JP2013168612A - Organic thin film photoelectric conversion element and organic thin film solar cell including the same - Google Patents

Organic thin film photoelectric conversion element and organic thin film solar cell including the same Download PDF

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JP2013168612A
JP2013168612A JP2012032532A JP2012032532A JP2013168612A JP 2013168612 A JP2013168612 A JP 2013168612A JP 2012032532 A JP2012032532 A JP 2012032532A JP 2012032532 A JP2012032532 A JP 2012032532A JP 2013168612 A JP2013168612 A JP 2013168612A
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JP5854401B2 (en
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Takahiro Kono
隆広 河野
Yosei Shibata
陽生 柴田
Nagatoshi Komura
長利 甲村
Yuji Yoshida
郵司 吉田
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National Institute of Advanced Industrial Science and Technology AIST
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Abstract

PROBLEM TO BE SOLVED: To improve photoelectric conversion characteristics while suppressing aggregation of a p-type organic semiconductor material, in a photoelectric conversion element in which a low molecular material having high crystallinity is used as the p-type organic semiconductor material.SOLUTION: An organic thin film photoelectric conversion element 10 includes a photoelectric conversion layer 14 between a pair of electrodes 12, the photoelectric conversion layer including a bulk heterojunction layer formed by mixing a p-type organic semiconductor material and an n-type organic semiconductor material. Oligothiophene having a bulky substituent is used as the p-type organic semiconductor material of the photoelectric conversion layer 14.

Description

本発明は、一対の電極の間にｐ型有機半導体材料とｎ型有機半導体材料とを含む光電変換層を備えた有機薄膜光電変換素子及びこれを用いた有機薄膜太陽電池に関する。   The present invention relates to an organic thin film photoelectric conversion element including a photoelectric conversion layer including a p-type organic semiconductor material and an n-type organic semiconductor material between a pair of electrodes, and an organic thin film solar cell using the same.

シリコン系や無機化合物系の光電変換素子及びこれを用いた太陽電池と比べて有機薄膜光電変換素子及びこれを用いた太陽電池は、低コスト・低温プロセスが可能であること、色素による着色が可能であること、作製が容易である等の利点から、非常に盛んに研究されている。   Compared to silicon-based and inorganic compound-based photoelectric conversion devices and solar cells using the same, organic thin-film photoelectric conversion devices and solar cells using the same can be processed at low cost and low temperature, and can be colored with pigments. It has been studied very actively because of its advantages such as being easy to manufacture.

有機薄膜光電変換素子では、ｐ型有機半導体材料の上にｎ型有機半導体材料を乗せる平面ヘテロ接合型有機薄膜光電変換素子が一般的であったが、近年、ｐ型有機半導体材料とｎ型有機半導体材料とを混合したバルクヘテロ接合型有機薄膜光電変換素子が盛んに研究されるようになってきた(図１参照)。これは、有機分子は一般的に励起子拡散長が小さいと言われているが、バルクヘテロ接合構造を用いることにより、ｐｎ接合界面が増えることで励起子拡張長の範囲内に、ｐｎ接合界面を作り出すことができるからであり、バルクヘテロ接合構造は有機薄膜光電変換素子において非常に有用な構造である。   In the organic thin film photoelectric conversion element, a planar heterojunction organic thin film photoelectric conversion element in which an n type organic semiconductor material is placed on a p type organic semiconductor material has been common, but in recent years, a p type organic semiconductor material and an n type organic semiconductor have been used. Bulk heterojunction organic thin film photoelectric conversion elements mixed with semiconductor materials have been actively studied (see FIG. 1). This is because organic molecules are generally said to have a small exciton diffusion length, but by using a bulk heterojunction structure, the pn junction interface increases within the range of the exciton extension length by increasing the pn junction interface. This is because a bulk heterojunction structure is a very useful structure in an organic thin film photoelectric conversion element.

特許第４７８３９５８号公報Japanese Patent No. 4783958

Jun Sakai，Tetsuya Taima，and Kazuhiro Saito，"Efficient oligothiophene:fullerene bulk heterojunction organicphotovoltaic cells"，Organic Electronics，vol.9，2008，pp582-590.Jun Sakai, Tetsuya Taima, and Kazuhiro Saito, "Efficient oligothiophene: fullerene bulk heterojunction organicphotovoltaic cells", Organic Electronics, vol. 9, 2008, pp582-590. Jun Sakai，Tetsuya Taima，Toshihiro Yamanari，and Kazuhiro Saito,"Annealing effect in the sexithiophene：C70 small molecule bulk heterojunction organic photovoltaiccells"，Solar Energy Materials & Solar Cells，Vol.93，2009，pp1149-1153.Jun Sakai, Tetsuya Taima, Toshihiro Yamanari, and Kazuhiro Saito, "Annealing effect in the sexithiophene: C70 small molecule bulk heterojunction organic photovoltaic cells", Solar Energy Materials & Solar Cells, Vol.93, 2009, pp1149-1153.

有機薄膜光電変換素子の材料に関して、ｐ型有機半導体材料の開発は盛んに行われており、様々な材料が報告されている。しかしながら、高特性な高分子材料に比べて低分子材料の開発については数が非常に少なく、特性の改善も今後の課題である。その理由の一つとして、有機薄膜光電変換素子のバルクヘテロ接合層における凝集のコントロールの難しさが挙げられる。   With regard to materials for organic thin film photoelectric conversion elements, development of p-type organic semiconductor materials has been actively conducted, and various materials have been reported. However, the development of low molecular weight materials is very small compared to high-performance polymer materials, and improvement of characteristics is a future issue. One reason for this is the difficulty in controlling aggregation in the bulk heterojunction layer of the organic thin film photoelectric conversion element.

有機薄膜光電変換素子に用いられる低分子材料は、結晶性が高く凝集がしやすい傾向がある。このような分子の凝集が起こると、ｐｎ接合界面の接触面積(電荷分離界面の面積)が小さくなると共に、表面粗さも増して綺麗な積層構造の形成が困難となって、有機薄膜光電変換素子の光電変換特性の低下へと繋がる。   Low molecular weight materials used for organic thin film photoelectric conversion elements tend to have high crystallinity and easily aggregate. When such molecular aggregation occurs, the contact area of the pn junction interface (area of the charge separation interface) decreases, and the surface roughness increases, making it difficult to form a beautiful laminated structure. This leads to a decrease in photoelectric conversion characteristics.

また、このような凝集しやすい材料をバルクヘテロ接合型の有機薄膜光電変換素子に用いる場合に、バルクヘテロ接合層において分子の凝集を抑えて良好な光電変換特性を得るには、例えば特許文献１に記載されているように、フラーレン過多な状態にしなければならないことがすでに見出されている。   In addition, when such a material that easily aggregates is used for a bulk heterojunction type organic thin film photoelectric conversion element, in order to suppress molecular aggregation in the bulk heterojunction layer and obtain good photoelectric conversion characteristics, for example, Patent Document 1 describes. As it has been found, it has already been found that fullerenes must be brought to an excessive state.

凝集しやすい低分子材料の代表的な例が、オリゴチオフェンの一種であるα−セキシチオフェン(以下、α-６Ｔと記載する。)である。特許文献１、非特許文献１及び非特許文献２に記載されているように、α-６Ｔをｐ型有機半導体材料、フラーレンをｎ型有機半導体材料として用いられたバルクヘテロ接合(ＢＨＪ)型対応電池は、非常に高い開放電圧(〜０.７Ｖ)を有する。しかしながら、最も光電変換効率を高くするには、バルクヘテロ接合層の(α-６Ｔ：フラーレン)の割合を１：５とフラーレン過多にする必要がある。これよりもｐ型有機半導体材料の割合が多い場合、ｐ型有機半導体材料はミクロな繊維状の凝集体を形成してしまう。このような状態では、電荷分離界面に到達できる励起子が減少することや、表面のラフネスが大きいためにＢＣＰ(bathocuprone：バソクプロイン)等のホールブロック効果を持つバッファ層や背面電極層を綺麗に形成できないことなどに起因して、光電変換効率の低下が起こる。   A typical example of a low-molecular material that easily aggregates is α-sexithiophene (hereinafter referred to as α-6T), which is a kind of oligothiophene. As described in Patent Literature 1, Non-Patent Literature 1 and Non-Patent Literature 2, a bulk heterojunction (BHJ) type battery using α-6T as a p-type organic semiconductor material and fullerene as an n-type organic semiconductor material Has a very high open circuit voltage (˜0.7 V). However, in order to obtain the highest photoelectric conversion efficiency, it is necessary to make the ratio of (α-6T: fullerene) in the bulk heterojunction layer 1: 5, ie, fullerene excess. When the proportion of the p-type organic semiconductor material is larger than this, the p-type organic semiconductor material forms a micro fibrous aggregate. In such a state, the number of excitons that can reach the charge separation interface is reduced, and the surface roughness is large, so the buffer layer and back electrode layer such as BCP (bathocuprone) are effectively formed. Due to the inability to do so, a decrease in photoelectric conversion efficiency occurs.

さらに、バルクヘテロ接合層におけるｐ型有機半導体材料を減らしてしまうことは、電荷分離界面の分布を減らすことや、有機薄膜光電変換素子中のｐ型有機半導体材料の光吸収性能を低下させることの原因となる。したがって、有機薄膜光電変換素子の光電変換特性を改善させるためには、バルクヘテロ接合層におけるｐ型有機半導体材料の混合比率を高める必要がある。   Furthermore, reducing the p-type organic semiconductor material in the bulk heterojunction layer is a cause of reducing the distribution of the charge separation interface and reducing the light absorption performance of the p-type organic semiconductor material in the organic thin film photoelectric conversion element. It becomes. Therefore, in order to improve the photoelectric conversion characteristics of the organic thin film photoelectric conversion element, it is necessary to increase the mixing ratio of the p-type organic semiconductor material in the bulk heterojunction layer.

