JP2016139735A - Photoelectric conversion layer and photoelectric conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photoelectric conversion layer which has high carrier mobility in a collector part and is capable of enhancing photoelectric conversion efficiency, and to provide a photoelectric conversion device.SOLUTION: The photoelectric conversion layer includes: a quantum dot accumulation part 1 having a plurality of quantum dots 1a; and a collector part 3 arranged on at least one main surface of the quantum dot accumulation part 1. The collector part 3 has: a collector base 5 formed of a bulk body having a higher conductivity than the quantum dot accumulation part 1; and a nanostructure layer 7 formed of the same material as the collector base 5 and having a larger band gap than the collector base 5. The nanostructure layer 7 is arranged between the quantum dot accumulation part 1 and the collector base 5.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a photoelectric conversion layer and a photoelectric conversion device.

  A photoelectric conversion device known as a quantum dot solar cell uses, as carriers, electrons that are excited when sunlight of a specific wavelength hits the quantum dots and holes that are generated when the electrons are excited from the valence band to the conduction band. Use.

  The quantum dot is usually surrounded by a barrier layer having a larger band gap than the quantum dot itself.

  Therefore, theoretically, it is considered that energy relaxation due to electron phonon emission does not occur easily and it is difficult to disappear. However, when quantum dots are integrated to form quantum dot integrated parts, they are generated in quantum dots. The carriers (electrons, holes) easily bond with the defects existing in the quantum dot integrated portion including the barrier layer and disappear, thereby reducing the carrier density and reducing the amount of charge that can reach the electrode. There is a problem that the photoelectric conversion efficiency cannot be increased.

  In recent years, various structures for increasing the carrier collection capability in the photoelectric conversion layer have been proposed for such problems (see, for example, Patent Document 1).

  FIG. 6A is a schematic cross-sectional view showing an example of a conventional photoelectric conversion layer, and FIG. 6B schematically shows the band structure of FIG. Here, the symbol Ec represents the energy level of the conduction band in the band structure, and Ev represents the energy level of the valence band. A symbol Eg represents an energy gap. In the photoelectric conversion layer 100 shown in FIG. 6A, a current collector 101 made of a bulk body capable of collecting carriers is superposed on one main surface of a quantum dot integration unit 103 in which a plurality of quantum dots are integrated. It becomes the composition.

JP 2009-536790 Gazette

  In the case of the photoelectric conversion layer described above, the current collector 101 is mainly formed of a semiconductor such as zinc oxide, and thus has a certain conductivity, but still has carriers in the current collector 101. Since the mobility of C is low, there is a problem that the conversion efficiency of the photoelectric conversion layer cannot be increased.

  Accordingly, an object of the present invention is to provide a photoelectric conversion layer and a photoelectric conversion device that have high carrier mobility in the current collector and can increase the photoelectric conversion efficiency.

The photoelectric conversion layer of the present invention is a photoelectric conversion layer comprising a quantum dot integrated portion having a plurality of quantum dots, and a current collector disposed on at least one main surface of the quantum dot integrated portion, The current collector is a current collector base made of a bulk body having a higher conductivity than the quantum dot integrated part, and a nanostructure layer made of the same material as the current collector base and having a larger energy gap than the current collector base; And the nanostructure layer is disposed between the quantum dot integrated portion and the current collecting base portion.

  In the photoelectric conversion device of the present invention, the above photoelectric conversion layer is disposed between two conductor layers.

  According to the present invention, the carrier mobility in the current collector can be increased, and the photoelectric conversion efficiency can be improved.

It is a cross-sectional schematic diagram which partially shows 1st Embodiment of the photoelectric converting layer of this invention, (a) is when a nanostructure layer is a quantum grain, (b) is when a nanostructure layer is a quantum wire, c) is the case where the nanostructure layer is a quantum thin film. It is a schematic diagram of the band structure of the photoelectric converting layer of Fig.1 (a). It is a cross-sectional schematic diagram which partially shows 2nd Embodiment of the photoelectric converting layer of this invention, (a) is the diameter of a quantum grain, (b) is the wire diameter of a quantum wire, (c) is a quantum thin film. It is shown that the thickness of each is smaller on the quantum dot integrated part side than on the current collecting base part side. It is a cross-sectional schematic diagram which partially shows one Embodiment of the photoelectric conversion apparatus of this invention. It is process drawing which shows the manufacturing method of the photoelectric conversion apparatus of this embodiment. (A) is a cross-sectional schematic diagram which shows an example of the conventional photoelectric converting layer, (b) shows typically the band structure of (a).

