JP2010073730A - Tandem type photoelectric conversion element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photoelectric conversion element having excellent photoelectric conversion efficiency.
A photoelectric conversion layer (E) containing a conductive polymer (d) and an electron acceptor (a) is provided between two electrode layers (Y) formed in layers on a substrate (T). It is a tandem photoelectric conversion element (TP) in which 2 to 4 photoelectric conversion elements (P) are laminated, and the maximum absorption wavelength of at least two photoelectric conversion elements (P) is different, and the photoelectric conversion element ( The half width of the absorption band of P) is 150 nm or less, and in each photoelectric conversion layer (E), the value of the energy level of the lowest empty orbit of the conductive polymer (d) and the electron acceptor (a) A tandem photoelectric conversion element (TP) characterized in that the difference in energy level values of the lowest unoccupied orbit is 1 eV or less.
[Selection] Figure 1

Description

  The present invention relates to a photoelectric conversion element. Specifically, for example, the present invention relates to a photoelectric conversion element used for a solar cell element or an optical sensor element.

  An organic thin film solar cell is a solar cell in which a photoelectric conversion layer having a conductive polymer (hole acceptor) and an electron transport layer (electron acceptor) is disposed between two different electrodes, such as silicon. Compared to a representative inorganic solar cell, there are advantages that the manufacturing process is easy and the area can be increased at low cost. However, since the photoelectric conversion efficiency is low, it has been difficult to put it into practical use.

  As a promising method for improving this low photoelectric conversion efficiency, a tandem photoelectric conversion element in which a plurality of photoelectric conversion layers are stacked can be given.

  As a tandem photoelectric conversion element, for example, it is formed to include a multilayer film in which conductive polymers (hole acceptors) and electron transport layers (electron acceptors) are alternately stacked in one photoelectric conversion layer. Examples include an element (Patent Document 1) or an element in which photoelectric conversion layers and electrodes are alternately stacked (Patent Document 2). However, the light absorption wavelength region is the same as that of a single layer, and only light in a specific wavelength region is used. It could not be used for power generation, and it was difficult to greatly improve the photoelectric conversion efficiency.

  On the other hand, in the tandem photoelectric conversion element (Patent Document 3) in which the layers having different absorption wavelength maxima of each photoelectric conversion layer are stacked, utilization of a wider wavelength region of sunlight can be achieved. The half-width is wide and the difference in the energy level of the lowest vacant orbit between the conductive polymer (hole acceptor) and the electron transport layer (electron acceptor) is large. In this case, the photoelectric conversion efficiency is greatly improved. It was difficult to do.

  As described above, various studies have been made on tandem organic thin-film solar cell elements. However, since the half-value width of the absorption band is wide, the energy level of excited electrons due to energy transfer inside the photoelectric conversion layer. Cannot be prevented, and high photoelectric conversion efficiency cannot be expected. In other words, in order to improve the photoelectric conversion efficiency of the organic thin-film solar cell element, it is possible to prevent relaxation of the energy level of the excited electrons due to energy transfer inside the photoelectric conversion layer (narrow the half-value width of the absorption band). Is essential.

  Furthermore, it is not expected that high photoelectric conversion efficiency can be obtained because the difference between the minimum empty orbital (LUMO) values of the conductive polymer (hole acceptor) and the electron transport layer (electron acceptor) is excessive. This is the reason why the open circuit voltage can be improved by reducing the difference in LUMO between the conductive polymer (hole acceptor) and the electron transport layer (electron acceptor). Indispensable for improving efficiency.

JP 2007-288161 A JP 2007-115849 A JP 2006-278484 A

In the conventional tandem photoelectric conversion element, the energy level of the excited electrons is prevented from being relaxed by the energy transfer inside the photoelectric conversion layer, and a larger open circuit voltage cannot be obtained. It cannot be expected to obtain photoelectric conversion efficiency.
The subject of this invention is providing the photoelectric conversion element which can obtain high photoelectric conversion efficiency.

The inventors of the present invention have reached the present invention as a result of studies to achieve the above object.
That is, the present invention provides a photoelectric conversion layer (E) containing a conductive polymer (d) and an electron acceptor (a) between two electrode layers (Y) formed in layers on a substrate (T). A tandem photoelectric conversion element (TP) formed by laminating 2 to 4 photoelectric conversion elements (P) having different maximum absorption wavelengths of at least two photoelectric conversion elements (P), and photoelectric conversion The half width of the absorption band of the element (P) is 150 nm or less, and the value of the energy level of the lowest empty orbit of the conductive polymer (d) in each photoelectric conversion layer (E) and the electron acceptor (a ) Of the lowest empty orbital energy level is 1 eV or less, a tandem photoelectric conversion element (TP)
It is.

  The tandem photoelectric conversion element of the present invention can achieve high photoelectric conversion efficiency.

The reason why the tandem photoelectric conversion element of the present invention can achieve high photoelectric conversion efficiency is as follows:
(1) It is possible to prevent relaxation of energy levels of excited electrons due to energy transfer inside the conductive polymer having a light absorption region,
(2) This is because the open-circuit voltage can be improved by reducing the difference between the minimum empty orbit (LUMO) values of the conductive polymer (hole acceptor) and the electron transport layer (electron acceptor). .

