JP2009084145A - Si POLYCRYSTALLINE INGOT, METHOD OF PRODUCING Si POLYCRYSTALLINE INGOT, AND Si POLYCRYSTALLINE WAFER - Google Patents
Si POLYCRYSTALLINE INGOT, METHOD OF PRODUCING Si POLYCRYSTALLINE INGOT, AND Si POLYCRYSTALLINE WAFER Download PDFInfo
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Abstract
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本発明は、高効率な太陽電池用を作製するのに必要な、高品質で高均質な太陽電池用のＳｉ多結晶インゴット、Ｓｉ多結晶インゴットの製造方法およびＳｉ多結晶ウェハーに関するものである。 The present invention relates to a Si polycrystal ingot for a high-quality and highly homogeneous solar cell, a method for producing the Si polycrystal ingot, and a Si polycrystal wafer that are necessary for producing a highly efficient solar cell.
現在、国内外において、Ｓｉ融液から一方向成長を利用したキャスト成長法を用いて大容積のＳｉ多結晶インゴットを成長させ、そのインゴットを薄板に切り出してＳｉ多結晶ウェハーを作製し、太陽電池にデバイス化する方法が、実用技術として主流を占めている。一方向成長を利用したキャスト成長法とは、ルツボ内に入れたＳｉ融液を、ルツボ底面から上方向に向かって凝固させて、Ｓｉバルク多結晶インゴットを成長させる方法である。この手法で作製したＳｉ多結晶インゴットは、結晶粒サイズが通常0.1cm〜0.5cm程度と小さく、また時々1cm以上の大きさの結晶粒が混ざることもあるが、インゴット全体積の９０％以上の体積部分が平均幅で1cm以下の小さな結晶粒で占められている。 Currently, in Japan and overseas, a large-volume Si polycrystalline ingot is grown from a Si melt using a unidirectional growth method, and the ingot is cut into a thin plate to produce a Si polycrystalline wafer. The method of making it into a device dominates as a practical technology. The cast growth method using unidirectional growth is a method of growing a Si bulk polycrystalline ingot by solidifying the Si melt contained in the crucible upward from the bottom of the crucible. The Si polycrystal ingot produced by this method has a crystal grain size usually as small as about 0.1 cm to 0.5 cm, and sometimes crystal grains with a size of 1 cm or more are sometimes mixed, but more than 90% of the total volume of the ingot The volume part is occupied by small crystal grains with an average width of 1 cm or less.
また、このＳｉ多結晶インゴットでは、不特定の断面でこのインゴットを切り出した時、その断面積の最大でも５０％程度が、通常ではせいぜい20%以下が、±１５°の範囲内で方位が同一の結晶面を有する結晶粒で構成されている。ただし、ここでの結晶粒の定義として、その結晶粒内に双晶を内包するものは一つの結晶粒とする。そのため、このＳｉ多結晶インゴットから切り出して作製したＳｉ多結晶ウェハーにおいては、結晶粒サイズが通常0.1cm〜0.5cm程度と小さく、また時々1cm以上の大きさの結晶粒が混ざることもあるが、１枚のウェハーの面積の90%以上の面積部分が平均幅で1cm以下の小さな結晶粒で占められている。また、このＳｉ多結晶ウェハーでは、その面積の最大でも50%程度が、通常ではせいぜい20%以下が、±１５°の範囲内で方位が同一の結晶面を有する結晶粒で構成されている。 Further, in this Si polycrystal ingot, when this ingot is cut out at an unspecified cross section, the maximum cross section is about 50%, usually no more than 20%, but the orientation is the same within a range of ± 15 °. It is comprised by the crystal grain which has a crystal plane. However, as a definition of the crystal grain here, a crystal grain that includes twins in the crystal grain is a single crystal grain. Therefore, in a Si polycrystalline wafer produced by cutting out from this Si polycrystalline ingot, the crystal grain size is usually as small as about 0.1 cm to 0.5 cm, and sometimes crystal grains of a size of 1 cm or more may be mixed, Over 90% of the area of one wafer is occupied by small crystal grains with an average width of 1 cm or less. Further, in this Si polycrystalline wafer, about 50% of the maximum area, usually 20% or less, is composed of crystal grains having crystal planes having the same orientation within a range of ± 15 °.