よって、本願発明の目的は、従来技術に存する課題を解消して、高い結晶性を有する低分子材料をｐ型有機半導体材料として使用する光電変換素子において、ｐ型有機半導体材料の凝集を抑制しつつ光電変換特性を向上させることにある。   Therefore, the object of the present invention is to eliminate the problems existing in the prior art and suppress the aggregation of the p-type organic semiconductor material in the photoelectric conversion element using the low-molecular material having high crystallinity as the p-type organic semiconductor material. While improving the photoelectric conversion characteristics.

上記目的に鑑み、本発明は、一対の電極の間にｐ型有機半導体材料とｎ型有機半導体材料とを混合したバルクヘテロ接合層を含む光電変換層を備えた有機薄膜光電変換素子において、前記光電変換層の前記ｐ型有機半導体材料が嵩高い置換基を有するオリゴチオフェンである有機薄膜光電変換素子を提供する。   In view of the above object, the present invention provides an organic thin film photoelectric conversion element including a photoelectric conversion layer including a bulk heterojunction layer in which a p-type organic semiconductor material and an n-type organic semiconductor material are mixed between a pair of electrodes. Provided is an organic thin film photoelectric conversion element in which the p-type organic semiconductor material of the conversion layer is an oligothiophene having a bulky substituent.

上記有機薄膜光電変換素子では、嵩高い置換基を有したオリゴチオフェンをｐ型有機半導体材料として用いることによって、ｎ型有機半導体材料の凝集を抑制しつつ、ラフネスの低い高品質なバルクヘテロ接合層を形成することを可能とさせている。さらに、これにより、バルクヘテロ接合層におけるｎ型有機半導体材料の体積混合比率を低下させることが可能となる。   In the organic thin film photoelectric conversion element, by using an oligothiophene having a bulky substituent as a p-type organic semiconductor material, a high-quality bulk heterojunction layer with low roughness can be obtained while suppressing aggregation of the n-type organic semiconductor material. It is possible to form. Furthermore, this makes it possible to reduce the volume mixing ratio of the n-type organic semiconductor material in the bulk heterojunction layer.

上記有機薄膜光電変換素子では、前記嵩高い置換基は、ターシャリーブチル基又はオルトビフェニル基であることが好ましい。
また、前記ｎ型有機半導体材料は例えばフラーレンとすることができる。
さらに、前記バルクヘテロ接合層におけるｐ型有機半導体材料の混合体積比率が２５〜５０％であることが好ましい。 In the organic thin film photoelectric conversion element, the bulky substituent is preferably a tertiary butyl group or an orthobiphenyl group.
The n-type organic semiconductor material may be fullerene, for example.
Furthermore, it is preferable that the mixed volume ratio of the p-type organic semiconductor material in the bulk heterojunction layer is 25 to 50%.

また、本発明は、上記有機薄膜光電変換素子を用いた有機薄膜太陽電池を提供する。   Moreover, this invention provides the organic thin film solar cell using the said organic thin film photoelectric conversion element.

なお、本願における「嵩高い置換基」とは、オリゴチオフェン主鎖部よりも嵩高い置換基を意味する。   In addition, the “bulk substituent” in the present application means a substituent that is bulkier than the oligothiophene main chain.

本発明の有機薄膜光電変換素子及びこれを用いた有機薄膜太陽電池によれば、嵩高い置換基を有するオリゴチオフェンをｐ型有機半導体材料として用いることによって、ｐ型有機半導体材料の凝集を抑制し、ラフネスの低い高品質なバルクヘテロ接合層を形成して電荷分離界面の面積を増加させると共に、バルクヘテロ接合層におけるｐ型有機半導体材料の混合体積比率を増加させることができる。この結果、ｐ型有機半導体材料の凝集を抑制しつつ有機薄膜光電変換素子の光電変換効率を向上させることが可能となる。   According to the organic thin film photoelectric conversion element of the present invention and the organic thin film solar cell using the same, by using oligothiophene having a bulky substituent as the p type organic semiconductor material, the aggregation of the p type organic semiconductor material is suppressed. It is possible to form a high-quality bulk heterojunction layer with low roughness to increase the area of the charge separation interface and increase the mixing volume ratio of the p-type organic semiconductor material in the bulk heterojunction layer. As a result, it is possible to improve the photoelectric conversion efficiency of the organic thin film photoelectric conversion element while suppressing aggregation of the p-type organic semiconductor material.

有機薄膜光電変換素子の構造の模式図を示しており、(ａ)は平面ヘテロ接合型のものであり、(ｂ)はバルクヘテロ接合型のものである。The schematic diagram of the structure of an organic thin film photoelectric conversion element is shown, (a) is a plane heterojunction type, (b) is a bulk heterojunction type. 本発明に係る有機薄膜光電変換素子のｐ型有機半導体材料として用いられるオリゴチオフェンの一般構造と、そこに含まれるアリール基の例とを示す模式図である。It is a schematic diagram which shows the general structure of the oligothiophene used as a p-type organic-semiconductor material of the organic thin film photoelectric conversion element which concerns on this invention, and the example of the aryl group contained therein. 実験に用いられた化合物の構造を示す模式図であり、(ａ)はｔｅｒｔ-ブチルフェニル基含有α-クォーターチオフェン(ｔ-ＢｕＰｈ４Ｔ)、(ｂ)はｏｒｔｈｏ-ビフェニル基含有α-クォーターチオフェン(ｏ-ＢｉＰｈ４Ｔ)、(ｃ)はフェニル基含有α-クォーターチオフェン(Ｐｈ４Ｔ)、(ｄ)はα-セキシチオフェン(６Ｔ)をそれぞれ示している。It is a schematic diagram which shows the structure of the compound used for experiment, (a) is tert-butylphenyl group containing α-quarterthiophene (t-BuPh4T), (b) is ortho-biphenyl group-containing α-quarterthiophene (o -BiPh4T), (c) represents phenyl group-containing α-quarterthiophene (Ph4T), and (d) represents α-sexithiophene (6T). ｔ-ＢｕＰｈ４Ｔ、ｏ-ＢｉＰｈ４Ｔ、Ｐｈ４Ｔ、及び６Ｔについて、それぞれ、ＩＴＯ基板上に形成した単一成分膜のイオン化ポテンシャルの測定結果を示すグラフである。It is a graph which shows the measurement result of the ionization potential of the single component film | membrane formed on the ITO board | substrate about t-BuPh4T, o-BiPh4T, Ph4T, and 6T, respectively. ｔ-ＢｕＰｈ４Ｔ、ｏ-ＢｉＰｈ４Ｔ、Ｐｈ４Ｔ、及び６Ｔについて、それぞれ、ＩＴＯ基板上に形成した単一成分膜の吸収スペクトルの測定結果を示すグラフである。It is a graph which shows the measurement result of the absorption spectrum of the single component film | membrane formed on the ITO board | substrate about t-BuPh4T, o-BiPh4T, Ph4T, and 6T, respectively. ｔ-ＢｕＰｈ４Ｔ、ｏ-ＢｉＰｈ４Ｔ、Ｐｈ４Ｔ、及び６Ｔについて、それぞれ、ＩＴＯ基板上に形成した単一成分膜のＡＦＭ像を示している。AFM images of single component films formed on the ITO substrate are shown for t-BuPh4T, o-BiPh4T, Ph4T, and 6T, respectively. ｔ-ＢｕＰｈ４Ｔ、ｏ-ＢｉＰｈ４Ｔ、Ｐｈ４Ｔ、及び６Ｔについて、それぞれ、ＩＴＯ基板上に単一成分膜として形成した蒸着膜の(ａ)面内及び(ｂ)面内のＸ線回折（ＸＲＤ）パターンを示すグラフである。For t-BuPh4T, o-BiPh4T, Ph4T, and 6T, X-ray diffraction (XRD) patterns in the (a) plane and (b) plane of the deposited film formed as a single component film on the ITO substrate, respectively. It is a graph to show. ＩＴＯ基板上に形成した６Ｔとフラーレン(Ｃ60)との共蒸着膜のＡＦＭ像を示している。An AFM image of a co-deposited film of 6T and fullerene (C 60 ) formed on an ITO substrate is shown. ＩＴＯ基板上に形成したＰｈ４Ｔとフラーレン(Ｃ60)との共蒸着膜のＡＦＭ像を示している。An AFM image of a co-deposited film of Ph4T and fullerene (C 60 ) formed on an ITO substrate is shown. ＩＴＯ基板上に形成したｔ-ＢｕＰｈ４Ｔとフラーレン(Ｃ60)との共蒸着膜のＡＦＭ像を示している。An AFM image of a co-deposited film of t-BuPh4T and fullerene (C 60 ) formed on an ITO substrate is shown. ＩＴＯ基板上に形成したｏ-ＢｉＰｈ４Ｔとフラーレン(Ｃ60)との共蒸着膜のＡＦＭ像を示している。An AFM image of a co-deposited film of o-BiPh4T and fullerene (C 60 ) formed on an ITO substrate is shown. ｐ型有機半導体材料として、それぞれ、ｔ-ＢｕＰｈ４Ｔ、ｏ-ＢｉＰｈ４Ｔ、Ｐｈ４Ｔ、及び６Ｔを使用して作製した平面ヘテロ接合型有機薄膜光電変換素子を用いた有機薄膜太陽電池の太陽電池特性を比較した表である。The solar cell characteristics of organic thin film solar cells using planar heterojunction organic thin film photoelectric conversion elements fabricated using t-BuPh4T, o-BiPh4T, Ph4T, and 6T, respectively, as p-type organic semiconductor materials were compared. It is a table. ｐ型有機半導体材料として、それぞれ、ｔ-ＢｕＰｈ４Ｔ、ｏ-ＢｉＰｈ４Ｔ、Ｐｈ４Ｔ、及び６Ｔを使用して作製した平面ヘテロ接合型有機薄膜光電変換素子を用いた有機薄膜太陽電池の分光感度特性(ＩＰＣＥ)を示すグラフである。Spectral sensitivity characteristics (IPCE) of organic thin film solar cells using planar heterojunction organic thin film photoelectric conversion devices fabricated using t-BuPh4T, o-BiPh4T, Ph4T, and 6T, respectively, as p-type organic semiconductor materials It is a graph which shows. ｐ型有機半導体材料として、それぞれ、ｔ-ＢｕＰｈ４Ｔ、ｏ-ＢｉＰｈ４Ｔ、Ｐｈ４Ｔ、及び６Ｔを使用して作製したバルクヘテロ接合型有機薄膜光電変換素子を用いた有機薄膜太陽電池の太陽電池特性を比較した表である。Table comparing solar cell characteristics of organic thin film solar cells using bulk heterojunction organic thin film photoelectric conversion elements fabricated using t-BuPh4T, o-BiPh4T, Ph4T, and 6T, respectively, as p-type organic semiconductor materials It is. ｐ型有機半導体材料として、それぞれ、ｔ-ＢｕＰｈ４Ｔ、ｏ-ＢｉＰｈ４Ｔ、Ｐｈ４Ｔ、及び６Ｔを使用して作製したバルクヘテロ接合型有機薄膜光電変換素子を用いた有機薄膜太陽電池の分光感度特性(ＩＰＣＥ)を示すグラフである。Spectral sensitivity characteristics (IPCE) of organic thin-film solar cells using bulk heterojunction organic thin-film photoelectric conversion elements fabricated using t-BuPh4T, o-BiPh4T, Ph4T, and 6T, respectively, as p-type organic semiconductor materials It is a graph to show.

