Control of Crystal Growth toward Scalable Fabrication of Perovskite Solar Cells

With the impressive record power conversion efficiency (PCE) of perovskite solar cells exceeding 23%, research focus now shifts onto issues closely related to commercialization. One of the critical hurdles is to minimize the cell‐to‐module PCE loss while the device is being developed on a large scale. Since a solution‐based spin‐coating process is limited to scalability, establishment of a scalable deposition process of perovskite layers is a prerequisite for large‐area perovskite solar modules. Herein, this paper reports on the recent progress of large‐area perovskite solar cells. A deeper understanding of the crystallization of perovskite films is indeed essential for large‐area perovskite film formation. Various large‐area coating methods are proposed including blade, slot‐die, evaporation, and post‐treatment, where blade‐coating and gas post‐treatment have so far demonstrated better PCEs for an area larger than 10 cm². However, PCE loss rate is estimated to be 1.4 × 10^?2% cm^?2, which is 82 and 3.5 times higher than crystalline Si (1.7 × 10^?4% cm^?2) and thin film technologies (≈4 × 10^?3% cm^?2) respectively. Therefore, minimizing PCE loss upon scaling‐up is expected to lead to PCE over 20% in case of cell efficiency of >23%.     

High Areal Capacitance of N‐Doped Graphene Synthesized by Arc Discharge

The lack of cost effective, industrial‐scale production methods hinders the widespread applications of graphene materials. In spite of its applicability in the mass production of graphene flakes, arc discharge has not received considerable attention because of its inability to control the synthesis and heteroatom doping. In this study, a facile approach is proposed for improving doping efficiency in N‐doped graphene synthesis through arc discharge by utilizing anodic carbon fillers. Compared to the N‐doped graphene (1–1.5% N) synthesized via the arc process according to previous literature, the resulting graphene flakes show a remarkably increased doping level (≈3.5% N) with noticeable graphitic N enrichment, which is rarely achieved by the conventional process, while simultaneously retaining high turbostratic crystallinity. The electrolyte ion storage of synthesized materials is examined in which synthesized N‐doped graphene material exhibits a remarkable area normalized capacitance of 63 µF cm^?2. The surprisingly high areal capacitance, which is superior to that of most carbon materials, is attributed to the synergistic effect of extrinsic pseudocapacitance, high crystallinity, and abundance of exposed graphene edges. These results highlight the great potentials of N‐doped graphene flakes produced by arc discharge in graphene‐based supercapacitors, along with well‐studied active exfoliated graphene and reduced graphene oxide.     

End‐to‐end security‐reliability analysis of multi‐hop cognitive relaying protocol with TAS/SC‐based primary communication,total interference constraint and asymmetric fading channels

In this paper, we analyze the tradeoff between outage probability (OP) and intercept probability (IP) for a multi‐hop relaying scheme in cognitive radio (CR) networks. In the proposed protocol, a multi‐antenna primary transmitter (PT) communicates with a multi‐antenna primary receiver (PR), using transmit antenna selection (TAS) / selection combining (SC) technique, while a secondary source attempts to transmit its data to a secondary destination via a multi‐hop approach in presence of a secondary eavesdropper. The secondary transmitters such as source and relays have to adjust their transmit power to satisfy total interference constraint given by PR. We consider an asymmetric fading channel model, where the secondary channels are Rician fading, while the remaining ones experience the Rayleigh fading. Moreover, an optimal interference allocation method is proposed to minimize OP of the primary network. For the secondary network, we derive exact expressions of end‐to‐end OP and IP which are verified by Monte Carlo simulations.     

λ/64‐spaced compact ESPAR antenna via analog RF switches for a single RF chain MIMO system

In this study, an electronically steerable parasitic array radiator (ESPAR) antenna via analog radio frequency (RF) switches for a single RF chain MIMO system is presented. The proposed antenna elements are spaced at λ/64, and the antenna size is miniaturized via a dielectric radome. The optimum reactance load value is calculated via the beamforming load search algorithm. A switch simplifies the design and implementation of the reactance loads and does not require additional complex antenna matching circuits. The measured impedance bandwidth of the proposed ESPAR antenna is 1,500 MHz (1.75 GHz–3.25 GHz). The proposed antenna exhibits a beam pattern that is reconfigurable at 2.48 GHz due to changes in the reactance value, and the measured peak antenna gain is 4.8 dBi. The reception performance is measured by using a 4  4 BPSK signal. The measured average SNR is 17 dB when using the proposed ESPAR antenna as a transmitter, and the average SNR is 16.7 dB when using a four‐conventional monopole antenna.     