このため、通常のＳｉ多結晶インゴットやこのインゴットから切り出したＳｉ多結晶ウェハーを用いて太陽電池を作製した場合、多くの結晶粒界が存在し、しかもその中で全ての結晶粒界の50％程度がランダム粒界になっている。このため、亜粒界をはじめとする多くの結晶欠陥が発生し、高品質な結晶とはならず、太陽電池の発電効率も上がらないという問題点がある。 For this reason, when a solar cell is produced using a normal Si polycrystal ingot or a Si polycrystal wafer cut out from this ingot, there are many crystal grain boundaries, and 50% of all the crystal grain boundaries among them. The degree is a random grain boundary. For this reason, many crystal defects including subgrain boundaries are generated, resulting in a problem that the crystal does not become high quality and the power generation efficiency of the solar cell does not increase.
太陽電池の発電効率を高めるために、キャスト成長の初期段階にデンドライトを成長させ、平均結晶粒径が5mm以上の多結晶インゴットを成長させる方法が報告されている（特許文献１参照）。また、同様の方法でキャスト成長の初期段階にデンドライトを成長させることで、インゴットの成長方向の結晶方位を｛111｝面近傍に揃える方法が報告されている（特許文献２参照）。 In order to increase the power generation efficiency of solar cells, a method has been reported in which dendrites are grown in the initial stage of cast growth to grow polycrystalline ingots having an average crystal grain size of 5 mm or more (see Patent Document 1). In addition, a method has been reported in which dendrites are grown in the initial stage of cast growth by the same method to align the crystal orientation in the growth direction of the ingot in the vicinity of the {111} plane (see Patent Document 2).
しかしながら、特許文献１の方法では、結晶粒径を制御することはできても、結晶粒界の粒界性格やインゴットの結晶方位を制御することは不可能であり、単に成長初期段階にデンドライトを成長させるだけであり、デンドライトの成長方位やデンドライトの伸びる方向を制御することが困難である。また、特許文献２では、成長初期段階にデンドライトを成長させることで、インゴットの結晶方位を｛111｝面近傍に揃えることができると報告しているが、そもそもシリコンにおいては、｛111｝面が安定面であるため、成長初期段階にデンドライトを成長させない通常のキャスト法で作製されるインゴットにおいても、インゴットの成長方向の結晶方位は｛111｝面に揃っている。このようなインゴットの成長方向が｛111｝面に揃った多結晶では粒界性格を制御することは困難であり、その結果、ランダム粒界の割合が50％程度存在してしまうため、一方向成長の段階でランダム粒界から亜粒界が発生してしまい、インゴット上部の結晶品質が劣化し、太陽電池に用いることができない。 However, in the method of Patent Document 1, although it is possible to control the crystal grain size, it is impossible to control the grain boundary character of the grain boundary and the crystal orientation of the ingot. It is only allowed to grow, and it is difficult to control the growth direction of the dendrite and the direction in which the dendrite extends. Patent Document 2 reports that the crystal orientation of the ingot can be aligned in the vicinity of the {111} plane by growing dendrite in the initial stage of growth. In the first place, in silicon, the {111} plane is Since it is a stable surface, the crystal orientation in the growth direction of the ingot is aligned with the {111} plane even in an ingot produced by a normal casting method in which dendrite is not grown in the initial stage of growth. In such a polycrystal with the ingot growth direction aligned on the {111} plane, it is difficult to control the grain boundary character, and as a result, the ratio of the random grain boundary is about 50%. Subgrain boundaries are generated from random grain boundaries at the stage of growth, the crystal quality of the upper part of the ingot is deteriorated, and cannot be used for solar cells.
本発明は、このような課題に着目してなされたもので、高効率な太陽電池用を作製するのに必要な、高品質で高均質な太陽電池用のＳｉ多結晶インゴット、Ｓｉ多結晶インゴットの製造方法およびＳｉ多結晶ウェハーを提供することを目的としている。 The present invention has been made paying attention to such a problem, and is necessary for producing a high-efficiency solar cell. A high-quality, high-homogeneous solar cell Si ingot, Si polycrystal ingot It is an object of the present invention to provide a manufacturing method and a Si polycrystalline wafer.
