Video_1_Efficient Synapse Memory Structure for Reconfigurable Digital Neuromorphic Hardware.MP4

Spiking Neural Networks (SNNs) have high potential to process information efficiently with binary spikes and time delay information. Recently, dedicated SNN hardware accelerators with on-chip synapse memory array are gaining interest in overcoming the limitations of running software-based SNN in conventional Von Neumann machines. In this paper, we proposed an efficient synapse memory structure to reduce the amount of hardware resource usage while maintaining performance and network size. In the proposed design, synapse memory size can be reduced by applying presynaptic weight scaling. In addition, axonal/neuronal offsets are applied to implement multiple layers on a single memory array. Finally, a transposable memory addressing scheme is presented for faster operation of spike-timing-dependent plasticity (STDP) learning. We implemented a SNN ASIC chip based on the proposed scheme with 65 nm CMOS technology. Chip measurement results showed that the proposed design provided up to 200X speedup over CPU while consuming 53 mW at 100 MHz with the energy efficiency of 15.2 pJ/SOP.</p

Poly(benzodithiophene) Homopolymer for High-Performance Polymer Solar Cells with Open-Circuit Voltage of Near 1 V: A Superior Candidate To Substitute for Poly(3-hexylthiophene) as Wide Bandgap Polymer

Conjugated homopolymers can be synthesized more simply and reproducibly at lower cost than widely developing donor–acceptor (D–A) alternating copolymers. However, except for well-known poly­(3-hexylthiophene) (P3HT), almost no successful homopolymer-based polymer solar cells (PSCs) have been reported because of their relatively wide band gap and unoptimized energy levels that limit the values of short circuit current (<i>J</i>_SC) and open-circuit voltage (<i>V</i>_OC) in PSCs. Herein, we report the development of poly­(4,8-bis­(5-(2-ethylhexyl)­thiophen-2-yl)­benzo­[1,2-b:4,5-b’]­dithiophene) (PBDTT) homopolymer that has high light absorption coefficients and nearly perfect energy alignment with that of [6,6]-phenyl-C₇₁-butyric acid methyl ester (PC₇₁BM). Therefore, we were able to produce high-performance PSCs with the power conversion efficiency (PCE) of 6.12%, benefiting from both high <i>V</i>_OC (0.93 V) and <i>J</i>_SC (11.95 mA cm^–2) values. To the best of our knowledge, this PCE value is one of the highest values reported for the homopolymer donor-based PSCs. Significantly, the optimized condition of the device was achieved without any solvent additive or thermal treatment. Therefore, PBDTT is a promising candidate to take over the role of P3HT in tandem solar cells and ternary blend solar cells

Comparative Study of the Mechanical Properties of All-Polymer and Fullerene–Polymer Solar Cells: The Importance of Polymer Acceptors for High Fracture Resistance

High fracture resistance of polymer solar cells (PSCs) is of great importance to ensure long-term mechanical reliability, especially considering their potential in roll-to-roll printing processes and flexible devices. In this paper, we compare mechanical properties, such as the cohesive fracture energy, elastic modulus, and crack-onset strain, of all-polymer solar cells (all-PSCs) and fullerene-based solar cells (PCBM–PSCs) based on the same, representative low-bandgap polymer donor (PTB7-Th) as a function of acceptor content. The all-PSCs exhibit higher fracture energy (2.45 J m–2) than PCBM–PSCs (0.29 J m–2) at optimized device conditions. Additionally, a 15-fold higher crack-onset strain is observed in all-PSCs than in PCBM–PSCs. Dramatically different mechanical compliances observed for all-PSCs and PCBM–PSCs are investigated in detail by analysis of the blend morphologies as a function of acceptor content (either P­(NDI2HD-T) or PCBM acceptors). The superior fracture resistance of all-PSCs is attributed to the more ductile characteristics of the polymer acceptor and the large degree of plastic deformation during crack growth, in contrast to the brittle nature of PCBM and the weak interaction between the polymer-rich phase and highly aggregated PCBM-rich domains. Therefore, this work demonstrates that replacing a small-molecule acceptor (i.e., PCBM) with polymeric materials can be an effective strategy toward mechanically robust PSCs

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

Size-Controlled Polymer-Coated Nanoparticles as Efficient Compatibilizers for Polymer Blends

Polymer-coated gold nanoparticles (Au NPs) with controlled size and surface chemistry were successfully synthesized and applied to tailor the structures and properties of polytriphenylamine (PTPA) and polystyrene (PS) blends. Two different polymer-coated Au NPs with sizes of 5.9 nm (Au NP-1) and 20.7 nm (Au NP-2) were designed to be thermally stable above 200 °C and neutral to both PS and PTPA phases. Hence, both Au NPs localize at the PS/PTPA interface and function as compatibilizers in the PS/PTPA blend. To show the compatibilizing effect of the particles, the morphological behaviors of PS/PTPA blends containing different particle volume fractions (ϕ_<i>p</i>) of Au NPs were observed using cross-sectional TEM, and for quantitative analysis, the size distribution of PTPA droplets in the PS matrix was obtained for each sample. The number-average droplet diameter (<i>D</i>_<i>n</i>) of the PTPA domain in the blend was dramatically reduced from 1.4 μm to 500 nm at a small ϕ_<i>p</i> of 1.0 vol % Au NP-1. The same trend of decreasing <i>D</i>_<i>n</i> was also observed with the addition of larger Au NP-2, but a higher ϕ_<i>p</i> was required to obtain the same amount of reduction in the PTPA droplet size. The ϕ_<i>p</i> required to fully cover the PS/PTPA interface as a packed monolayer of Au NPs was calculated as 0.98 vol % for Au NP-1 and 3.38 vol % for Au NP-2, thus giving excellent agreement with critical ϕ_<i>p</i> values for the saturation of the PTPA droplet diameter <i>D</i>_<i>n</i>. To demonstrate the effectiveness of Au NPs as compatibilizers, polystyrene-<i>b</i>-poly(triphenylamine) (PS-<i>b</i>-PTPA) block copolymers were also synthesized and used as compatibilizers in the PS/PTPA blend. The decrease in <i>D</i>_<i>n</i> with the addition of PS-<i>b</i>-PTPA was always smaller than that with addition of Au NP-1 at the same ϕ_<i>p</i>, indicating that Au NPs are more effective compatibilizers. This different behavior can be attributed to the presence of PS-<i>b</i>-PTPA compatibilizers as micelles or free chains in the homopolymer matrix. In contrast, most Au NPs were strongly adsorbed to the PS/PTPA interface

