Role of dual SiOx: H based buffer at the p/i interface on the performance of single junction microcrystalline solar cells

In p-i-n structure a-Si solar cell a buffer layer with proper characteristics plays important role in improving the p/i interface of the cell, reducing mismatch of band gaps and number of recombination centres. However for p-i-n structure microcrystalline ( µc-Si: H) cell which has much less light induced degradation than a-Si:H cell, not much work has been done on development of proper buffer layer and its application to µc-Si:H cell. In this paper we have reported the development of two intrinsic oxide based microcrystalline layer having different characteristics for use as buffer layers at the p/i interface of µc-Si:H cell. Previously SiO_x:H buffer layer has been used at the p/i interface which showed positive effects. To explore the possibility of improving the performance of p-i-n structure µc-Si:H cell further we have thought it interesting to use two buffer layers with different characteristics at the p/i interface. The two buffer layers have been characterized in detail and applied at the p/i interface of the µc-Si:H cell with positive effects on all the PV parameters mainly improves the open circuit voltage (V_oc) and enhances short circuit current (I_sc). The maximum initial efficiency obtained is 8.97% with dual buffer which is 6.7% higher than that obtained by using conventional single buffer layer at the p/i interface. Stabilized efficiency of the cell with dual buffer is found to be ~9.5% higher than that with single buffer after 600 h of light soakings.     

Top-gate organic field-effect transistors fabricated on paper with high operational stability

We report on top-gate organic field-effect transistors (OFETs) fabricated on specialty paper, PowerCoat™ HD 230 from Arjowiggins Creative Papers coated with a buffer layer composed of a polyvinyl alcohol (PVA) and polyvinylpyrrolidine (PVP) blend. OFETs operate at low voltages and display average carrier mobility values of 1.7 ± 1.1 × 10⁻¹ cm²/Vs, average threshold voltage values of −1.4 ± 0.2 V, and average on/off current ratio of 10⁵. OFETs also display excellent operational stability demonstrated by stable 1000 scans of the transfer characteristics and by stable on-currents displaying less than 6% change during a DC bias stress test at V_DS = V_GS = −10 V for 1 h. Furthermore, OFETs on paper display a decrease of only 7% in their on-state current during a bending test. The performance of these OFETs on paper is comparable to that displayed by top-gate OFETs with the same geometry fabricated on glass substrates.     

Controllable memristive patterns in poly(9,9-dioctylfluorene)-based sandwich device

Currently, there are two prevalent types of I-V memristive patterns for memristive applications, 0-type and 8-type hysteresis loop, and their respective characteristics result in their specific applications in different situations, such as data storage and neuromorphic computing. In spite of the abundant achievements of these remarkable performances, scarce works are specially concerned about the relations and regulations between them for persuing the multiple functions in a single element, and an ideal platform with both the achievements and controllable transformations has been rarely reported. Herein, the novel organic material—poly(9,9-dioctylfluorene) (PFO) is utilized to construct the sandwich prototype. The electrical transporting properties are systematically investigated through particular programming protocols. The 0-type and 8-type memristive patterns are successfully obtained during low and high voltage sweeps, respectively. Then the sectionalized fitting results of the current curves, the carrier transporting behaviors as well as the regulations of device energy levels are associatively demonstrated to analyze the electrical activity-dependent transformations between different memristive patterns. More importantly, the appearance of the 8-type hysteresis loop can be regulated by the rectification property, and the rectification can be largely enhanced by the reconfiguration of device energy levels. Consequently, for the versatile memristive device, based on the 0-type hysteresis, it can serve as a data storage or artificial synapse element, and the rectification-modified memristive behaviors can effectively impede the unintended sneak current paths for high-density integration.     

在电路教学中培养学生的数学应用能力

在电路和电工技术教学中加强数学方法的运用是提高大学生数学应用意识和能力的重要手段,同时还可以加深对电路概念和方法的理解。本文结合置换定理、叠加定理、非正弦周期电路、暂态电路、正弦稳态电路相量分析以及电阻的星形和三角形连接的等效变换等教学内容,介绍了应用数学方法建立电路概念的体会,供读者参考。     

Effects of carrier phase estimation on front-end IQ mismatch compensation in mode division multiplexed MIMO coherent receiver

The effects of carrier phase estimation on IQ mismatch compensation are investigated and compared for coherent MIMO optical receiver. We investigate the impacts of phase IQ mismatch on required optical signal-to-noise ratio (OSNR) for coherent MIMO detection. The impacts of number of modes and analog-to-digital converter (ADC) resolution are also evaluated. The results show that decision-directed carrier phase estimator could compensate significant amount of IQ mismatch without employing additional compensation technique, and relaxes requirement of ADC resolution.     

