JP3727879B2

JP3727879B2 - Method for evaluating crystalline Si thin film

Info

Publication number: JP3727879B2
Application number: JP2001384761A
Authority: JP
Inventors: 靖之小林; 章二森田; 義道米倉; 宏次佐竹
Original assignee: Mitsubishi Heavy Industries Ltd
Current assignee: Mitsubishi Heavy Industries Ltd
Priority date: 2001-12-18
Filing date: 2001-12-18
Publication date: 2005-12-21
Anticipated expiration: 2021-12-18
Also published as: JP2003188398A

Description

【０００１】
【技術分野】
本発明は、結晶性Ｓｉ薄膜の評価方法に関する。なお、本願明細書において、「結晶性」及び「多結晶」の用語は、少なくとも結晶Ｓｉを含み、部分的に非晶質を含む場合をも意味するものとする。
【０００２】
【背景技術】
従来、薄膜型シリコン（Ｓｉ）光電変換装置としては、例えば図１に示すものが知られている。図１は、基板側から光が入射する形式である。
【０００３】
図中の付番１は、ガラス基板を示す。この基板１上には、ＩＴＯ，ＳｎＯ_２等からなる透明導電膜２を介して結晶性Ｓｉ薄膜（発電膜）３が形成されている。ここで、結晶性Ｓｉ薄膜３は、ｐ型の結晶性Ｓｉ膜３ａと、ｉ型の結晶性Ｓｉ発電膜３ｂと、ｎ型の結晶性Ｓｉ膜３ｃとから構成されている。前記結晶性Ｓｉ薄膜３上には、通常、図示しないが透明導電膜、金属電極膜が順次形成される。
【０００４】
こうした構成の太陽電池において、太陽光はガラス基板１側から入射して透明導電膜２を透過して各発電膜に入射する。太陽光は、発電膜３ｂに吸収されて、ｐ型の結晶性Ｓｉ膜３ａと、ｎ型の結晶性Ｓｉ膜３ｃとの間に起電力が発生し、電力を外部に取り出すことができる。ところで、こうした太陽電池において、発電膜３の製膜には一般にプラズマＣＶＤが用いられているが、装置依存性が大きいため、製膜後の膜質の評価を以てプラズマＣＶＤにおける製膜条件を設定するのが妥当である。
【０００５】
従来、結晶性Ｓｉ薄膜を有したＳｉ太陽電池の膜質の指標として、Ｘ線回折のθ−２θ法による（２２０），（１１１）面回折強度比を用いていた。しかし、同じθ-２θ法の強度比であっても発電特性のばらつきを抑えることが困難であり、強度比を制御して光電変換装置を製造しても発電特性の向上とばらつきの抑制が出来ないという問題があった。
【０００６】
従来、下記特許文献１には、特定の面（２２０）に優先的に配向した薄膜多結晶シリコンや、このシリコンからなる結晶核下地層を有するシリコン系光電変換素子などについて開示されている。
【０００７】
【特許文献１】
特開２００１−２３７４４６号公報
【０００８】
【発明の開示】
【０００９】
【発明が解決しようとする課題】
本発明は上記事情を考慮してなされたもので、ｐ層，ｉ層及びｎ層すべてあるいは少なくともｉ層を構成する結晶性Ｓｉ薄膜の良否を判断しえる結晶性Ｓｉ薄膜の評価方法を提供することを目的とする。
【００１０】
【課題を解決するための手段】
本発明は、透光性又は不透光性基板上に透明導電膜層を介して形成される、ｐ層，ｉ層及びｎ層からなるｐｉｎ型又はｎｉｐ型構造発電膜、さらに別の電極層を具備した光電変換装置における発電膜のうち、ｐ層，ｉ層及びｎ層すべてあるいは少なくともｉ層は結晶性Ｓｉ薄膜で構成され、その各結晶粒の基板に対する配向方位に関する体積分布をとった場合に、方位<１１０>に極大値をもち、方位<１１０>から１５°以上に傾いた方位に配向した結晶粒の体積が方位<１１０>における体積の半分以下となる製膜条件を特定する、製膜中又は製膜後の結晶性Ｓｉ薄膜を評価する方法であり、前記結晶性Ｓｉ薄膜のうち少なくともｉ層の方位<１１０>に、前記Ｓｉ薄膜主面に対する入射Ｘ線の入射角をθとしたとき、入射角θが０＜θ＜（２×Ｂｒａｇｇ角）で回折強度のピーク値を持つか否かにより結晶性Ｓｉ薄膜の良否を判断することを特徴とする結晶性Ｓｉ薄膜の評価方法である。
