Morphological Control of Donor/Acceptor Interfaces in All-Polymer Solar Cells Using a Pentafluorobenzene-Based Additive

We report a pentafluorobenzene-based additive (FPE) to control the donor/acceptor (D/A) interfacial morphology via quadrupolar electrostatic interactions between donor and acceptor polymers in all-polymer solar cells (all-PSCs). The morphology changes are investigated using a combination of atomic force microscopy, grazing incidence wide-angle X-ray scattering, and near-edge X-ray absorption fine-structure spectroscopy. Unlike a conventional solvent additive, such as 1,8-diiodooctane, a bicontinuous interpenetrating morphology without large-scale phase separation and an enhanced π–π stacking with face-on orientation are found in the FPE processed blended films. These morphology changes improve the charge carrier extraction and charge transport between D/A interfaces to achieve an increase in the photovoltaic performance of all-PSCs

Chemical Doping Effects in Multilayer MoS₂ and Its Application in Complementary Inverter

Multilayer MoS₂ has been gaining interest as a new semiconducting material for flexible displays, memory devices, chemical/biosensors, and photodetectors. However, conventional multilayer MoS₂ devices have exhibited limited performances due to the Schottky barrier and defects. Here, we demonstrate poly­(diketopyrrolopyrrole-terthiophene) (PDPP3T) doping effects in multilayer MoS₂, which results in improved electrical characteristics (∼4.6× higher on-current compared to the baseline and a high current on/off ratio of 10⁶). Synchrotron-based study using X-ray photoelectron spectroscopy and grazing incidence wide-angle X-ray diffraction provides mechanisms that align the edge-on crystallites (97.5%) of the PDPP3T as well as a larger interaction with MoS₂ that leads to dipole and charge transfer effects (at annealing temperature of 300 °C), which support the observed enhancement of the electrical characteristics. Furthermore, we demonstrate a complementary metal–oxide–semiconductor inverter that uses a p-type MoSe₂ and a PDPP3T-doped MoS₂ as charging and discharging channels, respectively

Selective Dissolution of Surface Nickel Close to Platinum in PtNi Nanocatalyst toward Oxygen Reduction Reaction

We report new insights in dissolution mechanisms of nickel in PtNi bimetallic nanoparticles (NPs) to develop active and durable oxygen reduction catalysts for fuel cells. Leaching out nickel by using acidic aqueous solution has been regarded as one of the most efficient chemical treatments to obtain a platinum-rich surface, which has shown both increased activity and stability during oxygen reduction reaction. In this work, we introduce a new approach using hydroquinone dissolved in ethanol to leach out nickel from PtNi NPs. The degree of alloying level is followed by X-ray photoelectron and absorption spectroscopies. Electrochemical measurements including potential cycling under oxygen reduction conditions allow us to investigate the dissolution behavior of nickel, depending on the chemical systems, and assess the relationship with electrochemical activity and stability. From comparative studies regarding the traditional acid treatment and the hydroquinone method introduced in this article, it is revealed that, while acid treatment preferentially removes oxidized Ni clusters, hydroquinone dissolves Ni atoms close to surface platinum. Electrochemical measurements help with the understanding of the different leaching mechanisms and highlight the influence of alloyed nickel on the activity of platinum and durability of the catalyst in the oxygen reduction reaction

Structural Analyses of Phase Stability in Amorphous and Partially Crystallized Ge-Rich GeTe Films Prepared by Atomic Layer Deposition