A highly nonlinear photonic quasi-crystal fiber with low confinement loss and flattened dispersion

We proposed a novel photonic quasi-crystal fiber with near-zero flattened dispersion, highly nonlinear coefficient, and low confinement loss by using the dual concentric core structure. By optimizing the structure parameter, the proposed photonic quasi-crystal fiber can achieve a nonlinear coefficient larger than 33 W⁻¹ km⁻¹ and near-zero flatten dispersion of 0 ± 3.4 ps/nm/km with a near-zero dispersion slope of 8.5 × 10⁻³ ps/nm²/km at the wavelength of 1550 nm. Near-zero flattened dispersion and low confinement loss in the ultralow order of 10⁻⁷ dB/m are simultaneously obtained in the wavelength range from 1373 to 1627 nm. Furthermore, two zero dispersion wavelengths can be achieved in a wide wavelength ranger from 1373 to 1725 nm. From the point of view of practical fabrication, the influence of deviation of each air hole diameter within 3% of imperfections on dispersion, nonlinearity, and is discussed to verify the robustness of our design.     

Enhanced intrinsic stability of the bulk heterojunction active layer blend of polymer solar cells by varying the polymer side chain pattern

Organic photovoltaics (OPVs) have acquired huge attention over the past years as potential renewable energy sources, adding attractive features such as aesthetics, semi-transparency, flexibility, large area printability, improved low-light performance, and cost-effectiveness to the well-known Si-based photovoltaics. Steady improvements in OPV power conversion efficiencies are continuously reported, notably for bulk heterojunction solar cells based on conjugated polymer:fullerene blends. However, apart from efficiency and cost, the stability of organic solar cell devices is of particular concern. Among the different factors contributing to OPV instability, gradual loss of the optimum phase-separated nanomorphology of the photoactive layer blend is a critical parameter. In this paper, we present the results of ‘shelf-life’ accelerated lifetime tests performed for devices containing a range of functionalized poly(3-alkylthiophene) (P3AT) donor polymers upon prolonged thermal stress. By the incorporation of functional moieties on the side chains of P3HT-based copolymers, a remarkable improvement of the intrinsic stability of the active layer blend morphology is accomplished, even for fairly low built-in ratios (5–15%) and without crosslinking to covalently anchor the polymer and/or fullerene molecules. Moreover, these alterations do not influence the initial power conversion efficiencies to a large extent. As such, the presented approach can be regarded as an attractive paradigm for OPV active layer stability.     

Response time and mechanism of Pd modified TiO2 gas sensor

In this work, gas response properties of Pd modified TiO₂ sensing films are discussed when exposed to H₂ and O₂. TiO₂ films are surface modified in PdCl₂-containing solution by the dipping method and treated for different treatment times to get different surface states. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and Kröger–Vink defect theory are used to characterize the sensing films. The gas response properties indicate that the sensor response time which related to the rate of change of sensor resistance is affected by the activation energy (E). In particular, the sensor treated at 900 °C for 2 h exhibits a response time of about 20–240 ms when exposed to H₂ and 40–130 ms when exposed to O₂ at 500–800 °C.     

Singular value decomposition based fusion for super-resolution image reconstruction

In this paper, we address a super-resolution problem of generating a high-resolution image from low-resolution images. The proposed super-resolution method consists of three steps: image registration, singular value decomposition (SVD)-based image fusion and interpolation. The contribution of this work is two-fold. First we customize an image registration approach using Scale Invariant Feature Transform (SIFT), Belief Propagation and Random Sampling Consensus (RANSAC) for super-resolution. Second, we propose SVD-based fusion to integrate the important features from the low-resolution images. The proposed image registration and fusion steps effectively maintain the important features and greatly improve the super-resolution results. Results, for a variety of image examples, show that the proposed method successfully generates high-resolution images from low-resolution images.