【００１１】
【発明の効果】
本発明によれば、ｐ層，ｉ層及びｎ層すべてあるいは少なくともｉ層を構成する結晶性Ｓｉ薄膜の良否を判断しえる結晶性Ｓｉ薄膜の評価方法を提供できる。
【００１２】
【発明を実施するための最良の形態】
本発明において、前記透光性基板としては例えばガラス基板が挙げられ、前記不透光性基板としては例えば金属、樹脂が挙げられる。また、「製膜中又は製膜後の結晶性Ｓｉ薄膜」とは、Ｓｉ薄膜のｐ層，ｉ層又はｎ層のいずれか、あるいは各層を形成したＳｉ薄膜、あるいは更に電極層まで形成した後のＳｉ薄膜を示し、電極層まで形成した場合はＳｉ薄膜からの回折Ｘ線のみが観察できるＢｒａｇｇ角を選択することになる。
【００１３】
一般に、製膜条件（例えばプラズマＣＶＤ装置における、基板温度、圧力、高周波の周波数、電力等）が異なると結晶性Ｓｉ薄膜中の結晶成長の様式が変化するために膜質が異なるが、θ-２θ法を用いた場合には異なる製膜条件の下で作製した試料が同じ結果を示すことがある。従って、本発明において、上記の結晶粒配向範囲をもつ結晶性Ｓｉ薄膜を得るには、試験過程で用いる評価法として、入射Ｘ線と回折Ｘ線とのなす２θ角はＢｒａｇｇ角の２倍に固定しながら、入射Ｘ線と結晶性Ｓｉ薄膜を形成した基板の角度を変化させるＸ線回折測定法を用いて行うことが好ましい。これは一般にθスキャン、またはＦｉｅｌｄ−Ｍｅｒｃｈａｎｔ法とも呼ばれ、この測定法の詳述は下記のとおりである。同じ目的の観察には、Ｓｃｈｕｌｚ法によるχ−φ成分スキャンを用いれば薄膜中の結晶粒分布を完全に把握できるが、薄膜結晶系Ｓｉのようにごく薄い薄膜ではＸ線回折強度が元々弱いため、十分な情報を得るためにはスキャン時間をかなりかけねばならない。また、薄膜結晶性Ｓｉは結晶粒径が小さく急峻な配向を示さないため、回折Ｘ線のχ成分はχ＝０を中心に同心円状の分布（繊維分布）を示す。
【００１４】
従って、Ｓｃｈｕｌｚ法によるχ−φ成分スキャンで全てのφ成分をスキャンする必要はない。このため、あるφの値で固定してχ成分のスキャンのみを行えば十分である。また、Ｓｃｈｕｌｚ法によるχ−φ成分スキャンでは専用アタッチメントを要するため、通常行なわれているθ−２θ法と併用する場合は多くの手間を必要とする。そこで、薄膜結晶系Ｓｉを簡便に計測するために検討した結果、θ−２θ法のアタッチメントのままでχ成分のスキャンのみを行っても同等の結果を得られることを見出した。ここで、薄膜が既知材料であれば薄膜を通過するＸ線減衰量を評価できるため、基板のＸ線応答特性を考慮して補正を行うと精度を高められるため、結晶性Ｓｉ薄膜の薄い場合は基板の影響を除いておく。以上の改善された手法を用いて、本発明でのＸ線回折測定を行う。
【００１５】
本発明における結晶性Ｓｉ薄膜を作製する上で用いる評価法では、方位<１１０>におけるｉ層の回折強度がＨのとき、Ｈ／２に対応した入射角の範囲で半値幅をもつことが好ましい。図２は、本発明中で用いるＸ線回折測定法で得られたＳｉ（２２０）面回折線の角度分布（スペクトル）において、方位＜１１０＞に単一ピークをもつガウス関数に似た対称形状を示し、かつその半値幅の小さいスペクトルを示す。この場合、結晶面（１１０）の法線が基板に垂直となっている、方位<１１０>に配向した結晶粒の密度が、他の方位に配向した結晶粒の密度よりも極めて大きいことを意味している。また、立方晶であるＳｉの結晶構造から、方位<１１０>に配向した結晶粒はその粒界部分において隣接する結晶粒との格子整合が取りやすく粒界のダングリングボンド密度が減少し、粒界における欠陥が減少し電気伝導特性が改善されるからである。
【００１６】
薄膜内部に存在する各結晶粒の基板に対する配向方位に関する体積分布において、方位<１１０>に極大値をもち、方位<１１０>から１５°以上に傾いた方位に配向した結晶粒の体積が方位<１１０>における体積の半分以下である特徴を満たす場合に対応して、図２において、高い<１１０>ピーク強度Ｈに対し、Ｈ／２に対応した入射角を夫々θ_１、θ_２としたとき、半値幅Ｔｗは（θ_２−θ_１）＝４０°、望ましくは３０°以下の狭い半値幅であることが好ましい。
