JPH054823B2

JPH054823B2 -

Info

Publication number: JPH054823B2
Application number: JP61239504A
Authority: JP
Inventors: Naoki Suyama; Hiroshi Uda; Kunyoshi Omura; Mikio Murozono
Original assignee: Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Holdings Corp
Priority date: 1986-10-08
Filing date: 1986-10-08
Publication date: 1993-01-20
Also published as: JPS6393167A

Description

[Detailed description of the invention]

産業上の利用分野本発明は太陽電池、特に室内等の低照度下で使
用可能なCdS／CdTe構造の光起電力素子の製造
方法に関するものである。従来の技術従来、CdS／CdTe構造の光起電力素子の製造
技術の一つとしてスクリーン印刷と、ベルトコン
ベア炉による焼成とを用いた製造方法がある。こ
の方法の特長は簡単に実施でき、かつ量産性に富
み、安価な光起電力素子が得られることにある。
この製造方法でCdS焼結膜を得る方法として粒径
２〜3μｍの高純度（5N）のCdS粉末に融剤とし
て10重量％のCdCl₂粉と適当量の粘結剤を加えて
作成したCdSペーストをガラス基板上に80メツシ
ユのポリエステル製スクリーンを用いて印刷し、
有孔蓋付きアルミナボートに入れベルトコンベア
式連続焼成炉で温度690℃近傍で焼成することに
よつて、CdS焼結膜を形成するものがある（例え
ば、日本、ジヤーナル・アプライド・フイジツク
ス、Part1、Vol.21、No.５、800−801、1982）。発明が解決しようとする問題点しかしながら上記のような製造方法では、CdS
焼結膜の膜厚が25μｍ以上になり、CdS側から光
が入射した場合接合部分に達する光量の絶対量が
減少する。またCdSの基礎吸収端（λ＝520nｍ）
以下の波長では光起電力効果がない。上記の点
は、短波長側にエネルギー分布をもち、かつ光エ
ネルギー量の少ない蛍光灯下で使用する太陽電池
において重要な問題である。基礎吸収端をより短
波長側にシフトさせる方法として、ZnS等のCdS
よりもバンドギヤツプの広い材料をCdS中に添加
することが考えられてきたが、印刷、焼成という
工程では、良好な膜が得られていない。さらに、
従来の条件で印刷のスクリメツシユを変えてCdS
膜厚を減少させた場合、焼結膜中のピンホールが
増加し、漏れ電流が増加する。また、一般にCdS
膜を減少させるとCdS粒径が減少し膜厚低下分以
上に膜抵抗が増加する。本発明は上記問題点に鑑み、室内等の蛍光灯な
どの低照度下で、光電変換特性の良好な光電素子
の製造方法を提供するものである。問題点を解決するための手段上記問題点を解決するために本発明の光起電力
素子の製造方法は、CdS焼成膜の膜厚を減少させ
ると同時にスクリーン印刷するための泥状物中に
ZnS粉末をCdS粉末に対し重量比で４〜12.5％加
えたものであり、好ましくはこれにさらに融剤と
してCdCl₂をCdS粉末とZnS粉末の合計量に対し
重量比で17.5〜30％加えたものである。作用本発明は上記した構成によつて、CdS側から光
が入射した合愛、接合部分に達する光量の絶対量
が増加し、ZnS添加によつて、無添加の場合と比
較してより短波長側に光起電力効果が発生する。
さらにZnS添加によつてCdS結晶形状が変わり、
膜厚が減少してもピンホールの少ない焼成膜が得
られる。そして、融剤であるCdCl₂量の最適化に
よつてCdS膜の膜透過率および膜抵抗が改善でき
る。ZnSを添加した場合、無添加の場合と比較し
て膜抵抗は増加するが、低照度で発生する微弱電
流の場合、光電変換特性には影響をあたえないレ
ベルであり、それ以上に前記の効果の方が大であ
る。実施例以下本発明の一実施例の光起電力素子の製造方
法について図面を参照しながら説明する。第１図は本発明の第１の実施例における光起電
力素子の断面図を示すものである。CdS焼成膜形
成用泥状物中のZnS粉末量及びCdCl₂量を変えて
形成した泥状物を図面１に示すようにアルカリ含
有量0.2％以下のバリウム硼珪酸ガラス基板１上
にスクリーン印刷した後、N₂雰囲気中において
690℃で30分間焼成することにより、ｎ型CdS−
ZnS焼結膜２を形成した。焼結膜の膜厚は、印刷
スクリーンのメツシユ数を変えて７〜25μｍのも
のを作製した。このｎ型CdS−ZnS焼結膜２上に
Cd粉末とTe粉末を1.05対1.00のモル比で配合し、
それに融剤としてCdCl₂をCdとTeの総重量に対
して0.5重量％、粘結剤としてプロピレングリコ
ールの適量を加えて混合し、泥状としたものをス
クリーン印刷して乾燥させた後、N₂雰囲気中に
おいて、580℃で60分間焼成することによつて
CdTe焼結膜３を形成した。次に、CdTe焼結膜
３上に適量のアクセプター不純物を添加した泥状
カーボンをスクリーン印刷して、カーボン膜４を
形成させた後、N₂雰囲気中において450℃で30分
間熱処理することにより、カーボン中に含まれて
いるアクセプター不純物がCdTe焼結膜３内にド
ープした。こうしたｎ形CdS−ZnS焼結膜２とＰ
型CdTe焼結膜３との間に光起電力効果をもつヘ
テロ接合を形成した。次にCdS−ZnS焼結膜２上
およびカーボン膜４上にそれぞれオーミツク電極
５，６を付けた後、各々の電極５，６からリード
線７を引き出した。このようにして得られた素子においてCdS−
ZnS焼結膜形成条件と白色蛍光灯200lx下での単
位面積当りの最大出力Pmax（μw／cm²）との関係
から、最適CdS−ZnS焼結膜形成条件について説
明する。まず、第１にCdS−ZnS膜中のZnS添加
量および融剤であるCdCl₂量を変えて作製した素
子の白色蛍光灯200lx下で最大出力Pmaxを第２
図に示す。なお、CdS−ZnS膜厚は25〜30μｍで
一定にした。図より、ZnS7.5％、CdCl₂25％で
Pmaxが極大値に示した。Pmaxの向上には、
ZnSを重量比で４〜12.5％添加し、CdCl₂を重量
比で17.5〜30％を加えることが適切であることが
わかる。次に、前記の最適条件範囲内でCdS−ZnS焼成
膜の膜厚を、印刷スクリーンメツシユを変えて調
製した素子の出力特性を第３図に示す。膜厚が減
少するとPmaxは増加し、12μｍ程度に最大値が
みられる。12μｍ以下に減少する膜抵抗が増加す
るため、Pmaxは減少する。したがつてPmax向
上には、CdS−ZnS膜厚を８〜20μｍの範囲で形
成することが適切であることがわかる。以上のように、本実施例によれば、CdS膜形成
用泥状物中のZnS量をCdS重量に対して重量比で
４〜12.5％、CdCl₂量を17.5〜30％の範囲で作製
し、印刷焼成後の膜厚を８〜20μｍにすることに
より、白色蛍光灯200lx下等の短波長成分の多い
低照度光源下で、出力特性の高い光起電力素子を
製造することができる。以下に本発明の第２の実施例について説明す
る。素子構造およびその製法は、上記実施例とほ
ぼ同一であるが、CdS、ZnS、CdCl₂粉末の混合
物をあらかじめ、微粉砕する点が異なる。 CdS粉末に対して重量比でZnSを75％、CdCl₂
を20％加え、CdS重量の２倍量の蒸留水を添加
し、遊星ボールミを用いて粉砕を行なつた。粉砕
後100℃で24時間以上乾燥し、上記実施例１の泥
状物として用いた。表１に粉砕時間と出力特性の
関係を示す。 INDUSTRIAL APPLICATION FIELD The present invention relates to a method for manufacturing a solar cell, particularly a photovoltaic element having a CdS/CdTe structure that can be used under low illuminance such as indoors. BACKGROUND ART Conventionally, as one of the manufacturing techniques for photovoltaic elements having a CdS/CdTe structure, there is a manufacturing method using screen printing and firing in a belt conveyor furnace. The advantage of this method is that it is easy to implement, has high mass productivity, and provides inexpensive photovoltaic devices.
