JP6445979B2 - Charge transport material for photoelectrochemical devices - Google Patents

Description

  The present invention relates to a charge transport material for a photoelectrochemical element used for a dye-sensitized solar cell, and a dye-sensitized solar cell using the same.

  In recent years, a wide range of studies on technologies using wind power, sunlight, and the like as renewable energy have been conducted. Among these, photoelectric conversion technology such as solar cells is one of the technologies that are attracting attention because it enables the use of renewable energy in general households.

  As a form of the solar cell using the photoelectric conversion technology, a crystalline silicon solar cell, an amorphous silicon solar cell, an organic thin-film solar cell, a dye-sensitized solar cell, and the like are listed from the classification of device materials and the like. Among these, crystalline silicon solar cells have been industrially produced for a long time, and have begun to spread with the recent improvement in conversion efficiency. Furthermore, from the viewpoints of price and material supply, various solar cells that can replace crystalline silicon solar cells have been energetically studied.

  Examples of various solar cells that can be substituted for crystalline silicon solar cells include dye-sensitized solar cells. The dye-sensitized solar cell is a solar cell using a semiconductor electrode made of a porous metal oxide such as titanium oxide carrying a dye such as a ruthenium complex, proposed in 1991 by Gratzel et al. Of Lausanne University of Technology. . Dye-sensitized solar cells are particularly actively researched because of their high photoelectric conversion efficiency and low cost of raw materials (see, for example, Non-Patent Document 1, Patent Document 1 and the like).

  Since the dye-sensitized solar cell has a complicated manufacturing process, it is difficult to increase the size of the cell. Further, since iodine is used as the electrolyte, corrosion durability of metal parts such as a current collector is required. Furthermore, in the pores of the semiconductor on which the dye is supported, there is a part where the semiconductor is exposed, and in this part, electrons transferred from the dye to the semiconductor react with iodine as an electrolyte (reverse electron transfer reaction). The problem is that voltage and current losses occur. For these problems, use of a corrosion-resistant current collector such as platinum (see, for example, Patent Document 2), modification of a semiconductor layer (see, for example, Patent Documents 3 and 4), electrolyte gel Various methods such as conversion (see, for example, Patent Document 5) have been proposed.

  However, in these conventional methods, halogen ions such as iodine are still used for the electrolyte, and only a limited electrode such as platinum can be used from the viewpoint of the corrosion resistance of the electrode. There is a problem that a material having excellent conductivity cannot be used. Furthermore, in the method of gelation of the electrolyte proposed in the prior art, the diffusibility of the charge transport material is lowered, and there is a possibility that current and voltage are lowered. Under such circumstances, development of a charge transport material that is non-iodine-based, has excellent diffusibility, and can impart excellent battery characteristics to a dye-sensitized solar cell is desired.

Japanese Patent Laid-Open No. 1-220380 Special table 2010-508636 JP 2000-285974 A JP 2001-35551 A JP 2002-363418 A

B.O'Regan and M.Gratzel, Nature, 353 (24), 737, 1991

  The main object of the present invention is to provide a charge transport material that is non-iodine-based, has excellent diffusibility, and can impart excellent battery characteristics to a dye-sensitized solar cell.

The present inventor has intensively studied to solve the above problems. As a result, the charge transport material for photoelectrochemical devices, which is composed of at least one of the nitroxyl radical compounds represented by the following formulas (1) and (2), is a non-iodine charge transport material, but has a diffusibility In addition, the present inventors have found that excellent battery characteristics can be imparted to a dye-sensitized solar cell. The present invention has been completed by further studies based on these findings.

In formula (1), X ¹ represents a group — (CH ₂ ) _n1 —OC (═O) —, a group — (CH ₂ ) _n1 —C (═O) O—, or a group —O—, ² represents a group —C (═O) O— (CH ₂ ) _n2 —, a group —OC (═O) — (CH ₂ ) _n2 —, or a group —O—, wherein n1 and n2 are each independently Y represents an integer of 0 to 10, Y represents a group — (CH ₂ ) _n3 — or a group — (CH ₂ CH ₂ O) _n4 —CH ₂ CH ₂ —, and n3 and n4 each represents an integer of 0 to 22 Indicates.

  In the formula (2), Z represents a P atom or a Si atom, and n Rs are each independently an H atom, an alkyl group having 1 to 18 carbon atoms, or 2,2,6,6-tetramethylpiperidine. -1-oxyl-4-yl group, m is an integer of 1 to 4, n is an integer of 0 to 3, and when Z is a P atom, n + m = 3, and Z is an Si atom. In this case, n + m = 4.

［式（１）中、Ｘ¹は、基−（ＣＨ₂）_n1−ＯＣ（＝Ｏ）−、基−（ＣＨ₂）_n1−Ｃ（＝Ｏ）Ｏ−、または基−Ｏ−を示し、Ｘ²は、基−Ｃ（＝Ｏ）Ｏ−（ＣＨ₂）_n2−、基−ＯＣ（＝Ｏ）−（ＣＨ₂）_n2−、または基−Ｏ−を示し、ｎ１及びｎ２は、それぞれ独立に０〜１０の整数を示し、Ｙは、基−（ＣＨ₂）_n3−または基−（ＣＨ₂ＣＨ₂Ｏ）_n4−ＣＨ₂ＣＨ₂−を示し、ｎ３及びｎ４は、それぞれ０〜２２の整数を示す。］

［式（２）中、ＺはＰ原子またはＳｉ原子を示し、ｎ個のＲは、それぞれ独立に、Ｈ原子、炭素数１〜１８のアルキル基、または２，２，６，６−テトラメチルピペリジン−１−オキシル−４−イル基を示し、ｍは１〜４の整数を示し、ｎは０〜３の整数を示し、ＺがＰ原子の場合、ｎ＋ｍ＝３であり、ＺがＳｉ原子の場合、ｎ＋ｍ＝４である。］
項２． 前記式（１）及び（２）で表されるニトロキシルラジカル化合物の分子量が、それぞれ１０００以下である、項１に記載の光電気化学素子用電荷輸送材料。
項３． 前記式（１）及び（２）で表されるニトロキシルラジカル化合物の分子量が、それぞれ３００以上である、項１または２に記載の光電気化学素子用電荷輸送材料。
項４． 前記式（１）において、Ｘ¹は、基−（ＣＨ₂）_n1−ＯＣ（＝Ｏ）−を示し、Ｘ²は、基−Ｃ（＝Ｏ）Ｏ−（ＣＨ₂）_n2−を示し、Ｙは、基−（ＣＨ₂）_n3−を示し、ｎ１及びｎ２は、それぞれ独立に０〜１０の整数を示し、ｎ３は、０〜２２の整数を示す、項１〜３のいずれかに記載の光電気化学素子用電荷輸送材料。
項５． 前記式（１）において、Ｘ¹は、基−（ＣＨ₂）_n1−Ｃ（＝Ｏ）Ｏ−を示し、Ｘ²は、基−ＯＣ（＝Ｏ）−（ＣＨ₂）_n2−を示し、Ｙは、基−（ＣＨ₂ＣＨ₂Ｏ）_n4−ＣＨ₂ＣＨ₂−を示し、ｎ１及びｎ２は、それぞれ独立に０〜１０の整数を示し、ｎ４は１〜２２の整数を示す、項１〜３のいずれかに記載の光電気化学素子用電荷輸送材料。
項６． 前記式（２）において、ＺがＰ原子であり、ｍが３である、項１〜５のいずれかに記載の光電気化学素子用電荷輸送材料。
項７． 前記式（２）において、ＺがＳｉ原子であり、ｍが３または４であり、ｍが３である場合はＲがＨ原子である、項１〜５のいずれかに記載の光電気化学素子用電荷輸送材料。
項８． 半導体及び色素を含む半導体電極と、
前記半導体電極に対向する対電極と、
前記半導体電極と前記対電極との間に設けられた電解質層と、
を備え、
前記電解質層が、項１〜７のいずれかに記載の光電気化学素子用電荷輸送材料を含む、
色素増感太陽電池。
項９． 下記式（１）及び（２）で表されるニトロキシルラジカル化合物の少なくとも１種の、光電気化学素子用電荷輸送材料としての使用。

