(19) & (11) EP 2 461 420 A1 (12) EUROPEAN PATENT APPLICATION published in accordance with Art. 153(4) EPC (43) Date of publication: (51) Int Cl.: 06.06.2012 Bulletin 2012/23 H01M 14/00 (2006.01) H01L 31/04 (2006.01) H01L 51/50 (2006.01) (21) Application number: 10804506.3 (86) International application number: (22) Date of filing: 29.07.2010 PCT/JP2010/062823 (87) International publication number: WO 2011/013760 (03.02.2011 Gazette 2011/05) (84) Designated Contracting States: • YAGUCHI, Mitsuo AL AT BE BG CH CY CZ DE DK EE ES FI FR GB Osaka 571-8686 (JP) GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO • YAMAKI, Takeyuki PL PT RO SE SI SK SM TR Osaka 571-8686 (JP) • NISHIDE, Hiroyuki (30) Priority: 31.07.2009 JP 2009180175 Tokyo 169-8050 (JP) 31.07.2009 JP 2009180176 • OYAIZU, Kenichi 16.06.2010 JP 2010137687 Tokyo 169-8050 (JP) • KATO, Fumiaki (71) Applicants: Tokyo 169-8050 (JP) • Panasonic Corporation • SUZUKA, Michio Osaka 5718501 (JP) Osaka 571-8686 (JP) • Waseda University • KAMBE, Shingo Tokyo 169-8050 (JP) Deceased (JP) (72) Inventors: (74) Representative: Appelt, Christian W. • SEKIGUCHI, Takashi Boehmert & Boehmert Osaka 540-6207 (JP) Pettenkoferstrasse 20-22 80336 München (DE) (54) PHOTOELECTRIC ELEMENT (57) Disclosed is a photoelectric element having an excellent conversion efficiency and provided with a hole transporting layer that is endowed with excellent hole transporting properties and a sufficiently large reaction interface. The photoelectric element of the invention has a pair of electrodes, an electron transporting layer and a hole transporting layer which are disposed between the elec- trodes, and an electrolyte solution. The hole transporting layer includes a first organic compound having a redox moiety capable of repeated oxidation and reduction. The electrolyte solution stabilizes a reduced state of the redox moiety. The organic compound and the electrolyte solu- tion together form a first gel layer. EP 2 461 420 A1 Printed by Jouve, 75001 PARIS (FR) EP 2 461 420 A1 Description TECHNICAL FIELD 5 [0001] The invention relates to a photoelectric element which converts light to electricity, or converts electricity to light. BACKGROUND ART [0002] In recent years, photoelectric elements have been used in power generating devices which carry out photoe- 10 lectric conversion, such as photoelectric cells and solar cells; light- emitting devices such as organic electroluminescent (EL) devices; optical display devices such as electrochromic display devices and electronic paper; and sensor elements which are sensitive to temperature, light or the like. [0003] It is essential for the hole transporting layer in a photoelectric element to have high hole transporting properties. Moreover, the size of the surface area of the interface is important to this hole transporting layer. Here, "interface" refers 15 to the interface between the hole transporting layer and a layer other than the hole transporting layer, at which interface holes are generated under the effects of energy from the exterior and which acts when holes are injected from the exterior. The hole transporting layer has hitherto been formed of a metal, organic semiconductor, inorganic semicon- ductor, conductive polymer, conductive carbon or the like. [0004] For example, in photoelectric conversion elements, the hole transporting layer for transporting holes is formed 20 of an organic material such as poly (3-hexylthiophene), triphenyldiamine (monomer, polymer, etc.), polyaniline, polypyr- role, polythiophene or a phthalocyanine compound. The conversion efficiency of photoelectric conversion elements is rising on account of the hole transporting abilities of such organic materials (see Patent Documents 1 to 3). [0005] Also, it has been reported that, in the formation of a hole transporting layer for a molecular solar cell, a structure obtained by chemical bonding between an electron-donating molecule (donor) and an electron accepting molecule 25 (acceptor) forms as a thin film on a substrate (see Non-Patent Document 1). [0006] However, in the hole transporting layers reported in the above literature, sufficient hole transporting properties and a sufficient size of the interface for the function as a hole transporting layer have not both been achieved at once. Hence, there currently exists a desire for a hole transporting layer which has better hole transporting properties and also has a sufficiently large interface. 