15 research outputs found
Cooptimization of Adhesion and Power Conversion Efficiency of Organic Solar Cells by Controlling Surface Energy of Buffer Layers
Here, we demonstrate
the cooptimization of the interfacial fracture energy and power conversion
efficiency (PCE) of polyÂ[<i>N</i>-9′-heptadecanyl-2,7-carbazole-<i>alt</i>-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)]
(PCDTBT)-based organic solar cells (OSCs) by surface treatments of
the buffer layer. The investigated surface treatments of the buffer
layer simultaneously changed the crack path and interfacial fracture
energy of OSCs under mechanical stress and the work function of the
buffer layer. To investigate the effects of surface treatments, the
work of adhesion values were calculated and matched with the experimental
results based on the Owens–Wendt model. Subsequently, we fabricated
OSCs on surface-treated buffer layers. In particular, ZnO layers treated
with polyÂ[(9,9-bisÂ(3′-(<i>N</i>,<i>N</i>-dimethylÂamino)Âpropyl)-2,7-fluorene)-<i>alt</i>-2,7-(9,9-dioctylfluorene)]
(PFN) simultaneously satisfied the high mechanical reliability and
PCE of OSCs by achieving high work of adhesion and optimized work
function
Important Role of Additive in Morphology of Stretchable Electrode for Highly Intrinsically Stable Organic Photovoltaics
Developing intrinsically stretchable organic photovoltaics
(IS-OPVs)
is crucial for serving as power sources in future portable and wearable
electronics. PEDOT:PSS is most commonly used to prepare highly conductive,
transparent electrodes with high stretchability. The mechanical properties
of PEDOT:PSS films are significantly affected by their morphology,
which is primarily determined by the processing additives used. We
investigate the effects of two additives, poly(ethylene glycol) (PEG)
and (3-glycidyloxypropyl)Âtrimethoxysilane (GOPS), on the stretchability
of the electrode. The PEG additive forms hydrogen bonds with sulfonyl
groups of PSS without significant interaction among itself, which
releases mechanical stress in the PSS-rich region of the PEDOT:PSS
films. On the other hand, the GOPS additive not only forms hydrogen
bonds with PSS but also undergoes a chemical reaction to create a
cross-linked structure within the film, which effectively enhances
the stretchable properties of the PEDOT:PSS film. In addition, the
GOPS promotes a more hydrophilic surface compared to PEG, resulting
in improved adhesion to the upper layer in IS-OPV devices. This improves
the stretchability of IS-OPV devices, as well as their solar cell
performance. We demonstrate IS-OPVs that are prepared using GOPS by
a non-spin-coating method and these devices exhibit higher performance
compared with PEG-based counterparts. Furthermore, the GOPS based
IS-OPV shows significantly improved mechanical stability, enabling
it to retain 90% of its initial efficiency when subjected to 20%
strain
Silver Nanowire/Carbon Sheet Composites for Electrochemical Syngas Generation with Tunable H<sub>2</sub>/CO Ratios
Generating
syngas (H<sub>2</sub> and CO mixture) from electrochemically
reduced CO<sub>2</sub> in an aqueous solution is one of the sustainable
strategies utilizing atmospheric CO<sub>2</sub> in value-added products.
However, a conventional single-component metal catalyst, such as Ag,
Au, or Zn, exhibits potential-dependent CO<sub>2</sub> reduction selectivity,
which could result in temporal variation of syngas composition and
limit its use in large-scale electrochemical syngas production. Herein,
we demonstrate the use of Ag nanowire (NW)/porous carbon sheet composite
catalysts in the generation of syngas with tunable H<sub>2</sub>/CO
ratios having a large potential window to resist power fluctuation.