【００１７】
これは、結晶粒の集団が特定方位に配向した場合、隣接する結晶粒の間に形成される粒界は基板に対し垂直になり、粒界の種類が特定のものに限られるためである。ここで、粒界は、これを構成する２結晶粒から規定される２種の面方位の結晶面で記述できる。そこで粒界の特性値として、２種の面方位から計算されるダングリングボンド密度の差を導入すると、この値が小さいほど粒界として望ましいものになる。特に方位<１１０>に配向した場合はダングリングボンド密度が小さく、良好な粒界になることが知られている。
【００１８】
以下、本発明の実施例に係る結晶性Ｓｉ薄膜光電変換装置について説明する。
【００１９】
まず、図１に示すようにガラス基板１上に透明導電膜２を介して結晶性Ｓｉ薄膜を代表的製膜条件で形成し、試料４を準備する。そして試料４を、結晶性Ｓｉ薄膜側をＸ線入射側に向けて図３に示すようにセットする。ここで、入射Ｘ線と回折Ｘ線とのなす２θ角はＢｒａｇｇ角（θ_{Ｂｒａｇｇ}）の２倍に固定しながら、試料４は回転できるようにセットするとともに、入射Ｘ線の試料４に対する入射角θは可変できるようにしたＸ線回折測定法を用いた。
【００２０】
このようにして、試料４の結晶性Ｓｉ薄膜面側にＸ線を入射させ、上述したように２×（θ_{Ｂｒａｇｇ}）に固定しながら、入射角θを可変しながらθスキャンすることにより、入射角θのスペクトル特性を描く。その結果、上述した前記結晶性Ｓｉ薄膜のうち少なくともｉ層の方位<１１０>に、前記Ｓｉ薄膜主面に対する入射角をθとしたとき、入射角θが０＜θ＜（２×θ_{Ｂｒａｇｇ}）で回折強度が高いピーク値を持つか否かを判断する。ここで、薄膜が既知材料であれば薄膜を通過する膜厚に対し指数関数的に減少するＸ線減衰量を評価できる。基板のＸ線応答特性を考慮して測定結果からの除去を行うと精度を高められるため、結晶性Ｓｉ薄膜の薄い場合は基板の影響を除いておく。
【００２１】
その結果、上述した図２に示すように（θ_２−θ_１）の狭い半値幅の領域で方位<１１０>で回折強度のピーク値をもてば、結晶性Ｓｉ薄膜の膜質が良質であり、太陽電池は高効率セルを有する。一方、図４に示すように、広い半値幅で方位<<１１０>で低い回折強度をもつか、あるいは方位<１１０>以外のピークの存在が認められれば、結晶性Ｓｉ薄膜の膜質が良質でなく、太陽電池は低効率セルを有する。このようにして良質と判断される結晶性Ｓｉ薄膜を作製する製膜条件を特定し、プラズマＣＶＤ装置個々の特性に合わせた製膜条件を絞込み決定する。
【００２２】
事実、以上の製膜条件絞込みを行った結果、結晶性Ｓｉ薄膜が図２に示すようなスペクトルを有する太陽電池(イ)、及び結晶性Ｓｉ薄膜が図４に示すようなスペクトルを有する太陽電池（ロ）について半値幅と発電効率との関係を調べたところ、図５〜図７に示すような結果が得られた。図５〜図７は、夫々太陽電池の特性値である、発電効率、短絡電流、形状因子と半値幅の関係を示したものである。本発明で用いるＸ線回折測定法においては、Ｂｒａｇｇ角を軸として対称に信号が現れるため、図５〜図７中の単峰ピークは方位<１１０>にピークをもつ太陽電池（イ）からの信号を意味し、双峰ピークは方位<１１０>以外にピークをもつ太陽電池（ロ）からの信号を意味する。
【００２３】
図５は発電効率と半値幅の関係を示したものであり、単峰ピークを示す太陽電池（イ）では半値幅の低下とともに発電効率が上昇しているが、双峰ピークを示す太陽電池（ロ）では約３０°までは半値幅の低下とともに発電効率が上昇するものの、約３０°以下の半値幅では半値幅の低下とともに発電効率が低下する。これはスペクトルに現れるピークの半値幅が結晶粒の配向の集中度を意味し、半値幅が小さいほど結晶粒の配向方位が揃っていることを意味することから、結晶粒の配向が揃うことで粒界の構成種が絞られて粒界の性質が改善されるものの、結晶粒が揃った後は粒界を構成する結晶粒の方位により粒界の性質が決まり、これ以上の変化がないためである。
【００２４】