To obtain a CdS sintered film using this production method, a CdS paste is prepared by adding 10% by weight of _CdCl2 powder as a flux and an appropriate amount of a binder to high-purity (5N) CdS powder with a particle size of 2 to 3 μm. printed on a glass substrate using an 80-mesh polyester screen,
There is a method that forms a CdS sintered film by placing it in an alumina boat with a perforated lid and firing it at a temperature of around 690℃ in a belt conveyor type continuous firing furnace (for example, Japan, Journal Applied Physics, Part 1, Vol. .21, No. 5, 800-801, 1982). Problems to be solved by the invention However, in the above manufacturing method, CdS
When the thickness of the sintered film becomes 25 μm or more and light is incident from the CdS side, the absolute amount of light reaching the bonded portion decreases. Also, the fundamental absorption edge of CdS (λ=520nm)
There is no photovoltaic effect at wavelengths below. The above point is an important problem in solar cells that have an energy distribution on the short wavelength side and are used under fluorescent lamps with a small amount of light energy. As a way to shift the fundamental absorption edge to shorter wavelengths, CdS such as ZnS
It has been considered to add a material with a wider band gap to CdS, but it has not been possible to obtain a good film through the printing and firing process. moreover,
CdS by changing the printing scrimmage under conventional conditions
When the film thickness is reduced, the number of pinholes in the sintered film increases, which increases leakage current. Also, generally CdS
When the film is reduced, the CdS grain size decreases, and the film resistance increases by more than the reduction in film thickness. In view of the above-mentioned problems, the present invention provides a method for manufacturing a photoelectric element with good photoelectric conversion characteristics under low illuminance such as indoor fluorescent lighting. Means for Solving the Problems In order to solve the above problems, the method for manufacturing a photovoltaic device of the present invention reduces the thickness of the fired CdS film and at the same time adds a layer to the slurry for screen printing.
4 to 12.5% by weight of ZnS powder is added to CdS powder, and preferably 17.5 to 30% by weight of CdCl ₂ is added as a flux to the total amount of CdS powder and ZnS powder. It is something. Effects According to the present invention, the above-described structure increases the absolute amount of light that reaches the bonding portion where light enters from the CdS side, and the addition of ZnS makes the process shorter than when no addition is made. A photovoltaic effect occurs on the wavelength side.
Furthermore, the CdS crystal shape changes due to the addition of ZnS,
Even if the film thickness is reduced, a fired film with fewer pinholes can be obtained. Furthermore, by optimizing the amount of CdCl ₂ which is a fluxing agent, the membrane permeability and membrane resistance of the CdS membrane can be improved. When adding ZnS, the film resistance increases compared to the case without addition, but in the case of weak currents generated at low illuminance, it is at a level that does not affect the photoelectric conversion characteristics, and the above effect is more is larger. Embodiment A method for manufacturing a photovoltaic device according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a cross-sectional view of a photovoltaic device according to a first embodiment of the present invention. A slurry formed by varying the amount of ZnS powder and CdCl ₂ in the slurry for forming a CdS fired film was screen printed on a barium borosilicate glass substrate 1 with an alkali content of 0.2% or less as shown in Figure 1. After that, in _N2 atmosphere
