Energy Transfer Induced by TADF Polymer Enables the Recycling of Excitons in Perovskite Solar Cells

Formamidinium lead triiodide (FAPbI₃) has been demonstrated as the most efficient perovskite system to date, due to its excellent thermal stability and an ideal bandgap approaching the Shockley-Queisser limit. Whereas, there are intrinsic quantum confinement effects in FAPbI₃, which lead to unwanted non-radiative recombination. Additionally, the black α-phase of FAPbI₃ is unstable under room temperature due to the significant residual tensile stress in the film. To simultaneously address the above issues, a thermally-activated delayed fluorescence polymer P1 is designed in the study to modify the FAPbI₃ film. Owing to the spectral overlap between the photoluminescence of P1 and absorption of the above-bandgap quantum wells of FAPbI₃, the Förster energy transfer occurs at the P1/FAPbI₃ interface, which further triggers the Dexter energy transfer within FAPbI₃. The exciton “recycling” can thus be realized, which reduces the non-radiative recombination losses in perovskite solar cells (PSCs). Moreover, P1 is found to introduce compressive stress into FAPbI₃, which relieves the tensile stress in perovskite. Consequently, the PSCs with P1 treatment achieve an outstanding power conversion efficiency (PCE) of 23.51%. Moreover, with the alleviation of stress in the perovskite film, flexible PSCs (f-PSCs) also deliver a high PCE of 21.40%.     

RBSiC陶瓷素坯连接研究

将碳化硅(Si C)微粉、酚醛树脂和炭黑等均匀混合,配置成连接浆料,真空除泡后连接Si C陶瓷素坯,高温反应烧结后得到反应烧结Si C(RBSi C)连接镜坯。讨论了浆料配方对焊缝显微结构的影响,测试了RBSi C连接坯体的力学性能和线膨胀系数。研究表明:连接浆料中加入聚乙二醇200(PEG200)和聚乙烯醇吡咯烷酮(PVP),能够有效分散炭黑,保证反应烧结过程中炭黑与硅完全反应,无残余碳存在,实现焊缝与基材之间显微结构的一致性;Si C连接坯体素坯和反应烧结后的抗弯强度值分别24.9 MPa和322.9 MPa,而且断裂位置在基材上;在-100~400℃范围内,RBSi C连接坯体与基体线膨胀系数差异仅为0.011 4 ppm。     

基于对比度调制法对条纹管激光雷达距离像的去噪方法

激光雷达的距离像是雷达成像系统区别于其他的成像系统（如红外成像系统、可见光成像系统）所特有的信息,它是对目标精确识别、打击的基础。如何对距离像去噪直接决定了下一步目标定位、识别的精确性。针对雷达距离像的特点,提出了一种基于对比度调制方法对条纹管激光雷达的距离像去噪方法,通过提取距离像噪声的对比度信息,用其调制未经过去噪的距离像,从而得到距离像中的噪声图像,最后用未经过处理的距离像减去噪声图像,得到图像即为去噪后距离像。研究表明该方法去噪效果明显,在去噪的同时很好地保持了距离像的边缘信息,去噪后图像的信噪比明显提高,距离像的属性也没有改变,这是其他方法对距离像去噪所不具有的优点。     

Reduction of PAPR of OFDM Signals Using Nonlinear Companding Transform

In this paper, we propose and evaluate a novel nonlinear companding transform (NCT) scheme for peak-to-average power ratio (PAPR) reduction in orthogonal frequency division multiplexing (OFDM) systems. The key idea of the proposed scheme is to transform the original Gaussian-distributed OFDM signals into a specific statistics form, whose target probability density function is defined by a piecewise function with an inflexion point. By properly choosing the transform parameters, this scheme can enable more flexibility and freedom in the companding form so that a favorable tradeoff between PAPR reduction and bit error rate (BER) performance can be achieved. Moreover, compared to existing NCT techniques, this scheme dramatically decreases the impact of companding distortion on the BER performance to reach a given PAPR level. The analytical expressions regarding the achievable transform gain in PAPR, complementary cumulative density function, attenuation coefficient, and selection criteria of transform parameters are derived. Simulation results justify the significance and accuracy of the analytical expressions presented.     