The local bonding structures of Ge<i>_x</i>Te_1–<i>x</i> (<i>x</i> = 0.5, 0.6, and 0.7) films prepared through atomic layer deposition (ALD) with Ge­(N­(Si­(CH₃)₃)₂)₂ and ((CH₃)₃Si)₂Te precursors were investigated using Ge K-edge X-ray absorption spectroscopy (XAS). The results of the X-ray absorption fine structure analyses show that for all of the compositions, the as-grown films were amorphous with a tetrahedral Ge coordination of a mixture of Ge–Te and Ge–Ge bonds but without any signature of Ge–GeTe decomposition. The compositional evolution in the valence band electronic structures probed through X-ray photoelectron spectroscopy suggests a substantial chemical influence of additional Ge on the nonstoichiometric GeTe. This implies that the ALD process can stabilize Ge-abundant bonding networks like −Te–Ge–Ge–Te– in amorphous GeTe. Meanwhile, the XAS results on the Ge-rich films that had undergone post-deposition annealing at 350 °C show that the parts of the crystalline Ge-rich GeTe became separated into Ge crystallites and rhombohedral GeTe in accordance with the bulk phase diagram, whereas the disordered GeTe domains still remained, consistent with the observations of transmission electron microscopy and Raman spectroscopy. Therefore, amorphousness in GeTe may be essential for the nonsegregated Ge-rich phases and the low growth temperature of the ALD enables the achievement of the structurally metastable phases

Comparison of the Atomic Layer Deposition of Tantalum Oxide Thin Films Using Ta(N^<i>t</i>Bu)(NEt₂)₃, Ta(N^<i>t</i>Bu)(NEt₂)₂Cp, and H₂O

The growth characteristics of Ta₂O₅ thin films by atomic layer deposition (ALD) were examined using Ta­(N^<i>t</i>Bu)­(NEt₂)₃ (TBTDET) and Ta­(N^<i>t</i>Bu)­(NEt₂)₂Cp (TBDETCp) as Ta-precursors, where ^<i>t</i>Bu, Et, and Cp represent <i>tert</i>-butyl, ethyl, and cyclopentadienyl groups, respectively, along with water vapor as oxygen source. The grown Ta₂O₅ films were amorphous with very smooth surface morphology for both the Ta-precursors. The saturated ALD growth rates of Ta₂O₅ films were 0.77 Å cycle^–1 at 250 °C and 0.67 Å cycle^–1 at 300 °C using TBTDET and TBDETCp precursors, respectively. The thermal decomposition of the amido ligand (NEt₂) limited the ALD process temperature below 275 °C for TBTDET precursor. However, the ALD temperature window could be extended up to 325 °C due to a strong Ta–Cp bond for the TBDETCp precursor. Because of the improved thermal stability of TBDETCp precursor, excellent nonuniformity of ∼2% in 200 mm wafer could be achieved with a step coverage of ∼90% in a deep hole structure (aspect ratio 5:1) which is promising for 3-dimensional architecture to form high density memories. Nonetheless, a rather high concentration (∼7 at. %) of carbon impurities was incorporated into the Ta₂O₅ film using TBDETCp, which was possibly due to readsorption of dissociated ligands as small organic molecules in the growth of Ta₂O₅ film by ALD. Despite the presence of high carbon concentration which might be an origin of large leakage current under electric fields, the Ta₂O₅ film using TBDETCp showed a promising resistive switching performance with an endurance cycle as high as ∼17 500 for resistance switching random access memory application. The optical refractive index of the deposited Ta₂O₅ films was 2.1–2.2 at 632.8 nm using both the Ta-precursors, and indirect optical band gap was estimated to be ∼4.1 eV for both the cases

Mussel-Inspired Anchoring of Polymer Loops That Provide Superior Surface Lubrication and Antifouling Properties

We describe robustly anchored triblock copolymers that adopt loop conformations on surfaces and endow them with unprecedented lubricating and antifouling properties. The triblocks have two end blocks with catechol-anchoring groups and a looping poly­(ethylene oxide) (PEO) midblock. The loops mediate strong steric repulsion between two mica surfaces. When sheared at constant speeds of ∼2.5 μm/s, the surfaces exhibit an extremely low friction coefficient of ∼0.002–0.004 without any signs of damage up to pressures of ∼2–3 MPa that are close to most biological bearing systems. Moreover, the polymer loops enhance inhibition of cell adhesion and proliferation compared to polymers in the random coil or brush conformations. These results demonstrate that strongly anchored polymer loops are effective for high lubrication and low cell adhesion and represent a promising candidate for the development of specialized high-performance biomedical coatings