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Jung, Junhee,Kim, Sunbo,Park, Jinjoo,Shin, Chonghoon,Pham, Duy Phong,Kim, Jiwoong,Chung, Sungyoun,Lee, Youngseok,Yi, Junsin American Scientific Publishers 2015 Journal of Nanoscience and Nanotechnology Vol.15 No.10
<P>This article mainly discusses the difference between p-i-n and n-i-p type solar cells. Their structural difference has an effect on cell performance, such as open circuit voltage and fill factor. Although the deposition conditions are the same for both p-i-n and n-i-p cases, the substrate layers for depositing p-type microcrystalline silicon layers differ. In n-i-p cells, the substrate layer is p-type amorphous silicon oxide layer; whereas, in p-i-n cells, the substrate layer is ZnO:Al. The interfacial change leads to a 12% difference in the crystallinity of the p-type microcrystalline silicon layers. When the p-type microcrystalline silicon layer's crystallinity was not sufficient to activate an internal electric field, the open, circuit voltage and fill factor decreased 0.075 V and 7.36%, respectively. We analyzed this problem by comparing the Raman spectra, electrical conductivity, activation energy and solar cell performance. By adjusting the thickness of the p-type microcrystalline silicon layer, we increased the open circuit voltage of the n-i-p cell from 0.835 to 0.91 V.</P>
Jung, Junhee,Ha, Kyungyeon,Cho, Jaehyun,Ahn, Shihyun,Park, Hyeongsik,Hussain, Shahzada Qamar,Choi, Mansoo,Yi, Junsin American Scientific Publishers 2013 Journal of Nanoscience and Nanotechnology Vol.13 No.12
<P>The preparation of thin film silicon solar cells containing Ag nanoparticles is reported in this article. Ag nanoparticles were deposited on fluorine doped tin oxide coated glass substrates by the evaporation and condensation method. a-Si:H solar cells were deposited on these substrates by cluster type plasma enhanced chemical vapor deposition. We discuss the double textured surface effect with respect to both the surface morphology of the substrate and the plasmonic effect of the Ag nanoparticles. Ag nanoparticles of various sizes from 10 to 100 nm were deposited. The haze values of the Ag embedded samples increased with increasing particle size whereas the optical transmittance decreased at the same conditions. The solar cell with the 30 nm size Ag nanoparticles showed a short circuit current density of 12.97 mA/cm2, which is 0.53 mA/cm2 higher than that of the reference solar cell without Ag nanoparticles, and the highest quantum efficiency for wavelengths from 550 to 800 nm. When 30 nm size nanoparticles were employed, the conversion efficiency of the solar cell was increased from 6.195% to 6.696%. This study reports the application of the scattering effect of Ag nanoparticles for the improvement of the conversion efficiency of amorphous silicon solar cells.</P>
Application of PCBM Layer as a Back Reflector of Micromorph Tandem Silicon Solar Cells
Jung, Junhee,Hwang, Ki-Hwan,Park, Hyeongsik,Nam, Sang-Hun,Boo, Jin-Hyo,Yi, Junsin American Scientific Publishers 2016 Journal of Nanoscience and Nanotechnology Vol.16 No.10
<P>We analyzed the effect of using PCBM layers as back reflector of tandem amorphous silicon solar cells. The new possibility of using polymer materials as a back reflector of inorganic silicon based solar cells was discussed. By applying the PCBM back reflector, short circuit current density increased from 9.83 mA/cm(2) to 11.7 mA/cm(2) with proper interface treatment. In order to obtain the tandem cell with high fill factor, HF treatment is required before depositing PCBM on n-mu c-Si:H. Series resistance can significantly be increased by little amount of native oxide. Comparison between the reference cell without back reflector and thickness optimized PCBM cell indicated a decrease in open circuit voltage from 1.41 to 1.29 V. These results implied that further optimization of electrical properties, such as electrical conductivity and activation energy is required to minimize the drop in terms of open circuit voltage and fill factor.</P>
Jung, Junhee,Kim, Sunbo,Shin, Chonghoon,Park, Jinjoo,Yi, Junsin American Scientific Publishers 2017 Journal of Nanoscience and Nanotechnology Vol.17 No.11
<P>This research paper discusses a backside reactive ion etching (RIE) process to improve the light trapping properties of micromorph tandem solar cells. Reflection mostly occurs at the interface between the and silver electrode layers. We increase the amount of diffused reflection by introducing an etched rough interface. Absorption of diffused and scattered light is more efficient due to the increased light path length in the cells. Surface morphology was observed by atomic force microscopy (AFM). From this experiment the short circuit current density increased from 10.39 to 11.03 mA/cm(2), measured and calculated by quantum efficiency results. As the etching time increases, the fill factor decreased due to increased recombination sites at the broader interface between the electrode and the n-mu c-Si:1-1 layer. We applied hydrogen treatment in order to reduce this side effect. By adjusting this technique with a H-2 gas source, we could get a higher fill factor of 74.65% and energy conversion efficiency of 11.44%.</P>
A Voice Activity Detection System Based on FPGA
Junhee Jung,Seunghun Jin,Dongkyun Kim,Hyung Soon Kim,Jong Suk Choi,Jae Wook Jeon 제어로봇시스템학회 2010 제어로봇시스템학회 국제학술대회 논문집 Vol.2010 No.10
In this paper, we present a FPGA-based voice activity detection system. DoV (Degree of Voicing) and QSNR (Quantile Signal-to-Noise Ratio) are used as parameters of the VAD algorithm of the proposed system. All VAD system functions are implemented using a dedicated parallel architecture, including signal capturing, DoV processing module and QSNR processing module. The system uses several DPRAMs (Dual Port RAMs) inside the FPGA as parallel buffers in which speech data and the intermediate result are stored, to speed up processing. The functional modules process data in parallel using those buffers. The sampling rate of the proposed system is 16 KHz, and the resolution of each sample is 16 bits. The system can generate the VAD result every 15 ms. The proposed system can be used in speech processing such as speech coding and speech recognition.
Park, Hyeongsik,Nam, Sang-Hun,Shin, Myunghun,Ju, Minkyu,Lee, Youn-Jung,Yu, Jung-Hoon,Jung, Junhee,Kim, Sunbo,Ahn, Shihyun,Boo, Jin-Hyo American Scientific Publishers 2016 Journal of Nanoscience and Nanotechnology Vol.16 No.5
<P>We developed a technique for forming textured aluminum-doped zinc oxide (ZnO: Al) transparent conductive oxide (TCO) films on glass substrates, which were etched using a mixture of hydrofluoric (HF) and hydrochloric (HCl) acids. The etching depth and surface roughness increased with an increase in the HF content and the etching time. The HF-based residues produced insoluble hexafluorosilicate anion-and oxide impurity-based semipermeable films, which reduced the etching rate. Using a small amount of HCl dissolved the Ca compounds, helping to fragment the semipermeable film. This formed random, complex structures on the glass substrates. The angled deposition of three layers of ZnO: Al led to the synthesis of multiscaled ZnO: Al textures on the glass substrates. The proposed approach resulted in textured ZnO: Al TCO films that exhibited high transmittance (similar to 80%) and high haze (>40%) values over wavelengths of 400-1000 nm, as well as low sheet resistances (<18 Omega/sq). Si tandem solar cells based on the ZnO: Al textured TCO films exhibited photocurrents and cell efficiencies that were 40% higher than those of cells with conventional TCO films.</P>