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Lan C.W.,National Taiwan University | Lan W.C.,Sino American Silicon Productions Inc. | Lee T.F.,National Taiwan University | Yu A.,Sino American Silicon Productions Inc. | And 4 more authors.
Journal of Crystal Growth | Year: 2012

Directional solidification (DS) has become the major process for growing multi-crystalline silicon (mc-Si) for solar cells in the photovoltaic industry. The control of grains, as well as the grain boundaries, is particularly important to the crystal quality, and thus the solar cell efficiency. In this paper, we review the progress in the grain control of DS mc-Si from lab-scale to industrial-scale experiments. The control of the growth front was found effective in improving the grain size, but the grain size was found decreased with growth due to the sub-grain formation. With a better control of nucleation and grain competition by increasing the undercooling through enhanced uniform or spot cooling, grains with more Σ3 or twin boundaries were obtained. As the grain size increased with height, the growth of dislocations was found much slower than that without grain growth. The conversion efficiency of the solar cells fabricated from the wafers with grain control was significantly improved. Moreover, the seeded growth was also discussed. © 2012 Elsevier B.V.


Yang Y.M.,Sino American Silicon Productions Inc. | Yu A.,Sino American Silicon Productions Inc. | Hsu B.,Sino American Silicon Productions Inc. | Hsu W.C.,Sino American Silicon Productions Inc. | And 2 more authors.
Progress in Photovoltaics: Research and Applications | Year: 2015

The low cost and high quality of multicrystalline silicon (mc-Si) based on directional solidification has become the main stream in photovoltaic (PV) industry. The mc-Si quality affects directly the conversion efficiency of solar cells, and thus, it is crucial to the cost of PV electricity. With the breakthrough of crystal growth technology, the so-called high-performance mc-Si has increased about 1% in solar cell efficiency from 16.6% in 2011 to 17.6% in 2012 based on the whole ingot performance. In this paper, we report our development of this high-performance mc-Si. The key ideas behind this technology for defect control are discussed. With the high-performance mc-Si, we have achieved an average efficiency of near 17.8% and an open-circuit voltage (Voc) of 633mV in production. The distribution of cell efficiency was rather narrow, and low-efficiency cells (<17%) were also very few. The power of the 60-cell module using the high-efficiency cells could reach 261 W as well. Copyright © 2013 John Wiley & Sons, Ltd.


Lan C.W.,National Taiwan University | Yang Y.M.,Sino American Silicon Productions Inc | Yu A.,Sino American Silicon Productions Inc | Wu Y.C.,National Taiwan University | And 3 more authors.
Solid State Phenomena | Year: 2016

In recent years, silicon solar cells continue to remain the main stream in photovoltaic(PV) industry, particularly of made from multi-crystalline silicon (mc-Si). The progress of crystalgrowth technology for mc-Si ingot using directional solidification (DS) is particularly significant.With the breakthrough of the so-called high-performance (HP) mc-Si technology in 2011, the mc-Sisolar cell efficiency had increased from 16.6% in 2011 to 18% or beyond in 2013. Nowadays, HPmc-Si, solar cells from a normal screen-printing aluminum back surface field (Al-BSF) productionline could easily reach 18.3%. With the passivated emitter and rear cell (PERC) structure usingPECVD alumina passivation, an average efficiency of over 19.2% could also be obtained. Theemerging of HP mc-Si almost blocked the development of mono-like technology in 2012, andpushed p-type mono-Si cells to higher efficiency by using advanced technology. Unlike theconventional way of having large grains and electrically-inactive twin boundaries, the growth of HPmc-Si is from small and uniform grains having more random GBs. The grains developed from suchgrain structures significantly relaxes the thermal stress and suppresses the massive generation andpropagation of dislocation clusters. Currently, most of commercial mc-Si ingots are grown by thisconcept, which could be implemented by seeded with small silicon particles or using nucleationagent coatings. The seeded growth has been well adopted in industry. However, the melting controlof the seed layer and the thick red zone induced remain key issues in mass production. Severalmethods have been considered to resolve these issues with some success. The use of nucleationagent layers is a simpler approach, but the control of initial grain structures remains challenging. © (2016) Trans Tech Publications, Switzerland.


Li T.F.,National Taiwan University | Yeh K.M.,National Taiwan University | Hsu W.C.,Sino American Silicon Productions Inc. | Lan C.W.,National Taiwan University | Lan C.W.,Industrial Technology Research Institute of Taiwan
Journal of Crystal Growth | Year: 2011

We report on an idea for grain control during directional solidification using a crucible with notches at the bottom for mc-Si solar materials. It was observed that with a proper notch size, the initial grain competition could be controlled with a proper cooling rate. The notch could enlarge the grains induced by the spot cooling method and the grains became dominant at the later stage of solidification. Furthermore, the crystals grown from the notch showed a higher minority carrier lifetime and a larger area of twins, with a much lower dislocation density as well. The electron back scattered diffraction (EBSD) analysis for the controlled crystals further indicated that the region near the notch had almost the same {1 1 2} orientation from the notch. The proposed method can be easily implemented in commercial ingot production. © 2010 Published by Elsevier B.V. All rights reserved.


