Sunbo Kim

Study of stacked-emitter layer for high efficiency amorphous/crystalline silicon heterojunction solar cells

A modified emitter, of stacked two layer structure, was investigated for high-efficiency amorphous/crystalline silicon heterojunction (HJ) solar cells. Surface area of the cells was 181.5 cm2. The emitter was designed to achieve a high open circuit voltage (Voc) and fill factor (FF). When doping of the emitter layer was increased, it was observed that the silicon dihydride related structural defects within the films increased, and the Voc of the HJ cell decreased. On the other hand, while the doping concentration of the emitter was reduced the FF of the cell reduced. Therefore, a combination of a high conductivity and low defects of a single emitter layer appears difficult to obtain, yet becomes necessary to improve the cell performance. So, we investigated a stacked-emitter with low-doped/high-doped double layer structure. A low-doped emitter with reduced defect density was deposited over the intrinsic hydrogenated amorphous silicon passivation layer, while the high-doped emitter with high conductivity w...

RF magnetron sputtered ITO:Zr thin films for the high efficiency a-Si:H/c-Si heterojunction solar cells

ITO and ITO:Zr films with various thicknesses were prepared on glass substrates by RF magnetron sputtering. We observed a decrease in sheet resistance with increasing film thickness that in good agreement with Fuchs-Sondheimer theory. The ITO films doped with ZrO2 (∼0.2 wt%) showed improvement in some of the electrical and optical properties of ITO films. The surface roughness of ITO:Zr films increased with increasing film thickness. ITO:Zr films with thickness of 120 nm showed highest work function of 5.13 eV, as estimated from XPS data. The ITO:Zr films were employed as front electrodes in HIT solar cells; the best device performance was found to be: Voc = 710 mV, Jsc = 34.44 mA/cm2, FF = 74.8%, η = 18.30% at a thickness of 120 nm. A maximum quantum efficiency (QE) of 89% was recorded for HIT solar cells at a wavelength of 700 nm for 120 nm thick ITO:Zr films.

Plasma Textured Glass Surface Morphologies for Amorphous Silicon Thin Film Solar Cells-A review

Copyright ©2016 KIEEME. All rights reserved. This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the original work is properly cited. pISSN: 1229-7607 eISSN: 2092-7592 DOI: http://dx.doi.org/10.4313/TEEM.2016.17.2.98 OAK Central: http://central.oak.go.kr

Effect of wet textured glass surface morphology on the haze ratio and aspect ratio for amorphous silicon thin film solar cells

The impact of controlling the aspect ratio variation on glass substrate for a p-i-n a-Si:H solar cell was investigated and reported. Compared to a flat glass substrate (Corning Eagle XG), we demonstrate an increase of haze ratio from 1% to 79.1%, and an increment in the aspect ratio from 0.1 to 1.16, which is an increase to a high slope angle, using wet chemical etching. Optical transmittance measurements show a major improvement of from 92% to 96% for a wavelength of between 300 and 1100 nm, compared to the reference flat glass. A p-i-n a-Si:H solar cell was simulated using Advanced Semiconductor Analysis simulation based on these haze ratio and aspect ratio results, and yielded an increase in short-circuit current density (Jsc) from 15.38 to 18.74 mA/cm2, as the aspect ratio was increased from 0.1 to 0.84.

Performance of hetero junction with intrinsic thin-layer solar cell depending upon contact resistivity of front electrode

Abstract. Low temperature curing of Ag paste for electrode formation in silicon hetero junction (SHJ) solar cells is important for providing better device characteristics. Ag paste is composed of solvent, various organic materials, and additives; hence its electrical and mechanical adhesion properties depend on the curing conditions. The adhesion of the Ag paste was determined by scratch test, whereas the specific contact resistance was measured using the transfer length method. Various Ag electrodes were formed at various curing temperatures within the temperature range of 160°C–240°C, at 20°C intervals. The curing time was also varied for another set of Ag electrodes. With 200°C temperature and for 20-min curing, the critical load of 20.06 N and specific contact resistance of 19.61  mΩ·cm2 were observed. Using the same conditions, the efficiency of the SHJ solar cell was found to be improved by 3.8%.

A new lower power Viterbi decoder architecture with glitch reduction

This paper presents a new algorithm for a lower power Add-Compare-Select (ACS) architecture and glitch minimization for the Viterbi decoder which can reduce the complexity of the computation using HSPICE. Our experimental results show an average 7% reduction in power with the same latency at a cost of 3% increase in area compared with the ACS unit introduced by Tsui et al. (1999).