  The prevention of relaxation of the energy level of the excited electrons in (1) is achieved by stacking two or more photoelectric conversion elements (P) having different maximum absorption wavelengths and having a half-value width of an absorption band of 150 nm or less. In addition, the improvement of the open circuit voltage of (2) can be achieved by setting the difference in the energy level of the lowest empty orbit between the conductive polymer (d) and the electron acceptor (a) to 1 eV or less.

The tandem photoelectric conversion element (TP) of the present invention contains a conductive polymer (d) and an electron acceptor (a) between two electrode layers (Y) formed in layers on a substrate (T). It is a tandem photoelectric conversion element (TP) formed by laminating 2 to 4 photoelectric conversion elements (P) each having a photoelectric conversion layer (E).
When five or more photoelectric conversion elements (P) are stacked, it is not preferable from the viewpoint of light transmittance.
Three to four photoelectric conversion elements (P) are preferably stacked for the reason of light transmittance and utilization of a wider wavelength region of sunlight, and more preferably four.
Regarding the maximum absorption wavelength of the photoelectric conversion element (P), the maximum absorption wavelengths of at least two photoelectric conversion elements (P) are different and at least when three or four photoelectric conversion elements (P) are laminated. It is preferable that the maximum absorption wavelengths of the three photoelectric conversion elements (P) are different, and when the four photoelectric conversion elements (P) are laminated, the maximum absorption wavelengths of all the photoelectric conversion elements (P) are different. More preferably.

  The half width of the absorption band of the photoelectric conversion element (P) is 150 nm or less, preferably 100 nm or less, and more preferably 80 nm or less. Here, the half-value width is the distance Δν = ν2 between two wavelengths ν1 and ν2 having ε = (1/2) εmax on both sides of νmax, where εmax is the absorbance at the maximum absorption wavelength νmax of one absorption band. Let ν1 be the half width. Further, the absorption region of the photoelectric conversion element (P) refers to a region of ν1 to ν2.

  In each photoelectric conversion layer (E), the difference between the value of the energy level of the lowest empty orbit of the conductive polymer (d) and the value of the energy level of the lowest empty orbit of the electron acceptor (a) is the photoelectric conversion layer. It directly affects the open circuit voltage of (E), and the smaller this difference, the greater the open circuit voltage. The difference in energy level value is 1 eV or less, preferably 0.8 eV or less. If the difference between the energy level values exceeds 1 eV, a sufficient open circuit voltage cannot be obtained.

  The photoelectric conversion element of the present invention comprises a photoelectric conversion layer (E) containing a conductive polymer (d) and an electron acceptor (a) between two electrodes (Y) formed on a substrate (T). A photoelectric conversion element having at least two kinds of photoelectric conversion elements (P) having different maximum absorption wavelengths, and a minimum of the conductive polymer (d) in each photoelectric conversion layer (E). The tandem photoelectric conversion element (TP) is characterized in that the difference between the value of the empty orbit and the value of the lowest empty orbit of the electron acceptor (a) is within 1 eV. As an example, FIG. 1 shows a schematic sectional view of a typical structure thereof. Details of each component will be described below.

(1) Substrate (T)
The substrate in the present invention will be described. The substrate may be either transparent or opaque, but a transparent substrate is desirable when the substrate surface is a photoreceptor. As this transparent substrate, a substrate excellent in moisture and gas barrier properties, solvent resistance, weather resistance and the like entering from the outside of the photoelectric conversion element is desirable. For example, a rigid plate such as quartz glass, a flexible resin such as a transparent resin film, etc. A substrate is mentioned. Furthermore, in the present invention, a flexible substrate is desirable from the viewpoint of excellent workability, low cost, and light weight. Examples of the transparent resin film include polyethylene terephthalate, polyethylene naphthalate, polycarbonate, polystyrene, polyethylene, polyvinylidene fluoride, polyimide, and polymethyl methacrylate.

(2) Electrode (Y)
Then, the electrode in this invention is demonstrated.
The electrode may or may not be layered on the substrate (T), but is preferably layered. The electrode does not necessarily have translucency, but when the electrode is layered on the substrate (T), it is preferable that at least one of the electrodes has translucency. It is preferable that the electrode is composed of two layers and has two layers. Any electrode may be used as long as it has conductivity, and it is formed by sputtering, ion plating, or the like. As the light transmissive electrode, a metal thin film made of a conductive transparent material such as indium-tin composite oxide (ITO), fluorine-doped SnO ₂ (FTO), SnO ₂ is preferable, and as the light shielding electrode, an alkali metal, Metal thin films such as alkaline earth metals are preferred. Although the thickness of this electrode is not specifically limited, For example, it is about 80-100 nm.