Yeh K.M.,National Taiwan University | Hseih C.K.,Sino American Silicon Productions Inc. | Hsu W.C.,Sino American Silicon Productions Inc. | Lan C.W.,National Taiwan University | Lan C.W.,Industrial Technology Research Institute of Taiwan
Progress in Photovoltaics: Research and Applications | Year: 2010

We report simple ideas for grain control by using active cooling and crucible insulation for high-quality multi-crystalline silicon (mc-Si) growth for solar cells. The method employed an active cooling spot to induce initial dendrite growth, and the solidification front was controlled to be slightly convex through crucible insulation. It was found that the percentage of grains having twins was significantly increased by the present approach. The dislocation density for those grains was also significantly lower. More importantly, the successful improvement showed that the grain size and the minority carrier lifetime increased along the growth direction. And the laser beam induced current (LBIC) measurement also showed muchhigher quantum efficiency for the twin area. Copyright © 2010 John Wiley & Sons, Ltd.


Hsieh C.C.,National Taiwan University | Wu Y.C.,National Taiwan University | Lan A.,National Taiwan University | Lan A.,Sino American Silicon Productions Inc. | And 3 more authors.
Journal of Crystal Growth | Year: 2015

The growth of solar silicon ingots by directional solidification using small random (chips) and large oriented (mono-chucks) seeds was carried out, and the defect formations using the ingots grown from the different seeds were compared. To have a similar growth environment, the seeds were placed side by side in the same crucible for the growth. It was observed that the silicon grown from small chips was more vulnerable to carbide precipitation, but the propagation of dislocation clusters was mitigated due to the existence of grain boundaries. On the other hand, the dislocation clusters could easily propagate in the mono-crystalline regime. As a result, as the ingot grew higher, more and larger dislocation clusters were found in the ingot from the large oriented seeds. Images from etched pits, photoluminescence, and minority lifetime were used for the comparison. Similar experiments were also carried in a commercial growth system, and the dislocation clusters in the growth from the small chip seeds were much less than that from the chuck seeds. © 2015 Elsevier B.V.


Wong Y.T.,National Taiwan University | Hsieh C.T.,National Taiwan University | Lan A.,National Taiwan University | Lan A.,Sino American Silicon Productions Inc. | And 2 more authors.
Journal of Crystal Growth | Year: 2014

The grain control in multi-crystalline silicon growth by directional solidification is crucial to the ingot quality. In order to study the nucleation and grain growth behavior, we carried out ingot growth using porous silica coatings, with different Si/SiO2ratios, and the traditional nitride coating for comparison, at the bottom of a small crucible. It was observed that with more silica in the coating, smaller and uniform grains, as well as columnar growth, could be obtained. As a result, more non-Σ grain boundaries were found as well. On the contrary, as silicon became a continuous phase in the coating, the grain refinement was less effective and their grain development in the porous coating was examined. The possible grain nucleation and growth mechanisms in the porous coatings were further proposed. © 2014 Elsevier B.V.


Wong Y.T.,National Taiwan University | Hsu C.,Sino American Silicon Productions Inc. | Lan C.W.,National Taiwan University
Journal of Crystal Growth | Year: 2014

Development of grain structures of multi-crystalline silicon from small spherical seeds with random orientations in directional solidification was investigated. The electron backscattered diffraction (EBSD) analyses of the grains at different pulling rates, i.e., 1, 5, and 20 cm/h, were carried out. It was found that {112}/{111} orientations were dominant at the low crucible pulling speed, while {111} at the high pulling speeds. The percentage of {100} grains was found very low near the top of the ingots. The percentage of non-Σ grain boundaries was around 70% at the beginning and decreased with the solidification distance, while Σ3 grain boundaries or twins increased indicating the importance of twin formation during the development of grain structures. The mechanisms for grain competition and selection were further discussed. © 2013 Elsevier B.V.


Hsieh C.C.,National Taiwan University | Lan A.,National Taiwan University | Lan A.,Sino American Silicon Productions Inc. | Hsu C.,Sino American Silicon Productions Inc. | Lan C.W.,National Taiwan University
Journal of Crystal Growth | Year: 2014

The control of impurity is crucial to the ingot quality and yield in the directional solidification of multi-crystalline silicon for solar cells. The major impurities, such as metals, are mainly from the quartz crucible and the silicon nitride coating. The use of high-purity materials mitigates the problem, but it also increases the cost. Another way is to use diffusion barriers between silicon and these materials to reduce the incorporation of impurities. In this study, polysilazane and barium oxide coatings with different layer configurations were considered. With the diffusion barrier layer, the lifetime of the ingot was improved and the red zone was reduced. The wetting behaviors of these diffusion barriers in contact with silicon were also discussed. © 2014 Elsevier B.V.

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