A novel phase noise reduction technique in oscillators usingdefected ground structure

A new technique to reduce the phase noise in microwave oscillators is developed using the resonant characteristic of the defected ground structure (DGS). Two kinds of oscillators have been designed and measured for the examination of the reduction of phase noise by the DGS. The first adopts the DGS section under the microstrip line at the gate circuit, while the second has only the conventional microstrip line. Measurement shows reduced phase noise by 10-15 dB in the oscillator with the DGS compared to the conventional one     

2D Image Construction from Low Resolution Response of a New Non‐invasive Measurement for Medical Application

This paper presents an application of digital signal processing to data acquired by the radio imaging method (RIM) that was adopted to measure moisture distribution inside the human body. RIM was originally developed for the mining industry; we are applying the method to a biomedical measurement because of its simplicity, economy, and safety. When a two‐dimensional image was constructed from the measured data, the method provided insufficient resolution because the wavelength of the measurement medium, a weak electromagnetic wave in a VHF band, was longer than human tissues. We built and measured a phantom, a model simulating the human body, consisting of two water tanks representing large internal organs. A digital equalizer was applied to the measured values as a weight function, and images were reconstructed that corresponded to the original shape of the two water tanks. As a result, a two‐dimensional image containing two individual peaks corresponding to the original two small water tanks was constructed. The result suggests the method was applicable to biomedical measurement by the assistance of digital signal processing. This technique may be applicable to home‐based medical care and other situations in which safety, simplicity, and economy are important.     

High-performance RF mixer and operational amplifier BiCMOS circuits using parasitic vertical bipolar transistor in CMOS technology

The electrical characteristics of the parasitic vertical NPN (V-NPN) BJT available in deep n-well 0.18-/spl mu/m CMOS technology are presented. It has about 20 of current gain, 7 V of collector-emitter breakdown voltage, 20 V of collector-base breakdown voltage, 40 V of Early voltage, about 2 GHz of cutoff frequency, and about 4 GHz of maximum oscillation frequency at room temperature. The corner frequency of 1/f noise is lower than 4 kHz at 0.5 mA of collector current. The double-balanced RF mixer using V-NPN shows almost free 1/f noise as well as an order of magnitude smaller dc offset compared with CMOS circuit and 12 dB flat gain almost up to the cutoff frequency. The V-NPN operational amplifier for baseband analog circuits has higher voltage gain and better input noise and input offset performance than the CMOS ones at the identical current. These circuits using V-NPN provide the possibility of high-performance direct conversion receiver implementation in CMOS technology.     

2/spl times/4 optical add-drop module with no difference in propagation length

We developed a micromachined X-type 2/spl times/4 optical add-drop module (OADM) featuring no difference in propagation length. Four pairs of lensed fibers are aligned in "X" position, and four micromirrors are located between the pairs of optical fibers. The OADM was fabricated utilizing a silicon-on-insulator process. Electrostatic comb actuators can be driven up to 90 /spl mu/m to change the light path within 1 ms. The insertion loss and the on-off ratio were less than 3 and 70 dB, respectively. The loss uniformity in every channel was 1.5 dB.     

A novel high-efficiency linear transmitter using injection-locked pulsed oscillator

This letter presents a novel high-efficiency linear transmitter using pulse-width modulation (PWM). An envelope of radio frequency (RF) input signal is modulated by the PWM. The modulated signal is applied to the gate bias of a class F injection-locked power oscillator and switches it on and off. By filtering the pulsed oscillating output signal of the injection-locked oscillator using high-Q bandpass filter, the input signal is restored. This technique enables the transmitter to have high efficiency with good linearity. Also, there is little distortion near saturation point of an active device. The measured results show efficiency of 54.6% and very good linearity in PCS band at 26.4-dBm output power.     

A weakness in the Bresson-Chevassut-Essiari-Pointcheval's Group Key Agreement scheme for low-power mobile devices

In this letter, we show that Bresson-Chevassut-Essiari-Pointcheval's Group Key Agreement scheme does not meet the main security properties: implicit key authentication, forward secrecy and known key security. Also, we propose an improved version, which fixes the security flaws, found in the scheme.