以下、図面を参照して、本発明による有機薄膜光電変換素子及びこれを用いた有機薄膜太陽電池を説明する。   Hereinafter, with reference to drawings, the organic thin film photoelectric conversion element by this invention and the organic thin film solar cell using the same are demonstrated.

最初に、図１を参照して、本発明による有機薄膜光電変換素子の一実施形態の全体構成を説明する。
有機薄膜光電変換素子１０は、対向する一対の電極１２と、一対の電極１２の間に設けられる光電変換層１４とを備える。光電変換効率を増加させるために、一対の電極１２と光電変換層１４との間に光電変換層１４を挟むようにホールブロッキング層１６と電子ブロッキング層１８とを設けることが好ましい。ホールブロッキング層１６の材料としては例えばＢＣＰなどを用いることができ、電子ブロッキング層１８の材料としては例えばＴＰＤ(トリフェルアミン誘導体)、α-ＮＰＤ(ジフェニルナフチルジアミン)、ＭｏＯｘ(酸化モリブデン：ｘ＝２〜４)などを用いることができる。しかしながら、ホールブロッキング層１６及び電子ブロッキング層１８の材料は上記に限定されるものではない。 Initially, with reference to FIG. 1, the whole structure of one Embodiment of the organic thin film photoelectric conversion element by this invention is demonstrated.
The organic thin film photoelectric conversion element 10 includes a pair of opposed electrodes 12 and a photoelectric conversion layer 14 provided between the pair of electrodes 12. In order to increase the photoelectric conversion efficiency, it is preferable to provide the hole blocking layer 16 and the electron blocking layer 18 so as to sandwich the photoelectric conversion layer 14 between the pair of electrodes 12 and the photoelectric conversion layer 14. As the material of the hole blocking layer 16, for example, BCP can be used, and as the material of the electron blocking layer 18, for example, TPD (triferamine derivative), α-NPD (diphenylnaphthyldiamine), MoOx (molybdenum oxide: x = 2). ~ 4) etc. can be used. However, the materials of the hole blocking layer 16 and the electron blocking layer 18 are not limited to the above.

一対の電極１２の電極材料は特に限定されないが、例えば、Ａｌ、Ａｕ、Ａｇ、Ｃｕ、Ｃｒ、Ｎｉ、Ｍｏ、Ｐｔなどの金属、Ｍｇ／Ａｇ混合物などの金属混合物、ＩＴＯ(Indium Tin Oxide：酸化インジウムスズ)、ＦＴＯ(Fluorine-doped Tiｎ Oxide：フッ素ドープ酸化スズ)、ＩＺＯ(Indium Zinc Oxide：インジウムドープ酸化亜鉛)、ＡＺＯ(Aluminium-doped Zinc Oxide：アルミニウムドープ酸化亜鉛)、ＺｎＯ(酸化亜鉛)などの金属酸化物、カーボンナノチューブ、Ｓｉ(シリコン)などによって作製された導電膜が一対の電極として用いられる。入射する光を内部へ透過させるために、一対の電極１２は、透明電極１２ａと背面電極１２ｂとによって構成されることが好ましい。この場合、透明電極１２ａは、例えば、ＩＴＯ、ＩＺＯ、ＦＴＯなどによって形成し、背面電極１２ｂは、例えば、Ａｌ、Ａｕ，Ａｇ、Ｃｒ、Ａｌ／ＬｉＦ混合物などの金属材料によって形成することができる。   The electrode material of the pair of electrodes 12 is not particularly limited. For example, a metal such as Al, Au, Ag, Cu, Cr, Ni, Mo, and Pt, a metal mixture such as a Mg / Ag mixture, ITO (Indium Tin Oxide: oxidation) Indium tin), FTO (Fluorine-doped Tin Oxide), IZO (Indium Zinc Oxide), AZO (Aluminium-doped Zinc Oxide), ZnO (zinc oxide), etc. A conductive film made of a metal oxide, carbon nanotube, Si (silicon), or the like is used as a pair of electrodes. In order to transmit incident light to the inside, the pair of electrodes 12 is preferably constituted by a transparent electrode 12a and a back electrode 12b. In this case, the transparent electrode 12a can be formed of, for example, ITO, IZO, FTO, or the like, and the back electrode 12b can be formed of, for example, a metal material such as Al, Au, Ag, Cr, or an Al / LiF mixture.

光電変換層１４は、ｐ型有機半導体材料とｎ型有機半導体材料とによって構成される。詳細には、図１(ａ)に示されている平面ヘテロ接合型有機薄膜光電変換素子では、ｐ型有機半導体材料層とｎ型有機半導体材料層とを積層して光電変換層を形成するのに対して、本発明の有機薄膜光電変換素子１０では、図１(ｂ)に示されているように、ｐ型有機半導体材料とｎ型有機半導体材料とを混合したバルクヘテロ接合層によって光電変換層１４を構成している。   The photoelectric conversion layer 14 is composed of a p-type organic semiconductor material and an n-type organic semiconductor material. Specifically, in the planar heterojunction organic thin film photoelectric conversion element shown in FIG. 1A, a p-type organic semiconductor material layer and an n-type organic semiconductor material layer are stacked to form a photoelectric conversion layer. On the other hand, in the organic thin film photoelectric conversion element 10 of the present invention, as shown in FIG. 1B, a photoelectric conversion layer is formed by a bulk heterojunction layer in which a p-type organic semiconductor material and an n-type organic semiconductor material are mixed. 14 is constituted.

ｎ型有機半導体材料としては、一般的な有機薄膜光電変換素子と同様に、フラーレンＣ６０、フラーレンＣ７０、カーボンナノチューブ、ペリレン誘導体などを用いることができる。一方、ｐ型有機半導体材料としては、分子の凝集を抑えるために、嵩高く、構造的にフレキシブル性を有した置換基を導入したオリゴチオフェンを用いる。ここで、「嵩高い」とは、オリゴチオフェン主鎖部よりも置換基が嵩高いことを意味する。   As an n-type organic semiconductor material, fullerene C60, fullerene C70, a carbon nanotube, a perylene derivative, etc. can be used like a general organic thin film photoelectric conversion element. On the other hand, as the p-type organic semiconductor material, an oligothiophene into which a bulky and structurally flexible substituent group is introduced is used in order to suppress molecular aggregation. Here, “bulky” means that the substituent is bulkier than the oligothiophene main chain.

嵩高く、構造的にフレキシブル性を有した置換基には、例えば、メチル(methyl)基、エチル(ethyl)基、アントラセニル(anthracenyl)基、ナフチル(naphtyl)基、ニトロ(nitro)基、ターシャリーブチル(tert-butyl)基、ｏ-メチル(o-methyl)基、ｏ-ビフェニル(o-biphenyl)基、アニシル(anisil)基などがある。これらを導入されたオリゴチオフェンの一般構造が図２に示されている。   Bulky and structurally flexible substituents include, for example, methyl, ethyl, anthracenyl, naphtyl, nitro, tertiary, Examples thereof include a butyl (tert-butyl) group, an o-methyl group, an o-biphenyl group, and an anisyl group. The general structure of oligothiophene into which these are introduced is shown in FIG.

チオフェン環を直線状に結合したオリゴチオフェンなどの分子は、凝集しやすく、フラーレンなどのｎ型有機半導体材料と十分に混和しにくいため、ｐ/ｎ接合界面の面積が小さくなると共に、表面の粗さも増して、光電変換特性の低下を招くことが知られている。本発明の発明者は、嵩高く、構造的にフレキシブル性を有した置換基をオリゴチオフェンに導入することによって、（１）分子間相互作用が弱まることにより凝集を抑制すること、及び（２）立体的に分子間に空間が生じるため、分子の結晶性が崩れるのと同時にフラーレンなどのｎ型有機半導体材料と混ざりやすくなる作用が得られると考え、このような作用を利用することで、バルクヘテロ接合層を形成する際に、フラーレン等のｎ型有機半導体材料がｐ型有機半導体材料だけでは生じてしまう空間に入りこむと共に、ｐ型有機半導体材料の凝集を抑制する効果も得られることを見出した。この結果、バルクヘテロ接合層において、ｎ型有機半導体材料とｐ型有機半導体材料とが均一に混和した状態が得られ、有機薄膜光電変換素子の光電変換効率を向上させることが可能となる。また、オリゴチオフェンをｐ型有機半導体材料として用いる場合、オリゴチオフェンの凝集を抑制するためにフラーレンなどのｎ型有機半導体材料を過多にしてバルクヘテロ接合層を形成していたが、本発明では、ｐ型有機半導体材料の凝集が抑制されるので、バルクヘテロ接合層におけるｐ型有機半導体材料の混合体積比率を低くすることができる。この結果、バルクヘテロ接合層におけるｐ/ｎ接合界面の面積が増加し、光電変換効率をさらに向上させることが可能となる。さらに、バルクヘテロ接合層の表面の粗さも小さくなるので、ホールブロック層や背面電極層をきれいに形成することができ、さらに光電変換効率を向上させることが可能となる。   Molecules such as oligothiophene with linearly linked thiophene rings tend to aggregate and are not sufficiently miscible with n-type organic semiconductor materials such as fullerenes, resulting in a smaller p / n junction interface area and a rough surface. Further, it is known that the photoelectric conversion characteristics are deteriorated. The inventor of the present invention introduces a bulky, structurally flexible substituent into oligothiophene to (1) suppress aggregation by weakening intermolecular interactions, and (2) Since there is a three-dimensional space between molecules, the crystallinity of the molecule is destroyed, and at the same time, it is thought that it can be easily mixed with n-type organic semiconductor materials such as fullerenes. When forming the bonding layer, it has been found that an n-type organic semiconductor material such as fullerene enters the space that is generated only by the p-type organic semiconductor material, and also has an effect of suppressing aggregation of the p-type organic semiconductor material. . As a result, an n-type organic semiconductor material and a p-type organic semiconductor material are uniformly mixed in the bulk heterojunction layer, and the photoelectric conversion efficiency of the organic thin film photoelectric conversion element can be improved. In addition, when oligothiophene is used as a p-type organic semiconductor material, a bulk heterojunction layer is formed with an excessive amount of n-type organic semiconductor material such as fullerene in order to suppress aggregation of oligothiophene. Since aggregation of the type organic semiconductor material is suppressed, the mixing volume ratio of the p type organic semiconductor material in the bulk heterojunction layer can be lowered. As a result, the area of the p / n junction interface in the bulk heterojunction layer is increased, and the photoelectric conversion efficiency can be further improved. Furthermore, since the roughness of the surface of the bulk heterojunction layer is also reduced, the hole block layer and the back electrode layer can be formed cleanly, and the photoelectric conversion efficiency can be further improved.