(3) Photoelectric conversion layer (E)
Then, the photoelectric converting layer used for this invention is demonstrated. The photoelectric conversion layer in the present invention contains a conductive polymer (d) and an electron transport layer (electron acceptor) (a), and preferably also serves as a hole transport layer (hole acceptor) (s). A conductive polymer (d) and an electron transport layer (electron acceptor) (a).
The form of the conductive polymer and the electron transport layer (electron acceptor) contained is not particularly limited, but is preferably a single layer structure of an electron hole transport layer in which both are mixed, that is, a bulk heterojunction. It is. By adopting this structure, a pn junction at the molecular level becomes possible, and thus an effect of increasing the volume involved in photoelectric conversion can be obtained.
The photoelectric conversion layer (E) as described above can be obtained by removing the solvent from the mixed solution of the conductive polymer (d) and the electron acceptor (a).

  In the present invention, at least two types of photoelectric conversion elements (P) having different maximum absorption wavelengths are laminated. By using this, relaxation of the energy level of the excited electrons due to energy transfer inside the conductive polymer (d) having the light absorption region can be prevented, so that high photoelectric conversion efficiency can be obtained.

As the above reason, the following is estimated.
Conventionally, a conductive polymer (d) having a wide absorption band has been used for the use of sunlight, but the energy transfer rate inside the conductive polymer (d) having a light absorption region is Since it is much faster than the charge separation rate, electrons that are excited to a high energy level by absorbing light of a short wavelength are relaxed to a level at the long wavelength end by intramolecular energy transfer, and then charge separation occurs. Therefore, a considerable portion of the energy that the electrons and holes excited and generated by the light energy of short wavelength should originally hold is lost. However, in the photoelectric conversion layer (E) using the conductive polymer (d) having an absorption region only at a specific wavelength, it is high in order to prevent relaxation of the energy level of excited electrons due to internal energy transfer. It is estimated that photoelectric conversion efficiency is obtained.

The conductive polymer (d) having an absorption region only at a specific wavelength specifically means that the half-value width of the absorption band of the conductive polymer (d) is 150 nm or less. Since the photoelectric conversion layer (E) contains the conductive polymer (d) and the electron acceptor (a), and only the conductive polymer (d) has a light absorption band, the photoelectric conversion layer ( It can be considered that the absorption band of E) is substantially the same as the absorption band of the conductive polymer (d).
In addition, in order to measure the light absorption band of the photoelectric conversion layer (E), the light absorption band of the photoelectric conversion element (P) may be measured.

  In the tandem photoelectric conversion element (TP) of the present invention, the stacked photoelectric conversion elements (P) may be connected either in parallel or in series. However, in order to increase the current to be extracted, parallel connection is preferable. In order to increase it, series is preferable.

When the number of stacked photoelectric conversion elements (P) is 4, the photoelectric conversion elements (P) have an ultraviolet blue region (300 to 449 nm) (E1), a green yellow region (450 to 666 nm) (E2), and an orange red region. It is preferable that four layers each having a maximum absorption wavelength in four wavelength regions of (667 to 931 nm) (E3) and near infrared region (932 to 1200 nm) (E4) are laminated.
Here, the handling of the boundary value of each area is determined by rounding off the value of one decimal place. For example, it is assumed that 449.4 nm or less is E1 as 449 nm, and 449.5 nm or more is 450 nm as E2.

When the number of stacked photoelectric conversion elements (P) is 3, the ultraviolet blue region (300 to 449 nm) (E1), the greenish yellow region (450 to 666 nm) (E2), and the orange red region (667 to 931 nm) (E3) It is preferable to laminate three layers each having a maximum absorption wavelength in the three wavelength regions.

When the number of stacked layers of the photoelectric conversion elements (P) is 2, the two-wavelength region of the ultraviolet blue region (300 to 449 nm) (E1) and the greenish yellow region (450 to 666 nm) (E2), or the ultraviolet blue region (300 ˜449 nm) (E1), two wavelength regions of orange-red region (667-931 nm) (E3), or green-yellow region (450-666 nm) (E2), two wavelength regions of orange-red region (667-931 nm) (E3) It is preferable to laminate two layers each having a maximum absorption wavelength.

  As described above, the conductive polymer (d) preferably functions as a hole transport layer (hole acceptor) (s) and has an absorption region only at a specific wavelength of each absorption region, For example, a polythiophene derivative, a polyfluorene derivative, etc. are mentioned. On the other hand, regarding the electron transport layer (electron acceptor) (a), those excellent in electron transport ability are preferable, and examples thereof include fullerene derivatives.

  For the photoelectric conversion layer (E1) having an absorption band in the ultraviolet blue region (300 to 449 nm), the conductive polymer (d1) preferably has an absorption band in the ultraviolet blue region (300 to 449 nm). Examples include polyfluorene derivatives and polythienoacenes.

  Regarding the photoelectric conversion layer (E2) having an absorption band in the green-yellow region (450 to 666 nm), the conductive polymer (d2) preferably has an absorption band in the green-yellow region (450 to 666 nm). For example, a polythiophene derivative Etc.

  For the photoelectric conversion layer (E3) having an absorption band in the orange-red region (667 to 931 nm), the conductive polymer (d3) preferably has an absorption band in the orange-red region (667 to 931 nm). Examples include porphyrin derivatives and phthalocyanine derivatives.