By baking at 690℃ for 30 minutes, n-type CdS−
A ZnS sintered film 2 was formed. The thickness of the sintered film was 7 to 25 μm by changing the number of meshes in the printing screen. On this n-type CdS-ZnS sintered film 2
Blending Cd powder and Te powder at a molar ratio of 1.05 to 1.00,
0.5% by weight of CdCl ₂ as a flux based on the total weight of Cd and Te and an appropriate amount of propylene glycol as a binder were added and mixed to form a slurry. After screen printing and drying, N ₂ By baking at 580℃ for 60 minutes in an atmosphere
A CdTe sintered film 3 was formed. Next, muddy carbon added with an appropriate amount of acceptor impurities is screen printed on the CdTe sintered film 3 to form a carbon film 4. After that, the carbon film 4 is heat-treated at 450°C for 30 minutes in an _N2 atmosphere. The acceptor impurities contained therein were doped into the CdTe sintered film 3. Such n-type CdS-ZnS sintered film 2 and P
A heterojunction with a photovoltaic effect was formed with the type CdTe sintered film 3. Next, after attaching ohmic electrodes 5 and 6 to the CdS-ZnS sintered film 2 and the carbon film 4, respectively, lead wires 7 were drawn out from each electrode 5 and 6. In the device thus obtained, CdS−
The optimal CdS-ZnS sintered film formation conditions will be explained from the relationship between the ZnS sintered film formation conditions and the maximum output Pmax (μw/cm ² ) per unit area under a white fluorescent lamp of 200 lx. First, the maximum output Pmax under a white fluorescent lamp of 200 lx was calculated by changing the amount of ZnS added in the CdS-ZnS film and the amount of CdCl ₂ as a fluxing agent.
As shown in the figure. Note that the CdS-ZnS film thickness was kept constant at 25 to 30 μm. From the figure, with ZnS7.5% and CdCl ₂ 25%
Pmax reached its maximum value. To improve Pmax,
It is found that it is appropriate to add 4 to 12.5% by weight of ZnS and 17.5 to 30% by weight of _CdCl2 . Next, FIG. 3 shows the output characteristics of devices prepared by varying the thickness of the CdS-ZnS fired film and the printing screen mesh within the range of the above-mentioned optimum conditions. As the film thickness decreases, Pmax increases, and the maximum value is seen at about 12 μm. As the membrane resistance decreases below 12 μm, Pmax decreases. Therefore, it can be seen that it is appropriate to form a CdS-ZnS film with a thickness in the range of 8 to 20 μm in order to improve Pmax. As described above, according to this example, the amount of ZnS in the CdS film-forming slurry is 4 to 12.5% by weight and the amount of CdCl ₂ is in the range of 17.5 to 30% relative to the weight of CdS. By setting the film thickness after printing and firing to 8 to 20 μm, a photovoltaic element with high output characteristics can be manufactured under a low-intensity light source with many short wavelength components, such as under a 200 lx white fluorescent lamp. A second embodiment of the present invention will be described below. The device structure and its manufacturing method are almost the same as in the above example, except that the mixture of CdS, ZnS, and CdCl ₂ powder is pulverized in advance. 75% ZnS and _CdCl2 by weight to CdS powder
20% of CdS was added, distilled water in an amount twice the weight of CdS was added, and the mixture was pulverized using a planetary ball mill. After pulverization, it was dried at 100°C for 24 hours or more and used as the slurry in Example 1 above. Table 1 shows the relationship between grinding time and output characteristics.