以下では、本発明の有機薄膜光電変換素子で用いられる嵩高く、構造的にフレキシブル性を有した置換基の例として、ターシャリーブチル基(tert-butyl基)、オルトビフェニル基(ortho-biphenyl基)を導入したオリゴチオフェンを用いた場合の効果を確認した実験結果について説明する。   In the following, examples of bulky and structurally flexible substituents used in the organic thin film photoelectric conversion device of the present invention include tertiary butyl group (tert-butyl group), ortho-biphenyl group (ortho-biphenyl group). The results of experiments confirming the effect of using oligothiophene with) introduced will be described.

以下の実験では、ターシャリーブチル基(tert-butyl基)、オルトビフェニル基(ortho-biphenyl基)を導入したオリゴチオフェンとして、それぞれ、ｔｅｒｔ-ブチルフェニル基含有α-クォーターチオフェン(以下、ｔ-ＢｕＰｈ４Ｔと記載する。)、ｏ-ビフェニル基含有α-クォーターチオフェン(以下、ｏ-ＢｉＰｈ４Ｔと記載する。)を用いた。ｔ-ＢｕＰｈ４Ｔ、ｏ-ＢｉＰｈ４Ｔのように、チオフェン主鎖骨格の両末端にベンゼン環を導入した材料では、ベンゼン環の導入により、分子の最高被占軌道（ＨＯＭＯ）準位を下げることができるため、これらをｐ型有機半導体材料として用いた有機薄膜光電変換素子では、従来のようにα-セキシチオフェン(以下、６Ｔと記載する。)をｐ型有機半導体材料として用いた有機薄膜光電変換素子よりも、高い開放電圧が期待できる。さらに、６Ｔとｔ-ＢｕＰｈ４Ｔ、ｏ-ＢｉＰｈ４Ｔは分子構造が大きく異なりすぎるため、ｔ-ＢｕＰｈ４Ｔ及びｏ-ＢｉＰｈ４Ｔと分子構造が比較的近く且つバルクヘテロ接合膜における凝集性が高い材料であるフェニル基含有α-クォーターチオフェン(以下、Ｐｈ４Ｔと記載する。)を比較対象として評価した。図３(ａ)〜(ｄ)は、それぞれ、ｔ-ＢｕＰｈ４Ｔ、ｏ-ＢｉＰｈ４Ｔ、Ｐｈ４Ｔ、６Ｔの構造を示している。   In the following experiments, tert-butylphenyl group-containing α-quarterthiophene (hereinafter referred to as t-BuPh4T) was used as an oligothiophene into which a tertiary butyl group (tert-butyl group) and an orthobiphenyl group (ortho-biphenyl group) were introduced. And o-biphenyl group-containing α-quarterthiophene (hereinafter referred to as o-BiPh4T) was used. For materials with benzene rings introduced at both ends of the thiophene main chain skeleton, such as t-BuPh4T and o-BiPh4T, the introduction of the benzene ring can lower the highest occupied molecular orbital (HOMO) level of the molecule. In organic thin film photoelectric conversion elements using these as p-type organic semiconductor materials, organic thin film photoelectric conversion elements using α-sexithiophene (hereinafter referred to as 6T) as p-type organic semiconductor materials as in the past. A higher open circuit voltage can be expected. Furthermore, since molecular structures of 6T, t-BuPh4T, and o-BiPh4T are very different from each other, the molecular structure is relatively close to that of t-BuPh4T and o-BiPh4T, and a phenyl group-containing α which is a material having high cohesiveness in a bulk heterojunction film. -Quarter thiophene (hereinafter referred to as Ph4T) was evaluated as a comparison target. 3A to 3D show the structures of t-BuPh4T, o-BiPh4T, Ph4T, and 6T, respectively.

実験で用いられたＰｈ４Ｔ、ｔ-ＢｕＰｈ４Ｔ、ｏ-ＢｉＰｈ４Ｔは、５,５'-２,２'-ビチオフェン（5,5'-dibromo-2,2'-bithiophene）を出発物質として適当な有機スズ試薬との間でＳｔｉｌｌｅカップリング反応を行うことにより、それぞれ合成し、精製は繰り返し昇華精製することで、純度を高めた。一般的に用いられるｐ型有機半導体材料の例である６Ｔは、東京化成工業株式会社から購入し、昇華精製を行ったものを用いた。   Ph4T, t-BuPh4T, and o-BiPh4T used in the experiment are suitable organotins starting from 5,5'-2,2'-bithiophene (5,5'-dibromo-2,2'-bithiophene). Each was synthesized by performing a Stille coupling reaction with a reagent, and purification was repeated by sublimation purification to increase purity. 6T, which is an example of a p-type organic semiconductor material that is generally used, was purchased from Tokyo Chemical Industry Co., Ltd. and subjected to sublimation purification.

実験では、原子間力顕微鏡(ＡＦＭ)及びＸ線回折(ＸＲＤ)を用いて、単一成分膜及び共蒸着膜(バルクヘテロ接合層)の性質を検討すると共に、単一成分膜及び共蒸着膜の状態を観察した。さらに、実際にバルクヘテロ接合型有機薄膜太陽電池を作成して、評価を行い、嵩高く、構造的にフレキシブル性を有した置換基をオリゴチオフェン化合物へ導入したことによるバルクヘテロ接合層の状態(例えば、結晶性、凝集性、グレインサイズ等)及びその太陽電池特性への影響を評価した。   In the experiment, using atomic force microscope (AFM) and X-ray diffraction (XRD), the properties of single-component films and co-deposited films (bulk heterojunction layers) were examined, and single-component films and co-deposited films were examined. The condition was observed. Furthermore, the bulk heterojunction organic thin film solar cell was actually created and evaluated, and the bulk heterojunction layer state (for example, by introducing a bulky and structurally flexible substituent into the oligothiophene compound (e.g., Crystallinity, cohesiveness, grain size, etc.) and their influence on solar cell characteristics were evaluated.

（薄膜評価〜単一成分膜〜）
単一成分膜は、酸素プラズマ洗浄したＩＴＯ基板上に図３(ａ)〜(ｄ)に示されている各オリゴチオフェンを蒸着法によって製膜し、形成された蒸着膜のイオン化ポテンシャル及び吸収スペクトルを測定した。図４は、ｔ-ＢｕＰｈ４Ｔ、ｏ-ＢｉＰｈ４Ｔ、Ｐｈ４Ｔ、６Ｔをそれぞれ用いて単一成分膜として形成した蒸着膜のイオン化ポテンシャルを光電子分光法により測定した結果を示しており、図５は、ｔ-ＢｕＰｈ４Ｔ、ｏ-ＢｉＰｈ４Ｔ、Ｐｈ４Ｔ、６Ｔをそれぞれ用いて単一成分膜として形成した蒸着膜のクロロホルム中における紫外可視吸収スペクトルの測定結果を示している。 (Thin film evaluation-single component film-)
The single component film is formed by depositing each oligothiophene shown in FIGS. 3A to 3D on an ITO substrate cleaned with oxygen plasma by the vapor deposition method, and the ionization potential and absorption spectrum of the formed vapor deposition film. Was measured. FIG. 4 shows the result of measuring the ionization potential of a deposited film formed as a single component film using t-BuPh4T, o-BiPh4T, Ph4T, and 6T, respectively, by photoelectron spectroscopy, and FIG. The measurement result of the ultraviolet visible absorption spectrum in chloroform of the vapor deposition film formed as a single component film | membrane using BuPh4T, o-BiPh4T, Ph4T, and 6T, respectively is shown.

図４に示されている測定結果から、イオン化ポテンシャルは、ｔ-ＢｕＰｈ４Ｔの場合が５.３７ｅＶ、ｏ-ＢｉＰｈ４Ｔの場合が５.５０ｅＶ、Ｐｈ４Ｔの場合が５.２６ｅＶ、６Ｔの場合が５.１１ｅＶであることが分かった。期待どおりに、ベンゼン環を主鎖末端に持つ材料ｔ-ＢｕＰｈ４Ｔ、ｏ-ＢｉＰｈ４Ｔ、Ｐｈ４Ｔが６Ｔよりも深いＨＯＭＯ準位を有することが確認された。   From the measurement results shown in FIG. 4, the ionization potential is 5.37 eV for t-BuPh4T, 5.50 eV for o-BiPh4T, 5.26 eV for Ph4T, and 5.11 eV for 6T. It turns out that. As expected, it was confirmed that materials t-BuPh4T, o-BiPh4T, and Ph4T having a benzene ring at the end of the main chain have a HOMO level deeper than 6T.