図６は短絡電流と半値幅の関係を示したものであり、単峰ピークを示す太陽電池（イ）では半値幅の低下とともに短絡電流が上昇し、双峰ピークを示す太陽電池（ロ）では約３０°以下の半値幅で若干低下するものの飽和傾向を示している。半値幅が小さいほど結晶粒の配向方位が揃っており、配向方位に当たる結晶粒が膜厚方向に長く成長したために、膜厚方向の電流経路内の粒界が少なくなっているためである。
【００２５】
図７は形状因子と半値幅の関係を示したものであり、発電効率と似た傾向を示している。これも発電効率と同じ理由で説明できる。これにより、太陽電池（イ）、（ロ）における結晶性Ｓｉ薄膜に対する評価が正しかったことが明らかである。
【００２６】
以上は、前述したように、ｐ層，ｉ層及びｎ層すべて、あるいは少なくともｉ層の結晶性Ｓｉを構成する各結晶粒の基板に対する配向方位に関する体積分布をとった場合に、方位<１１０>に極大値をもち、方位<１１０>から１５°以上に傾いた方位に配向した結晶粒の体積が方位<１１０>における体積の半分以下である特徴をもつ結晶性Ｓｉ薄膜であることが望ましいことを示している。
【００２７】
これを本発明記載の測定法で表現すると、結晶性薄膜Ｓｉの太陽電池において、Ｓｉ（２２０）面の回折線を観察して得た、本発明で用いるＸ線回折スペクトルで、Ｓｉ（２２０）面のBragg角に単一ピークをもつこと、つまり方位<１１０>にピークをもつ場合に、その半値幅が４０°以下、望ましくは３０°以下であることが、太陽電池として望ましい。これは、スペクトルに現れるピークの半値幅が３０〜４０°以上の場合、結晶粒配向が揃うことにより、粒界を構成する面方位の種類が絞られるためであるが、半値幅が３０〜４０°以下の場合、絞られた粒界種自体の性質に支配されるためである。
【００２８】
また、方位<１１０>にピークを持たない結晶性Ｓｉ薄膜においては、半値幅が２０度以上であることが性能上望ましい。これは製膜条件に対する装置上の制約のため、方位<１１０>にピークをもつ薄膜が作製できない場合に適用される。
【００２９】
なお、上記実施例では、ガラス基板上に透明導電膜を介して結晶性Ｓｉ薄膜を形成した試料にＸ線を入射してＳｉ薄膜の評価を行なう場合について述べたが、これに限らず、少なくとも、結晶性Ｓｉ薄膜のうちｉ層を形成した状態の試料にＸ線を入射してＳｉ薄膜の評価を行なえばよい。また、上記試料はｐｉｎ型発電膜の場合について述べたが、これに限らず、ｎｉｐ型発電膜の試料の場合についても同様に適用できる。
【００３０】
また、上記ｐｉｎ層あるいは少なくともｉ層が１個以上であり、かつｐｉｎ接合を２個以上有するＳｉ薄膜太陽電池セルにおいても同様の効果が得られることも明確である。
【図面の簡単な説明】
【図１】結晶性Ｓｉ薄膜を有した太陽電池の断面図。
【図２】本発明の一実施例に係る太陽電池における結晶性Ｓｉ薄膜に対する入射角と回折強度との関係を示す特性図。
【図３】本発明で用いるＸ線回折の測定法に関する説明図。
【図４】従来の太陽電池における結晶性Ｓｉ薄膜に対する入射角と回折強度との関係を示す特性図。
【図５】異なるスペクトル特性を有する太陽電池における半値幅と発電効率との関係を示す特性図。
【図６】異なるスペクトル特性を有する太陽電池における半値幅と短絡電流との関係を示す特性図。
【図７】異なるスペクトル特性を有する太陽電池における半値幅と形状因子との関係を示す特性図。
【符号の説明】
１…ガラス基板、２…透明導電膜、３…結晶性Ｓｉ薄膜（発電膜）、３ａ，３ｂ，３ｃ…結晶性Ｓｉ発電膜、４…試料。[0001]
【Technical field】
The present invention relates to a method for evaluating a crystalline Si thin film. In the specification of the present application, the terms “crystalline” and “polycrystalline” mean a case including at least crystalline Si and partially including amorphous.