太陽電池をクリーンエネルギーとして大々的に活用するためには、実用サイズのウェハーを用いて18%以上の変換効率がでる高効率太陽電池が作製可能な高品質かつ高均質なＳｉ多結晶インゴットやＳｉ多結晶ウェハーが不可欠である。しかし、高品質かつ高均質なＳｉ多結晶インゴットやＳｉ多結晶ウェハーがどの様なものであるか、真に何を抑えればこのようなインゴットやウェハーになるかは不明であった。 In order to make extensive use of solar cells as clean energy, high-quality and highly homogeneous Si polycrystal ingots and Si polycrystals that can produce high-efficiency solar cells with a conversion efficiency of 18% or more using a practical size wafer Crystal wafers are essential. However, it is unclear what kind of high-quality and highly uniform Si polycrystal ingots and Si polycrystal wafers are, and what is really suppressed to make such ingots and wafers.
そこで、本発明者らは、独自技術として、Ｓｉ多結晶インゴットやＳｉ多結晶ウェハーの結晶粒サイズ、結晶粒方位、粒界性格を制御できる結晶成長技術として、デンドライト利用キャスト成長法や浮遊キャスト成長法を考案し、高効率太陽電池が作製できる高品質かつ高均質なＳｉ多結晶インゴットやＳｉ多結晶ウェハーがどのようなものでなければならないかを研究してきた。 Therefore, the present inventors have developed, as a unique technology, a dendrite-based cast growth method or a floating cast growth as a crystal growth technology capable of controlling the crystal grain size, crystal grain orientation, and grain boundary character of a Si polycrystal ingot or Si polycrystal wafer. We have devised a method and have been studying what high-quality, high-homogeneous Si polycrystal ingots and Si polycrystal wafers should be capable of producing high-efficiency solar cells.
その結果、高効率な太陽電池用を作製するのに必要な、高品質で高均質な太陽電池用のＳｉバルク多結晶インゴット、Ｓｉ多結晶インゴットの製造方法およびＳｉ多結晶ウェハーを見出した。 As a result, the present inventors have found a high-quality, high-homogeneous solar cell Si bulk polycrystalline ingot, a method for producing a Si polycrystalline ingot, and a Si polycrystalline wafer, which are necessary for producing a highly efficient solar cell.
本発明によれば、全体積の２／３以上の体積部分が平均幅で１cm以上の大きさの結晶粒で占められており、かつ不特定の断面で切り出した時、その断面積の70%以上が、±１５°の範囲内で面方位が同一の結晶面を有する結晶粒で構成されていることを、特徴とするＳｉ多結晶インゴットが得られる。ただし、ここでの結晶粒の定義として、その結晶粒内に双晶を内包するものは一つの結晶粒とする。 According to the present invention, a volume part of 2/3 or more of the total volume is occupied by crystal grains having an average width of 1 cm or more, and 70% of the cross-sectional area when cut out with an unspecified cross section. The Si polycrystal ingot characterized in that the above is composed of crystal grains having crystal faces having the same plane orientation within a range of ± 15 ° is obtained. However, as a definition of the crystal grain here, a crystal grain that includes twins in the crystal grain is a single crystal grain.
また、本発明によれば、底面に平行に切り出した時、その断面積の70%以上が、±１５°の範囲内で面方位が{112}または{110}の結晶面を有する結晶粒で構成されていることを、特徴とするＳｉ多結晶インゴットが得られる。 Further, according to the present invention, when cut out parallel to the bottom surface, 70% or more of the cross-sectional area is a crystal grain having a crystal plane of {112} or {110} within a range of ± 15 °. A Si polycrystal ingot characterized by being configured is obtained.
また、本発明によれば、全重量が100kg以上であることを、特徴とするＳｉ多結晶インゴットが得られる。 Moreover, according to the present invention, a Si polycrystal ingot characterized by having a total weight of 100 kg or more can be obtained.
また、本発明によれば、Ｓｉ融液からキャスト法を利用してＳｉ多結晶インゴットを成長させるＳｉ多結晶インゴットの製造方法であって、Ｓｉ多結晶インゴット成長の初期過程において、前記Ｓｉ融液の入った坩堝底面に沿って成長するデンドライト結晶の発生位置を制御するよう、前記坩堝底面を線状形状、点状、円周状またはそれらを複数組み合わせた形状の冷却管で冷却することを、特徴とするＳｉ多結晶インゴットの製造方法が得られる。この本発明に係るＳｉ多結晶インゴットの製造方法によれば、本発明に係るＳｉ多結晶インゴットを製造することができる。 In addition, according to the present invention, there is provided a Si polycrystalline ingot manufacturing method for growing a Si polycrystalline ingot from a Si melt by using a casting method, wherein the Si melt is grown in an initial stage of the Si polycrystalline ingot growth. Cooling the crucible bottom surface with a cooling tube having a linear shape, a point shape, a circumferential shape, or a combination thereof, so as to control the generation position of the dendrite crystal growing along the crucible bottom surface containing A characteristic Si polycrystalline ingot manufacturing method is obtained. According to the method for producing a Si polycrystalline ingot according to the present invention, the Si polycrystalline ingot according to the present invention can be produced.