図５を参照すると、クロロホルム中における紫外可視吸収スペクトルの測定結果から、化合物ｔ-ＢｕＰｈ４Ｔ及びｏ-ＢｉＰｈ４Ｔの紫外可視吸収はＰｈ４や６Ｔと比べるとわずかに短波長シフトしていることが分かる。吸収末端から見積もったＨＯＭＯ-ＬＵＭＯギャップ(Ｅｇ)は、ｔ-ＢｕＰｈ４Ｔの場合が２.４９ｅＶ、ｏ-ＢｉＰＨ４Ｔの場合が２.５３ｅＶ、Ｐｈ４Ｔの場合が２.５１ｅＶであり、６Ｔの場合の２.４５ｅＶよりもＨＯＭＯ-ＬＵＭＯギャップ(Ｅｇ)がわずかに広がっていた。さらに、ＨＯＭＯ準位とＥｇから見積もったＬＵＭＯ準位は、ｔ-ＢｕＰｈ４Ｔの場合が２.８８ｅＶ、ｏ-ＢｉＰＨ４Ｔの場合が２.９７ｅＶ、Ｐｈ４Ｔの場合が２.７５ｅＶ、６Ｔの場合が２.６６ｅＶであった。   Referring to FIG. 5, it can be seen from the measurement result of the ultraviolet-visible absorption spectrum in chloroform that the ultraviolet-visible absorption of the compounds t-BuPh4T and o-BiPh4T is slightly shifted compared to Ph4 and 6T. The HOMO-LUMO gap (Eg) estimated from the absorption terminal is 2.49 eV for t-BuPh4T, 2.53 eV for o-BiPH4T, 2.51 eV for Ph4T, and 2.5 for 6T. The HOMO-LUMO gap (Eg) was slightly wider than 45 eV. Furthermore, the LUMO level estimated from the HOMO level and Eg is 2.88 eV for t-BuPh4T, 2.97 eV for o-BiPH4T, 2.75 eV for Ph4T, and 2.66 eV for 6T. Met.

図６は、ｔ-ＢｕＰｈ４Ｔ、ｏ-ＢｉＰｈ４Ｔ、Ｐｈ４Ｔ、及び６Ｔを用いて、それぞれ、ＩＴＯ基板上に単一成分膜として形成した蒸着膜のＡＦＭ像を示している。各単一成分膜はＩＴＯ基板上に０.２Å／ｓの蒸着速度で真空蒸着にて製膜した。各単一成分膜のＡＦＭ表面粗さ解析の結果から、ｔ-ＢｕＰｈ４Ｔ、ｏ-ＢｉＰｈ４Ｔ、Ｐｈ４Ｔ、及び６Ｔの各々により形成した単一成分膜の表面粗さ(ＲＭＳ)は、それぞれ、５.１２ｎｍ、２４.０６ｎｍ、７.４９ｎｍ、７.９７ｎｍであった。各単一成分膜の形状像においては、ｏ-ＢｉＰｈ４Ｔの薄膜構造がＰｈ４Ｔ及び６Ｔと比べて最も著しく異なっており、グレインサイズ(凝集体サイズ)が大きくなっていた。   FIG. 6 shows AFM images of vapor deposition films formed as single-component films on an ITO substrate using t-BuPh4T, o-BiPh4T, Ph4T, and 6T, respectively. Each single component film was formed on an ITO substrate by vacuum deposition at a deposition rate of 0.2 Å / s. From the results of AFM surface roughness analysis of each single component film, the surface roughness (RMS) of the single component film formed by each of t-BuPh4T, o-BiPh4T, Ph4T, and 6T is 5.12 nm, respectively. 24.06 nm, 7.49 nm, and 7.97 nm. In the shape image of each single component film, the thin film structure of o-BiPh4T was most significantly different from Ph4T and 6T, and the grain size (aggregate size) was large.

図７は、ｔ-ＢｕＰｈ４Ｔ、ｏ-ＢｉＰｈ４Ｔ、Ｐｈ４Ｔ、及び６Ｔを用いて、それぞれ、ＩＴＯ基板上に単一成分膜として形成した蒸着膜について、Ｘ線回折（ＸＲＤ）パターンを測定した結果であり、(ａ)は各単一成分膜の面外のＸＲＤパターンの測定結果、(ｂ)は各単一成分膜の面内のＸＲＤパターンの測定結果を示している。   FIG. 7 is a result of measuring an X-ray diffraction (XRD) pattern of a deposited film formed as a single component film on an ITO substrate using t-BuPh4T, o-BiPh4T, Ph4T, and 6T, respectively. , (A) shows the measurement result of the out-of-plane XRD pattern of each single component film, and (b) shows the measurement result of the in-plane XRD pattern of each single component film.

図７(ａ)に示されている面外ＸＲＤの測定結果を参照すると、Ｐｈ４Ｔを用いた単一成分膜だけでなく、ｔ-ＢｕＰｈ４Ｔ、ｏ-ＢｉＰｈ４Ｔを用いた単一成分膜でもピークが出現していることから、面外方向への結晶性を有していることが分かる。面外ＸＲＤの第一回折ピークの２θ／θ(ｄ-ｓｐａｃｉｎｇ)は、ｔ-ＢｕＰｈ４Ｔの場合が３.９０°(２２.６３Å)、ｏ-ＢｉＰｈ４Ｔの場合が４.１３°(２１.４Å)、Ｐｈ４Ｔの場合が３.４６°(２５.５１Å)、６Ｔの場合が３.６２°(２４.３８Å)であった。今回合成した材料の分子長は、ＤＦＴ(離散フーリエ変換)計算により求めると約２１〜２５Å程度であることから、ｄ-ｓｐａｃｉｎｇの値と非常に類似しており、ｔ-ＢｕＰｈ４Ｔ、ｏ-ＢｉＰｈ４Ｔ、Ｐｈ４Ｔ、及び６Ｔは、図７(ｃ)に示されているように、分子の長軸方向を基板面に対して向けて薄膜成長していることが示唆された。   Referring to the out-of-plane XRD measurement results shown in FIG. 7 (a), peaks appear not only in single-component films using Ph4T but also in single-component films using t-BuPh4T and o-BiPh4T. Therefore, it can be seen that it has crystallinity in the out-of-plane direction. The 2θ / θ (d-spacing) of the first diffraction peak of out-of-plane XRD is 3.90 ° (22.63 °) for t-BuPh4T and 4.13 ° (21.4 °) for o-BiPh4T. In the case of Ph4T, it was 3.46 ° (25.51 °), and in the case of 6T, it was 3.62 ° (24.38 °). Since the molecular length of the material synthesized this time is about 21 to 25 mm when calculated by DFT (discrete Fourier transform) calculation, it is very similar to the value of d-spacing, and t-BuPh4T, o-BiPh4T, As shown in FIG. 7C, it was suggested that Ph4T and 6T were grown in a thin film with the long axis direction of the molecule directed toward the substrate surface.

面外ＸＲＤの第一回折ピークの半値幅は、ｔ-ＢｕＰｈ４Ｔの場合が０.２６６°、ｏ-ＢｉＰｈ４Ｔの場合が０.２４３°、Ｐｈ４Ｔの場合が０.０９８０°、６Ｔの場合が０.１２４°であり、半値幅の小さなＰｈ４Ｔが最も高い結晶性を有し、続いて６Ｔ、ｏ-ＢｉＰｈ４Ｔ、ｔ-ＢｕＰｈ４Ｔの順に結晶性が下がっていることが分かった。   The full width at half maximum of the first diffraction peak of out-of-plane XRD is 0.266 ° for t-BuPh4T, 0.243 ° for o-BiPh4T, 0.0980 ° for Ph4T, and 0.6 for 6T. It was found that Ph4T having a small half width at 124 ° had the highest crystallinity, and subsequently the crystallinity decreased in the order of 6T, o-BiPh4T, and t-BuPh4T.

また、図７(ｂ)に示されている面内ＸＲＤの測定結果から、ｔ-ＢｕＰｈ４Ｔの面内方向の膜の結晶性が低いことが明らかとなった（図７(ｃ)に示されているように分子が直立していることから、πスタック方向には秩序性が乏しいものと考えられる）。一方で、ｏ-ＢｉＰｈ４Ｔ、Ｐｈ４Ｔ、及び６Ｔは面内ＸＲＤでピークが観測され、第一回折ピークの半値幅は、ｏ-ＢｉＰｈ４Ｔの場合が０.６３°、Ｐｈ４Ｔの場合が０.６４°、６Ｔの場合が１.１°であった。   Also, from the in-plane XRD measurement results shown in FIG. 7 (b), it became clear that the crystallinity of the film in the in-plane direction of t-BuPh4T is low (as shown in FIG. 7 (c)). As the molecule is upright, the order is considered to be poor in the π-stack direction). On the other hand, o-BiPh4T, Ph4T, and 6T have peaks observed by in-plane XRD, and the half width of the first diffraction peak is 0.63 ° for o-BiPh4T, 0.64 ° for Ph4T, The case of 6T was 1.1 °.

面外ＸＲＤの測定結果から、図７(ｃ)に示されているように分子がほぼ直立していることが示唆されており、面内ＸＲＤの測定結果にも回折ピークが存在することから、これらの薄膜はπスタック方向には秩序性が存在することが示唆された。   From the measurement result of out-of-plane XRD, it is suggested that the molecule is almost upright as shown in FIG. 7C, and the diffraction peak also exists in the measurement result of in-plane XRD. It was suggested that these thin films are ordered in the π stack direction.