【表】以上のように、CdS、ZnSそして融剤である
CdCl₂粉末の混合物に蒸留水を加えた系であらか
じめ微粉砕することによつて、従来より白色蛍光
灯200lx下での最大出力を向上させることができ
る。なお、実施例ではCdS粉にZnS粉を混合して
CdS−ZnS焼成膜を形成したが、CdSとZnSの固
溶体粉末を用いてCdS−ZnS焼成膜を形成しても
同様の効果を得ることができる。発明の効果以上の本発明は、ｎ−CdS膜とｐ−CdTe膜を
用いた光起電力素子において、CdS膜形成用の泥
状物作製に際し、CdS粉末に対して重量比でZnS
を４〜12.5％、CdCl₂量を17.3〜30％の範囲で添
加し、あらかじめ微粉砕し、焼成後の膜厚を８〜
20μｍの範囲で形成することによつて、白色蛍光
灯200lx等の短波長成分の多い低照度光源下で出
力特性の高い光起電力素子を製造することができ
る。[Table] As shown above, CdS, ZnS and flux
By pre-pulverizing the CdCl ₂ powder mixture in a system in which distilled water is added, the maximum output under a 200 lx white fluorescent lamp can be improved compared to conventional methods. In addition, in the example, ZnS powder was mixed with CdS powder.
Although a CdS-ZnS fired film was formed, similar effects can be obtained by forming a CdS-ZnS fired film using a solid solution powder of CdS and ZnS. Effects of the Invention The present invention described above has the advantage that in a photovoltaic device using an n-CdS film and a p-CdTe film, when preparing a slurry for forming a CdS film, Zn
4 to 12.5% of CdCl ₂ and 17.3 to 30% of CdCl 2 are added, pulverized in advance, and the film thickness after firing is 8 to 30%.
By forming the film in the range of 20 μm, it is possible to manufacture a photovoltaic element with high output characteristics under a low-intensity light source with many short wavelength components, such as a 200 lx white fluorescent lamp.

