Photoelectric conversion element and solar cell

1. A photoelectric conversion element comprising a substrate, a first electrode, a photoelectric conversion layer, a hole transport layer and a second electrode, wherein

the photoelectric conversion layer comprises a semiconductor and a sensitizing dye,

the hole transport layer comprises a polymer having a repeat unit represented by Formula (1) or (2),

wherein at least one of R 1 -R 4 is a straight chain or a branched chain alkyl group having 1 to 24 carbon atoms, a cycloalkyl group having 3 to 9 carbon atoms, an alkoxy group having 1 to 18 carbon atoms, a polyethylene oxide group having 1 to 18 carbon atoms or an aryl group, and remaining substituent is a hydrogen atom,

wherein n is an integer of 1 to 3, m is an integer of 0 to 2n+4, R 5 is a halogen atom or an alkyl group, and when a plurality of R 5 groups are contained, each R 5 group may be different from each other,

the polymer has an absorbance of 0.2 to 1.0, and

the sensitizing dye has a substructure represented by Formula (3) ,

wherein R 6 represents a hydrogen atom, a substituted or non-substituted alkyl group, an alkenyl group, an alkynyl group, an aryl group, an amino group, a cyano group or a heterocyclic group, Y represents a sulfur atom, an oxygen atom or a selenium atom, R 7 and R 8 each represents a hydrogen atom, a halogen atom, a hydroxyl group, a thiol group, a cyano group, a substituted or non-substituted alkyl group, an aryl group, an alkenyl group, an alkynyl group, an alkoxy group, an amino group or a heterocyclic group, provided that these groups may be mutually combined to form a ring structure, n represents an integer of 0 or more, and in the case when n≧2, two or more R 7 may be the same or different and two or more R 8 may be the same or different, X represents an acidic group, and, when a carbon-carbon double bond is included in Formula (3), the double bond may be either a cis-form or a trans-form.

2. The photoelectric conversion element of claim 1 , wherein at least one of R 1 -R 4 of Formula (1) is a straight chain alkyl group having 6 to 18 carbon atoms.

3. The photoelectric conversion element of claim 1 , wherein n of Formula (2) is 1 .

4. The photoelectric conversion element of claim 1 , wherein the semiconductor comprises a titanium oxide.

5. The photoelectric conversion element of claim 1 , wherein the polymer further comprises a repeat unit derived from a divalent organic group represented by Formula (4),

Ar   Formula (4)

wherein Ar represents an organic divalent group having a π-conjugated structure.

6. The photoelectric conversion element of claim 5 , wherein the repeat unit derived from the divalent organic group represented by Formula (4) is derived from a thiophene derivative, a pyrrole derivative or a furan derivative.

7. The photoelectric conversion element of claim 1 , wherein the hole transport layer comprises a salt comprising an organic anion.

8. The photoelectric conversion element of claim 1 , wherein the hole transport layer comprises Li[(CF 3 SO 2 ) 2 N].

9. The photoelectric conversion element of claim 1 , wherein a content of the polymer in the hole transport layer is 50 to 100 mass % based on the mass of the hole transport layer.

10. The photoelectric conversion element of claim 1 , wherein a content of the polymer in the hole transport layer is 90 to 100 mass % based on the mass of the hole transport layer.

11. The photoelectric conversion element of claim 1 , wherein the hole transport layer is subjected to hole doping and an amount of doped hole is 0.15 to 0.66 hole per one repeat unit represented by Formula (1) or (2).

12. The photoelectric conversion element of claim 11 , wherein an ionization potential of the polymer being subjected to hole doping is 4.5 eV to 5.5 eV.

13. The photoelectric conversion element of claim 11 , wherein an ionization potential of the polymer being subjected to hole doping is 4.7 eV to 5.3 eV.

14. The photoelectric conversion element of claim 1 , wherein the polymer is formed via electropolymerization carried out on the photoelectric conversion layer.

15. The photoelectric conversion element of claim 14 , wherein the polymer is formed via electropolymerization while being irradiated with light.

16. The photoelectric conversion element of claim 1 , wherein the photoelectric conversion layer is formed via electropolymerization employing a monomer represented by Formula (1′) or (2′), or a multimer thereof,

wherein at least one of R 1 -R 4 is a straight chain or a branched chain alkyl group having 1 to 24 carbon atoms, a cycloalkyl group having 3 to 9 carbon atoms, an alkoxy group having 1 to 18 carbon atoms, a polyethylene oxide group having 1 to 18 carbon atoms or an aryl group, and remaining substituent is a hydrogen atom,

wherein n is an integer of 1 to 3, m is an integer of 0 to 2n+4, R 5 is a halogen atom or an alkyl group, and when a plurality of R 5 groups are contained, each R 5 group may be different from each other.

17. A solar cell employing the photoelectric conversion element of claim 1 .