［式（１）中、Ｘ¹は、基−（ＣＨ₂）_n1−ＯＣ（＝Ｏ）−、基−（ＣＨ₂）_n1−Ｃ（＝Ｏ）Ｏ−、または基−Ｏ−を示し、Ｘ²は、基−Ｃ（＝Ｏ）Ｏ−（ＣＨ₂）_n2−、基−ＯＣ（＝Ｏ）−（ＣＨ₂）_n2−、または基−Ｏ−を示し、ｎ１及びｎ２は、それぞれ独立に０〜１０の整数を示し、Ｙは、基−（ＣＨ₂）_n3−または基−（ＣＨ₂ＣＨ₂Ｏ）_n4−ＣＨ₂ＣＨ₂−を示し、ｎ３及びｎ４は、それぞれ０〜２２の整数を示す。］

［式（２）中、ＺはＰ原子またはＳｉ原子を示し、ｎ個のＲは、それぞれ独立に、Ｈ原子、炭素数１〜１８のアルキル基、または２，２，６，６−テトラメチルピペリジン−１−オキシル−４−イル基を示し、ｍは１〜４の整数を示し、ｎは０〜３の整数を示し、ＺがＰ原子の場合、ｎ＋ｍ＝３であり、ＺがＳｉ原子の場合、ｎ＋ｍ＝４である。］That is, this invention provides the invention of the aspect hung up below.
Item 1. A charge transport material for a photoelectrochemical device, comprising at least one nitroxyl radical compound represented by the following formulas (1) and (2).

[In the formula (1), X ¹ represents a group — (CH ₂ ) _n1 —OC (═O) —, a group — (CH ₂ ) _n1 —C (═O) O—, or a group —O—, X ² represents a group —C (═O) O— (CH ₂ ) _n2 —, a group —OC (═O) — (CH ₂ ) _n2 —, or a group —O—, wherein n1 and n2 are each independently Represents an integer of 0 to 10, Y represents a group — (CH ₂ ) _n3 — or a group — (CH ₂ CH ₂ O) _n4 —CH ₂ CH ₂ —, and n3 and n4 each represents 0 to 22 Indicates an integer. ]

[In the formula (2), Z represents a P atom or a Si atom, and n Rs are each independently an H atom, an alkyl group having 1 to 18 carbon atoms, or 2,2,6,6-tetramethyl. Represents a piperidin-1-oxyl-4-yl group, m represents an integer of 1 to 4, n represents an integer of 0 to 3, and when Z is a P atom, n + m = 3, and Z represents a Si atom. In this case, n + m = 4. ]
Item 2. Item 2. The charge transport material for a photoelectrochemical device according to Item 1, wherein the molecular weights of the nitroxyl radical compounds represented by the formulas (1) and (2) are each 1000 or less.
Item 3. Item 3. The charge transport material for a photoelectrochemical device according to Item 1 or 2, wherein the molecular weights of the nitroxyl radical compounds represented by the formulas (1) and (2) are each 300 or more.
Item 4. In the formula (1), X ¹ represents a group — (CH ₂ ) _n1 —OC (═O) —, X ² represents a group —C (═O) O— (CH ₂ ) _n2 —, Y represents group — (CH ₂ ) _n3 —, n1 and n2 each independently represent an integer of 0 to 10, and n3 represents an integer of 0 to 22, Charge transport material for photoelectrochemical devices.
Item 5. In the formula (1), X ¹ represents a group — (CH ₂ ) _n1 —C (═O) O—, X ² represents a group —OC (═O) — (CH ₂ ) _n2 —, Y represents a group — (CH ₂ CH ₂ O) _n4 —CH ₂ CH ₂ —, n1 and n2 each independently represent an integer of 0 to 10, and n4 represents an integer of 1 to 22, The charge transport material for photoelectrochemical elements according to any one of to 3.
Item 6. Item 6. The charge transport material for a photoelectrochemical device according to any one of Items 1 to 5, wherein in the formula (2), Z is a P atom and m is 3.
Item 7. Item 6. The photoelectrochemical element according to any one of Items 1 to 5, wherein, in the formula (2), when Z is a Si atom, m is 3 or 4, and m is 3, R is an H atom. Charge transport material.
Item 8. A semiconductor electrode comprising a semiconductor and a dye;
A counter electrode facing the semiconductor electrode;
An electrolyte layer provided between the semiconductor electrode and the counter electrode;
With
The electrolyte layer includes the charge transport material for a photoelectrochemical device according to any one of Items 1 to 7,
Dye-sensitized solar cell.
Item 9. Use of at least one nitroxyl radical compound represented by the following formulas (1) and (2) as a charge transport material for a photoelectrochemical device.

[In the formula (1), X ¹ represents a group — (CH ₂ ) _n1 —OC (═O) —, a group — (CH ₂ ) _n1 —C (═O) O—, or a group —O—, X ² represents a group —C (═O) O— (CH ₂ ) _n2 —, a group —OC (═O) — (CH ₂ ) _n2 —, or a group —O—, wherein n1 and n2 are each independently Represents an integer of 0 to 10, Y represents a group — (CH ₂ ) _n3 — or a group — (CH ₂ CH ₂ O) _n4 —CH ₂ CH ₂ —, and n3 and n4 each represents 0 to 22 Indicates an integer. ]

[In the formula (2), Z represents a P atom or a Si atom, and n Rs are each independently an H atom, an alkyl group having 1 to 18 carbon atoms, or 2,2,6,6-tetramethyl. Represents a piperidin-1-oxyl-4-yl group, m represents an integer of 1 to 4, n represents an integer of 0 to 3, and when Z is a P atom, n + m = 3, and Z represents a Si atom. In this case, n + m = 4. ]

  According to the present invention, there is provided a charge transport material for a photoelectrochemical device that is a non-iodine charge transport material but has excellent diffusibility and can impart excellent battery characteristics to a dye-sensitized solar cell. Can do. Specifically, the charge transport material of the present invention has a 2,2,6,6-tetramethylpiperidin-1-oxyl-4-yl group (as shown in the above formulas (1) and (2)). The radical structure of the molecule is designed to be bulky while the molecular weight of the nitroxyl radical compound as a whole is reduced by having a specific structure in the group containing the radical unit. Yes. For this reason, when the charge transport material of the present invention is used as an electrolyte of a dye-sensitized solar cell, a decrease in diffusion rate due to an increase in molecular weight is effectively suppressed. Furthermore, as described above, in the conventional dye-sensitized solar cell, there is a portion where the semiconductor is exposed in the pores of the semiconductor on which the dye is supported, and in this portion, the semiconductor and the electrolyte undergo a reverse electron transfer reaction. It is known that a loss of voltage and current occurs, but in the present invention, the charge transport material is suppressed from being taken into the pores of the semiconductor due to the bulk of the charge transport material. The occurrence of transfer reactions is reduced. Therefore, by using the charge transport material of the present invention for the electrolyte layer of the dye-sensitized solar cell, excellent battery characteristics can be imparted to the dye-sensitized solar cell. Furthermore, since the charge transport material of the present invention is a non-iodine-based charge transport material, when the charge transport material is used in the electrolyte layer of a dye-sensitized solar cell, the current collector is made of platinum or the like. It is not necessary to use an expensive metal, and a dye-sensitized solar cell can be manufactured at a lower cost.

  The charge transport material for a photoelectrochemical device of the present invention is characterized by comprising at least one nitroxyl radical compound represented by the above formulas (1) and (2). Hereinafter, the charge transport material for a photoelectrochemical element of the present invention and the dye-sensitized solar cell using the charge transport material will be described in detail.

1. Charge transport material for photoelectrochemical device The charge transport material for photoelectrochemical device of the present invention comprises at least one nitroxyl radical compound represented by the following formulas (1) and (2).