These Ag NW/carbon sheet composite catalysts have a potential window
increased by 10 times for generating syngas with the proper H<sub>2</sub>/CO ratio (1.7–2.15) for the Fischer–Tropsch
process and an increased syngas production rate of about 19 times
compared to that of a Ag foil. Additionally, we tuned the H<sub>2</sub>/CO ratio from ∼2 to ∼10 by adjusting only the quantity
of the Ag NWs under the given electrode potential. We believe that
our Ag NW/carbon sheet composite provides new possibilities for designing
electrode structures with a large potential window and controlled
CO<sub>2</sub> reduction products in aqueous solutions
Mechanical Properties of Polymer–Fullerene Bulk Heterojunction Films: Role of Nanomorphology of Composite Films
This
paper reports the tensile properties and fracture mechanism
of PTB7:PC<sub>71</sub>BM bulk heterojunction (BHJ) films as a function
of composition mixing ratio. An increased concentration of fullerene
makes the BHJ films stiffer and more brittle, and fracture occurs
along aggregated fullerene domain boundaries. The tensile strength
is maximized at a polymer–fullerene content ratio of 1:1. Furthermore,
an additive, 1,8-diiodoctane (DIO), in the films induces fine nanomorphology,
which increases the stiffness and strength and reduces the ductility
of the films further. This is especially true under a high PC<sub>71</sub>BM load due to the expanded interfacial surface areas between
the PC<sub>71</sub>BM and PTB7 polymer domains. The photovoltaic performance
of the BHJ films on polydimethylsiloxane (PDMS) substrates after tensile
stretching cycles is also examined in detail
Highly Transparent Au-Coated Ag Nanowire Transparent Electrode with Reduction in Haze
Ag nanowire transparent electrode
has excellent transmittance and sheet resistance, yet its optical
haze still needs to be improved in order for it to be suitable for
display applications. Ag nanowires are known to have high haze because
of the geometry of the nanowire and the high light scattering characteristic
of the Ag. In this study, a Au-coated Ag nanowire structure was proposed
to reduce the haze, where a thin layer of Au was coated on the surface
of the Ag nanowires using a mild [AuÂ(en)<sub>2</sub>]ÂCl<sub>3</sub> galvanic displacement reaction. The mild galvanic exchange allowed
for a thin layer of Au coating on the Ag nanowires with minimal truncation
of the nanowire, where the average length and the diameter were 13.0
μm and 60 nm, respectively. The Au-coated Ag nanowires were
suspended in methanol and then electrostatically sprayed on a flexible
polycarbonate substrate that revealed a clear reduction in haze with
a 2–4% increase in total transmittance, sheet resistance ranges
of 80–90%, and 8.8–36.8 Ohm/sq. Finite difference time
domain simulations were conducted for Au-coated Ag nanowires that
indicated a significant reduction in the average scattering from 1
to 0.69 for Au layer thicknesses of 0–10 nm
Improved Internal Quantum Efficiency and Light-Extraction Efficiency of Organic Light-Emitting Diodes via Synergistic Doping with Au and Ag Nanoparticles
This paper reports the distinct roles
of Au and Ag nanoparticles (NPs) in organic light-emitting diodes
(OLEDs) depending on their sizes. Au and Ag NPs that are 40 and 50
nm in size, respectively, are the most effective for enhancing the
performance of green OLEDs. The external quantum efficiencies (EQEs)
of green OLEDs doped with Au and Ag NPs (40 and 50 nm, respectively)
are improved by 29.5% and 36.1%, respectively, while the power efficiencies
(PEs) are enhanced by 47.9% and 37.5%, respectively. Furthermore,
combining the Au and Ag NPs produces greater enhancements. The EQE
and PE of the codoped OLEDs are improved by 63.9% and 68.8%, respectively,
through the synergistic behavior of the different NPs. Finite-difference
time-domain simulations confirm that the localized surface-plasmon
resonance of the Au NPs near 580 nm improves the radiative recombination
rate (<i>k</i><sub>rad</sub>) of green-light emitters locally
(<50 nm), while the Ag NPs cause relatively long-range and broadband
enhancements in <i>k</i><sub>rad</sub>. The simulations
of various domain sizes verify that the light-extraction efficiency
(LEE) can be enhanced by more than 4.2% by applying Ag NPs. Thus,
size-controlled Au and Ag NPs can synergistically enhance OLEDs by
improving both the internal quantum efficiency and LEE
Extremely Robust and Patternable Electrodes for Copy-Paper-Based Electronics
We
propose a fabrication process for extremely robust and easily
patternable silver nanowire (AgNW) electrodes on paper. Using an auxiliary
donor layer and a simple laminating process, AgNWs can be easily transferred
to copy paper as well as various other substrates using a dry process.