また、本発明によれば、Ｓｉ多結晶インゴットから切り出され、表面積の70%以上の面積部分が平均幅で１cm以上の大きさの結晶粒で占められており、かつ前記表面積の70%以上が、±１５°の範囲内で面方位が同一の結晶面を有する結晶粒で構成されていることを、特徴とするＳｉ多結晶ウェハーが得られる。ただし、ここでの結晶粒の定義として、その結晶粒内に双晶を内包するものは一つの結晶粒とする。 Further, according to the present invention, an area portion of 70% or more of the surface area that is cut out from the Si polycrystalline ingot is occupied by crystal grains having an average width of 1 cm or more, and 70% or more of the surface area is occupied. A Si polycrystalline wafer characterized by being composed of crystal grains having crystal planes having the same plane orientation within a range of ± 15 ° can be obtained. However, as a definition of the crystal grain here, a crystal grain that includes twins in the crystal grain is a single crystal grain.
また、本発明によれば、前記表面積の70%以上が、±１５°の範囲内で面方位が{112}または{110}の結晶面を有する結晶粒で構成されていることを、特徴とするＳｉ多結晶ウェハーが得られる。 Further, according to the present invention, 70% or more of the surface area is composed of crystal grains having a crystal plane of {112} or {110} within a range of ± 15 °, Si polycrystalline wafer is obtained.
また、本発明によれば、全面積が100cm2以上であることを、特徴とするＳｉ多結晶ウェハーが得られる。 Moreover, according to the present invention, a Si polycrystalline wafer characterized in that the total area is 100 cm 2 or more can be obtained.
本発明により、従来から実現が渇望されていた、低コストかつ高効率な太陽電池を実現可能な、目指すべき高品質かつ高均質なＳｉ多結晶インゴットやＳｉ多結晶ウェハーの概念が明らかとなり、太陽電池の普及に対して大きな効果が期待できる。本発明により、高効率な太陽電池用を作製するのに必要な、高品質で高均質な太陽電池用のＳｉ多結晶インゴット、Ｓｉ多結晶インゴットの製造方法およびＳｉ多結晶ウェハーを提供することができる。 According to the present invention, the concept of a high-quality and high-homogeneity Si polycrystalline ingot or Si polycrystalline wafer to be achieved, which can realize a low-cost and high-efficiency solar cell that has been eagerly desired to be realized, has been clarified. A great effect on the spread of batteries can be expected. According to the present invention, it is possible to provide a high-quality, high-homogeneous solar cell Si polycrystalline ingot, a method for producing a Si polycrystalline ingot, and a Si polycrystalline wafer, which are necessary for producing a highly efficient solar cell. it can.
以下、本発明について詳細に説明する。
キャスト成長炉を用いて、石英坩堝内に入れたＳｉ原料を融解した後、一方向成長の初期段階に、石英坩堝底面の下方向から線状形状の冷却管を近づけることにより、石英坩堝内のＳｉ融液を線状に局部的に冷却した。これにより、デンドライト結晶が、局部的に冷却された線状の冷却管の直上の融液からのみ、坩堝底面に沿って成長した。その後、温度勾配中で坩堝を移動させることにより一方向成長を行い、Ｓｉバルク多結晶インゴットを作製した。比較のため、線状の冷却管を使用せずに成長初期に坩堝底面に沿ってデンドライト結晶を成長させた後、一方向成長させた従来のＳｉバルク多結晶インゴットも作製した。この場合、線状の形状の冷却管で説明したが、冷却管の形状が点状または円周状または線状形状も含み複数にそれらを組み合わせた形状の冷却管を用いて冷却しても、条件の最適化により所望の効果が得られる。
Hereinafter, the present invention will be described in detail.