In the formula (1), X ¹ represents a group — (CH ₂ ) _n1 —OC (═O) —, a group — (CH ₂ ) _n1 —C (═O) O—, or a group —O—. X ² is a group -C (= O) O- (CH 2) n2 -, group -OC (= O) - (CH 2) n2 -, or a group -O-. n1 and n2 each independently represent an integer of 0 to 10. Y represents a group — (CH ₂ ) _n3 — or a group — (CH ₂ CH ₂ O) _n4 —CH ₂ CH ₂ —. n3 and n4 each represent an integer of 0-22. In addition, for example, in the group —X ¹ —Y—X ² — in the formula (1), when both X ¹ and X ² become a group —O— and Y is a single bond, the group —O—O— Therefore, the compound represented by the formula (1) is generally unstable. As described above, in the formula (1), those in which the group —X ¹ —Y—X ² — contains a bond —O—O— are usually unstable, and thus the group —X ¹ —Y—X ² -May not contain a bond -O-O-.

  In the formula (2), Z represents a P atom or a Si atom. n R's each independently represent an H atom, an alkyl group having 1 to 18 carbon atoms, or a 2,2,6,6-tetramethylpiperidin-1-oxyl-4-yl group. m shows the integer of 1-4. n shows the integer of 0-3. When Z is a P atom, n + m = 3, and when Z is a Si atom, n + m = 4.

  The upper limit of the molecular weight of the charge transport material of the present invention (nitroxyl radical compounds represented by formulas (1) and (2)) is not particularly limited, but the semiconductor and From the viewpoint of suppressing the reverse electron transfer reaction and imparting excellent battery characteristics to the dye-sensitized solar cell, it is preferably 1000 or less. If the molecular weight is too large, the occurrence of the reverse electron transfer reaction in the pores of the semiconductor can be reduced, but the diffusibility in the electrolyte solution is lowered and the charge transport efficiency per molecule is also reduced. Therefore, it may be difficult to impart excellent battery characteristics to the dye-sensitized solar cell.

  Further, the lower limit of the molecular weight of the charge transport material of the present invention (nitroxyl radical compounds represented by formulas (1) and (2)) is not particularly limited, but is preferably 300 or more from the same viewpoint as described above. More preferably, it is 380 or more, More preferably, 500 or more is mentioned. If the molecular weight is too small, the charge transport material can easily enter the pores of the semiconductor and the reverse electron transfer reaction from the semiconductor to the charge transport material is likely to occur, leading to a decrease in current density, and a dye-sensitized solar cell. In some cases, it may be difficult to impart excellent battery characteristics.

When the charge transport material of the present invention is a nitroxyl radical compound represented by the formula (1), the reverse electron transfer reaction with the semiconductor is suppressed while enhancing the diffusibility in the electrolytic solution, and the dye-sensitized solar cell From the viewpoint of imparting excellent battery characteristics to X ¹ , in formula (1), X ¹ is a group — (CH ₂ ) _n1 —OC (═O) —, and X ² is a group —C (═O). O— (CH ₂ ) _n2 — and Y is preferably a group — (CH ₂ ) _n3 —. That is, as a preferable charge transport material in the present invention, a nitroxyl radical compound represented by the following formula (1a) can be mentioned. In formula (1a), n1 and n2 are each independently an integer of 0 to 10, and n3 is an integer of 0 to 22.

Further, when the charge transport material of the present invention is a nitroxyl radical compound represented by the formula (1), the reverse electron transfer reaction with the semiconductor is suppressed while increasing the diffusibility in the electrolytic solution, and the dye sensitization. From the viewpoint of imparting excellent battery characteristics to the solar cell, in Formula (1), X ¹ is a group — (CH ₂ ) _n1 —C (═O) O—, and X ² is a group —OC ( ═O) — (CH ₂ ) _n2 —, Y is preferably a group — (CH ₂ CH ₂ O) _n4 —CH ₂ CH ₂ —, and n4 is preferably an integer of 1 to 22. That is, as a preferable charge transport material in the present invention, a nitroxyl radical compound represented by the following formula (1b) can be mentioned. In formula (1b), n1 and n2 are each independently an integer of 0 to 10.

  In addition, when the charge transport material of the present invention is a nitroxyl radical compound represented by the formula (2), the reverse electron transfer reaction with the semiconductor is suppressed while increasing the diffusibility in the electrolytic solution, and the dye sensitization. From the viewpoint of imparting excellent battery characteristics to the solar cell, in the formula (2), m is preferably an integer of 2 to 4, and more preferably 3 or 4. That is, in the nitroxyl radical compound represented by the formula (2), the number of TEMPO groups is preferably 2 to 4, and more preferably 3 or 4.

When the charge transport material of the present invention is a nitroxyl radical compound represented by the formula (2) and Z is a P atom, the reverse electron transfer reaction with the semiconductor is carried out while enhancing the diffusibility in the electrolytic solution. From the viewpoint of suppressing and imparting excellent battery characteristics to the dye-sensitized solar cell, m is preferably 3 in the formula (2). That is, as a preferable charge transport material in the present invention, a nitroxyl radical compound represented by the following formula (2a) can be mentioned.

In addition, when the charge transport material for a photoelectrochemical device of the present invention is a nitroxyl radical compound represented by the formula (2) and Z is a Si atom, the semiconductor is improved in diffusibility in an electrolytic solution. In the formula (2), m is preferably 3 or 4 from the viewpoint of suppressing the reverse electron transfer reaction with the dye-sensitized solar cell, and m is preferably In the case of 3, R is more preferably an H atom. That is, preferred charge transport materials in the present invention include nitroxyl radical compounds represented by the following formulas (2b) and (2c).

  The method for producing the charge transport material of the present invention is not particularly limited, and a known production method can be adopted. For example, by reacting a bifunctional compound with a 2,2,6,6-tetramethylpiperidine-1-oxyl compound having a functional group (a TEMPO compound having a functional group), two TEMPOs per molecule. A nitroxyl radical compound represented by formula (1) having a group can be synthesized. The bifunctional compound is not particularly limited as long as it is a compound capable of introducing a TEMPO group, and examples thereof include dicarboxylic acids and dialcohols. Further, the TEMPO compound having a functional group is not particularly limited as long as it can react with two functional groups of the bifunctional compound and introduce two TEMPO compounds into the bifunctional compound. Each of the bifunctional compound and the TEMPO compound having a functional group may be used alone or in combination of two or more.

  Specific examples of the dicarboxylic acid that is a bifunctional compound include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, dodecyldicarboxylic acid, hexadecane Saturated hydrocarbon dicarboxylic acids such as dicarboxylic acid and octadecane dicarboxylic acid; ethylene glycol dicarboxylic acid, diethylene glycol dicarboxylic acid, triethylene glycol dicarboxylic acid, tetraethylene glycol dicarboxylic acid, pentaethylene glycol dicarboxylic acid, hexaethylene glycol dicarboxylic acid, heptaethylene Examples thereof include polyethylene glycol dicarboxylic acids such as glycol dicarboxylic acid, octaethylene glycol dicarboxylic acid, and nonaethylene glycol dicarboxylic acid. Among these, adipic acid, piperic acid, suberic acid, azelaic acid, sebacin are used from the viewpoints of solubility in an electrolyte solution used in dye-sensitized solar cells as described later, molecular size, and charge transport efficiency. Saturated hydrocarbon dicarboxylic acids such as acids; polyethylene glycol dicarboxylic acids such as ethylene glycol dicarboxylic acid, triethylene glycol dicarboxylic acid, and tetraethylene glycol dicarboxylic acid are preferred.

  Specific examples of dialcohols that are bifunctional compounds include ethanediol, propanediol, butanediol, pentanediol, hexanediol, heptanediol, octanediol, nonanediol, decanediol, undecanediol, dodecanediol, hexadecanediol, Saturated hydrocarbon diols such as octadecanediol; polyethylene glycol diols such as ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, hexaethylene glycol, heptaethylene glycol, octaethylene glycol, nonaethylene glycol, etc. Is mentioned. Among these, from the viewpoints of solubility in the electrolyte solution used for dye-sensitized solar cells as described later, voltage loss suppression effect, etc., saturation of butanediol, pentanediol, hexanediol, heptanediol, octanediol, etc. Hydrocarbon diols; polyethylene glycol diols such as diethylene glycol, triethylene glycol and tetraethylene glycol are preferred.

