• Korean Journal of Materials Research
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• v.28 no.1
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• pp.38-42
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• 2018

Continuous efforts are being made to improve the efficiency of Si solar cells, which is the prevailing technology at this time. As opposed to the standard front-lit solar cell design, the back-lit design suffers no shading loss because all the metal electrodes are placed on one side close to the pn junction, which is referred to as the front side, and the incoming light enters the denuded back side. In this study, a systematic comparison between the two designs was conducted by means of computer simulation. Medici, a two-dimensional semiconductor device simulation tool, was utilized for this purpose. The $0.6{\mu}m$ wavelength, the peak value for the AM-1.5 illumination, was chosen for the incident photons, and the minority-carrier recombination lifetime (${\tau}$), a key indicator of the Si substrate quality, was the main variable in the simulation on a p-type $150{\mu}m$ thick Si substrate. Qualitatively, minority-carrier recombination affected the short circuit current (Isc) but not the opencircuit voltage (Voc). The latter was most affected by series resistance associated with the electrode locations. Quantitatively, when ${\tau}{\leq}500{\mu}s$, the simulation yielded the solar cell power outputs of $20.7mW{\cdot}cm^{-2}$ and $18.6mW{\cdot}cm^{-2}$, respectively, for the front-lit and back-lit cells, a reasonable 10 % difference. However, when ${\tau}$ < $500{\mu}s$, the difference was 20 % or more, making the back-lit design less than competitive. We concluded that the back-lit design, despite its inherent benefits, is not suitable for a broad range of Si solar cells but may only be applicable in the high-end cells where float-zone (FZ) or magnetic Czochralski (MCZ) Si crystals of the highest quality are used as the substrate.

• 한국신재생에너지학회:학술대회논문집
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• 2006.06a
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• pp.228-231
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• 2006

This paper briefly introduces silicon based thin film solar cells: amorphous (a-Si:H), microcrystalline ${\mu}c-Si:H$ single junction and $a-Si:H/{\mu}c-Si:H$ tandem solar cells. The major difference of a-Si:H and ${\mu}c-Si:H$ cells comes from electro-optical properties of intrinsic Si-films (active layer) that absorb incident photon and generate electron-hole pairs. The a-Si:H film has energy band-gap (Eg) of 1.7-1.8eV and solar cells incorporating this wide Eg a-Si:H material as active layer commonly give high voltage and low current, when illuminated, compared to ${\mu}c-Si:H$ solar cells that employ low Eg (1.1eV) material. This Eg difference of two materials make possible tandem configuration in order to effectively use incident photon energy. The $a-Si:H/{\mu}c-Si:H$ tandem solar cells, therefore, have a great potential for low cost photovoltaic device by its various advantages such as low material cost by thin-film structure on low cost substrate instead of expensive c-Si wafer and high conversion efficiency by tandem structure. In this paper, the structure, process and operation properties of Si-based thin-film solar cells are discussed.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.8
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• pp.654-658
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• 2011

This paper was investigated the electrical properties for optimal operating conditions of monocrystalline silicon solar cell. The output of electricity for monocrystalline solar cell was investigated according to the distances between solar cell and halogen lamp and to the resistances by the variable resistor.

• Journal of Electrical Engineering and information Science
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• v.2 no.5
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• pp.65-71
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• 1997

We present heterojunction solar cells with a structure of metal/a-Si:H(n-i-p)/poly-Si(n-p)/metal for the terrestrial applications. This cell consists fo two component cells: a top n-i-p junction a-Si:Hi cell with wide-bandgap 1.8eV and a bottom n-p junction poly-Si cell with narrow-bandgap 1.1eV. The efficiency influencing factors of the solar cell were investigated in terms of simulation an experiment. Three main topics of the investigated study were the bottom cell with n-p junction poly-Si, the top a-Si:H cell with n-i-p junction, and the interface layer effects of heterojunction cell. The efficiency of bottom cell was improved with a pretreatment temperature of 900$^{\circ}C$, surface polishing, emitter thickness of 0.43$\mu\textrm{m}$, top Yb metal, and grid finger shading of 7% coverage. The process optimized cell showed a conversion efficiency about 16%. Top cell was grown by suing a photo-CVD system which gave an ion damage free and good p/i-a-Si:H layer interface. The heterojunction interface effect was examined with three different surface states; a chemical passivation, thermal oxide passivation, and Yb metal. the oxide passivated cell exhibited the higher photocurrent generation and better spectral response.