  For the photoelectric conversion layer (E4) having an absorption band in the near infrared region (932 to 1200 nm), the conductive polymer (d4) preferably has an absorption band in the near infrared region (932 to 1200 nm), For example, a cyanine derivative etc. are mentioned.

  Any order may be sufficient as the lamination | stacking order of a photoelectric conversion element (P), For example, what was laminated | stacked in order from the low wavelength side (E1, E2, E3, order of E4) etc. are mentioned.

  In the present invention, as the weight ratio of the conductive polymer (d) and the electron transport layer (electron acceptor) (a) used in the above-described photoelectric conversion layer, an electron hole transport layer having good electron transport ability is formed. Although not particularly limited, for example, (d) / (a) = 1/10 to 1/1 is preferable, and may be appropriately changed to an optimal mixing ratio depending on the combination of other constituent material types. preferable.

  In the present invention, the film thickness of the above-described photoelectric conversion layer is not particularly limited, and any film thickness may be used. However, if the film thickness is too thin, the film is short-circuited, and if it is too thick, the film resistance becomes high. Therefore, the film thickness used for a general photoelectric conversion element is preferable, for example, 20 to 800 nm.

  In the present invention, the method for forming the photoelectric conversion layer described above is not particularly limited as long as it can be uniformly formed in a predetermined film thickness, and any method may be used. For example, a spin coating method or a die coating method can be used.

(5) Other structure The other structure used for this invention is demonstrated. A charge extraction layer (i) may be formed in the photoelectric conversion element of the present invention for the purpose of promoting the movement of charges.
The constituent compound and the number of layers are not particularly limited. For example, as the hole extraction layer (i), poly (styrenesulfonate) / poly (2,3-dihydrothieno [3,4-b] -1,4-dioxin) (hereinafter referred to as “PEDOT / PSS”) and the like.

  When using the tandem photoelectric conversion element (TP) of the present invention as a solar cell element (S), the conductive polymer (d) and the two electrodes (Y) formed on the substrate (T) A photoelectric conversion layer (E) containing an electron acceptor (a), comprising at least two types of photoelectric conversion elements having photoelectric conversion layers (E) having different maximum absorption wavelengths, and each In the photoelectric conversion layer (E), a solar cell element (S) in which a difference between a value of the lowest empty orbit of the conductive polymer (d) and a value of the lowest empty orbit of the electron acceptor (a) is within 1 eV, As for the configuration and the like, those described above for the tandem photoelectric conversion element (TP) are preferable.

  When the tandem photoelectric conversion element (TP) of the present invention is used as a photosensor element (U), a conductive polymer (d) and a conductive polymer (d) are formed between two electrodes (Y) formed on a substrate (T). A photoelectric conversion layer (E) containing an electron acceptor (a), comprising at least two types of photoelectric conversion elements having photoelectric conversion layers (E) having different maximum absorption wavelengths, and each In the photoelectric conversion layer (E), the photosensor element (U) has a difference between the value of the lowest empty orbit of the conductive polymer (d) and the value of the lowest empty orbit of the electron acceptor (a) within 1 eV, As for the configuration and the like, those described above for the tandem photoelectric conversion element (TP) are preferable.

EXAMPLES Hereinafter, although an Example demonstrates this invention in more detail, this invention is not limited to this.
Hereinafter, unless otherwise specified, “parts” and “wt” mean “parts by weight” and% means% by weight.

<Measuring method of difference δ between energy level value of lowest empty orbit of conductive polymer (d) and value of energy level of lowest empty orbit of electron acceptor (a)>
By measuring the first reduction potential of the conductive polymer (d) and the electron acceptor (a) by cyclic voltammetry (manufactured by ALS: Model 1000), the conductive polymer (d) and the electron acceptor ( The energy level of each lowest empty orbit in a) is calculated. The difference between the energy levels of the lowest empty orbit is δ.

<Measurement method of maximum absorption wavelength of photoelectric conversion element (P)>
The maximum absorption wavelength of the photoelectric conversion element (P) was measured by transmitting light to the photoelectric conversion element (P) using an ultraviolet-visible near-infrared spectrophotometer (manufactured by Shimadzu Corporation; UV-3600). .

(Production Example 1) Conductive polymer (d) for ultraviolet blue region (300 to 449 nm) (E1)
As the conductive polymer, pentathienoacene (hereinafter referred to as PTA, a compound represented by the general formula (1)) was synthesized.

Synthesis of PTA (General Formula (1)) 2.0 g of 3-bromothieno [3,2-b] thiophene (manufactured by Tokyo Chemical Industry Co., Ltd.) was dissolved in 30 ml of diethyl ether and cooled to -78 ° C. 6.3 ml of a 6 mol / ln-butyllithium hexane solution (manufactured by Wako Pure Chemical Industries, Ltd.) was added dropwise over 5 minutes, and the mixture was stirred for 40 minutes while maintaining -78 ° C. to give bis (benzenesulfonyl) sulfide (described below). 1.44 g) was added and the mixture was further stirred at -78 ° C for 1 hour. The temperature was raised to 25 ° C. and stirred for 12 hours. 50 ml of water and 150 ml of diethyl ether were added, and the organic layer was separated. This organic layer was washed with 150 ml of saturated brine and dried over anhydrous magnesium sulfate, and then the solvent was distilled off under reduced pressure. Purification by silica gel column chromatography (developing solvent; hexane) gave 584 mg of bis (3-bromothieno [3,2-b] thienyl) sulfide (hereinafter referred to as 3BTTS). This synthesis method was based on the method described in Journal of the American Chemical Society, 2005, 127, 13281-13286.