  Specific examples of the TEMPO compound having a functional group include 4-hydroxy TEMPO, 4-hydroxymethyl TEMPO, 4- (2-hydroxyethyl) TEMPO, 4- (3-hydroxypropyl) TEMPO, 4- (4- Hydroxy TEMPO compounds such as hydroxybutyl) TEMPO, 4- (5-hydroxypentyl) TEMPO, 4- (6-hydroxyhexyl) TEMPO; 4-carboxy TEMPO, 4-carboxymethyl TEMPO, 4- (2-carboxyethyl) TEMPO , 4- (3-carboxypropyl) TEMPO, 4- (4-carboxybutyl) TEMPO, 4- (5-carboxypentyl) TEMPO, 4- (6-carboxyhexyl) TEMPO, and the like; 4-chloro TEMPO; 4-bromo TEMPO, 4-iodo TEMPO, 4-bromomethyl TEMPO, 4- (2-bromoethyl) TEMPO, 4- (3-bromopropyl) TEMPO, 4- (4-bromobutyl) TEMPO, 4- (5-bromopentyl) ) TEMPO, halogen-containing TEMPO compounds such as 4- (6-bromohexyl) TEMPO, and the like can be used.

  For example, when dicarboxylic acid is used as a bifunctional compound, a compound having two TEMPO groups per molecule is synthesized by esterifying sebacic acid and 4-hydroxy TEMPO with thionyl chloride. Can do. Further, for example, in the case of using a diol compound as a bifunctional compound, 1,8-octanediol and 4-carboxy TEMPO are esterified with thionyl chloride, thereby obtaining two TEMPO groups per molecule. It is possible to synthesize a compound having

  In addition, for example, by reacting a trifunctional compound or a tetrafunctional compound with a TEMPO compound having a functional group, the nitro represented by the formula (2) having 1 to 4 TEMPO groups per molecule. A xyl radical compound can be synthesized. The manufacturing method in particular of a nitroxyl radical compound represented by Formula (2) is not restrict | limited, A well-known method is employable. For example, by using phosphorus or silicon halide such as phosphorus trichloride or silicon tetrachloride as a trifunctional compound or tetrafunctional compound and reacting this with a TEMPO compound having active hydrogen, 1 to 1 per molecule. A nitroxyl radical compound represented by the formula (2) having four TEMPO groups can be synthesized. More specifically, a phosphorus halide or silicon halide having fluorine, chlorine, bromine, iodine or the like, and a TEMPO compound having active hydrogen such as 4-hydroxy-TEMPO, in the presence of a neutralizing agent such as triethylamine. The nitroxyl radical compound represented by the formula (2) can be synthesized by reacting with

  Specific examples of the trifunctional compound or tetrafunctional compound include, for example, phosphorus halides such as phosphorus trifluoride, phosphorus trichloride, phosphorus tribromide, phosphorus triiodide; silicon tetrafluoride, silicon tetrachloride, Examples thereof include silicon halides such as silicon tetrabromide and silicon tetraiodide. In addition to phosphorus halide and silicon halide, halides such as aluminum, boron, titanium, tin, and antimony can also be used. Among these halides, phosphorus trichloride, silicon tetrachloride and the like are preferable from the viewpoint of easy availability.

  The TEMPO compound having active hydrogen is not particularly limited as long as it can react with the functional group of the above-described trifunctional compound or tetrafunctional compound and has a TEMPO group, but preferably 4-hydroxy TEMPO, 4-hydroxymethyl TEMPO, 4- (2-hydroxyethyl) TEMPO, 4- (3-hydroxypropyl) TEMPO, 4- (4-hydroxybutyl) TEMPO, 4- (5-hydroxypentyl) TEMPO, 4- (6 -Hydroxyalkyl TEMPO compounds such as -hydroxyhexyl) TEMPO. Among these, from the viewpoint of suppressing the loss of voltage and current, 4-hydroxy TEMPO, 4- (2-hydroxyethyl) TEMPO, 4- (4-hydroxybutyl) TEMPO, 4- (6-hydroxyhexyl) TEMPO are preferable. The TEMPO compound having active hydrogen may be used alone or in combination of two or more.

  The molecular weight of the nitroxyl radical compound represented by the formulas (1) and (2) can be measured by a known method. As a method for measuring the molecular weight, for example, a general method such as gel permeation chromatography (GPC) or mass spectrometry (MS) can be employed. For example, in the case of the gel permeation chromatography method, for example, 2695 and 2414 manufactured by Waters are used as the GPC apparatus, columns OH-pak SB-202.5HQ and SB-203HQ manufactured by SHOWDEX, and N, N-dimethyl as the mobile phase. The number average molecular weight can be calculated by standard polystyrene conversion using formamide. For example, in the case of mass spectrometry, measurement can be performed using, for example, an LCMS-2010EV system manufactured by Shimadzu Corporation as an MS apparatus. In addition, about the same compound, when the molecular weight can be measured by both the gel permeation chromatography method (GPC) and the mass spectrometry (MS) method, the molecular weight is the value measured by the mass spectrometry (MS). To do.

  Moreover, the ratio (introduction rate) of the TEMPO group in the charge transport material (sample) composed of the nitroxyl radical compound represented by the formulas (1) and (2) can be confirmed by electron spin resonance (ESR) measurement. it can. In ESR, FR-30EX manufactured by JEOL is used as an ESR measuring apparatus, and a compound having a known TEMPO group content such as 4-hydroxy TEMPO, 4-acetamido TEMPO, etc. is accurately weighed in a quartz glass tube as a standard sample. Then, the spin signal is measured by ESR measurement, and then the spin intensity is obtained by integration twice. On the other hand, a quartz glass tube is filled with a weighed sample, and the spin strength is similarly determined by ESR measurement. Subsequently, the ratio (introduction rate) of the TEMPO groups in the charge transport material can be calculated by comparing the spin intensity ratio between the standard sample and the sample and the charged sample molar ratio.

Ratio of TEMPO group in sample (mol%) = (B) / (A) / number of TEMPO groups per molecule × 100
(A) Standard sample spin intensity / mol
(B) Sample spin intensity / mol

  In the present invention, the charge transport material may be composed of only one kind of nitroxyl radical compound, or may be composed of two or more kinds of nitroxyl radical compounds. The charge transport material of the present invention comprising the nitroxyl radical compound represented by the formulas (1) and (2) may be used as a charge transport material in combination with other charge transport materials. Other charge transport materials are not particularly limited, and may be non-iodine-based or iodine-based.

  The charge transport material for a photoelectrochemical device of the present invention is non-iodine-based, has excellent diffusibility in an electrolytic solution, and further effectively suppresses reverse electron transfer reaction with a semiconductor. It can be suitably used as an electrolyte for such a dye-sensitized solar cell.

2. Dye-sensitized solar cell The dye-sensitized solar cell of the present invention includes a semiconductor electrode containing a semiconductor and a dye, a counter electrode facing the semiconductor electrode, and an electrolyte layer provided between the semiconductor electrode and the counter electrode. The electrolyte layer includes the charge transport material for a photoelectrochemical element as an electrolyte. According to the dye-sensitized solar cell of the present invention, since the electrolyte layer includes the charge transport material of the present invention, the electrolyte layer has excellent battery characteristics, and further uses a non-iodine charge transport material. It is not necessary to use an expensive metal such as platinum for the body, and a cheaper dye-sensitized solar cell can be obtained.

  As a semiconductor electrode, what is used for a well-known dye-sensitized solar cell can be used. For example, after applying a semiconductor to a glass or plastic electrode plate that has been subjected to a conductive treatment with tin or zinc-doped indium oxide (ITO, IZO) or the like, a semiconductor layer is formed, and then baked at a high temperature. A semiconductor electrode can be obtained by chemical adsorption on the surface of the semiconductor layer.

  As the semiconductor, those used in known dye-sensitized solar cells can be adopted, preferably titanium, zinc, niobium, tin, vanadium, indium, tungsten, tantalum, zirconium, molybdenum, manganese, iron, copper, nickel, iridium. And porous metal oxides composed of oxides such as rhodium, chromium and ruthenium. One type of semiconductor may be used alone, or two or more types may be used in combination.

