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 poly­[<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 poly­[(9,9-bis­(3′-(<i>N</i>,<i>N</i>-dimethyl­amino)­propyl)-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)­trimethoxysilane (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 H₂/CO Ratios

Generating syngas (H₂ and CO mixture) from electrochemically reduced CO₂ in an aqueous solution is one of the sustainable strategies utilizing atmospheric CO₂ in value-added products. However, a conventional single-component metal catalyst, such as Ag, Au, or Zn, exhibits potential-dependent CO₂ 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 H₂/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 H₂/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 H₂/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 CO₂ 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:PC₇₁BM 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 PC₇₁BM load due to the expanded interfacial surface areas between the PC₇₁BM 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 [Au­(en)₂]­Cl₃ 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>_rad) of green-light emitters locally (<50 nm), while the Ag NPs cause relatively long-range and broadband enhancements in <i>k</i>_rad. 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