• Proceedings of the KIEE Conference
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• 1998.07d
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• pp.1361-1363
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• 1998

Poly-Si grain boundaries act as potential barriers as well as recombination centers for the photo-generated carriers in solar cells. Thereby, grain boundaries of poly-Si are considered as a major source of the poly-Si cell efficiency was reduced This paper investigated grain boundary effect of poly-Si wafer prior to the solar cell fabrication. By comparing I-V characteristics inner grain, on and across the grain boundary, we were able to detect grain potentials. To reduce grain boundary effect we carried out pretreatment, $POCl_3$ gettering, and examined carrier lifetime. This paper focuses on resistivity variation effect due to grain boundary of poly-Si. The resistivity of the inner grain was $2.2{\Omega}-cm$, on the grain boundary$2.3{\Omega}-cm$, across the grain boundary $2.6{\Omega}-cm$. A measured resistivity varied depending on how many grains were included inside the four point probes. The resistivity increased as the number of grain boundaries increased. Our result can contribute to achieve high conversion efficiency of poly-Si solar cell by overcoming the grain boundary influence.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.426.1-426.1
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• 2016

We report high work function Aluminum doped zinc oxide (AZO) films as insertion layer as a function of O2 flow rate between transparent conducting oxides (TCO) and hydrogenated amorphous silicon oxide (a-SiOx:H) layer to improve open circuit voltage (Voc) and fill factor (FF) for high efficiency thin film solar cell. However, amorphous silicon (a-Si:H) solar cells exhibit poor fill factors due to a Schottky barrier like impedance at the interface between a-SiOx:H windows and TCO. The impedance is caused by an increasing mismatch between the work function of TCO and that of p-type a-SiOx:H. In this study, we report on the silicon thin film solar cell by using as insertion layer of O2 reactive AZO films between TCO and p-type a-SiOx:H. Significant efficiency enhancement was demonstrated by using high work-function layers (4.95 eV at O2=2 sccm) for engineering the work function at the key interfaces to raise FF as well as Voc. Therefore, we can be obtained the conversion efficiency of 7 % at 13mA/cm2 of the current density (Jsc) and 63.35 % of FF.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.1
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• pp.18-21
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• 2013

$SiO_2$ layer grown by rapid thermal oxidation and $SiN_x$ layer were used for passivating the surface of n-type silicon solar cell, instead of only $SiN_x$ layer generally used in photovoltaic industry. The rapid thermal oxidation provides the reduction of processing time and avoids bulk life time degradation during the processing. Improvement of 30 mV in Voc and $2.7mA/cm^2$ in Jsc was obtained by applying these two layers. This improvement led to fabrication of a large area ($239cm^2$) n-type solar cell with 17.34% efficiency. Internal quantum efficiency measurement indicates that the improvement comes from the front side passivation, but not the rear side, by using $SiO_2/SiN_x$ stack.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.257.2-257.2
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• 2015

In this paper, we report on the 10.33% efficient thin film/bulk tandem solar cells with the top cell made of amorphous silicon thin film and p-type bulk crystalline silicon bottom cell. The tunneling junction layers were used the doped nanocrystalline Si layers. It has to allow an ohmic and low resistive connection. For player and n-layer, crystalline volume fraction is ~86%, ~88% and dark conductivity is $3.28{\times}10-2S/cm$, $3.03{\times}10-1S/cm$, respectively. Optimization of the tunneling junction results in fill factor of 66.16 % and open circuit voltage of 1.39 V. The open circuit voltage was closed to the sum of those of the sub-cells. This tandem structure could enable the effective development of a new concept of high-efficiency and low cost cells.

• Korean Journal of Materials Research
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• v.30 no.5
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• pp.262-266
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• 2020

In this paper, we investigated the effect of the passivation stack with Al₂O₃, hydrogenated silicon nitride (SiN_x:H) stack and Al₂O₃, silicon oxynitride (SiON_x) stack in the n type bifacial solar cell on monocrystalline silicon. SiNx:H and SiON_x films were deposited by plasma enhanced chemical vapor deposition on the Al₂O₃ thin film deposited by thermal atomic layer deposition. We focus on passivation properties of the two stack structure after laser ablation process in order to improve bifaciality of the cell. Our results showed SiN_x:H with Al₂O₃ stack is 10 mV higher in implied open circuit voltage and 60 ㎲ higher in minority carrier lifetime than SiON_x with Al₂O₃ stack at Ni silicide formation temperature for 1.8% open area ratio. This can be explained by hydrogen passivation at the Al₂O₃/Si interface and Al₂O₃ layer of laser damaged area during annealing.

• New & Renewable Energy
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• v.2 no.2 s.6
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• pp.4-8
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• 2006

Reduction of optical losses in crystalline silicon solar cells by surface modification is one of the most important issues of silicon photovoltaics. Porous Si layers on the front surface of textured Si substrates have been investigated with the aim of improving the optical losses of the solar cells, because an anti-reflection coating and a surface passivation can be obtained simultaneously in one process. We have demonstrated the feasibility of a very efficient porous Si AR layer, prepared by a simple, cost effective, electrochemical etching method. Silicon p-type CZ (100) oriented wafers were textured by anisotropic etching in sodium carbonate solution. Then, the porous Si layer were formed by electrochemical etching in HF solutions. After that, the properties of porous Si in terms of morphology, structure and reflectance are summarized. The surface morphology of porous Si layers were investigated using SEM. The formation of a porous Si layer about $0.1{\mu}m$ thick on the textured silicon wafer result in an effective reflectance coefficient Reff lower than 5% in the wavelength region from 400 to 1000nm. Such a surface modification allows improving the Si solar cell characteristics.