After melting the Si raw material put in the quartz crucible using a cast growth furnace, the linear shaped cooling tube is approached from the lower side of the bottom of the quartz crucible to the initial stage of unidirectional growth. The Si melt was locally cooled linearly. Thereby, the dendrite crystal grew along the crucible bottom only from the melt immediately above the linear cooling pipe cooled locally. Then, the unidirectional growth was performed by moving the crucible in the temperature gradient, and the Si bulk polycrystalline ingot was produced. For comparison, a conventional Si bulk polycrystal ingot grown in one direction after a dendrite crystal was grown along the bottom of the crucible at the initial stage of growth without using a linear cooling tube was also produced. In this case, the cooling pipe having a linear shape has been described, but even if the cooling pipe is cooled using a cooling pipe having a shape including a dot shape, a circumferential shape, or a linear shape, and a combination of them. The desired effect can be obtained by optimizing the conditions.
Ｓｉ多結晶インゴットから10cm×10cmの角型で、厚さ２５０μmのＳｉ多結晶ウェハーを切り出し、太陽電池を試作して、性能を評価した。太陽電池の試作プロセスは、ウェハーの表面に、ドーパントとしてリンを含む溶液をスピンコータにより塗布し、拡散炉で800〜900℃程度に加熱することにより、表面に不純物拡散層であるｎ+層を形成した。次に、スパッタリング法により、ITO膜を形成した。次に、スクリーン印刷法により、ウェハーの裏面にアルミニウムペーストを印刷し、これを700℃程度で加熱することで、裏面のアルミニウム電極と、アルミニウムを多量に含んだp+層を形成した。次に、スクリーン印刷法により、ウェハーの表面に、櫛型形状に銀ペーストを塗布し、600℃程度で加熱することにより、銀ペーストとｎ+層との間にオーミック接触を取り、太陽電池を完成させた。 A 10 cm × 10 cm square silicon wafer having a thickness of 250 μm was cut out from a Si polycrystal ingot, a solar cell was prototyped, and performance was evaluated. In the solar cell prototype process, a solution containing phosphorus as a dopant is applied to the surface of a wafer by a spin coater and heated to about 800 to 900 ° C. in a diffusion furnace to form an n + layer as an impurity diffusion layer on the surface. did. Next, an ITO film was formed by sputtering. Next, an aluminum paste was printed on the back surface of the wafer by screen printing and heated at about 700 ° C. to form an aluminum electrode on the back surface and a p + layer containing a large amount of aluminum. Next, by applying a silver paste in a comb shape on the surface of the wafer by screen printing and heating at about 600 ° C., ohmic contact is made between the silver paste and the n + layer, and the solar cell is mounted. Completed.
完成した太陽電池に、100mW/cm2の擬似太陽光を照射し、温度25℃の下で、電流電圧特性を測定し、最大出力から変換効率を求めた。図１は、本発明のＳｉ多結晶インゴットから試作した太陽電池の効率（変換効率ηdendrite）と、従来のキャスト法によるインゴットから試作した太陽電池の効率（変換効率ηnormal）との比である。本発明によるＳｉ多結晶インゴットによる太陽電池は、平均結晶粒サイズが3ｃｍで、±１５°の範囲内で結晶粒方位が｛112｝面に75％揃ったＳｉ多結晶インゴットから切り出したＳｉ多結晶ウェハーを用いた。図１から、従来のインゴットによる太陽電池の効率は、インゴット上部程、効率が低下していることが分かる。 The completed solar cell was irradiated with 100 mW / cm 2 pseudo-sunlight, the current-voltage characteristics were measured at a temperature of 25 ° C., and the conversion efficiency was determined from the maximum output. FIG. 1 is a ratio between the efficiency of a solar cell prototyped from the Si polycrystalline ingot of the present invention (conversion efficiency η dendrite ) and the efficiency of a solar cell prototyped from an ingot produced by a conventional casting method (conversion efficiency η normal ). . The solar cell using the Si polycrystal ingot according to the present invention has an average crystal grain size of 3 cm and a Si polycrystal cut from a Si polycrystal ingot having a crystal grain orientation of 75% in the {112} plane within a range of ± 15 °. A wafer was used. From FIG. 1, it can be seen that the efficiency of the solar cell using the conventional ingot decreases as the upper portion of the ingot increases.