[0002]
[Background]
Conventionally, as a thin film silicon (Si) photoelectric conversion device, for example, the one shown in FIG. 1 is known. FIG. 1 shows a form in which light is incident from the substrate side.
[0003]
Number 1 in the figure indicates a glass substrate. A crystalline Si thin film (power generation film) 3 is formed on the substrate 1 via a transparent conductive film 2 made of ITO, SnO ₂ or the like. Here, the crystalline Si thin film 3 includes a p-type crystalline Si film 3a, an i-type crystalline Si power generation film 3b, and an n-type crystalline Si film 3c. Although not shown, a transparent conductive film and a metal electrode film are usually formed on the crystalline Si thin film 3 in sequence.
[0004]
In the solar cell having such a configuration, sunlight enters from the glass substrate 1 side, passes through the transparent conductive film 2, and enters each power generation film. The sunlight is absorbed by the power generation film 3b, and an electromotive force is generated between the p-type crystalline Si film 3a and the n-type crystalline Si film 3c, and the power can be extracted outside. By the way, in such a solar cell, plasma CVD is generally used for film formation of the power generation film 3. However, since the apparatus dependency is large, film formation conditions in plasma CVD are set by evaluating film quality after film formation. Is reasonable.
[0005]
Conventionally, the (220), (111) plane diffraction intensity ratio according to the θ-2θ method of X-ray diffraction has been used as an index of film quality of a Si solar cell having a crystalline Si thin film. However, even if the intensity ratio of the same θ-2θ method is used, it is difficult to suppress variations in power generation characteristics, and even if a photoelectric conversion device is manufactured by controlling the intensity ratio, it is possible to improve power generation characteristics and suppress variations. There was no problem.
[0006]
Conventionally, the following Patent Document 1 discloses a thin film polycrystalline silicon preferentially oriented on a specific surface (220), a silicon-based photoelectric conversion element having a crystal nucleus base layer made of this silicon, and the like.
[0007]
[Patent Document 1]
JP-A-2001-237446
DISCLOSURE OF THE INVENTION
[0009]
[Problems to be solved by the invention]
The present invention has been made in view of the above circumstances, and provides a method for evaluating a crystalline Si thin film that can judge the quality of the crystalline Si thin film constituting all or at least the p layer, i layer, and n layer. For the purpose.
[0010]
[Means for Solving the Problems]
The present invention relates to a pin-type or nip-type structure power generation film formed of a p-layer, an i-layer, and an n-layer on a translucent or non-translucent substrate through a transparent conductive film layer, and another electrode layer Among the power generation films in the photoelectric conversion device comprising the above, when the p-layer, i-layer and n-layer all or at least the i-layer is composed of a crystalline Si thin film, and the volume distribution of the orientation direction of each crystal grain with respect to the substrate is taken In addition, a film forming condition is specified in which the volume of a crystal grain having a maximum value in the azimuth <110> and oriented in an azimuth inclined at 15 ° or more from the azimuth <110> is less than half of the volume in the azimuth <110>. This is a method for evaluating a crystalline Si thin film during film formation or after film formation, and the incident angle of incident X-rays with respect to the main surface of the Si thin film is set to θ in at least the i-layer orientation <110> of the crystalline Si thin film Where the incident angle θ is 0 <θ <(2 × Bra An evaluation method of a crystalline Si thin film characterized by determining the quality of the crystalline Si thin film by whether a peak value of the diffraction intensity at g angle).
[0011]
【The invention's effect】
According to the present invention, it is possible to provide a method for evaluating a crystalline Si thin film that can judge the quality of the crystalline Si thin film that constitutes all or at least the p layer, i layer, and n layer.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
In the present invention, examples of the light transmissive substrate include a glass substrate, and examples of the light transmissive substrate include a metal and a resin. In addition, “crystalline Si thin film during or after film formation” refers to any one of the p-layer, i-layer, and n-layer of the Si thin film, the Si thin film on which each layer is formed, or even the electrode layer. When the Si thin film is formed up to the electrode layer, the Bragg angle at which only the diffracted X-rays from the Si thin film can be observed is selected.
