastomers. The resulting SPM-<b>2</b> was observed to be highly stretchable (up to 17 000% strain),
tough (fracture energy ∼30 000 J/m<sup>2</sup>), and
self-healing, which are highly desirable properties and are superior
to previously reported elastomers and tough hydrogels. Furthermore,
a gold, thin film electrode deposited on this SPM substrate retains
its conductivity and combines high stretchability (∼400%),
fracture/notch insensitivity, self-healing, and good interfacial adhesion
with the gold film. Again, these properties are all highly complementary
to commonly used polydimethylsiloxane-based thin film metal electrodes.
Last, we proceed to demonstrate the practical utility of our fabricated
electrode via both in vivo and in vitro measurements of electromyography
signals. This fundamental understanding obtained from the investigation
of these SPMs will facilitate the progress of intelligent soft materials
and flexible electronics