Fabrication of honeycomb textured glass substrate and nanotexturing of zinc oxide front electrode for its application in high efficiency thin film amorphous silicon solar cell

Abstract. A significant part of broad band sunlight remains unabsorbed in a simple structured amorphous silicon solar cell. This absorption can be enhanced by adopting a light-trapping scheme with the help of a textured front surface and back reflector. For this purpose, honeycomb-type texture was fabricated on a glass surface by chemical etching. A 3  μm×3  μm honeycomb patterned optical-mask was used to create an image-pattern of an etch-mask on the glass surfaces. We used 0.5% hydrofluoric acid (HF) as an etchant solution with an optimized etching time ranging between 25 and 28 min. This single textured glass shows an enhancement in diffused transmission of light. In solar cell application, a 630-nm-thick Al-doped ZnO (AZO) layer was deposited over the textured glass surface. An additional random etching was carried out on the AZO with 1% HF acid solution for 10 s. This results to a double textured AZO superstrate on which solar cells were fabricated. The solar cells show higher short circuit current density to 17.2  mA/cm2. Finally, we obtained photovoltaic conversion efficiency of an optimized solar cell as 10.75% (with the corresponding Jsc as 17.03  mA/cm2).

The Compromise Condition for High Performance of the Single Silicon Heterojunction Solar Cells

For optimum performance of the hydrogenated amorphous silicon/crystalline silicon (a-Si : H/c-Si) heterojunction solar cells, featuring a doping concentration, localized states, as well as thickness of emitter layer are crucial, since Fermi level, surface passivated quality, and light absorption have to be compromised themselves. For this purpose, the effect of both doping concentration and thickness of emitter layer was investigated. It was found that with gas phase doping concentration and emitter layer thickness of 3% and 7 nm, solar cell efficiency in excess of 14.6% can be achieved. For high gas phase doping concentration, the degradation of open-circuit voltage as well as cell efficiency was obtained due to the higher disorder in the emitter layer. The heavily doped along with thicker in thickness of emitter layer results in light absorption on short wavelength, then diminishing short-circuit current density.

High Efficiency Inorganic/Inorganic Amorphous Silicon/Heterojunction Silicon Tandem Solar Cells

We investigated high-efficiency two-terminal tandem photovoltaic (PV) devices consisting of a p/i/n thin film silicon top sub-cell (p/i/n-TFS) and a heterojunction with an intrinsic thin-layer (HIT) bottom sub-cell. We used computer simulations and experimentation. The short-circuit current density (Jsc) of the top sub-cell limits the Jsc of the p/i/n-TFS/HIT tandem PV device. In order to improve the Jsc of the top sub-cell, we used a buffer-layer at the p/i and i/n interface and a graded forward-profile (f-p) band gap hydrogenated amorphous silicon germanium active layer, namely i-layer, in the top sub-cell. These two approaches showed a remarkable raise of the top sub-cell’s Jsc, leading to the increase of the Jsc of the PV tandem device. Furthermore, in order to minimize the optical loss, we employed a double-layer anti-reflective coating (DL-ARC) with a magnesium fluoride/indium tin oxide double layer on the front surface. The reduction in broadband reflection on the front surface (with the DL-ARC) and the enhanced optical absorption in the long wavelength region (with the graded f-p band gap) resulted in the high Jsc, which helped achieve the efficiency up to 16.04% for inorganic-inorganic c-Si-based tandem PV devices.

Light scattering through multi-textured periodic glass surface morphologies for a-Si thin film solar cells

Front transparent conductive oxide (TCO) films play a vital role in amorphous silicon based thin film solar cells due to their high transparency, conductivity and excellent light scattering properties. The precise surface morphology with better step coverage for the front TCO films is a hot research topic now a days. Since the low step coverage of TCO films suffered non uniformity and hence low performance of amorphous silicon thin film solar cells (a-Si TFSCs). We report novel multi-textured periodic textured glass surface morphologies with high transmittance and better step coverage of AZO films for the a-Si TFSCs. The SF6/Ar plasma etching of glass substrates was used for the high roughness and haze ratio while wet (Buffered Hydro Fluoric acid (BHF)) chemical etching was performed for the better step coverage by controlling the shape of textured glass surface morphology. The pyramid shaped textured glass surface morphologies offered the lowest sheet resistance, high transmittance and roughness for the RF magnetron sputtered AZO films. The AZO films showed the highest total transmittance and haze ratio of 90.19% and 54.29% in the visible wavelength region with lowest sheet resistance of 6.242 Ω/□ for 800 nm thickness. The AZO films deposited on the pyramid glass surface showed the better step coverage. The minor variation in sheet resistance and resistivity of the AZO films was related to the step coverage of the AZO films that is closely related with the shape and angle of the surface morphology. The AZO films with low sheet resistance, high transmittance and step coverage can be employed to improve the performance of future a-Si thin film solar cells.