（薄膜評価〜共蒸着膜(バルクヘテロ接合層)〜）
バルクヘテロ接合層は、酸素プラズマ洗浄したＩＴＯ基板上に、図３(ａ)〜(ｄ)に示されている各オリゴチオフェン(ｐ型有機半導体材料)とフラーレン(Ｃ60)(ｎ型有機半導体材料)とを共蒸着することによって作製し、それぞれの場合において、混合比率をｐ型有機半導体材料：フラーレン＝１：１，１：３，１：５の割合でそれぞれ製膜し、ＡＦＭ測定を行った。図８は、ＩＴＯ基板上にバルクヘテロ接合層として形成した６Ｔとフラーレンとの共蒸着膜のＡＦＭ像であり、図９は、ＩＴＯ基板上にバルクヘテロ接合層として形成したＰｈ４Ｔとフラーレンとの共蒸着膜のＡＦＭ像であり、図１０は、ＩＴＯ基板上にバルクヘテロ接合層として形成したｔ-ＢｕＰｈ４Ｔとフラーレンとの共蒸着膜のＡＦＭ像であり、図１１は、ＩＴＯ基板上にバルクヘテロ接合層として形成したｏ-ＢｉＰｈ４Ｔとフラーレンとの共蒸着膜のＡＦＭ像である。 (Thin film evaluation-co-deposited film (bulk heterojunction layer)-)
The bulk heterojunction layer is formed on an oxygen plasma-cleaned ITO substrate and each oligothiophene (p-type organic semiconductor material) and fullerene (C 60 ) (n-type organic semiconductor material) shown in FIGS. ), And in each case, film formation was performed at a mixing ratio of p-type organic semiconductor material: fullerene = 1: 1, 1: 3, 1: 5, and AFM measurement was performed. It was. FIG. 8 is an AFM image of a co-deposited film of 6T and fullerene formed as a bulk heterojunction layer on an ITO substrate, and FIG. 9 is a co-deposition film of Ph4T and fullerene formed as a bulk heterojunction layer on the ITO substrate. FIG. 10 is an AFM image of a co-deposited film of t-BuPh4T and fullerene formed as a bulk heterojunction layer on an ITO substrate, and FIG. 11 is formed as a bulk heterojunction layer on the ITO substrate. It is an AFM image of a co-deposited film of o-BiPh4T and fullerene.

図８に示されているＡＦＭ像から分かるように、ｐ型有機半導体材料として６Ｔを用いた共蒸着膜(バルクヘテロ接合層)では、混合比率がｐ型有機半導体材料：フラーレン＝１：１，１：３の場合において、ｐ型有機半導体材料である６Ｔのミクロな繊維状の凝集が確認された。また、図９に示されているＡＦＭ像から分かるように、ｐ型有機半導体材料としてＰｈ４Ｔを用いた共蒸着膜(バルクヘテロ接合層)では、混合比率がｐ型有機半導体材料：フラーレン＝１：１，１：３の場合だけでなく、混合比率がｐ型有機半導体材料：フラーレン＝１：５の場合においても、ミクロな繊維状の凝集の形状像が現れていた。すなわち、Ｐｈ４Ｔは凝集性の高い材料であることが単一成分膜のＡＦＭ像やＸＲＤだけでなく、バルクヘテロ接合膜のＡＦＭ像からも示唆された。さらに、図８及び図９に示されているように、ｐ型有機半導体材料として６Ｔを用いた共蒸着膜(バルクヘテロ接合層)では、混合比率がｐ型有機半導体材料：フラーレン＝１：１，１：３，１：５のときのＲＭＳ値がそれぞれ４２.１２ｎｍ，２１.７３ｎｍ，１.５５ｎｍであり、ｐ型有機半導体材料としてＰｈ４Ｔを用いた共蒸着膜(バルクヘテロ接合層)では、混合比率がｐ型有機半導体材料：フラーレン＝１：１，１：３，１：５のときのＲＭＳ値がそれぞれ４１.０ｎｍ，２８.３ｎｍ，１４.６ｎｍとなった。このように、ｐ型有機半導体材料としてＰｈ４Ｔ及び６Ｔを用いた場合には、ｐ型有機半導体材料の混合比率が高い共蒸着膜において表面粗さ解析によるＲＭＳ値が高くなっていた。これは凝集体の存在に由来する。   As can be seen from the AFM image shown in FIG. 8, in the co-deposited film (bulk heterojunction layer) using 6T as the p-type organic semiconductor material, the mixing ratio is p-type organic semiconductor material: fullerene = 1: 1,1. : 3, 6T microfibrous aggregation of p-type organic semiconductor material was confirmed. Further, as can be seen from the AFM image shown in FIG. 9, in the co-deposited film (bulk heterojunction layer) using Ph4T as the p-type organic semiconductor material, the mixing ratio is p-type organic semiconductor material: fullerene = 1: 1. , 1: 3 as well as in the case where the mixing ratio is p-type organic semiconductor material: fullerene = 1: 5, a microfibrous aggregated shape image appeared. That is, it was suggested that Ph4T is a highly cohesive material not only from AFM images and XRD of single component films but also from AFM images of bulk heterojunction films. Further, as shown in FIGS. 8 and 9, in the co-deposited film (bulk heterojunction layer) using 6T as the p-type organic semiconductor material, the mixing ratio is p-type organic semiconductor material: fullerene = 1: 1, The RMS values at 1: 3, 1: 5 are 42.12 nm, 21.73 nm, and 1.55 nm, respectively, and the co-evaporated film (bulk heterojunction layer) using Ph4T as the p-type organic semiconductor material has a mixing ratio. Of the p-type organic semiconductor material: fullerene = 1: 1, 1: 3, 1: 5, the RMS values were 41.0 nm, 28.3 nm, and 14.6 nm, respectively. Thus, when Ph4T and 6T are used as the p-type organic semiconductor material, the RMS value by the surface roughness analysis is high in the co-deposited film having a high mixing ratio of the p-type organic semiconductor material. This is due to the presence of aggregates.

一方、図１０及び図１１に示されているＡＦＭ像から分かるように、嵩高く、構造的にフレキシブル性を有した置換基を導入したｔ-ＢｕＰｈ４Ｔ、ｏ-ＢｉＰｈ４Ｔをｐ型有機半導体材料として用いた共蒸着膜(バルクヘテロ接合層)では、混合比率がｐ型有機半導体材料：フラーレン＝１：１，１：３，１：５の場合でも、ｐ型有機半導体材料由来のミクロな繊維状の凝集は確認されなかった。また、図１０及び図１１に示されているように、ｐ型有機半導体材料としてｔ-ＢｕＰｈ４Ｔを用いた共蒸着膜(バルクヘテロ接合層)では、混合比率がｐ型有機半導体材料：フラーレン＝１：１，１：３，１：５のときのＲＭＳ値がそれぞれ２.９０ｎｍ，１.２３ｎｍ，２.７８ｎｍであり、ｐ型有機半導体材料としてｏ-ＢｉＰｈ４Ｔを用いた共蒸着膜(バルクヘテロ接合層)では、混合比率がｐ型有機半導体材料：フラーレン＝１：１，１：３，１：５のときのＲＭＳ値がそれぞれ１.０６ｎｍ，１.２２ｎｍ，１.２７ｎｍとなった。このように、バルクヘテロ接合層の形成にあたってフラットな薄膜形成が可能なｔ-ＢｕＰｈ４Ｔやｏ-ＢｉＰｈ４Ｔをｐ型有機半導体材料として用いた場合には、ｐ型有機半導体材料の混合比率が高い共蒸着膜においてもＲＭＳ値が低いことが分かった。   On the other hand, as can be seen from the AFM images shown in FIGS. 10 and 11, t-BuPh4T and o-BiPh4T into which bulky and structurally flexible substituents are introduced are used as p-type organic semiconductor materials. In the case of the co-deposited film (bulk heterojunction layer), even when the mixing ratio is p-type organic semiconductor material: fullerene = 1: 1, 1: 3, 1: 5, micro fibrous aggregates derived from the p-type organic semiconductor material Was not confirmed. Further, as shown in FIGS. 10 and 11, in the co-deposited film (bulk heterojunction layer) using t-BuPh4T as the p-type organic semiconductor material, the mixing ratio is p-type organic semiconductor material: fullerene = 1: Co-deposited films (bulk heterojunction layers) having RMS values of 1,1: 3, 1: 5, respectively, 2.90 nm, 1.23 nm, and 2.78 nm, and using o-BiPh4T as a p-type organic semiconductor material Then, when the mixing ratio was p-type organic semiconductor material: fullerene = 1: 1, 1: 3, 1: 5, the RMS values were 1.06 nm, 1.22 nm, and 1.27 nm, respectively. As described above, when t-BuPh4T or o-BiPh4T capable of forming a flat thin film is used as a p-type organic semiconductor material when forming a bulk heterojunction layer, a co-evaporated film having a high mixing ratio of the p-type organic semiconductor material It was also found that the RMS value was low.

さらに、図６に示されている単一成分膜のＡＦＭ像と比較すると、嵩高く、構造的にフレキシブル性を有した置換基を導入した材料ｔ-ＢｕＰｈ４Ｔ、ｏ-ＢｉＰｈ４Ｔをｐ型有機半導体材料として用いた共蒸着膜(バルクヘテロ接合層)では、単一成分膜で見られたような凝集体(グレイン)は観測されなかった。また、ｐ型有機半導体材料としてＰｈ４Ｔや６Ｔを用いた共蒸着膜(バルクヘテロ接合層)の凝集体の形状も単一膜とは大きく異なっていた。これらのことから、凝集体の形成はフラーレンとの相互作用で共蒸着膜形成時に特異的に起こる事象として捉えることができる。   Further, when compared with the AFM image of the single component film shown in FIG. 6, the bulky material t-BuPh4T and o-BiPh4T into which structurally flexible substituents are introduced are used as p-type organic semiconductor materials. In the co-deposited film (bulk heterojunction layer) used as an agglomerate, aggregates (grains) as observed in the single component film were not observed. Moreover, the shape of the aggregate of the co-deposited film (bulk heterojunction layer) using Ph4T or 6T as the p-type organic semiconductor material was also significantly different from that of the single film. From these facts, the formation of aggregates can be regarded as an event that occurs specifically during the formation of a co-deposited film by interaction with fullerene.