Intercalating a polymeric binder between the AgNWs and the substrate
through a simple printing technique enhances adhesion, not only guaranteeing
high foldability of the electrodes, but also facilitating selective
patterning of the AgNWs. Using the proposed process, extremely crease-tolerant
electronics based on copy paper can be fabricated, such as a printed
circuit board for a 7-segment display, portable heater, and capacitive
touch sensor, demonstrating the applicability of the AgNWs-based electrodes
to paper electronics
Extremely Robust and Patternable Electrodes for Copy-Paper-Based Electronics
We
propose a fabrication process for extremely robust and easily
patternable silver nanowire (AgNW) electrodes on paper. Using an auxiliary
donor layer and a simple laminating process, AgNWs can be easily transferred
to copy paper as well as various other substrates using a dry process.
Intercalating a polymeric binder between the AgNWs and the substrate
through a simple printing technique enhances adhesion, not only guaranteeing
high foldability of the electrodes, but also facilitating selective
patterning of the AgNWs. Using the proposed process, extremely crease-tolerant
electronics based on copy paper can be fabricated, such as a printed
circuit board for a 7-segment display, portable heater, and capacitive
touch sensor, demonstrating the applicability of the AgNWs-based electrodes
to paper electronics
Wearable Textile Battery Rechargeable by Solar Energy
Wearable electronics represent a
significant paradigm shift in
consumer electronics since they eliminate the necessity for separate
carriage of devices. In particular, integration of flexible electronic
devices with clothes, glasses, watches, and skin will bring new opportunities
beyond what can be imagined by current inflexible counterparts. Although
considerable progresses have been seen for wearable electronics, lithium
rechargeable batteries, the power sources of the devices, do not keep
pace with such progresses due to tenuous mechanical stabilities, causing
them to remain as the limiting elements in the entire technology.
Herein, we revisit the key components of the battery (current collector,
binder, and separator) and replace them with the materials that support
robust mechanical endurance of the battery. The final full-cells in
the forms of clothes and watchstraps exhibited comparable electrochemical
performance to those of conventional metal foil-based cells even under
severe folding–unfolding motions simulating actual wearing
conditions. Furthermore, the wearable textile battery was integrated
with flexible and lightweight solar cells on the battery pouch to
enable convenient solar-charging capabilities
Wearable Textile Battery Rechargeable by Solar Energy
Wearable electronics represent a
significant paradigm shift in
consumer electronics since they eliminate the necessity for separate
carriage of devices. In particular, integration of flexible electronic
devices with clothes, glasses, watches, and skin will bring new opportunities
beyond what can be imagined by current inflexible counterparts. Although
considerable progresses have been seen for wearable electronics, lithium
rechargeable batteries, the power sources of the devices, do not keep
pace with such progresses due to tenuous mechanical stabilities, causing
them to remain as the limiting elements in the entire technology.
Herein, we revisit the key components of the battery (current collector,
binder, and separator) and replace them with the materials that support
robust mechanical endurance of the battery. The final full-cells in
the forms of clothes and watchstraps exhibited comparable electrochemical
performance to those of conventional metal foil-based cells even under
severe folding–unfolding motions simulating actual wearing
conditions. Furthermore, the wearable textile battery was integrated
with flexible and lightweight solar cells on the battery pouch to
enable convenient solar-charging capabilities