[0013]
In general, when the film forming conditions (for example, substrate temperature, pressure, high frequency, power, etc. in a plasma CVD apparatus) are different, the film quality is different because the mode of crystal growth in the crystalline Si thin film changes. When the method is used, samples prepared under different film forming conditions may show the same results. Therefore, in the present invention, in order to obtain a crystalline Si thin film having the above-mentioned crystal grain orientation range, as an evaluation method used in the test process, the 2θ angle formed by incident X-rays and diffracted X-rays is twice the Bragg angle. It is preferable to use an X-ray diffraction measurement method in which the angle of the substrate on which the incident X-ray and the crystalline Si thin film are formed is changed while being fixed. This is generally called a θ scan or a Field-Merchant method, and details of this measurement method are as follows. For observation of the same purpose, the distribution of crystal grains in the thin film can be completely grasped using the χ-φ component scan by the Schulz method, but the X-ray diffraction intensity is inherently weak in a very thin film such as a thin film crystal system Si. To get enough information, you have to spend a lot of scanning time. Further, since the thin film crystalline Si has a small crystal grain size and does not exhibit a steep orientation, the χ component of the diffracted X-ray shows a concentric distribution (fiber distribution) centering on χ = 0.
[0014]
Therefore, it is not necessary to scan all the φ components by the χ-φ component scan by the Schulz method. For this reason, it is sufficient to scan only the χ component with a fixed value of φ. In addition, since the χ-φ component scan by the Schulz method requires a dedicated attachment, a lot of labor is required when used in combination with the usual θ-2θ method. Therefore, as a result of studying for simple measurement of the thin film crystalline Si, it was found that the same result can be obtained even if only the scan of the χ component is performed with the θ-2θ method attached. Here, if the thin film is a known material, the amount of X-ray attenuation that passes through the thin film can be evaluated. Therefore, if correction is performed in consideration of the X-ray response characteristics of the substrate, the accuracy can be improved. Remove the influence of the substrate. The X-ray diffraction measurement according to the present invention is performed using the improved method described above.
[0015]
In the evaluation method used for producing the crystalline Si thin film in the present invention, when the diffraction intensity of the i layer in the orientation <110> is H, it is preferable to have a half width in the range of the incident angle corresponding to H / 2. . FIG. 2 shows a symmetric shape similar to a Gaussian function having a single peak in the orientation <110> in the angular distribution (spectrum) of the Si (220) plane diffraction line obtained by the X-ray diffraction measurement method used in the present invention. And a spectrum with a small half width. In this case, the normal of the crystal plane (110) is perpendicular to the substrate, meaning that the density of crystal grains oriented in the <110> direction is extremely higher than the density of crystal grains oriented in other directions. are doing. In addition, from the crystal structure of Si, which is a cubic crystal, crystal grains oriented in the <110> direction are easily lattice-matched with the adjacent crystal grains at the grain boundary portion, and the dangling bond density at the grain boundaries is reduced. This is because defects in the field are reduced and electric conduction characteristics are improved.
[0016]
In the volume distribution of the orientation direction of each crystal grain present in the thin film with respect to the substrate, the volume of the crystal grain having a maximum value in the orientation <110> and oriented in an orientation tilted by 15 ° or more from the orientation <110> 2 corresponds to the case where the characteristic of the volume less than half of 110> is satisfied, in FIG. 2, when the incident angles corresponding to H / 2 are θ ₁ and θ ₂ for the high <110> peak intensity H, respectively. The half-value width Tw is preferably (θ ₂ −θ ₁ ) = 40 °, preferably a narrow half-value width of 30 ° or less.
[0017]
This is because when a group of crystal grains is oriented in a specific orientation, the grain boundaries formed between adjacent crystal grains are perpendicular to the substrate, and the types of grain boundaries are limited to specific ones. Here, the grain boundary can be described by crystal planes having two kinds of plane orientations defined by two crystal grains constituting the grain boundary. Therefore, when a difference in dangling bond density calculated from two kinds of plane orientations is introduced as a characteristic value of the grain boundary, the smaller this value, the more desirable as the grain boundary. In particular, it is known that when oriented in the <110> direction, the dangling bond density is small and a good grain boundary is obtained.
[0018]
Hereinafter, a crystalline Si thin film photoelectric conversion device according to an example of the present invention will be described.