  Moreover, what is used for a well-known dye-sensitized solar cell can be employ | adopted as a pigment | dye adsorb | sucked to a semiconductor layer, Preferably a ruthenium complex pigment | dye is mentioned. Specific examples of the ruthenium complex dye include N3, black dye, bipyridine-carboxylic acid group, bipyridine, phenanthroline, quinoline, and β-diketonate complex. In addition to ruthenium complex dyes, metal complex dyes such as Os metal complexes, Fe metal complexes, Cu metal complexes, Pt metal complexes, and Re metal complexes, methine dyes such as cyanine dyes and merocyanine dyes, mercurochrome dyes, xanthene series Organic dyes such as dyes, porphyrin dyes, phthalocyanine dyes, cyanidin dyes, rhodamine dyes, azo dyes, and coumarin dyes can also be used. A pigment | dye may be used individually by 1 type and may be used in combination of 2 or more type.

  Moreover, what is used for a well-known dye-sensitized solar cell can be used as a counter electrode facing a semiconductor electrode. For example, a glass or plastic electrode plate coated with platinum, conductive carbon or the like as a conductive agent can be used. In the dye-sensitized solar cell of the present invention, since a non-iodine charge transport material is used as the electrolyte, aluminum, copper, or the like can be used as the counter electrode material.

  The electrolyte layer includes the charge transport material of the present invention and an electrolytic solution. As the electrolytic solution, those used in known dye-sensitized solar cells can be adopted, and it is preferable to use an electrochemically stable solution that dissolves and swells the charge transport material of the present invention. Specific examples of the electrolyte include carbonates such as dimethyl carbonate, diethyl carbonate, ethylene carbonate and propylene carbonate; alcohols such as methanol and ethanol; ethers such as tetrahydrofuran, dioxane and diethyl ether; nitriles such as acetonitrile and benzonitrile. Aprotic polar solvents such as N, N-dimethylformamide, N-methylpyrrolidone and dimethyl sulfoxide. One type of electrolytic solution may be used alone, or two or more types may be used in combination. The electrolyte layer may further contain known additives such as a viscosity modifier and a pH adjuster.

  In the dye-sensitized solar cell of the present invention, the concentration of the charge transport material of the present invention in the electrolyte layer is preferably about 0.05 to 20M, more preferably 0.1 to 15M from the viewpoint of improving battery characteristics. Degree. “M” means mol / L.

  Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples. However, the present invention is not limited to the examples. In addition, the molecular weight of the compound obtained by the Example and the comparative example was measured by the mass spectrometry (atmospheric pressure ionization method) using the Shimadzu Corporation LCMS-2010EV system. However, the molecular weight of the compound of Comparative Example 1 is the number average molecular weight measured by gel permeation chromatography. Specifically, as GPC equipment, Waters 2695 and 2414 are used, SHOWDEX columns OH-pak SB-202.5HQ and SB-203HQ are used, and N, N-dimethylformamide is used as the mobile phase. The number average molecular weight was calculated by polystyrene conversion. Moreover, the introduction rate of the TEMPO group (radical unit) is the same as in the above ESR measurement method, using an electron spin resonance (FR-30EX manufactured by JEOL) as an ESR measurement apparatus and using 4-hydroxy TEMPO as a standard sample ( ESR) measurement was performed by comparing the spin strength ratio between the standard sample and the sample and the charged sample molar ratio.

[Example 1] Synthesis of bis (2,2,6,6-tetramethyl-4-piperidyl-1-oxyl) sebacic acid ester (compound (A))

  Nitrogen was sufficiently bubbled through a 200 mL four-necked flask equipped with a stirrer, a nitrogen gas inlet tube, a thermometer, and a reflux condenser, and then 50 mL of tetrahydrofuran, 1.11 g (0.011 mol) of triethylamine, 4-hydroxy- 2,72,6,6-tetramethylpiperidine (manufactured by Tokyo Chemical Industry Co., Ltd., trade name: TEMPOL) 1.72 g (0.010 mol) was charged to obtain a uniform solution. Next, after cooling this four-necked flask to 10 ° C. or less with ice water, 1.01 g (0.005 mol) of sebacic acid (manufactured by Tokyo Chemical Industry Co., Ltd.), 1.31 g (0.011 mol) of thionyl chloride 20 mL of a tetrahydrofuran solution containing was continuously added dropwise to the homogeneous solution. After completion of the dropping, the reaction was continued for 2 hours while keeping the reaction solution at 10 ° C. or lower, and then the reaction was continued at room temperature for another 2 hours. Next, after filtering the reaction solution, water was added and extraction with diethyl ether was repeated several times. Further, the reaction product obtained by removing the ether with an evaporator was subjected to column purification with hexane-chloroform to obtain 2.18 g of a reddish brown solid. The obtained product had a molecular weight measured by mass spectrometry of 510, and bis (2,2,6,6-tetramethyl-4-piperidyl-1-oxyl) sebacic acid ester was obtained (see above). Compound of formula (A)). Moreover, when the ESR measurement was performed, the introduction rate of the TEMPO group (radical unit) was 98 mol%.

[Example 2]
Synthesis of bis (2- (2,2,6,6-tetramethyl-4-piperidyl-1-oxyl) ethyl) sebacic acid ester (compound (B))

(Example 2-1) Intermediate (B1): Synthesis of ethyl (2,2,6,6-tetramethyl-4-piperidylidene) acetate 500 mL equipped with a stirrer, nitrogen gas introduction tube, thermometer, reflux condenser After thoroughly bubbling nitrogen through the four-necked flask, 4.0 g (0.10 mol) of sodium hydride and 100 mL of diethyl ether were mixed, and 25.1 g (0.11 mol) of triethyl phosphonoacetate was slowly added. And added. Next, 80 mL of diethyl ether solution of 10.9 g (0.07 mol) of 2,2,6,6-tetramethyl-4-piperidone was slowly added, and the reaction was continued for 15 hours. Then, water was added, extraction was repeated several times with diethyl ether, dehydrated with magnesium sulfate, and then the solvent was removed with an evaporator to obtain 8.7 g (0.039 mol) of intermediate (B1). In addition, it was confirmed that the obtained product had a molecular weight of 225 measured by mass spectrometry, and ethyl (2,2,6,6-tetramethyl-4-piperidylidene) acetate was obtained (above Intermediate of formula (B1)).

Example 2-2 Intermediate (B2): Synthesis of ethyl (2,2,6,6-tetramethyl-4-piperidyl) acetate 500 mL equipped with a stirrer, nitrogen gas inlet tube, thermometer, reflux condenser After thoroughly bubbling nitrogen through the four-necked flask, 8.7 g (0.039 mol) of the intermediate (B1) was added to 120 mL of ethyl alcohol and dissolved. Then, 0.8 g of 10% palladium / carbon was added, and the reaction was continued at 60 ° C. for 4 hours after stirring for 1 hour so that the reaction vessel was filled with hydrogen gas. After cooling, the reaction solution was filtered, and the solvent was removed from the obtained filtrate with an evaporator to obtain 8.6 g (0.038 mol) of intermediate (B2). In addition, it was confirmed that the obtained product had a molecular weight of 227 measured by mass spectrometry, and ethyl (2,2,6,6-tetramethyl-4-piperidyl) acetate was obtained (above Intermediate of formula (B2)).

(Example 2-3) Intermediate (B3): Synthesis of 2- (2,2,6,6-tetramethyl-4-piperidyl) ethanol A stirrer, a nitrogen gas introduction tube, a thermometer, and a reflux condenser were provided. After thoroughly bubbling nitrogen through a 500 mL four-necked flask, 46 mL of 1M lithium aluminum hydride / diethyl ether solution was added, and then 8.6 g (0.038 mol) of the above intermediate (B2) in 100 mL of diethyl ether. The solution was added slowly and the reaction was continued for 1 hour. Thereafter, water was slowly added to stop the reaction, and the extraction was repeated several times with a diethyl ether / chloroform mixed solution. After dehydration with magnesium sulfate, the intermediate (B3) was removed by removing the solvent with an evaporator. 6.8 g (0.037 mol) was obtained. The obtained product had a molecular weight measured by mass spectrometry of 185, and it was confirmed that 2- (2,2,6,6-tetramethyl-4-piperidyl) ethanol was obtained ( Intermediate of the above formula (B3)).

