• Korean Journal of Materials Research
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• v.25 no.7
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• pp.336-340
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• 2015

For rear metallization with Al paste, Al back contacts require good passivation, high reflectance, and a processing temperature window compatible with the front metal. In this paper, the effect of the firing ambient during the metallization process on the formation of Al rear metal was investigated. We chose three different gases as ambient gases during the firing process. Using SEM, we observed the formation of a back surface field in $N_2$, $O_2$, and Air ambients. To determine the effect of the ambient on Voc, the suns-Voc tool was used. In this study, we described the mechanism of burn-out of organic materials in Al paste during the firing process. The oxygen ambient plays an important role in the burn-out process. We calculated the efficiency with obtained the back surface recombination velocities using PC1D simulation. It was found that the presence of oxygen during the firing process influenced the uniform back surface field because the organic materials in the Al paste were efficiently burned out during heating. The optimized temperature with oxygen flow shows an absolute efficiency of 19.1% at PC1D simulation.

• Electrical & Electronic Materials
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• v.10 no.10
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• pp.1034-1040
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• 1997

A solar cell conversion effiency was degraded by grain boundary effect in polycrystalline silicon. Grain boundaries acted as potential barriers as well as recombination centers for the photo-generated carriers. To reduce these effects of the grain boundaries we investigated various influencing factors such as emitter thickness thermal treatment preferential chemical etching of grain boundaries grid design contact metal and top metallization along boundaries. Pretreatment in $N_2$atmosphere and gettering by POCl$_3$and Al were performed to obtain multicrystalline silicon of the reduced defect density. Structural electrical and optical properties of slar cells were characterized before and after each fabrication process. Improved conversion efficiencies of solar cell were obtained by a combination of pretreatment above 90$0^{\circ}C$ emitter layer of 0.43${\mu}{\textrm}{m}$ Al diffusion in to grain boundaries on rear side fine grid finger top Yb metal and buried contact metallization along grain boundaries.

• 한국태양에너지학회:학술대회논문집
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• 2011.11a
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• pp.34-39
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• 2011

Screen printing method is a common way to fabricate the crystalline silicon solar cell with low-cost and high-efficiency. The screen printing metallization use silver paste and aluminum paste for front and rear contact, respectively. Especially the rear contact between aluminum and silicon is important to form the back surface filed (Al-BSF) after firing process. BSF plays an important role to reduces the surface recombination due to $p^+$ doping of back surface. However, Al electrode on back surface leads to bow occurring by differences in coefficient of thermal expansion of the aluminum and silicon. In this paper, we studied the properties of mono crystalline silicon solar cell for rear electrode with aluminum and aluminum-boron in order to characterize bow and BSF of each paste. The 156*156 $m^2$ p-type silicon wafers with $200{\mu}m$ thickness and 0.5-3 ${\Omega}\;cm$ resistivity were used after texturing, diffusion, and antireflection coating. The characteristics of solar cells was obtained by measuring vernier callipers, scanning electron microscope and light current-voltage. Solar cells with aluminum paste on the back surface were achieved with $V_{OC}$ = 0.618V, JSC = 35.49$mA/cm^2$, FF(Fill factor) = 78%, Efficiency = 17.13%.

• Proceedings of the KIEE Conference
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• 1997.07d
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• pp.1430-1432
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• 1997

A solar cell conversion effiency was degraded by grain boundary effect in polycrystalline silicon. To reduce these effects of the grain boundaries, we investigated various influencing factors such as preferential chemical etching of grain boundaries, grid design, transparent conductive thin film, and top metallization along grain boundaries. Pretreatment in $N_2$ atmosphere and gettering by $POCl_3$ and Al were performed to obtain polycrystalline silicon of the reduced defect density. Structural, electrical, and optical properties of solar cells were characterized. Improved conversion efficiencies of solar cell were obtained by a combination of Al diffusion into grain boundaries on rear side, fine grid finger, top Yb metal grid on Cr thin film of $200{\AA}$ and buried contact metallization along grain boundaries.