[0019]
First, as shown in FIG. 1, a crystalline Si thin film is formed on a glass substrate 1 through a transparent conductive film 2 under typical film forming conditions, and a sample 4 is prepared. Then, the sample 4 is set as shown in FIG. 3 with the crystalline Si thin film side facing the X-ray incident side. Here, while the 2θ angle formed by the incident X-ray and the diffracted X-ray is fixed to twice the Bragg angle (θ _Bragg ), the sample 4 is set so as to be rotatable, and the incident angle of the incident X-ray with respect to the sample 4 is set. An X-ray diffraction measurement method was used that made θ variable.
[0020]
In this way, X-rays are incident on the crystalline Si thin film surface side of the sample 4 and fixed by 2 × (θ _Bragg ) as described above. Draw spectral characteristics of angle θ. As a result, the incident angle θ is 0 <θ <(2 × θ _Bragg ), where θ is the incident angle with respect to the main surface of the Si thin film in the orientation <110> of at least the i layer of the crystalline Si thin film described above. To determine whether the diffraction intensity has a high peak value. Here, if the thin film is a known material, the X-ray attenuation amount that decreases exponentially with respect to the film thickness passing through the thin film can be evaluated. If the removal from the measurement result is performed in consideration of the X-ray response characteristic of the substrate, the accuracy can be improved. Therefore, when the crystalline Si thin film is thin, the influence of the substrate is excluded.
[0021]
As a result, as shown in FIG. 2 described above, if the peak value of the diffraction intensity is obtained at the orientation <110> in the narrow half-value width region of (θ ₂ −θ ₁ ), the quality of the crystalline Si thin film is good. The solar cell has a high efficiency cell. On the other hand, as shown in FIG. 4, the film quality of the crystalline Si thin film is good if it has a wide half-value width and a low diffraction intensity at the orientation <110> or the presence of peaks other than the orientation <110>. In contrast, solar cells have low efficiency cells. In this way, the film forming conditions for producing the crystalline Si thin film judged to be of good quality are specified, and the film forming conditions matching the individual characteristics of the plasma CVD apparatus are narrowed down and determined.
[0022]
In fact, as a result of narrowing down the above film forming conditions, the solar cell (a) in which the crystalline Si thin film has a spectrum as shown in FIG. 2 and the solar cell in which the crystalline Si thin film has a spectrum as shown in FIG. When the relationship between the full width at half maximum and power generation efficiency was examined for (b), the results shown in FIGS. 5 to 7 were obtained. 5 to 7 show the relationship between the power generation efficiency, the short-circuit current, the shape factor, and the half-value width, which are characteristic values of the solar cell, respectively. In the X-ray diffraction measurement method used in the present invention, a signal appears symmetrically with the Bragg angle as an axis. Therefore, the single peak in FIGS. 5 to 7 is from a solar cell (A) having a peak in the azimuth <110>. This means a signal, and the bimodal peak means a signal from a solar cell (b) having a peak other than the orientation <110>.
[0023]
FIG. 5 shows the relationship between the power generation efficiency and the half-value width. In the solar cell (a) showing a single peak, the power generation efficiency increases as the half-value width decreases. In (b), the power generation efficiency increases with a decrease in the half-value width up to about 30 °, but the power generation efficiency decreases with a decrease in the half-value width at a half-value width of about 30 ° or less. This means that the half-value width of the peak appearing in the spectrum means the degree of concentration of the crystal grains, and the smaller the half-value width means that the orientation directions of the crystal grains are aligned. Although the grain boundary constituents are narrowed down and the grain boundary properties are improved, after the crystal grains are aligned, the grain boundary properties are determined by the orientation of the crystal grains constituting the grain boundaries, and there is no further change. It is.
[0024]
FIG. 6 shows the relationship between the short-circuit current and the half-value width. In the solar cell (a) showing a single peak, the short-circuit current increases as the half-value width decreases, and in the solar cell (b) showing a bimodal peak. Although it slightly decreases at a half width of about 30 ° or less, it shows a saturation tendency. This is because as the half width is smaller, the orientation direction of the crystal grains is aligned, and the crystal grains corresponding to the orientation direction grow longer in the film thickness direction, so that the grain boundaries in the current path in the film thickness direction are reduced.
[0025]
FIG. 7 shows the relationship between the form factor and the half width, and shows a tendency similar to the power generation efficiency. This can also be explained for the same reason as the power generation efficiency. This clearly shows that the evaluation of the crystalline Si thin film in the solar cells (A) and (B) was correct.