Example 2-4 Intermediate (B4): Synthesis of 2- (2,2,6,6-tetramethyl-4-piperidyl-1-oxyl) ethanol Stirrer, nitrogen gas inlet tube, thermometer, reflux cooling Into a 500 mL four-necked flask equipped with a tube, 6.8 g (0.037 mol) of the above intermediate (B3), 145 mL of water, 16.3 mL of 35% aqueous hydrogen peroxide (0.19 mol), diethyl 50 mL of ether, 0.6 g (0.015 mol) of ethylenediaminetetraacetic acid disodium, and 0.6 g (0.02 mol) of sodium tungstate were added, and the reaction was continued at room temperature for 24 hours. Thereafter, the ether layer was extracted with chloroform, washed with water several times, dehydrated with magnesium sulfate, and the solvent was removed with an evaporator to obtain 4.9 g (0.024 mol) of intermediate (B4). Obtained. In addition, the obtained product had a molecular weight measured by mass spectrometry of 200, and 2- (2,2,6,6-tetramethyl-4-piperidyl-1-oxyl) ethanol was obtained. Was confirmed (intermediate of the above formula (B4)).

Example 2-5 Synthesis of Compound (B): Bis (2- (2,2,6,6-tetramethyl-4-piperidyl-1-oxyl) ethyl) sebacic acid ester

  In a 200 mL four-necked flask equipped with a stirrer, a nitrogen gas inlet tube, a thermometer, and a reflux condenser, 4.0 g (0.02 mol) of the intermediate (B4) and 2.02 g (0.02 mol) of triethylamine were added. ), A 20 mL solution of dichloromethane containing 2.5 g (0.01 mol) of sebacic acid dichloride (manufactured by Tokyo Chemical Industry Co., Ltd.) was continuously added dropwise to a 30 mL solution of dichloromethane. Next, the reaction was carried out for 2 hours while keeping the reaction solution at 10 ° C. or lower, and then the reaction was continued for another 16 hours at room temperature. Next, water was added to the reaction solution, and extraction with diethyl ether was repeated several times, followed by washing with dilute hydrochloric acid water and water in this order. After dehydration with magnesium sulfate, the solvent was removed with an evaporator to obtain 5.4 g of a crude product. The crude product was subjected to silica gel column purification using hexane-chloroform as a developing solution to obtain 3.5 g (0.006 mol) of a reddish brown solid. The product obtained has a molecular weight of 566 as measured by mass spectrometry and is bis (2- (2,2,6,6-tetramethyl-4-piperidyl-1-oxyl) ethyl) sebacic acid ester (compound (B)). Moreover, when the ESR measurement was performed, the introduction rate of the TEMPO group (radical unit) was 98 mol%.

Example 3 Synthesis of bis (6- (2,2,6,6-tetramethyl-4-piperidiyl-1-oxyl) hexyl) sebacic acid ester

Example 3-1 Intermediate (C1): Synthesis of 2- (2,2,6,6-tetramethyl-4-piperidyl-1-oxyl) acetaldehyde Examples 2-1 to 2- In the same manner as in No. 4, 22.8 g (0.114 mol) of intermediate (B4) was synthesized. Next, in a 1000 mL four-necked flask equipped with a stirrer, a nitrogen gas inlet tube, a thermometer, and a reflux condenser, 22.8 g (0.114 mol) of intermediate (B4) and 80.0 g of pyridinium dichromate were added. (0.230 mol) and 200 mL of dichloromethane were added, and the reaction was continued for 10 hours with stirring. Thereafter, 300 mL of diethylethanol was added, filtration and washing were performed, and the solvent was removed by an evaporator to obtain a crude product. The obtained crude product was subjected to silica gel column purification using a hexane-chloroform developing solution to obtain 14.7 g (0.074 mol) of intermediate (C1). The obtained product had a molecular weight measured by mass spectrometry of 198, and 2- (2,2,6,6-tetramethyl-4-piperidyl-1-oxyl) acetaldehyde was obtained. Was confirmed (intermediate (C1) of the above formula).

Example 3-2 Synthesis of methyl-6- (2,2,6,6-tetramethyl-4-piperidyl-1-oxyl) hexa-2,4-dienoic acid Stirrer, nitrogen gas inlet tube, thermometer After thoroughly bubbling nitrogen through a 500 mL four-necked flask equipped with a reflux condenser, sodium hydride (4.1 g, 0.103 mol) and diethyl ether (300 mL) were mixed, and triethylphosphonocrotonate 29 was mixed. .4 g (0.117 mol) was added slowly. Next, 100 mL of a diethyl ether solution of 14.7 g (0.074 mol) of the intermediate (C1) was slowly added, and the reaction was continued for 15 hours. Then, water was added, extraction was repeated several times with diethyl ether, dehydrated with magnesium sulfate, and the solvent was removed with an evaporator to obtain 13.9 g (0.047 mol) of intermediate (C2). The obtained product had a molecular weight of 294 as measured by mass spectrometry, and methyl-6- (2,2,6,6-tetramethyl-4-piperidyl-1-oxyl) hexa-2,4- It was confirmed that dienoic acid was obtained (intermediate (C2) of the above formula).

Example 3-3 Intermediate (C3): Synthesis of methyl-6- (2,2,6,6-tetramethyl-4-piperidyl-1-oxyl) hexanoic acid Stirrer, nitrogen gas inlet tube, thermometer Then, nitrogen was sufficiently bubbled through a 500 mL four-necked flask equipped with a reflux condenser, and then 13.9 g (0.047 mol) of the intermediate (C2) was added to 200 mL of ethyl alcohol and dissolved. Next, 1.4 g of 10% palladium / carbon was added, and under stirring, the reaction vessel was filled with hydrogen gas for 1 hour, and then the reaction was continued at 60 ° C. for 4 hours. After cooling, the reaction solution was filtered, and the solvent was removed from the obtained filtrate with an evaporator to obtain 7.4 g (0.025 mol) of intermediate (C3). The obtained product has a molecular weight of 298 measured by mass spectrometry, and methyl-6- (2,2,6,6-tetramethyl-4-piperidyl-1-oxyl) hexanoic acid is obtained. (Intermediate of the above formula (C3)).

Example 3-4 Intermediate (C4): Synthesis of 2- (2,2,6,6-tetramethyl-4-piperidyl-1-oxyl) hexal Stirrer, nitrogen gas inlet tube, thermometer, reflux cooling After thoroughly bubbling nitrogen through a 500 mL four-necked flask equipped with a tube, 53 mL of lithium aluminum hydride / diethyl ether 1M solution was added, and then 7.4 g (0.025 mol) of the above intermediate (C3). Was slowly added in 200 mL of diethyl ether, and the reaction was continued for 1 hour. Thereafter, water was slowly added to stop the reaction, and the extraction was repeated several times with a diethyl ether / chloroform mixed solution. After dehydration with magnesium sulfate, the intermediate (C4) was removed by removing the solvent with an evaporator. 4.4 g (0.017 mol) was obtained. In addition, it was confirmed that the obtained product had a molecular weight measured by mass spectrometry of 256, and 2- (2,2,6,6-tetramethyl-4-piperidyl) hexanol was obtained ( Intermediate of the above formula (C4)).

Example 3-5 Compound (C): Bis (6- (2,2,6,6-tetramethyl-4-piperidiyl-1-oxyl) hexyl) Synthesis of sebacic acid ester

  Product 3 was obtained in the same manner as in Example 2-5 except that 2.6 g (0.010 mol) of intermediate (C4) was used instead of intermediate (B4) in Example 2-5 above. .9 g was obtained. The obtained product had a molecular weight of 678 measured by mass spectrometry, and was bis (6- (2,2,6,6-tetramethyl-4-piperidyl-1-oxyl) hexyl) sebacic acid ester. (0.006 mol) was confirmed to be obtained (compound (C) of the above formula). Moreover, when ESR measurement was performed, the introduction rate of TEMPO groups (radical units) in the product was 99 mol%.