（セル評価）
ｐ型有機半導体材料のオリゴチオフェンとして、それぞれ、ｔ-ＢｕＰｈ４Ｔ、ｏ-ＢｉＰｈ４Ｔ、Ｐｈ４Ｔ、及び６Ｔを使用して、図１(ａ)に示されるような平面ヘテロ接合型有機薄膜光電変換素子を用いた太陽電池及び図１(ｂ)に示されるようなバルクヘテロ接合型有機薄膜光電変換素子を用いた有機薄膜太陽電池を作成した。何れの有機薄膜光電変換素子でも、透明電極材料としてＩＴＯ、背面電極材料としてＡｌ、電子ブロッキング層材料としてＭｏＯx、ホールブロッキング層材料としてＢＣＰ、ｐ型有機半導体材料としてオリゴチオフェン(ｔ-ＢｕＰｈ４Ｔ、ｏ-ＢｉＰｈ４Ｔ、Ｐｈ４Ｔ、又は６Ｔ)、ｎ型有機半導体材料としてフラーレン(Ｃ60)を用いた。詳細には、平面ヘテロ接合型有機薄膜光電変換素子の構造は、ＩＴＯ／ＭｏＯx(１５ｎｍ)／オリゴチオフェン(２５ｎｍ)／Ｃ60(７０ｎｍ)／ＢＣＰ(６ｎｍ)／Ａｌ(８０ｎｍ)とした（括弧内は各層の厚さ）。また、バルクヘテロ接合型有機薄膜光電変換素子における共蒸着膜(バルクヘテロ接合層)の混合比率は、蒸着レート比率により制御し、その構造はＩＴＯ／ＭｏＯｘ(１５ｎｍ)／オリゴチオフェン：Ｃ60(５０ｎｍ)／Ｃ60(３０ｎｍ)／ＢＣＰ(６ｎｍ)／Ａｌ(８０ｎｍ)とした(括弧内は各層の厚さ)。上記の構造の有機薄膜光電変換素子を有した有機薄膜太陽電池をソーラーシュミレータ(ＡＭ１.５Ｇ)で１００ｍＷ／ｃｍ2の光照射下で測定を行い、各層におけるフラーレン(Ｃ60)との混合比率を変えて太陽電池特性を調査した。一般に太陽電池の光電変換効率(ＰＣＥ)は次の式で求めることが出来る。

ＰＣＥ(％)＝電流密度(Jsc)×開放電圧(Voc)×形状因子(FF)／入射エネルギー
（１） (Cell evaluation)
As the oligothiophene of the p-type organic semiconductor material, t-BuPh4T, o-BiPh4T, Ph4T, and 6T are used, respectively, and a planar heterojunction organic thin film photoelectric conversion element as shown in FIG. 1A is used. And an organic thin film solar cell using a bulk heterojunction organic thin film photoelectric conversion element as shown in FIG. In any organic thin film photoelectric conversion element, ITO as a transparent electrode material, Al as a back electrode material, MoOx as an electron blocking layer material, BCP as a hole blocking layer material, oligothiophene (t-BuPh4T, o- as a p-type organic semiconductor material) BiPh4T, Ph4T, or 6T), and fullerene (C 60 ) was used as the n-type organic semiconductor material. Specifically, the structure of the planar heterojunction organic thin film photoelectric conversion element was ITO / MoOx (15 nm) / oligothiophene (25 nm) / C 60 (70 nm) / BCP (6 nm) / Al (80 nm) (in parentheses). Is the thickness of each layer). Further, the mixing ratio of the co-deposited film (bulk heterojunction layer) in the bulk heterojunction type organic thin film photoelectric conversion element is controlled by the deposition rate ratio, and the structure is ITO / MoOx (15 nm) / oligothiophene: C 60 (50 nm) / C 60 (30 nm) / BCP (6 nm) / Al (80 nm) (the thickness in parentheses is the thickness of each layer). The organic thin film solar cell having the organic thin film photoelectric conversion element having the above structure is measured with a solar simulator (AM1.5G) under light irradiation of 100 mW / cm 2 , and the mixing ratio of fullerene (C 60 ) in each layer is determined. The solar cell characteristics were investigated by changing. Generally, the photoelectric conversion efficiency (PCE) of a solar cell can be obtained by the following formula.

PCE (%) = current density (Jsc) x open circuit voltage (Voc) x form factor (FF) / incident energy
(1)

ｐ型有機半導体材料としてｔ-ＢｕＰｈ４Ｔ、ｏ-ＢｉＰｈ４Ｔ、Ｐｈ４Ｔ、及び６Ｔをそれぞれ用いた平面ヘテロ接合型有機薄膜太陽電池の太陽電池特性及び分光感度特性(ＩＰＣＥ：Incident Photon to Current Conversion)の測定結果をそれぞれ図１２及び図１３に示し、ｐ型有機半導体材料としてｔ-ＢｕＰｈ４Ｔ、ｏ-ＢｉＰｈ４Ｔ、Ｐｈ４Ｔ、及び６Ｔをそれぞれ用いたバルクヘテロ接合型有機薄膜太陽電池の太陽電池特性及び分光感度特性(ＩＰＣＥ)の測定結果をそれぞれ図１４及び図１５に示す。なお、図１５(ａ)は、ｐ型有機半導体材料として用いるｏ-ＢｉＰｈ４Ｔ、Ｐｈ４Ｔ、及び６Ｔの共蒸着膜(バルクヘテロ接合層)における混合比率をｐ型有機半導体材料：フラーレン＝１：１，１：３，１：５に変えたときの分光感度特性を表すグラフであり、図１５(ｂ)は、ｐ型有機半導体材料として用いるｔ-ＢｕＰｈ４Ｔの共蒸着膜(バルクヘテロ接合層)における混合比率をｐ型有機半導体材料：フラーレン＝１：１，１：３，１：５に変えたときの分光感度特性を表すグラフである。   Measurement results of solar cell characteristics and spectral sensitivity characteristics (IPCE: Incident Photon to Current Conversion) of planar heterojunction organic thin film solar cells using t-BuPh4T, o-BiPh4T, Ph4T, and 6T as p-type organic semiconductor materials, respectively 12 and 13 respectively, and solar cell characteristics and spectral sensitivity characteristics (IPCE) of bulk heterojunction organic thin film solar cells using t-BuPh4T, o-BiPh4T, Ph4T, and 6T as p-type organic semiconductor materials, respectively. The measurement results are shown in FIGS. 14 and 15, respectively. In FIG. 15A, the mixing ratio in the o-BiPh4T, Ph4T, and 6T co-deposited films (bulk heterojunction layers) used as the p-type organic semiconductor material is shown as p-type organic semiconductor material: fullerene = 1: 1,1. 15 is a graph showing the spectral sensitivity characteristic when changed to 3: 5, and FIG. 15B shows the mixing ratio in the co-deposited film (bulk heterojunction layer) of t-BuPh4T used as the p-type organic semiconductor material. It is a graph showing the spectral sensitivity characteristic when it changes into p-type organic-semiconductor material: fullerene = 1: 1, 1: 3, 1: 5.

図１２から分かるように、ｐ型有機半導体材料としてｔ-ＢｕＰｈ４Ｔ、ｏ-ＢｉＰｈ４Ｔを用いた平面ヘテロ接合型有機薄膜太陽電池の開放電圧Ｖｏｃは、それぞれ、０.６４Ｖ，０.６５Ｖであり、ｐ型有機半導体材料として６ＴやＰｈ４Ｔを用いた平面ヘテロ接合型有機薄膜太陽電池の０.３５Ｖ，０.４４Ｖと比べて非常に高い。この理由は化合物ｔ-ＢｕＰｈ４Ｔ、ｏ-ＢｉＰｈ４Ｔのイオン化ポテンシャルが高いことが主な要因である。その結果、ｐ型有機半導体材料としてｔ-ＢｕＰｈ４Ｔ、ｏ-ＢｉＰｈ４Ｔをそれぞれ用いた平面ヘテロ接合型有機薄膜太陽電池の光電変換効率(ＰＣＥ)はそれぞれ１.０％，０.８０％となり、ｐ型有機半導体材料として６ＴやＰｈ４Ｔを用いた平面ヘテロ接合型有機薄膜太陽電池の光電変換効率の０.５１％，０.６６％よりも高くなっている。また、図１３に示されている分光感度特性(ＩＰＣＥ)の測定結果から分かるように、４００〜６００ｎｍにおいて、ｏ-ＢｉＰｈ４Ｔ由来のピークが他のオリゴチオフェン由来のピークと比べて高い。そのために、ｐ型有機半導体材料としてｏ-ＢｉＰｈ４Ｔを用いた平面ヘテロ接合型有機薄膜太陽電池の短絡電流密度(Ｊｓｃ)はｐ型有機半導体材料として他のオリゴチオフェン誘導体を用いた平面ヘテロ接合型有機薄膜太陽電池の短絡電流密度よりも高くなっている。   As can be seen from FIG. 12, the open-circuit voltages Voc of the planar heterojunction organic thin-film solar cells using t-BuPh4T and o-BiPh4T as p-type organic semiconductor materials are 0.64V and 0.65V, respectively. Compared to 0.35V and 0.44V of planar heterojunction organic thin film solar cells using 6T or Ph4T as the type organic semiconductor material. This is mainly due to the high ionization potential of the compounds t-BuPh4T and o-BiPh4T. As a result, the photoelectric conversion efficiencies (PCE) of the planar heterojunction organic thin film solar cells using t-BuPh4T and o-BiPh4T as p-type organic semiconductor materials are 1.0% and 0.80%, respectively, and p-type. The photoelectric conversion efficiency of the planar heterojunction organic thin film solar cell using 6T or Ph4T as the organic semiconductor material is higher than 0.51% and 0.66%. Further, as can be seen from the measurement result of the spectral sensitivity characteristic (IPCE) shown in FIG. 13, the peak derived from o-BiPh4T is higher than the peak derived from other oligothiophene at 400 to 600 nm. Therefore, the short-circuit current density (Jsc) of the planar heterojunction organic thin film solar cell using o-BiPh4T as the p-type organic semiconductor material is the planar heterojunction organic using another oligothiophene derivative as the p-type organic semiconductor material. It is higher than the short circuit current density of the thin film solar cell.