[Brief explanation of drawings]

第１図は本発明の製造方法により得られる光起
電力素子の一例を示す断面図、第２図はCdS粉末
に対するZnSの添加量及びCdCl₂の添加量と最大
光電変換出力との関係を示す図、第３図はCdS膜
厚と最大光電変換出力との関係を示す図である。１……ガラス基板、２……CdS−ZnS焼結膜、
３……CdTe焼結膜、４……カーボン膜、５……
オーミツク電極、６……オーミツク電極、７……
リード線。 Figure 1 is a cross-sectional view showing an example of a photovoltaic device obtained by the manufacturing method of the present invention, and Figure 2 shows the relationship between the amount of ZnS added to the CdS powder, the amount of CdCl ₂ added, and the maximum photoelectric conversion output. 3 are diagrams showing the relationship between CdS film thickness and maximum photoelectric conversion output. 1...Glass substrate, 2...CdS-ZnS sintered film,
3... CdTe sintered film, 4... Carbon film, 5...
Ohmic electrode, 6... Ohmic electrode, 7...
Lead.

Claims

[Claims] 1. A first film made of CdS and ZnS or a compound semiconductor containing these is formed on a substrate by a screen printing and sintering process, and a semiconductor material forms a pn junction with the first film. In the method for manufacturing a photovoltaic device in which a second film consisting of:
Consisting of CdS powder, ZnS powder or solid solution powder of CdS and ZnS, a binder and _CdCl2 , the amount of ZnS powder is 4 to 12.5% by weight relative to the CdS powder,
A method for manufacturing a photovoltaic device, characterized in that the amount of CdCl ₂ added is 17.5 to 30% by weight relative to the total amount of CdS and ZnS, and the thickness of the first film is 8 to 20 μm. 2. Claim 1, wherein the substrate is glass.
A method for manufacturing a photovoltaic device as described in . 3. Claim 1, wherein the substrate is barium borosilicate glass with an alkali content of 0.3% by weight or less.
A method for manufacturing a photovoltaic device as described in . 4. A patent claim in which a system in which a dispersion medium is added to a mixture of CdS, ZnS, and CdCl ₂ powder is pulverized in advance and mixed uniformly, and then a binder is added to the dried product to create a slurry. A method for manufacturing a photovoltaic device according to item 1.