[0026]
As described above, the orientation <110> is obtained when the volume distribution of the orientation direction with respect to the substrate of all the p-layer, i-layer, and n-layer, or at least each crystal grain constituting the crystalline Si of the i-layer is taken. It is desirable that the crystalline Si thin film has a feature that the volume of crystal grains oriented in an orientation tilted by 15 ° or more from the orientation <110> is less than half of the volume in the orientation <110>. Is shown.
[0027]
When this is expressed by the measurement method described in the present invention, it is an X-ray diffraction spectrum used in the present invention obtained by observing a diffraction line on the Si (220) plane in a crystalline thin-film Si solar cell. It is desirable for a solar cell to have a single peak at the Bragg angle of the surface, that is, when it has a peak in the orientation <110>, its half-value width is 40 ° or less, preferably 30 ° or less. This is because when the half width of the peak appearing in the spectrum is 30 to 40 ° or more, the types of plane orientations constituting the grain boundaries are narrowed by aligning the crystal grain orientation, but the half width is 30 to 40. This is because in the case of ° or less, it is governed by the nature of the narrowed grain boundary seed itself.
[0028]
Further, in a crystalline Si thin film having no peak in the orientation <110>, it is desirable in terms of performance that the full width at half maximum is 20 degrees or more. This is applied when a thin film having a peak in the orientation <110> cannot be produced due to apparatus restrictions on the film forming conditions.
[0029]
In the above-described embodiment, the case where the Si thin film is evaluated by making X-rays incident on the sample in which the crystalline Si thin film is formed on the glass substrate via the transparent conductive film is described. The Si thin film may be evaluated by making X-rays incident on a sample of the crystalline Si thin film in which the i layer is formed. Moreover, although the said sample demonstrated the case of the pin type power generation film, it is applicable not only to this but the case of the sample of a nip type power generation film similarly.
[0030]
It is also clear that the same effect can be obtained in a Si thin-film solar cell having one or more pin layers or at least i layers and having two or more pin junctions.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a solar cell having a crystalline Si thin film.
FIG. 2 is a characteristic diagram showing a relationship between an incident angle and a diffraction intensity with respect to a crystalline Si thin film in a solar cell according to an embodiment of the present invention.
FIG. 3 is an explanatory diagram relating to a measurement method of X-ray diffraction used in the present invention.
FIG. 4 is a characteristic diagram showing a relationship between an incident angle and a diffraction intensity with respect to a crystalline Si thin film in a conventional solar cell.
FIG. 5 is a characteristic diagram showing a relationship between a half-value width and power generation efficiency in solar cells having different spectral characteristics.
FIG. 6 is a characteristic diagram showing a relationship between a half-value width and a short-circuit current in solar cells having different spectral characteristics.
FIG. 7 is a characteristic diagram showing a relationship between a half-value width and a shape factor in solar cells having different spectral characteristics.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Glass substrate, 2 ... Transparent electrically conductive film, 3 ... Crystalline Si thin film (power generation film), 3a, 3b, 3c ... Crystalline Si power generation film, 4 ... Sample.

Claims

A photoelectric device having a pin-type or nip-type structured power generation film formed of a p-layer, an i-layer, and an n-layer formed on a translucent or non-translucent substrate via a transparent conductive film layer, and another electrode layer Among the power generation films in the conversion device, all or at least the i-layer and the p-layer, the i-layer, and the i-layer are composed of a crystalline Si thin film, and the orientation <110> has a local maximum value, and specifies the film-forming conditions in which the volume of crystal grains oriented in an orientation inclined by 15 ° or more from the orientation <110> is less than half of the volume in the orientation <110>. It is a method for evaluating a crystalline Si thin film after film formation,
The incident angle θ is 0 <θ <(2 × Bragg angle), where θ is the incident angle of incident X-rays with respect to the Si thin film main surface in at least the i-layer orientation <110> of the crystalline Si thin film. A method for evaluating a crystalline Si thin film, wherein the quality of the crystalline Si thin film is judged based on whether or not it has a peak value of diffraction intensity.

3. The method for evaluating a crystalline Si thin film according to claim 2, wherein when the diffraction intensity of the i layer in the azimuth <110> is H, the FWHM has a full width at half maximum in an incident angle range corresponding to H / 2.

Evaluation of the crystalline Si thin film uses X-ray diffraction measurement that changes the angle between the incident X-ray and the substrate on which the crystalline Si thin film is formed while fixing the 2θ angle of the diffracted X-ray to twice the Bragg angle. 4. The method for evaluating a crystalline Si thin film according to claim 2, wherein the method is performed.