  After dissolving 1.0 g of 3BTTS in 100 ml of diethyl ether and cooling to −10 ° C., 4.7 ml of 1.6 mol / ln-butyllithium hexane solution was added dropwise over 5 minutes, and kept at −10 ° C. for 2 hours. Stir. Suspension obtained by suspending 0.95 g of copper (II) chloride (manufactured by Wako Pure Chemical Industries, Ltd.) in 30 ml of diethyl ether was added, the temperature was raised to 25 ° C., and the mixture was stirred for 12 hours. 50 ml of water and 150 ml of diethyl ether were added, and the organic layer was separated. This organic layer was washed with 150 ml of saturated brine and dried over anhydrous magnesium sulfate, and then the solvent was distilled off under reduced pressure. Purification by silica gel column chromatography (developing solvent: hexane) gave 250 mg of PTA. This synthesis method was based on the method described in Journal of the American Chemical Society, 2005, 127, 13281-13286.

The above bis (benzenesulfonyl) sulfide was synthesized by the following method.
25.0 g of sodium benzenesulfinate (manufactured by Wako Pure Chemical Industries, Ltd.) was suspended in 400 ml of benzene, and a mixed solution of 4.8 ml of sulfur dichloride and 25 ml of benzene was added dropwise over 30 minutes. After stirring at 25 ° C. for 2 hours, the precipitate was removed by filtration, and the solvent was distilled off under reduced pressure. The residue was recrystallized from benzene to obtain 19 g of bis (benzenesulfonyl) sulfide. This synthesis method was based on the method described in Journal of Organic Chemistry, 1971, 36, 1645-1648.

(Production Example 2) Electron acceptor (a) for ultraviolet blue region (300 to 449 nm) (E1)
As the fullerene derivative, 2-phenyl [60] fulleropyrrolidine (hereinafter referred to as PFP, a compound represented by the general formula (2)) was synthesized.

Synthesis of PFP (general formula (2)) 156 mg of glycine (manufactured by Wako Pure Chemical Industries, Ltd.), 149 mg of benzaldehyde (manufactured by Wako Pure Chemical Industries, Ltd.), 500 mg of fullerene [C60] (manufactured by Wako Pure Chemical Industries, Ltd.) After adding to 200 ml, the solution was stirred at 120 ° C. for 16 hours. After the solvent was distilled off under reduced pressure, the residue was purified by silica gel column chromatography (developing solvent; toluene) to obtain 70 mg of phenylfulleropyrrolidine derivative PFP. This synthesis method was based on the method described in Journal of Organic Chemistry, 2001, 66, pages 5033-5041, or Journal of the American Chemical Society, 2003, 125, 15093-15100.

Example 1 Parallel tandem photoelectric conversion element (TP-1) in which four photoelectric conversion elements (P) are stacked.
(Production of photoelectric conversion element (P1) having an absorption band in the ultraviolet blue region (300 to 449 nm))
(Creation of transparent electrode (Y))
As the transparent substrate and the transparent conductive film, a polyethylene terephthalate (hereinafter referred to as PET) film with an ITO film having a size of 25 mm square and a sheet resistance of 10 Ω / cm ⁻² was used. And after forming the mask of a predetermined shape on the ITO film | membrane, the ITO film | membrane was patterned by immersing this in 1N hydrochloric acid for 1 hour, and the transparent electrode was formed.

(Creation of hole extraction layer)
1.3% by weight of poly (styrene sulfonate) / poly (2,3-dihydrothieno [3,4-b] -1, on a PET film on which a transparent electrode made of an ITO film is formed as described above. 4-dioxin) (hereinafter referred to as “PEDOT / PSS”) (product name: BaytronP, manufactured by Bayer), spin-coated at 120 ° C. for 30 minutes to form a PEDOT / PSS film having a thickness of about 100 nm. This was used as a transparent conductive film.

(Creation of photoelectric conversion layer (E1))
Furthermore, a mixed solution of PTA (conductive polymer synthesized in Production Example 1) / PFP (conductive polymer synthesized in Production Example 2) (weight ratio is 1/4) in a slightly larger range than the PEDOT / PSS film. (PTA: PFP = 15 mg: 60 mg dissolved in 5.0 mL of chlorobenzene) was spin-coated on the transparent conductive film, dried at 25 ° C. for 1 hour under a nitrogen stream, and further at 25 ° C. The film was dried under reduced pressure for 3 hours to form a photoelectric conversion layer.

(Create counter electrode)
Finally, an Al film having a thickness of 125 nm was formed as a counter electrode on the photoelectric conversion layer by vacuum deposition. The photoelectric conversion element (P1) was manufactured as described above.
About the absorption region of this photoelectric conversion element (P1), when measured according to the measurement method of the maximum absorption wavelength of the photoelectric conversion element (P), the maximum absorption wavelength is 344 nm, the absorption region is 300 to 360 nm, and the half width is It was 60 nm.