• Current Photovoltaic Research
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• v.4 no.1
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• pp.12-15
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• 2016

Screen printing technique followed by firing has commonly been used as metallization for both laboratory and industrial based solar cells. In the solar cell industry, the firing process is usually conducted in a belt furnace and needs to be optimized for fabricating high efficiency solar cells. The printed-Al layer on the silicon is rapidly heated at over $800^{\circ}C$ which forms a layer of back surface field (BSF) between Si-Al interfaces. The BSF layer forms $p-p^+$ structure on the rear side of cells and lower rear surface recombination velocity (SRV). To have low SRV, deep $p^+$ layer and uniform junction formation are required. In this experiment, firing process was carried out by using conventional tube furnace with $N_2$ gas atmosphere to optimize $V_{oc}$ of laboratory cells. To measure the thickness of BSF layer, selective etching was conducted by using a solution composed of hydrogen fluoride, nitric acid and acetic acid. The $V_{oc}$ and pseudo efficiency were measured by Suns-$V_{oc}$ to compare cell properties with varied firing condition.

• Current Photovoltaic Research
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• v.4 no.4
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• pp.145-149
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• 2016

Characteristic of aluminum-silicon alloy paste which is applied on the rear side of PERC cell was investigated. The paste was made by aluminum-silicon alloy with eutectic composition to avoid the formation of void which is responsible for the degradation of the open-circuit voltage. Also, the glass frit component of the paste was changed to improve the adhesion of aluminum-silicon paste. We observed the formation of void and local back surface field between aluminum electrode and silicon base by SEM. The light IV, quantum efficiency and reflectance of the solar cells were characterized and compared for each paste.

• 한국신재생에너지학회:학술대회논문집
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• 2009.06a
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• pp.91-91
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• 2009

태양전지의 전극소성 시 알루미늄 후면 전극이 실리콘으로 확산되어 후면전계(Back Surface Field)를 형성한다. 후면 패시베이션층은 후면반사율을 높여 내부광흡수경로를 늘리고 후면재결합속도를 감소시킨다. 본 논문은 후면 패시베이션층이 알루미늄 후면전계 형성에 미치는 영향 및 온도에 따른 변화를 관찰하였다. 절삭손상(Saw damage)이 제거된 실리콘 기판의 후면에 패시베이션층이 없는 것과 후면 패시베이션층으로 사용되는 실리콘 산화막을 형성시킨 시편을 제작하였다. 알루미늄 후면전극을 스크린 인쇄 후 소성온도를 달리하여 실리콘과 알루미늄과의 반응을 비교하였다. 주사전자현미경(SEM)을 사용하여 시편의 단면사진으로부터 소성온도에 따른 실리콘과 알루미늄간의 반응 여부를 관찰하였고, 열분석을 통해 반응 온도를 조사하였다. 패시베이션층이 없는 경우에는 약 $600^{\circ}C$부터 실리콘과 알루미늄간의 반응이 시작되었고, 패시베이션층이 있는 경우에는 약 $700^{\circ}C$부터 반응이 시작되는 결과를 얻었다.

• Solar Energy
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• v.17 no.4
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• pp.3-11
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• 1997

Because grain boundaries in polycrystalline silicon act as potential barriers and recombination centers for the photo-generated charge carriers, these defects degrade conversion effiency of solar cell. To reduce these effects of grain boundaries, we investigated various influencing factors such as thermal treatment, various grid pattern, selective wet etching for grain boundaries, buried contact metallization along grain boundaries, grid on metallic thin film. Pretreatment above $900^{\circ}C$ in $N_2$ atmosphere, gettering by $POCl_3$ and Al treatment for back surface field contributed to obtain a high quality poly-Si. To prevent carrier losses at the grain boundaries, we carried out surface treatment using Schimmel etchant. This etchant delineated grain boundaries of $10{\mu}m$ depth as well as surface texturing effect. A metal AI diffusion into grain boundaries on rear side reduced back surface recombination effects at grain boundaries. A combination of fine grid with finger spacing of 0.4mm and buried electrode along grain boundaries improved short circuit current density of solar cell. A ultra-thin Chromium layer of 20nm with transmittance of 80% reduced series resistance. This paper focused on the grain boundary effect for terrestrial applications of solar cells with low cost, large area, and high efficiency.