一方、図１４及び図１５に示されている太陽電池特性及び分光感度特性(ＩＰＣＥ)の測定結果から、嵩高く、構造的にフレキシブル性を有した置換基であるターシャリーブチル(tert-butyl)基、オルトビフェニル(ortho-Biphenyl)基を導入した化合物ｔ-ＢｕＰｈ４Ｔ、ｏ-ＢｉＰｈ４Ｔをｐ型有機半導体材料として用いた有機薄膜太陽電池では、共蒸着膜(バルクヘテロ接合層)におけるｐ型有機半導体材料の混合比率を増やすことができることが示された。ｐ型有機半導体材料としてオリゴチオフェンを用い且つｎ型有機半導体材料としてフラーレンを用いた従来のバルクヘテロ接合型有機薄膜太陽電池では、最適な混合比率はｐ型有機半導体材料：フラーレン＝１：５であり、ｐ型有機半導体材料の混合比率が高いバルクヘテロ接合層においては非常に低い光電変換特性しか得ることができなかった。これに対して、本発明に従って、嵩高く、構造的にフレキシブル性な置換基を導入したｔ-ＢｕＰｈ４Ｔ、ｏ-ＢｉＰｈ４Ｔをｐ型有機半導体材料として用いたバルクヘテロ接合型有機薄膜太陽電池では、図１４及び図１５に示されているように、結晶性の高いＰｈ４Ｔや６Ｔをｐ型有機半導体材料として用いたものと比べて、バルクヘテロ接合層におけるｐ型有機半導体材料の混合比率が高い場合でも高い光電変換特性を得ることができることが分かる。このような結果が得られたのは、嵩高く構造的にフレキシブル性を有した置換基を用いることにより、分子間相互作用が弱まる効果や、立体的に分子間に距離が生じるため空間が生じるといった効果が表れ、バルクヘテロ接合層を形成した際にｐ型有機半導体材料の凝集を起こさずに、ｐ型有機半導体材料とフラーレンが均一に混合したラフネスの少ないバルクヘテロ接合層を形成できるためである。   On the other hand, from the measurement results of the solar cell characteristics and spectral sensitivity characteristics (IPCE) shown in FIGS. 14 and 15, tertiary butyl which is a bulky and structurally flexible substituent is shown. In an organic thin film solar cell using a compound t-BuPh4T or o-BiPh4T introduced with an ortho-Biphenyl group as a p-type organic semiconductor material, the p-type organic semiconductor material in the co-deposited film (bulk heterojunction layer) It was shown that the mixing ratio of can be increased. In a conventional bulk heterojunction organic thin film solar cell using oligothiophene as a p-type organic semiconductor material and fullerene as an n-type organic semiconductor material, the optimal mixing ratio is p-type organic semiconductor material: fullerene = 1: 5 In the bulk heterojunction layer having a high mixing ratio of the p-type organic semiconductor material, only very low photoelectric conversion characteristics could be obtained. In contrast, in the bulk heterojunction type organic thin film solar cell using t-BuPh4T and o-BiPh4T into which bulky and structurally flexible substituents are introduced as a p-type organic semiconductor material according to the present invention, FIG. As shown in FIG. 15 and FIG. 15, compared with those using high crystallinity Ph4T or 6T as the p-type organic semiconductor material, a high photoelectric property is obtained even when the mixing ratio of the p-type organic semiconductor material in the bulk heterojunction layer is high. It can be seen that conversion characteristics can be obtained. These results were obtained because of the use of bulky and structurally flexible substituents, and the effect of weakening intermolecular interactions and the steric distance between the molecules. This is because, when the bulk heterojunction layer is formed, the p-type organic semiconductor material is not aggregated and a bulk heterojunction layer with less roughness in which the p-type organic semiconductor material and fullerene are uniformly mixed can be formed.

本発明では、嵩高く、構造的にフレキシブル性を有した置換基(例えばターシャリーブチル基、オルトビフェニル基)を有するオリゴチオフェンを合成し、有機薄膜太陽電池の光電変換素子のｐ型有機半導体材料に適用した。その結果、従来まで問題とされていたミクロ繊維状構造の形成を抑制し、ラフネスの低い高品質なバルクヘテロ接合層の作製に成功したものである。オリゴチオフェンをｐ型有機半導体材料として用いたバルクヘテロ接合型有機薄膜光電変換素子において、このミクロ繊維状の凝集体の発生は、バルクヘテロ接合層におけるｐ型有機半導体材料の体積混合比率を大きく低下させる原因であった。ｐ型有機半導体材料としてオリゴチオフェン系材料を用いたバルクヘテロ型有機薄膜光電変換素子では、一般的に、体積混合比率がｐ型有機半導体材料：フラーレン＝１：５のようにフラーレン過多な条件でのみフラットで高品質な薄膜が形成できたが、本発明で提案した分子構造を有するオリゴチオフェンを用いることにより、ｐ型有機半導体材料とフラーレンの体積混合比率を１：１〜１：３へと飛躍的に増大させる効果が得られた。これは、嵩高く、構造的にフレキシブル性を有した置換基を有するオリゴチオフェンを用いることにより、バルクヘテロ接合層中のｐ型有機半導体材料の凝集を抑えることができるため、ナノメートルの間隔で分子を混ぜることができたからと考えられる。本発明は、上記の予測から、オリゴチオフェンをｐ型有機半導体材料として用いたバルクヘテロ接合型光電変換素子やこれを用いた有機薄膜太陽電池において、効率の良い電荷分離界面の分布や形状を形成できることを見出したものである。   In the present invention, an oligothiophene having a bulky and structurally flexible substituent (for example, a tertiary butyl group or an orthobiphenyl group) is synthesized, and a p-type organic semiconductor material for a photoelectric conversion element of an organic thin film solar cell Applied to. As a result, formation of a microfibrous structure, which has been regarded as a problem until now, has been suppressed, and a high-quality bulk heterojunction layer with low roughness has been successfully produced. In a bulk heterojunction organic thin film photoelectric conversion element using oligothiophene as a p-type organic semiconductor material, the occurrence of this microfibrous aggregate causes the volume mixing ratio of the p-type organic semiconductor material in the bulk heterojunction layer to be greatly reduced. Met. In a bulk hetero type organic thin film photoelectric conversion element using an oligothiophene-based material as a p-type organic semiconductor material, generally, only under conditions where the volume mixing ratio is fullerene excess such as p-type organic semiconductor material: fullerene = 1: 5. Although a flat and high-quality thin film could be formed, the volume mixing ratio of the p-type organic semiconductor material and fullerene jumped from 1: 1 to 1: 3 by using the oligothiophene having the molecular structure proposed in the present invention. Increase effect. This is because the use of an oligothiophene having a bulky and structurally flexible substituent can suppress aggregation of the p-type organic semiconductor material in the bulk heterojunction layer, so that the molecules can be spaced at nanometer intervals. It is thought that it was possible to mix. From the above prediction, the present invention can form an efficient charge separation interface distribution and shape in a bulk heterojunction photoelectric conversion element using oligothiophene as a p-type organic semiconductor material and an organic thin film solar cell using the same. Is found.

さらに、本発明ではオリゴチオフェンの構造修飾に伴う単一成分膜や共蒸着膜(バルクヘテロ接合層)における結晶性や凝集性の変化を観察することによって、共蒸着膜(バルクヘテロ接合層)における凝集体の形成過程を追跡し、これらの結果から、ｐ型有機半導体材料の凝集体の形成はフラーレンが存在するバルクヘテロ接合層形成時に特異的に起こる事象であることを見出した。   Furthermore, in the present invention, by observing changes in crystallinity and cohesiveness in the single component film and co-deposited film (bulk heterojunction layer) accompanying the structural modification of oligothiophene, aggregates in the co-deposited film (bulk heterojunction layer) From these results, it was found that the formation of aggregates of p-type organic semiconductor material is an event that occurs specifically during the formation of a bulk heterojunction layer in which fullerene is present.

１０ 有機薄膜光電変換素子
１２ 電極
１２ａ 透明電極
１２ｂ 背面電極
１４ 光電変換層
１６ ホールブロッキング層
１８ 電子ブロッキング層 DESCRIPTION OF SYMBOLS 10 Organic thin film photoelectric conversion element 12 Electrode 12a Transparent electrode 12b Back electrode 14 Photoelectric conversion layer 16 Hole blocking layer 18 Electron blocking layer

Claims (5)

一対の電極の間にｐ型有機半導体材料とｎ型有機半導体材料とを混合したバルクヘテロ接合層を含む光電変換層を備えた有機薄膜光電変換素子において、
前記光電変換層の前記ｐ型有機半導体材料が嵩高い置換基を有するオリゴチオフェンであることを特徴とする有機薄膜光電変換素子。 In an organic thin film photoelectric conversion element including a photoelectric conversion layer including a bulk heterojunction layer in which a p-type organic semiconductor material and an n-type organic semiconductor material are mixed between a pair of electrodes,
The organic thin film photoelectric conversion element, wherein the p-type organic semiconductor material of the photoelectric conversion layer is an oligothiophene having a bulky substituent. 前記嵩高い置換基は、ターシャリーブチル基又はオルトビフェニル基である、請求項１に記載の有機薄膜光電変換素子。   The organic thin film photoelectric conversion element according to claim 1, wherein the bulky substituent is a tertiary butyl group or an orthobiphenyl group. 前記ｎ型有機半導体材料はフラーレンである、請求項１又は請求項２に記載の有機薄膜光電変換素子。   The organic thin film photoelectric conversion element according to claim 1, wherein the n-type organic semiconductor material is fullerene. 前記バルクヘテロ接合層におけるｐ型有機半導体材料の混合体積比率が２５〜５０％である、請求項１から請求項３の何れか一項に記載の有機薄膜光電変換素子。   The organic thin film photoelectric conversion element according to any one of claims 1 to 3, wherein a mixed volume ratio of the p-type organic semiconductor material in the bulk heterojunction layer is 25 to 50%. 請求項１から請求項４の何れか一項に記載の有機薄膜光電変換素子を用いた有機薄膜太陽電池。   The organic thin film solar cell using the organic thin film photoelectric conversion element as described in any one of Claims 1-4.
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