前述の本発明のＳｉ多結晶インゴットは、成長初期段階に坩堝底面に沿ってデンドライト成長を発現させ、しかる後にそのデンドライト結晶の上面にＳｉ多結晶を成長させることにより、結晶粒サイズを大きくし、かつ成長方向が<110>か<112>方向になるように制御し、結晶粒方位を揃えている。この時、坩堝底面に沿って成長するデンドライト結晶の発生位置を制御して、デンドライト結晶の発生比率や制御性を一層向上させて、大きな結晶粒の存在比率や結晶粒方位の揃った比率を高めるために、坩堝底面に線状形状をした冷却管を接近させて坩堝底面付近の温度分布を制御している。これに対して、従来のデンドライト結晶を利用したキャスト法によるインゴットは、成長初期段階でデンドライト結晶の発現比率の制御を行っていないため、全体積の２／３以上の体積部分を平均幅で１cm以上の大きさの結晶粒に揃えたり、不特定の断面で切り出した時、その断面積の70%以上が、±１５°の範囲内で面方位が同一の結晶面を有する結晶粒で構成されている特徴を出すことができない。 The aforementioned Si polycrystal ingot of the present invention expresses dendrite growth along the bottom of the crucible in the initial stage of growth, and then grows Si polycrystal on the upper surface of the dendrite crystal, thereby increasing the crystal grain size, In addition, the growth direction is controlled to be <110> or <112> to align the crystal grain orientation. At this time, the generation position and controllability of the dendrite crystals are further improved by controlling the generation position of the dendrite crystals growing along the bottom surface of the crucible, and the ratio of large crystal grains existing and the ratio of crystal grain orientations are increased. For this purpose, a linear cooling pipe is brought close to the bottom of the crucible to control the temperature distribution near the bottom of the crucible. On the other hand, ingots produced by the conventional casting method using dendrite crystals do not control the expression ratio of dendrite crystals at the initial stage of growth, so that the volume of 2/3 or more of the total volume is 1 cm in average width. When aligned with crystal grains of the above size or cut out with an unspecified cross section, 70% or more of the cross-sectional area is composed of crystal grains having crystal planes with the same plane orientation within a range of ± 15 °. I can not put out the characteristics that are.
表１は、本発明のＳｉ多結晶インゴットから作製した太陽電池、および従来のＳｉ単結晶ウェハーを用いて作製した太陽電池の変換効率の比較データである。本発明のＳｉ多結晶インゴットは、デンドライト利用キャスト法により作製され、平均結晶粒サイズが3ｃｍで、±１５°の範囲内で結晶粒方位が｛112｝面に75％揃っている。表１から、本発明によるＳｉ多結晶ウェハーの太陽電池の変換効率が、Ｓｉ単結晶ウェハーの太陽電池の変換効率に大変近い値が得られ、本発明によるＳｉ多結晶インゴットの品質が、Ｓｉ単結晶に近いことがわかる。 Table 1 shows comparison data of conversion efficiencies of a solar cell manufactured from the Si polycrystalline ingot of the present invention and a solar cell manufactured using a conventional Si single crystal wafer. The Si polycrystal ingot of the present invention is produced by a dendrite casting method, has an average crystal grain size of 3 cm, and has a crystal grain orientation of 75% in the {112} plane within a range of ± 15 °. From Table 1, the conversion efficiency of the solar cell of the Si polycrystalline wafer according to the present invention is very close to the conversion efficiency of the solar cell of the Si single crystal wafer, and the quality of the Si polycrystalline ingot according to the present invention is It turns out that it is close to a crystal.
図２は、Ｓｉ多結晶ウェハー中の結晶粒サイズとその占有率との比較である。デンドライト利用キャスト法により作製した、本発明によるＳｉ多結晶インゴットから切り出した本発明によるＳｉ多結晶ウェハー中の結晶粒サイズおよびその占有率と、通常のキャスト法で作製したＳｉ多結晶ウェハー中の結晶粒サイズおよびその占有率との比較をしめす。どちらのＳｉ多結晶インゴットも内径50mmの坩堝を用いて作製した。図２から、本発明のＳｉ多結晶ウェハー中の主たる結晶粒サイズは１３ｍｍで、その占有率が８５％であることが分かる。 FIG. 2 is a comparison between the crystal grain size in the Si polycrystalline wafer and its occupation ratio. Grain size and occupancy in the Si polycrystalline wafer according to the present invention cut out from the Si polycrystalline ingot according to the present invention produced by the dendritic cast method, and crystals in the Si polycrystalline wafer produced by the usual casting method Comparison with grain size and occupancy is shown. Both Si polycrystal ingots were prepared using a crucible having an inner diameter of 50 mm. FIG. 2 shows that the main crystal grain size in the Si polycrystalline wafer of the present invention is 13 mm and the occupation ratio is 85%.