Secondary User Selection Scheme Using Adaptive Genetic Algorithms for Cooperative Spectrum Sensing Under Correlated Shadowing

Cooperative spectrum sensing has been shown to be an effective approach to improve the detection performance by exploiting the spatial diversity among multiple secondary users (or unlicensed users). However, due to correlated shadowing and cooperation overhead in practical cognitive radio networks, it is desired to select an appropriate set of secondary users which have little correlation with each other to participate in cooperation so as to achieve the effective tradeoff between detection performance and cooperation overhead. In this paper, we first study the hypothesis testing model and detection performance of cooperative spectrum sensing under the correlated log-normal shadowing scenario. Afterwards, based on whether the false-alarm and missed-detection probabilities are constrained, three optimization problems are formulated to find the optimal set of secondary users participating in cooperation, which take into account the tradeoff between detection performance and cooperation overhead. Then the solutions using adaptive genetic algorithms are presented for the optimization problems. Finally, simulation experiments demonstrate that our proposed schemes are very effective.     

BGA封装技术研究

介绍了 BGA技术的研究现状 ,着重从芯片互连、基板材料及封装设计等方面讨论了该技术的发展前景。     

High-Speed CMOS Sample-and-Hold Amplifier

The sample-and-hold (S/ H) circuit is a key module for many applications[1 ] totransform a continuous time signal into discrete one. In analog to digital (A/ D)converters,the front-end of the S/ H amplifier must be of both high speed...     

Studies of high DC current induced degradation in III-V nitridebased heterojunctions

We report experiments on high dc current stressing in commercial III-V nitride based heterojunction light-emitting diodes. Stressing currents ranging from 100 mA to 200 mA were used. Degradations in the device properties were investigated through detailed studies of the current-voltage (I-V) characteristics, electroluminescence, deep-level transient Fourier spectroscopy and flicker noise. Our experimental data demonstrated significant distortions in the I-V characteristics subsequent to electrical stressing. The room temperature electroluminescence of the devices exhibited a 25% decrement in the peak emission intensity. Concentration of the deep-levels was examined by deep-level transient Fourier spectroscopy, which indicated an increase in the density of deep-traps from 2.7×10¹³ cm^-3 to 4.2×10¹³ cm^-3 at E₁=E _C-1.1 eV. The result is consistent with our study of 1/f noise, which exhibited up to three orders of magnitude increase in the voltage noise power spectra. These traps are typically located at energy levels beyond the range that can be characterized by conventional techniques including DLTS. The two experiments, therefore, provide a more complete picture of trap generation due to high dc current stressing     

A blind SNR estimator for digital bandpass signals

A subspace-based blind Signal-to-Noise Ratio （SNR） estimation algorithm for digital bandpass signals in Additive White Gaussian Noise （AWGN） channel is discussed. The lower bounds of the mean and variance of the estimation are derived, and simulations are performed for the commonly used digital bandpass signals, such as MPSK （M=2, 4, 8）, MFSK （M=2, 4） and MQAM （M=16, 64, 128, 256） signals. Theoretical analyses and simulation results indicate that the proposed algorithm is effective even when the SNR is below 0dB. Furthermore, the algorithm can provide a blind estimator in that it needs neither the parameters of the received signals, such as the carrier frequency, symbol rate and modulation scheme, nor the synchronization of the system.     

用穆斯堡尔效应研究磷酸—铁锈反应产物

用穆斯堡尔效应研究了α—Fe和铁锈的各主要组份(α-,γ-,δ-,am-FeOOH;α-,γ-Fe_2O_3和F_3O_4)与商品磷酸系锈控涂料主要活性组份—20％磷酸酒精液的作用,结果表明除Fe_3O_4的作用产物系三价铁无定形磷酸盐外。其余产物都为酸式磷酸盐FeH_3(PO_4)_2·2 1/2H_2O。另外,在Fe_3O_4和在α-Fe的反应产物中还存在多种高自旋二价铁的产物。环境中的NaCl及H_2O会不同程度地改变上述反应产物的结构,而O_2对二价铁磷酸盐变成三价铁磷酸盐是必须的。作者用形核长大和高聚物聚沉两种不同沉淀机制对以上结果作了解释。