  Further, when the difference δ between the value of the energy level of the lowest empty orbit of the conductive polymer (d) and the value of the energy level of the lowest empty orbit of the electron acceptor (a) was measured, The value of the LUMO energy level was −2.0 eV, the value of the LUMO energy level of PFP was −2.8 eV, and δ was 0.8 eV.

(Creation of photoelectric conversion element (P2) having an absorption band in a green-yellow region (450 to 666 nm))
The PTA / PFP mixed solution in the photoelectric conversion element (P1) is poly-3-hexylthiophene-2,5-diyl (hereinafter referred to as P3HT) (manufactured by Wako Pure Chemical Industries, Ltd., product name 044746) / PCBM (frontier carbon). A photoelectric conversion element (P2) was formed in the same manner as the photoelectric conversion element (P1) except that it was replaced with a mixed solution. As a specific mixed solution, a solution containing P3HT: PCBM = 15 mg: 60 mg in 5.0 mL of chlorobenzene was used.

  About the absorption region of this photoelectric conversion element (P2), when measured similarly to (P1), the maximum absorption wavelength was 532 nm, the absorption region was 510 to 580 nm, and the half width was 70 nm.

    Further, when δ of the photoelectric conversion element (P2) was measured in the same manner as in (P1), the value of the LUMO energy level of P3HT was −3.0 eV, and the value of the LUMO energy level of PCBM was − 3.7 eV and δ was 0.7 eV.

(Production of photoelectric conversion element (P3) having an absorption band in the orange-red region (667 to 931 nm))
The PTA / PFP mixed solution in the photoelectric conversion element (P1) is replaced with the photoelectric conversion element (P1) except that it is replaced with a phthalocyanine copper (hereinafter referred to as CuPc) (manufactured by Wako Pure Chemical Industries, Ltd.) / PCBM mixed solution. Similarly, a photoelectric conversion element (P3) was formed. As a specific mixed solution, a solution containing CuPc: PCBM = 15 mg: 60 mg in 5.0 mL of chlorobenzene was used.

  The absorption region of this photoelectric conversion element (P3) was measured in the same manner as (P1). As a result, the maximum absorption wavelength was 677 nm, the absorption region was 670 to 700 nm, and the half width was 30 nm.

  Further, when δ of the photoelectric conversion element (P3) was measured in the same manner as (P1), the value of the LUMO energy level of CuPc was −3.6 eV, and the value of the LUMO energy level of PCBM was − 3.7 eV and δ was 0.1 eV.

(Preparation of photoelectric conversion element (P4) having an absorption band in the orange-red region (932 to 1200 nm))
The photoelectric conversion element (P1) except that the PTA / PFP mixed solution was replaced with a mixed solution of YKR3080 (manufactured by Yamamoto Kasei Co., Ltd.) / Fullerene [C60] (manufactured by Wako Pure Chemical Industries, Ltd.). A photoelectric conversion element (P4) was formed in the same manner as in P1). As a specific mixed solution, a solution containing YKR3080: fullerene [C60] = 15 mg: 60 mg in 5.0 mL of chlorobenzene was used.

  The absorption region of this photoelectric conversion element (P4) was measured in the same manner as in (P1). As a result, the maximum absorption wavelength was 1005 nm, the absorption region was 950 to 1030 nm, and the half width was 80 nm.

  Further, when δ of the photoelectric conversion element (P4) was measured in the same manner as in (P1), the value of the LUMO energy level of YKR3080 was −4.0 eV, and the LUMO energy level of fullerene [C60]. The value was −4.5 eV and δ was 0.5 eV.

  The above photoelectric conversion elements (P1 to P4) were stacked and connected in parallel to form a tandem photoelectric conversion element (TP-1).

(Example 2) Four tandem photoelectric conversion elements (TP-2) in which four photoelectric conversion elements (P) are stacked
In Example 1, a tandem photoelectric conversion element (TP-2) was formed in the same manner as in Example 1 except that parallel was replaced in series.

(Example 3) Three tandem photoelectric conversion elements (TP-3) in which three photoelectric conversion elements (P) are stacked.
The photoelectric conversion elements (P1 to P3) produced in Example 1 were stacked and connected in parallel to form a tandem photoelectric conversion element (TP-3).

(Example 4) Two tandem photoelectric conversion elements (TP-4) in which two photoelectric conversion elements (P) are stacked.
The photoelectric conversion elements (P1 and P2) produced in Example 1 were stacked and connected in parallel to form a tandem photoelectric conversion element (TP-4).

(Example 5) Two tandem photoelectric conversion elements (TP-5) in which two photoelectric conversion elements (P) are stacked.
The photoelectric conversion elements (P1 and P3) produced in Example 1 were stacked and connected in parallel to form a tandem photoelectric conversion element (TP-5).