Bright and Stable ZnSeTe Core/Shell Quantum Dots Enabled by Surface Passivation with Organozinc Halide Ligands

Improving the quantum yield and stability of environmentally friendly colloidal quantum dots (CQDs) is crucial for next-generation commercial optoelectronics. Recent research suggests that passivation of both cations and anions on the CQD surfaces leads to high photoluminescence quantum yields (PLQYs). Zinc carboxylate and zinc chloride can bind to both cations and anions; however, these bindings result in poor colloidal and PL stabilities of CQDs. Here, we develop bright and stable ZnSeTe/ZnSe/ZnSeS/ZnS CQDs by introducing the organozinc halide 4-methylbenzylzinc chloride (4MBZC), which is capable of dual-ion passivation. This ligand system displays a near-unity QY of 99.0% with blue emission at 436.8 nm and a narrow full width at half-maximum of 24.4 nm. Moreover, the surface-modified CQDs (4MBZC-QDs) exhibit enhanced colloidal and PL stabilities compared to zinc carboxylate and zinc chloride-coated CQDs (Zn(St)2-QDs and ZnCl2-QDs). 4MBZC-QDs exhibit no aggregation and maintain 84.8% of the initial PLQY even after storage for 1728 h, while those of Zn(St)2-QDs and ZnCl2-QDs are at 3.6 and 23.2%, respectively. The Zn–Cl parts of the organometallic passivate both the Zn and S of the ZnS shell, and the aromatic moieties of the ligand suppress particle aggregation. Our surface engineering approach guides the development of eco-friendly photoelectric devices

Au@Polymer Core–Shell Nanoparticles for Simultaneously Enhancing Efficiency and Ambient Stability of Organic Optoelectronic Devices

In this paper, we report and discuss our successful synthesis of monodispersed, polystyrene-coated gold core–shell nanoparticles (Au@PS NPs) for use in highly efficient, air-stable, organic light-emitting diodes (OLEDs) and organic photovoltaics (OPVs). These core–shell NPs retain the dual functions of (1) the plasmonic effect of the Au core and (2) the stability and solvent resistance of the cross-linked PS shell. The monodispersed Au@PS NPs were incorporated into a poly­(3,4-ethylenedioxythiophene):poly­(styrenesulfonate) (PEDOT:PSS) film that was located between the ITO substrate and the emitting layer (or active layer) in the devices. The incorporation of the Au@PS NPs provided remarkable improvements in the performances of both OLEDs and OPVs, which benefitted from the plasmonic effect of the Au@PS NPs. The OLED device with the Au@PS NPs achieved an enhancement of the current efficiency that was 42% greater than that of the control device. In addition, the power conversion efficiency was increased from 7.6% to 8.4% in PTB7:PC₇₁BM-based OPVs when the Au@PS NPs were embedded. Direct evidence of the plasmonic effect on optical enhancement of the device was provided by near-field scanning optical microscopy measurements. More importantly, the Au@PS NPs induced a remarkable and simultaneous improvement in the stabilities of the OLED and OPV devices by reducing the acidic and hygroscopic properties of the PEDOT:PSS layer

Improved Elasticity and Conductivity in a Ni@Ag/Silicone Rubber Composite due to Lowered Percolation Threshold via Magnetic-Field-Induced Alignment

Elastic and conductive electrodes are required for deformable electronic devices. The electrical conductivity and elasticity of a composite material are governed by the proportions of conductive filler and polymer matrix, respectively. Achieving these two features simultaneously is challenging because of the trade-offs between them. The conductive filler content must be higher than the percolation threshold to achieve conductivity. However, if the percolation threshold could be lowered, conductivity could be achieved even with a low content of the conductive filler, and elasticity could be achieved simultaneously by increasing the content of the polymer matrix. Herein, a Ni@Ag/silicone rubber composite with a decreased percolation threshold via magnetic field alignment is reported. The magnetic/conductive particles were arranged and compressed in a parallel straight-line pattern using an external magnetic field. The resulting pseudo-one-dimensional (1D) morphology lowered the percolation threshold of the composite by more than 20% and maintained its electrical properties at 20% cyclic stretching. However, composites that were oriented one way were only able to withstand stretching in a perpendicular direction. By creating a cross-directional orientation procedure, we were able to resolve this problem. In addition, factors affecting the conductivity and elasticity, such as the strength and direction of the magnetic force and the content of the multi-walled carbon nanotubes (MWCNTs), were studied. The MWCNTs served as the nonmagnetic conductive secondary filler, helped control viscosity, and improved the elasticity. Through an light-emitting diode (LED) demonstration, it was proved that the magnetic-field-induced alignment process can be applied to a circular electrode circuit for deformable electronics