図３は、Ｓｉ多結晶ウェハーの結晶粒分布より、結晶粒サイズおよび結晶粒方位の分布を比較した後方散乱電子線回折パターン（EBSP）である。図３(a)は、本発明によるＳｉ多結晶ウェハーで、図３(b)は通常の方法で作製したＳｉ多結晶ウェハーであり、いずれも成長方向と垂直に切断し、ウェハーを切り出した。図３(a)から、本発明によるＳｉ多結晶インゴットでは、結晶粒サイズが大きく揃い、かつその結晶粒方位が同じ方向に揃っていることが分かる。 FIG. 3 is a backscattered electron diffraction pattern (EBSP) comparing the distribution of crystal grain size and crystal grain orientation from the crystal grain distribution of the Si polycrystalline wafer. FIG. 3 (a) is a Si polycrystalline wafer according to the present invention, and FIG. 3 (b) is a Si polycrystalline wafer produced by a normal method, both of which were cut perpendicular to the growth direction and cut out. From FIG. 3 (a), it can be seen that in the Si polycrystal ingot according to the present invention, the crystal grain sizes are large and the crystal grain orientations are aligned in the same direction.
図４は、本発明による成長初期に坩堝底面に線状形状をした冷却管を接近させてデンドライトの発生位置を制御して成長させたＳｉ多結晶インゴットと、線状形状の冷却管を使用せずに成長初期に任意の位置でデンドライトを発生させて作製したＳｉバルク多結晶インゴットとを、成長方向に平行な方向に切断したインゴットの縦断面の結晶粒方位の分布を比較した後方散乱電子線回折パターン（EBSP）である。本発明により作製したインゴットは、図３(a)で示したように、成長方向と垂直に切り出した断面だけでなく、成長方向と平行な方向の断面においても結晶粒サイズが大きく、かつ結晶粒方位が揃っていることが分かる。 FIG. 4 shows a Si polycrystal ingot grown by controlling a dendrite generation position by bringing a linearly shaped cooling tube close to the bottom of the crucible at the initial stage of growth according to the present invention, and a linearly shaped cooling tube. Backscattered electron beam comparing the distribution of grain orientation in the longitudinal section of an ingot that was cut in a direction parallel to the growth direction from a bulk Si ingot produced by generating dendrites at an arbitrary position in the early stage of growth It is a diffraction pattern (EBSP). As shown in FIG. 3 (a), the ingot produced according to the present invention has a large crystal grain size and a crystal grain size not only in a cross section cut out perpendicular to the growth direction but also in a cross section parallel to the growth direction. You can see that the direction is aligned.
図５は、太陽電池の動作時の発光を示す図面である。15mm×15mmの寸法の太陽電池に、外部電圧を印加し、太陽電池の動作時と同等の電流密度である30mA/cm2の電流を流した場合の発光を、CCDカメラにより撮影したときの図である。図５では、異なる３種類の太陽電池を比較しており、それぞれ図５(a)は市販されているキャスト結晶から切り出したＳｉ多結晶ウェハーを用いて作製した太陽電池、図５(b)はデンドライト利用キャスト法により作製した、本発明による平均結晶粒サイズが3ｃｍで、結晶粒方位が｛112｝面に75％揃ったＳｉ多結晶インゴットから切り出した、本発明によるＳｉ多結晶ウェハーを用いて作製した太陽電池、図５(c)は浮遊キャスト法により作製した、本発明による平均結晶粒サイズが3ｃｍで、結晶粒方位が｛112｝面に75％揃ったＳｉ多結晶インゴットから切り出した、本発明によるＳｉ多結晶ウェハーを用いて作製した太陽電池のデータである。図５(a)では、表面の櫛型電極の陰による暗部に加えて表面に多数の暗線が見られることが明確であり、結晶粒が微細であり、キャリアの再結合中心となる粒界や欠陥が多数存在する。一方、図５(b)および(c)における本発明によるＳｉ多結晶ウェハーの太陽電池では、そのような暗線は見られないことからも、高品質なＳｉ多結晶ウェハーが実現され、太陽電池の高効率化が可能であることがわかる。 FIG. 5 is a diagram showing light emission during operation of the solar cell. Figure when the solar cell dimension of 15 mm × 15 mm, by applying an external voltage, the light emission in passing a current of 30 mA / cm 2 is equivalent to the current density and the time of operation of the solar cell were taken by the CCD camera It is. In FIG. 5, three different types of solar cells are compared. FIG. 5 (a) is a solar cell manufactured using a Si polycrystalline wafer cut from a commercially available cast crystal, and FIG. Using a Si polycrystalline wafer according to the present invention cut from a Si polycrystalline ingot having an average grain size of 3 cm according to the present invention and a crystal grain orientation of 75% aligned on the {112} plane, produced by a dendritic cast method. The produced solar cell, FIG. 5 (c), was produced from a Si polycrystal ingot produced by the floating cast method and having an average crystal grain size of 3 cm and a crystal grain orientation of 75% on the {112} plane. It is the data of the solar cell produced using the Si polycrystalline wafer by this invention. In FIG. 5 (a), it is clear that many dark lines are seen on the surface in addition to the dark part due to the shade of the comb electrode on the surface, the crystal grains are fine, and the grain boundaries and recombination centers of the carriers There are many defects. On the other hand, in the solar cell of the Si polycrystalline wafer according to the present invention in FIGS. 5 (b) and (c), since such dark lines are not seen, a high-quality Si polycrystalline wafer is realized, and the solar cell of the solar cell is realized. It can be seen that high efficiency is possible.