[Example 4] Synthesis of bis (2,2,6,6-tetramethyl-4-piperidyl) oxalate (compound (D))

  In a 200 mL four-necked flask equipped with a stirrer, a nitrogen gas inlet tube, a thermometer, and a reflux condenser, 1.7 g (0.01 g) of 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl was added. Mol), 1.0 g (0.01 mol) of triethylamine, and 20 mL of dichloromethane, the solution was cooled to 10 ° C. or lower, and then 20 mL of a solution of 0.6 g (0.005 mol) of oxalyl dichloride in dichloromethane was slowly added. The mixture was further reacted for 2 hours, and further continued at room temperature for 16 hours. The obtained reaction solution was filtered, water was added, and extraction with diethyl ether was repeated several times. Further, the reaction product obtained by removing the ether with an evaporator was subjected to column purification with hexane-chloroform to obtain 1.5 g of a reddish brown solid. The obtained product had a molecular weight of 398 measured by mass spectrometry, and it was confirmed that 0.004 mol of bis (2,2,6,6-tetramethyl-4-piperidyl) oxalate was obtained. (Compound (D) of the above formula). Moreover, when ESR measurement was performed, the introduction rate of TEMPO groups (radical units) in the product was 98 mol%.

Example 5 Synthesis of diethylene glycol bis (2,2,6,6-tetramethylpiperidine-1-oxyl-4-carboxylate) (Compound E)

  To a 50 mL three-necked flask, 4.8 g (0.02 mol) of 4-carboxy-2,2,6,6-tetramethylpiperidine and 10 mL of chloroform were added, and 7.1 g (0 .06 mol) and a small amount of DMF were added, and the reaction was carried out at 50 ° C. for 4 hours. Next, after cooling the reaction solution to 10 ° C. or lower, 1.1 g (0.01 mol) of diethylene glycol, 10 mL of dichloromethane, and 2.4 (0.02 mol) of triethylamine were slowly added and reacted for 2 hours. The reaction was continued for 16 hours at room temperature. Next, water was added to the reaction solution, followed by extraction with dichloromethane, followed by washing with dilute hydrochloric acid and water in this order. Further, after dehydration with magnesium sulfate, the solvent was removed with an evaporator to obtain 5.3 g of a crude product. Got. The crude product was subjected to silica gel column purification using hexane-chloroform as a developing solution to obtain 5.0 g of a reddish brown solid. The obtained product had a molecular weight measured by mass spectrometry of 470, and diethylene glycol bis (2,2,6,6-tetramethylpiperidine-1-oxyl-4-carboxylate) was obtained. Confirmed (compound (E) of the above formula). Moreover, when ESR measurement was performed, the introduction rate of TEMPO groups (radical units) in the product was 99 mol%.

[Example 6] Synthesis of tris (2,2,6,6-tetramethylpiperidin-4-yl-1-oxyl) phosphite (compound (F))

  Nitrogen was sufficiently bubbled through a 100 mL four-necked flask equipped with a stirrer, a nitrogen gas inlet tube, a thermometer, and a reflux condenser connected with a calcium chloride tube, and then 4-hydroxy TEMPO 3 g (17.4 mmol), triethylamine After 1.8 g (17.7 mmol) and 20 mL of chloroform were added and dissolved, the mixture was cooled to 10 ° C. or lower. Thereafter, a mixture of 0.8 g of phosphorus trichloride (5.8 mmol) and 10 mL of chloroform was slowly added from a 50 mL dropping funnel and the stirring was maintained for 2 hours, and then the reaction was continued at room temperature for 14 hours. . Thereafter, triethylamine hydrochloride was removed by filtration, and the solvent was removed from the obtained filtrate by an evaporator. 2.9 g of the obtained crude product was subjected to column purification using silica gel with chloroform as a developing solution to obtain a product. The obtained product had a molecular weight of 544 as measured by mass spectrometry, and 2.1 g of tris (2,2,6,6-tetramethylpiperidin-4-yl-1-oxyl) phosphite (yield 66%) ) Was obtained (compound (F) of the above formula). Moreover, when ESR measurement was performed, the introduction rate of TEMPO groups (radical units) in the product was 99 mol%.

[Example 7] Synthesis of tetrakis (2,2,6,6-tetramethylpiperidin-4-yl-1-oxyl) orthosilicate (compound (G))

  Nitrogen was sufficiently bubbled through a 100 mL four-necked flask equipped with a stirrer, a nitrogen gas inlet tube, a thermometer, and a reflux condenser connected with a calcium chloride tube, and then 3.5 g (20.3 mmol) of 4-hydroxy TEMPO. Then, 2.7 g (26.7 mmol) of triethylamine and 20 mL of chloroform were added and dissolved, and then cooled to 10 ° C. or lower. Thereafter, a mixed solution of 0.74 g (4.1 mmol) of silicon tetrachloride and 10 mL of chloroform was slowly added from a dropping funnel of 50 mL volume, and after stirring was maintained for 1 hour, the reaction was further maintained at room temperature for 4 hours. . Thereafter, triethylamine hydrochloride was removed by filtration, and the solvent was removed from the obtained filtrate by an evaporator. 2.4 g of the obtained crude product was subjected to column purification using silica gel in a chloroform developing solution to obtain a product. The obtained product had a molecular weight of 712 measured by mass spectrometry, and 1.8 g of tetrakis (2,2,6,6-tetramethylpiperidin-4-yl-1-oxyl) orthosilicate (yield 58%). ) Was obtained (compound (G) of the above formula). Moreover, when ESR measurement was performed, the introduction rate of TEMPO groups (radical units) in the product was 99 mol%.

[Example 8] Preparation of tris (2,2,6,6-tetramethylpiperidin-4-yl-1-oxyl) hydrogenated orthosilicate (compound (H)) 0.74 g of silicon tetrachloride was changed to 0.56 g Except that, the same operation as in Example 7 was performed to obtain a product. The product obtained has a molecular weight of 558 as measured by mass spectrometry and is 0.8 g of tris (2,2,6,6-tetramethylpiperidin-4-yl-1-oxyl) hydrogenated orthosilicate (yield) 44%) was obtained (compound (H) of the above formula). Moreover, when ESR measurement was performed, the introduction rate of TEMPO groups (radical units) in the product was 99 mol%.

[Comparative Example 1] Synthesis of poly (2,2,6,6-tetramethyl-4-piperidinyl-1-oxyl methacrylate) (Compound (I)) A stirrer, a nitrogen gas inlet tube, a thermometer, and a reflux condenser are provided. Into a 200 mL four-necked flask, 50 mL of tetrahydrofuran was charged, and 2,2,6,6-tetramethyl-4-piperidinyl methacrylate (Evonik Degussa Japan, trade name: TAA-ol-methacrylate) 10 g (44.4 mmol), 2,2′-azobis (2,4-dimethylvaleronitrile) (manufactured by Wako Pure Chemical Industries, Ltd., trade name: V-65) 0.8 g (3.4 mmol) was charged, A homogeneous solution was obtained. While maintaining the temperature at 25 ° C., oxygen in the reaction system was removed through nitrogen gas, and then a polymerization reaction was performed at 60 ° C. for 10 hours with stirring. The solvent was removed from the resulting reaction solution at 40 ° C. under reduced pressure, and then drying was continued at 80 ° C. to obtain 9.5 g of a white solid polymer.
Next, 100 mL of methanol was charged into a 200 mL four-necked flask equipped with a stirrer, a nitrogen gas introduction tube, a thermometer, and a reflux condenser, and 9.5 g of the polymer obtained above and 35% peroxidation were stirred. Hydrogen water 15.34 ml (0.18 mol) and sodium tungstate 0.06 g were added. The reaction was continued for 10 hours while maintaining the reaction solution at 60 ° C. After confirming that no peroxide remained on KI starch paper, methanol was removed under reduced pressure, and then drying was continued at 80 ° C. to obtain 9.1 g of a red solid polymer oxide. (Compound (I)). The number average molecular weight of the obtained polymer oxide was 6000 (GPC). Further, when ESR measurement was performed, the ratio of 2,2,6,6-tetramethylpiperidine 1-oxyl group (radical unit) in the polymer oxide was 95 mol%.