30 Patent Document 1: Japanese Patent Application Laid-open No. 2009-088045 Patent Document 2: Japanese Patent Application Laid-open No. 2009-065216 Patent Document 3: Japanese Patent Application Laid-open No. 2009-054936 Non-Patent Document 1: H. Imabori and S. Fukuzumi: "Bunshi taiyo denchi no tenbo [The outlook for molecular 35 solar cells]", Kagaku Kogyo, July 2001, p. 41 SUMMARY OF INVENTION TECNICAL PROBLEM 40 [0007] In light of the above, the object of this invention is to provide a photoelectric element having an excellent conversion efficiency, which element is endowed with excellent hole transporting properties and a sufficiently large reaction interface. 45 SOLUTION TO PROBLEM [0008] The photoelectric element according to the present invention includes a pair of electrodes, an electron trans- porting layer and a hole transporting layer which are disposed between the electrodes, and an electrolyte solution. The hole transporting layer includes a first organic compound having a redox moiety capable of repeated oxidation and 50 reduction, the electrolyte solution stabilizes the reduced state of the redox moiety, and the organic compound and the electrolyte solution together form a first gel layer. [0009] The photoelectric element of the invention may further include a sensitizing dye which is present in the first gel layer. [0010] In the photoelectric element of the invention, the hole transporting layer may include a nitroxide radical polymer. 55 [0011] In the photoelectric element of the invention, the electron transporting layer may include at least one compound selected from the group consisting of viologen derivatives, phenoxyl derivatives and quinone derivatives. [0012] In the photoelectric element of the invention, the open circuit voltage A (V) after 5 minutes of irradiation with 200 lux light and the open circuit voltage B (V) when 5 minutes have elapsed after shielding of the light following irradiation 2 EP 2 461 420 A1 may satisfy the following condition: 5 [0013] In the photoelectric element of the invention, the electron transporting layer may further include a second organic compound having a redox moiety capable of repeated oxidation and reduction, the second organic compound and the electrolyte solution may together form a second gel layer, and the electron transporting layer may have a higher 10 redox potential than the hole transporting layer. [0014] The photoelectric element of the invention may further include a sensitizing dye which carries out an electron transfer reaction with either or both of the electron transporting layer and the hole transporting layer. [0015] The invention both increases the hole transporting properties of the hole transporting layer and also increases the size of the reaction interface, thereby improving the conversion efficiency of the photoelectric element. 15 ADVATAGEOUS EFFECTS OF INVENTION [0016] According to the present invention, the hole transport property of the hole transport layer improves while the reaction interface becomes wide, improving the conversion efficiency of the photoelectric element. 20 BRIEF DESCRIPTION OF DRAWINGS [0017] 25 FIG. 1 is a schematic cross-sectional diagram showing one embodiment of the invention. FIG. 2 is a schematic cross-sectional diagram showing another embodiment of the invention. FIG. 3 is a graph showing the results from measurements of the change in the open circuit voltage when the photoelectric element obtained in Example 1 was irradiated with light, then shielded from light. FIG. 4 is a graph showing the results from measurements of the change in the open circuit voltage when the 30 photoelectric element obtained in Comparative Example 1 was irradiated with light, then shielded from light. DESCRIPTION OF EMBODIMENTS [0018] In a first embodiment of the invention, a photoelectric element is formed of an electron transporting layer 3 and 35 a hole transporting layer 4 which are disposed between a pair of electrodes 2 and 5. The hole transporting layer 4 includes an organic compound having a redox moiety which is capable of repeated oxidation and reduction. The organic compound is with an electrolyte solution that stabilizes the oxidized state of the redox moiety to form a gel layer 6. A sensitizing dye is present in the gel layer 6. [0019] In this embodiment, the organic compound of the hole transporting layer 4 and the electrolyte solution together 40 form the gel layer 6, thus making the reaction interface of the organic compound larger and increasing the conversion efficiency. [0020] Moreover, in this embodiment, in addition to the organic compound of the hole transporting layer 4 and the electrolyte solution together forming the gel layer 6, because a sensitizing dye is present in the gel layer 6, the organic compound reaction interface is even larger, increasing the conversion efficiency, and the hole transfer efficiency from 45 the sensitizing dye to the organic compound of the hole transporting layer 4 increases, resulting in a higher hole trans- porting efficiency. [0021] In this embodiment, it is preferable for the hole transporting