太陽電池の普及拡大のためには、太陽電池の低価格化が必要であり、太陽電池用のＳｉ多結晶インゴットにも低価格化の要求がある。キャスト成長法のようなバッチ式の製造方法で得られるＳｉ多結晶インゴットは、一回で製造するインゴットを大型化することで、低価格化を実現できる。本発明のＳｉ多結晶インゴットにおいても、一回での製造重量を１００Kg以上とすることで、工業的に生産した時に、低価格が実現できる。 In order to increase the spread of solar cells, it is necessary to reduce the cost of solar cells, and there is a demand for lowering the cost of Si polycrystal ingots for solar cells. A Si polycrystal ingot obtained by a batch-type manufacturing method such as a cast growth method can be reduced in price by increasing the size of the ingot manufactured at a time. Even in the Si polycrystal ingot of the present invention, when the production weight at one time is 100 kg or more, a low price can be realized when industrially produced.
Ｓｉ多結晶ウェハーを用いた太陽電池は、その発電量はウェハー面積に比例するので、発電量を増したい場合には、ウェハー面積を広くする必要があるが、小面積のウェハーを多数電気的に接続すると、接続のロスが多くなり、結果的に発電効率の低下を招くという問題点がある。そこで、発電効率を維持したままで、発電量を大きくするためには、実用的なＳｉ多結晶ウェハーにおいて、その全面積を100cm2以上とする必要がある。 Solar cells using Si polycrystalline wafers have a power generation amount proportional to the wafer area, so if you want to increase the amount of power generation, you need to increase the wafer area. When connected, there is a problem that connection loss increases, resulting in a decrease in power generation efficiency. Therefore, in order to increase the power generation amount while maintaining the power generation efficiency, it is necessary to make the total area of the practical Si polycrystalline wafer 100 cm 2 or more.
Claims (5)
Ｓｉ多結晶インゴット成長の初期過程において、前記Ｓｉ融液の入った坩堝底面に沿って成長するデンドライト結晶の発生位置を制御するよう、前記坩堝底面を線状形状、点状、円周状またはそれらを複数組み合わせた形状の冷却管で冷却することを、特徴とするＳｉ多結晶インゴットの製造方法。 A method for producing a Si polycrystalline ingot, wherein a Si polycrystalline ingot is grown from a Si melt by using a casting method,
In the initial stage of Si polycrystalline ingot growth, the bottom surface of the crucible is linear, dot-shaped, circumferential or so as to control the generation position of dendritic crystals growing along the bottom surface of the crucible containing the Si melt. A method for producing a Si polycrystal ingot, characterized by cooling with a cooling pipe having a combination of a plurality of the above.
The high-Si content according to claim 4, wherein 70% or more of the surface area is composed of crystal grains having a crystal plane of {112} or {110} within a range of ± 15 °. Crystal wafer.
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| WO2012111850A1 (en) * | 2011-02-18 | 2012-08-23 | 株式会社Sumco | Polycrystalline wafer, method for producing same and method for casting polycrystalline material |
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| JP2014205598A (en) * | 2013-04-15 | 2014-10-30 | 国立大学法人東北大学 | METHOD FOR PRODUCING Si POLYCRYSTALLINE INGOT, AND Si POLYCRYSTALLINE INGOT |
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