[Comparative Example 2] 4-Methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl (manufactured by Sigma-Aldrich) was used for the following evaluation (Compound J).

[Diffusion coefficient evaluation]
Using the compounds (A) to (J) of Examples 1 to 8 and Comparative Examples 1 and 2 as charge transport materials, the mobility of these charge transport materials in the electrolyte solution, that is, the diffusion coefficient was evaluated by the following procedure. did. For reference, the “Electrochemical Measurement Manual Basics (Electrochemical Society)” was referred to. Pt as working electrode and counter electrode, Ag / Ag + as reference electrode, 0.1M tetrabutylammonium tetrafluoroborane / acetonitrile solution as electrolyte, 1mM compound (A) to (J) dissolved in electrolyte as evaluation sample The diffusion coefficient in the electrolyte was evaluated using an electrochemical analyzer (660B from BAS). The results are shown in Table 1.

  As shown in Table 1, from the evaluation of the diffusion coefficient, a compound having a large molecular weight of 6000 (number average molecular weight by GPC measurement) slows the physical movement of the molecule and decreases the diffusion rate, whereas a compound having a small molecular weight It can be seen that the diffusion rate increases because the physical movement of the molecules increases.

[Production of dye-sensitized solar cell and evaluation of battery characteristics]
Using the compounds (A) to (J) of Examples 1 to 8 and Comparative Examples 1 and 2 as electrolytes, dye-sensitized solar cells were produced in the following manner, and battery characteristics were evaluated. A dispersion of titanium oxide as a semiconductor was applied to a glass substrate (ITO) in which tin oxide was used as a conductive agent, and baked at 450 ° C. Subsequently, the glass substrate was immersed at room temperature in acetonitrile containing D205 (manufactured by Mitsubishi Paper Industries Co., Ltd.) as a dye, and the dye was adsorbed to obtain a semiconductor electrode containing a semiconductor and the dye. Next, an electrode on which platinum is vapor-deposited is used as the counter electrode, the cell is assembled with the semiconductor electrode and the counter electrode at intervals of 0.5 mm, and the compound (A) is added to a 0.1 M lithium bistrifluoromethanesulfonylimide / acetonitrile solution. An electrolytic solution in which ~ (J) was dissolved as an evaluation sample was added and sealed with a photocurable resin to obtain a dye-sensitized solar cell. A white bias light source was used, and the voltage and current values were measured with a spectral sensitivity measuring device (Spectro Instruments Co., Ltd. CEP-2000). The results are shown in Table 2.

  As shown in Table 2, both the current density and the open-circuit voltage were high in the dye-sensitized solar cells using the compounds (A) to (H) of Examples 1 to 8 as electrolytes. On the other hand, when the compound (I) of Comparative Example 1 was used as an electrolyte, both the current density and the open circuit voltage were small. This is considered to be due to the fact that the compound (I) has a large molecular weight of 6000, so that the diffusion rate is low, which is disadvantageous in charge transfer, and is hardly involved in charge transfer in the pores of titanium oxide. . Also when the compound (J) of Comparative Example 2 was used as the electrolyte, both the current density and the open circuit voltage were small. This is because the molecular weight of the compound (J) is considerably small as 186, and the physical diffusion is inhibited by the compound (J) entering into the pores of the titanium oxide, so that the charge transfer is disadvantageous. Furthermore, a low molecular weight compound has a high diffusion rate and is advantageous for charge transfer. However, since the molecular weight of compound (J) is too small, a reverse electron transfer reaction due to direct contact with titanium oxide as a semiconductor occurs. It is thought that voltage loss occurred and led to a decrease in current density.

Claims (9)

A charge transport material for a photoelectrochemical device, comprising at least one nitroxyl radical compound represented by the following formulas (1) and (2).

[In the formula (1), X ¹ represents a group — (CH ₂ ) _n1 —OC (═O) — , X ² represents a group —C (═O) O— (CH ₂ ) _n2 — , n1 and n2 each independently represent an integer of 0 to 10, Y represents a group — (CH ₂ ) _n3 —, and _n3 represents an integer of 0 to 22. ]

[In the formula (2), Z represents a P atom or a Si atom, and n Rs are each independently an H atom, an alkyl group having 1 to 18 carbon atoms, or 2,2,6,6-tetramethyl. Represents a piperidin-1-oxyl-4-yl group, m represents an integer of 1 to 4, n represents an integer of 0 to 3, and when Z is a P atom, n + m = 3, and Z represents a Si atom. In this case, n + m = 4. ] A charge transport material for a photoelectrochemical device, comprising at least one nitroxyl radical compound represented by the following formulas (1) and (2).

[In the formula (1), X ¹ represents a group — (CH ₂ ) _n1 —C (═O) O— , X ² represents a group —OC (═O) — (CH ₂ ) _n2 — , n1 and n2 each independently represents an integer of 0 to 10, Y represents a group — (CH ₂ CH ₂ O) _n4 —CH ₂ CH ₂ —, and n4 represents an integer of 1 to 22. ]

[In the formula (2), Z represents a P atom or a Si atom, and n Rs are each independently an H atom, an alkyl group having 1 to 18 carbon atoms, or 2,2,6,6-tetramethyl. Represents a piperidin-1-oxyl-4-yl group, m represents an integer of 1 to 4, n represents an integer of 0 to 3, and when Z is a P atom, n + m = 3, and Z represents a Si atom. In this case, n + m = 4. ] The charge transport material for a photoelectrochemical device according to claim 1 or 2 , wherein the molecular weights of the nitroxyl radical compounds represented by the formulas (1) and (2) are each 1000 or less. The charge transport material for photoelectrochemical elements according to any one of claims 1 to 3, wherein the nitroxyl radical compounds represented by the formulas (1) and (2) each have a molecular weight of 300 or more. The charge transport material for a photoelectrochemical element according to any one of claims 1 to 4 , wherein, in the formula (2), Z is a P atom and m is 3. In said Formula (2), when Z is Si atom, m is 3 or 4, m is 3, R is a H atom, The photoelectrochemistry in any one of Claims 1-4 Charge transport material for devices. A semiconductor electrode comprising a semiconductor and a dye;
A counter electrode facing the semiconductor electrode;
An electrolyte layer provided between the semiconductor electrode and the counter electrode;
With
A dye-sensitized solar cell, wherein the electrolyte layer includes the charge transport material for a photoelectrochemical element according to any one of claims 1 to 6 . Use of at least one nitroxyl radical compound represented by the following formulas (1) and (2) as a charge transport material for a photoelectrochemical device.

[In the formula (1), X ¹ represents a group — (CH ₂ ) _n1 —OC (═O) — , X ² represents a group —C (═O) O— (CH ₂ ) _n2 — , n1 and n2 each independently represent an integer of 0 to 10, Y represents a group — (CH ₂ ) _n3 —, and _n3 represents an integer of 0 to 22. ]

[In the formula (2), Z represents a P atom or a Si atom, and n Rs are each independently an H atom, an alkyl group having 1 to 18 carbon atoms, or 2,2,6,6-tetramethyl. Represents a piperidin-1-oxyl-4-yl group, m represents an integer of 1 to 4, n represents an integer of 0 to 3, and when Z is a P atom, n + m = 3, and Z represents a Si atom. In this case, n + m = 4. ] Use of at least one nitroxyl radical compound represented by the following formulas (1) and (2) as a charge transport material for a photoelectrochemical device.

[In the formula (1), X ¹ represents a group — (CH ₂ ) _n1 —C (═O) O— , X ² represents a group —OC (═O) — (CH ₂ ) _n2 — , n1 and n2 each independently represents an integer of 0 to 10, Y represents a group — (CH ₂ CH ₂ O) _n4 —CH ₂ CH ₂ —, and n4 represents an integer of 1 to 22. ]

[In the formula (2), Z represents a P atom or a Si atom, and n Rs are each independently an H atom, an alkyl group having 1 to 18 carbon atoms, or 2,2,6,6-tetramethyl. Represents a piperidin-1-oxyl-4-yl group, m represents an integer of 1 to 4, n represents an integer of 0 to 3, and when Z is a P atom, n + m = 3, and Z represents a Si atom. In this case, n + m = 4. ]