(Example 6) Two tandem photoelectric conversion elements (TP-6) in which two photoelectric conversion elements (P) are stacked.
The photoelectric conversion elements (P2 and P3) produced in Example 1 were stacked and connected in parallel to form a tandem photoelectric conversion element (TP-6).

(Comparative example 1) Single layer type photoelectric conversion element (P'-1)
Evaluation was performed using the single-layer photoelectric conversion element (P′-1) made only in the photoelectric conversion element (P1) manufactured in Example 1.

(Comparative example 2) Single layer type photoelectric conversion element (P'-2)
Evaluation was performed using the single-layer photoelectric conversion element (P′-2) made only in the photoelectric conversion element (P2) manufactured in Example 1.

(Comparative example 3) Single layer type photoelectric conversion element (P'-3)
Evaluation was performed using the single-layer photoelectric conversion element (P′-3) made only in the photoelectric conversion element (P3) manufactured in Example 1.

Comparative Example 4 Parallel tandem type in which two photoelectric conversion elements (P) having a difference in LUMO energy level between the conductive polymer (d) and the electron acceptor (a) of 1 eV or more are stacked. Photoelectric conversion element (TP'-4)
A photoelectric conversion element (P5) was formed in the same manner as the photoelectric conversion element (P1) except that the PTA / PFP mixed solution in the photoelectric conversion element (P1) was replaced with a PTA / fullerene [C60] mixed solution. As a specific mixed solution, a solution containing PTA: fullerene [C60] = 15 mg: 60 mg in 5.0 mL of chlorobenzene was used.

About the absorption region of this photoelectric conversion element (P5), when measured in the same manner as (P1), the maximum absorption wavelength was 344 nm, the absorption region was 300 to 360 nm, and the half width was 60 nm.
The LUMO energy level of PTA is −2.0 eV, the LUMO energy level of fullerene [C60] is −4.5 eV, and δ is −2.5 eV.

  Further, a photoelectric conversion element (P6) was formed in the same manner as the photoelectric conversion element (P2) except that the P3HT / PCBM mixed solution in the photoelectric conversion element (P2) was replaced with a P3HT / fullerene [C60] mixed solution. . As a specific mixed solution, a solution containing P3HT: fullerene [C60] = 15 mg: 60 mg in 5.0 mL of chlorobenzene was used.

About the absorption region of this photoelectric conversion element (P6), when measured similarly to (P1), the maximum absorption wavelength was 532 nm, the absorption region was 510 to 580 nm, and the half-value width was 70 nm.
The LUMO energy level of P3HT is −3.0 eV, the LUMO energy level of fullerene [C60] is −4.5 eV, and δ is −1.5 eV.

  The above photoelectric conversion elements (P5 and P6) were stacked and connected in parallel to form a tandem photoelectric conversion element (TP′-4).

(Comparative example 5) Two tandem photoelectric conversion elements (TP′-5) in which two photoelectric conversion elements (P) each having a half width of an absorption band of 150 nm or more are stacked.
The photoelectric conversion element (P7) is the same as the photoelectric conversion element (P1) except that the PTA / PFP mixed solution in the photoelectric conversion element (P1) is replaced with a pentacene (manufactured by Wako Pure Chemical Industries, Ltd.) / PFP mixed solution. ) Was formed. As a specific mixed solution, a solution containing pentacene: PFP = 15 mg: 60 mg in 5.0 mL of chlorobenzene was used.

About the absorption region of this photoelectric conversion element (P7), when measured in the same manner as (P1), the maximum absorption wavelength was 670 nm, the absorption region was 400 to 700 nm, and the half width was 300 nm.
The value of LUMO energy level of pentacene is −3.0 eV, the energy level value of LUMO of PFP is −2.8 eV, and δ is −0.2 eV.

  Furthermore, the photoelectric conversion element was the same as the photoelectric conversion element (P2) except that the P3HT / PCBM mixed solution in the photoelectric conversion element (P2) was replaced with a rubrene (Sigma Aldrich Japan Co., Ltd.) / PCBM mixed solution. (P8) was formed. As a specific mixed solution, a solution containing rubrene: PCBM = 15 mg: 60 mg in 5.0 mL of chlorobenzene was used.

The absorption region of this photoelectric conversion element (P8) was measured in the same manner as in (P1). As a result, the maximum absorption wavelength was 540 nm, the absorption region was 430 to 590 nm, and the half width was 160 nm.
The LUMO energy level of rubrene is −3.2 eV, the energy level of the LUMO of PCBM is −3.7 eV, and δ is −0.5 eV.

  The above photoelectric conversion elements (P7 and P8) were overlapped and connected in parallel to form a tandem photoelectric conversion element (TP'-5).

