Browsing by Author "Li, Wei"

Now showing 1 - 4 of 4

Diammonium and Monoammonium Mixed-Organic-Cation Perovskites for High Performance Solar Cells with Improved Stability
(2017-09-20)
Lu, Jianfeng
;
Jiang, Liangcong
;
Li, Wei
;
Li, Feng
;
Pai, Narendra K.
Remarkable power conversion efficiencies (PCE) of metal-halide perovskite solar cells (PSCs) are overshadowed by concerns about their ultimate stability, which is arguably the prime obstacle to commercialization of this promising technology. Herein, the problem is addressed by introducing ethane-1,2-diammonium (+NH3(CH2)(2)NH3+, EDA(2+)) cations into the methyl ammonium (CH3NH3+, MA(+)) lead iodide perovskite, which enables, inter alia, systematic tuning of the morphology, electronic structure, light absorption, and photoluminescence properties of the perovskite films. Incorporation of < 5 mol% EDA(2+) induces strain in the perovskite crystal structure with no new phase formed. With 0.8 mol% EDA(2+), PCE of the MAPbI(3)-based PSCs (aperture of 0.16 cm(2)) improves from 16.7% +/- 0.6% to 17.9% +/- 0.4% under 1 sun irradiation, and fabrication of larger area devices (aperture 1.04 cm(2)) with a certified PCE of 15.2% +/- 0.5% is demonstrated. Most importantly, EDA(2+)/MA(+)-based solar cells retain 75% of the initial performance after 72 h of continuous operation at 50% relative humidity and 50 degrees C under 1 sun illumination, whereas the MAPbI(3) devices degrade by approximately 90% within only 15 h. This substantial improvement in stability is attributed to the steric and coulombic interactions of embedded EDA(2+) in the perovskite structure.
Progress in high-strain perovskite piezoelectric ceramics
(2019-01-01)
Hao, Jigong
;
Li, Wei
;
Zhai, Jiwei
;
Chen, Haydn
;
國際半導體學院
High strain piezoelectric ceramics are the state-of-the-art materials for high precision, positioning devices. A comprehensive review of the latest developments of the various types of perovskite piezoelectric ceramic systems is presented herein, with special attention given to three promising families of lead-free perovskite ferroelectrics: the barium titanate, alkaline niobate and bismuth perovskites. Included in this review are details of phase transition behavior, strain enhancement approaches, material reliabilities as well as the status of some promising applications. This current review describes both compositional and structural engineering approaches that are intended to achieve enhanced strain properties in perovskite piezoelectric ceramics. The factors that affect the strain behavior of high-strain perovskite piezoelectric ceramics are addressed. The reliability characteristics of these high-strain ferroelectrics as well as the recent approaches to the long-term electrical, thermal and time-stability enhancement are summarized. Several promising applications of high-strain perovskite materials are introduced, which take advantages of their characteristics; examples include high-energy storage, pyroelectric and electro-caloric effect and luminescent properties.
Robust online music identification using spectral entropy in the compressed domain
(2014)
Yin, Changqing
;
Li, Wei
;
Luo, Yuanqing
;
Tseng, Li-Chuan
;
電子工程學系及電子研究所
Audio identification has been an active research field with wide applications for years. However, most of previously reported methods work on the raw audio format in spite of the fact that nowadays compressed format audio, especially MP3 music, has grown into the dominant way to transmit on the Internet. So far, most of the previous methods take advantage of MDCT coefficients or derived energy type of features. As a first attempt, in this paper we propose a novel audio fingerprinting algorithm utilizing compressed-domain spectral entropy as audio features. Such fingerprint exhibits strong robustness against various audio signal distortions such as recompression, noise interference, echo addition, equalization, band-pass filtering, pitch shifting, and moderate time-scale modification etc. In addition, the algorithm for compressed-domain can be applied in Internet of Things (IoT). Experimental results show that in our test database which is composed of 9823 popular songs, a 5s music clip is able to transmit in IoT and identify its original recording, with more than 90% top five precision rate even under the above severe time-frequency audio signal distortions.
Stochastic Gradient Descent with Hyperbolic-Tangent Decay on Classification
(2019-01-01)
Hsueh, Bo-Yang
;
Li, Wei
;
Wu, I-Chen
;
資訊工程學系
;
Department of Computer Science
Learning rate scheduler has been a critical issue in the deep neural network training. Several schedulers and methods have been proposed, including step decay scheduler, adaptive method, cosine scheduler and cyclical scheduler. This paper proposes a new scheduling method, named hyperbolic-tangent decay (HTD). We run experiments on several benchmarks such as: ResNet, Wide ResNet and DenseNet for CIFAR-10 and CIFAR-100 datasets, LSTM for PAMAP2 dataset, ResNet on ImageNet and Fashion-MNIST datasets. In our experiments, HTD outperforms step decay and cosine scheduler in nearly all cases, while requiring less hyperparameters than step decay, and more flexible than cosine scheduler. Code is available at https: //github.com/BIGBALLON/HTD.