(Evaluation method of photoelectric conversion element)
The photoelectric conversion element was measured by irradiating the photoelectric conversion element with simulated light (air passage amount AM1.5G, incident energy 100 mW / cm ² ) of a solar simulator (manufactured by Kansai Scientific Machinery Co., Ltd .: XES-502S). Irradiation conditions: Temperature 25 ° C

Using a KEITHLEY MODEL 2400 source meter, an I (current) -V (voltage) curve was measured, and I _sc (short circuit current), V _oc (open voltage), I _MAX (current at the maximum output point), V _MAX ( Voltage at the maximum output point).
Generally, the photoelectric conversion efficiency of a photoelectric conversion element is represented by the following formula.
Photoelectric conversion efficiency η = J _sc (short circuit current density) × V _oc (open circuit voltage) × ff (form factor) / incident energy Here, J _sc (short circuit current density) and ff (form factor) are obtained by the following equations. It was.
Form factor ff = (I _MAX × V _MAX ) / (I _sc × V _oc )
Short-circuit current density J _sc = I _sc / S (effective light receiving area)
However, S = 2.5 cm × 2.5 cm = 6.25 cm ²
The measurement results are shown in Table 1.

By comparing Examples 1-4 and Comparative Examples 1-3, it can be seen that the tandem photoelectric conversion element (TP) exhibits a photoelectric conversion efficiency superior to that of the conventional single-layer photoelectric conversion element (P). .
Further, by comparing Example 4 with Comparative Example 4, the open circuit voltage is improved when the difference in the LUMO energy level between the conductive polymer (d) and the electron acceptor (a) is within 1 eV. Is seen.
Furthermore, by comparing Example 4 and Comparative Example 5, when the half-value width of the absorption band of the photoelectric conversion element (P) is within 150 nm, an improvement in photoelectric conversion efficiency η can be seen.

  The present invention is not limited to use as a solar cell, a color sensor, and the like, but can be widely applied to electronic devices and electronic components that include photoelectric conversion elements.

It is a schematic sectional drawing which shows an example (parallel type) of the photoelectric conversion element of this invention.

Explanation of symbols

(T1) to (T4) Substrate (Y1) to (Y4) and (Y′1) to (Y′4) Electrode (i1) to (i4) Hole extraction layer (E1) to (E4) Photoelectric conversion layer

Claims (13)

  A photoelectric conversion element having a photoelectric conversion layer (E) containing a conductive polymer (d) and an electron acceptor (a) between two electrode layers (Y) formed in layers on a substrate (T) ( A tandem photoelectric conversion element (TP) formed by laminating 2 to 4 P), wherein at least two photoelectric conversion elements (P) have different maximum absorption wavelengths, and absorption of the photoelectric conversion element (P) The half width of the band is 150 nm or less, and the value of the energy level of the lowest empty orbit of the conductive polymer (d) and the lowest empty orbit of the electron acceptor (a) in each photoelectric conversion layer (E). A tandem photoelectric conversion element (TP), wherein a difference in energy level is 1 eV or less.   The tandem photoelectric conversion element (TP) according to claim 1, wherein the photoelectric conversion elements (P) are connected in series, or the photoelectric conversion elements (P) are connected in parallel.   The tandem photoelectric conversion element (TP) according to claim 1 or 2, wherein four photoelectric conversion elements (P) are stacked, and each photoelectric conversion element (P) has a different maximum absorption wavelength.   The maximum absorption wavelengths of four different photoelectric conversion elements (P) are respectively the ultraviolet blue region (300 to 449 nm) (E1), the green yellow region (450 to 666 nm) (E2), and the orange red region (667 to 931 nm) ( The tandem photoelectric conversion element (TP) according to claim 3, which is in E3) and a near infrared region (932 to 1200 nm) (E4).   The tandem photoelectric conversion element (TP) according to claim 1 or 2, wherein three photoelectric conversion elements (P) are stacked, and each photoelectric conversion element (P) has a different maximum absorption wavelength.   The maximum absorption wavelengths of three different photoelectric conversion elements (P) are respectively the ultraviolet blue region (300 to 449 nm) (E1), the green yellow region (450 to 666 nm) (E2), and the orange red region (667 to 931 nm). The tandem photoelectric conversion element (TP) according to claim 5, which is in (E3).   The tandem photoelectric conversion element (TP) according to claim 1 or 2, wherein two photoelectric conversion elements (P) are stacked, and each photoelectric conversion element (P) has a different maximum absorption wavelength.   The maximum absorption wavelength of two different photoelectric conversion elements (P) is in the ultraviolet blue region (300 to 449 nm) (E1) and the greenish yellow region (450 to 666 nm) (E2), respectively. Tandem photoelectric conversion element (TP).   The maximum absorption wavelengths of two different photoelectric conversion elements (P) are in the ultraviolet blue region (300 to 449 nm) (E1) and the orange red region (667 to 931 nm) (E3), respectively. Tandem type photoelectric conversion element (TP).   The maximum absorption wavelength of two different photoelectric conversion elements (P) is in the green-yellow region (450 to 666 nm) (E2) and the orange-red region (667 to 931 nm) (E3), respectively. Tandem photoelectric conversion element (TP).   The tandem photoelectric conversion element (TP) according to any one of claims 1 to 10, wherein the electron acceptor (a) contains a fullerene derivative (F).   The tandem photoelectric conversion element (TP) according to any one of claims 1 to 11, wherein the tandem photoelectric conversion element (TP) is a solar cell element (S).   The tandem photoelectric conversion element (TP) according to any one of claims 1 to 11, wherein the tandem photoelectric conversion element (TP) is an optical sensor element (U).

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