FIG. 1 is a schematic cross-sectional view partially showing a first embodiment of the photoelectric conversion layer of the present invention, where (a) is a quantum dot in the nanostructure layer, and (b) is a quantum wire in the nanostructure layer. In the case of (c), the nanostructure layer is a quantum thin film. Here, the quantum thin film (c) has a two-dimensionally expanded structure on the depth side of the drawing. Further, FIG. 1 shows a configuration in which the photoelectric conversion layer 1 is one layer, but the present invention is not limited to this, and the present invention is also applicable to a case where the photoelectric conversion layer 1 has two or more layers. FIG. 2 is a schematic diagram of the band structure of the photoelectric conversion layer in FIG. Here, the symbol Ec represents the energy level of the conduction band in the band structure, and Ev represents the energy level of the valence band. A symbol Eg represents an energy gap. The solid energy line (L ₀ ) is obtained when the current collector 3 is not provided with the nanostructure layer 7, and the broken energy line (L ₁ ) is obtained when the current collector 3 is provided with the nanostructure layer 7. Represent.

The photoelectric conversion layers A ₁ , A _2, and A ₃ of the embodiment shown in FIG. 1 are arranged on a quantum dot integrated unit 1 in which a plurality of quantum dots 1 a are integrated and on at least one main surface of the quantum dot integrated unit 1. And a film-like current collecting unit 3. In this case, the current collector 3 is made of the same material as the current collector base 5 and the current collector base 5 made of a bulk material made of a material having higher conductivity than the quantum dot integrated portion 1, and has an energy gap larger than that of the current collector base 5. And a large nanostructure layer 7. In this case, the nanostructure layer 7 is disposed between the quantum dot integrated portion 1 and the current collecting base portion 5. Here, the quantum dot integrated unit 1 is a layer that generates conductive carriers C such as electrons and holes when absorbing light of a specific wavelength such as sunlight, while the current collecting unit 3 is connected to the quantum dot integrated unit 1. This is a layer having a function of collecting the carrier C generated in the above manner.

According to the photoelectric conversion layers A ₁ , A ₂ , and A ₃ of the present embodiment, the nanostructure layer 7 having the quantum effect is made of the same material on the current collector 3 provided adjacent to the quantum dot integrated unit 1. By providing and arranging the nanostructure layer 7 having the quantum effect so as to be adjacent to the quantum dot integrated portion 1 side, the energy level (Ec) of the conduction band in the band structure in the current collecting portion 3 is changed to the quantum dot integrated portion. Since it can be high on the one side and low on the side of the current collecting base 5 opposite to the quantum dot integrated portion 1, the energy line (L ₁ ) facing the thickness direction of the current collecting portion 3 can be given a gradient. Thereby, the mobility of the carrier C in the current collection part 3 can be raised, and photoelectric conversion efficiency can be improved. This is because the bulk structure of the material constituting the current collector 3 is changed to the nanostructured layer 5 having a quantum effect, so that the energy gap (Eg) widens in the nanostructured layer 7, thereby causing the nanostructured layer This is because the energy level (Ec) of the conduction band in 7 has changed to a level higher than that of the current collector base 5 side. Here, the bulk body refers to a crystal phase or an amorphous phase, or a phase in which these are combined to form a film or plate with high density. The electrical conductivity of the quantum dot integrated part 1 and the current collecting base part 5 made of a bulk body is obtained by, for example, a four-terminal method using a cut piece of the photoelectric conversion layer A1 as a measurement sample.

In this case, the nanostructure layer 7 is preferably any one of the quantum grains 7a, the quantum wires 7b, and the quantum thin film 7c, as shown in FIGS. . When the nanostructure layer 7 is the above-described structure, the carrier C such as electrons is surely lower in dimension than the bulk body (three-dimensional) (two-dimensional for quantum thin films, one-dimensional for quantum wires, and zero-dimensional for quantum grains). The energy level of the conduction band located in the intermediate region between the current collector base 5 and the quantum dot integrated portion 1 is formed between the current collector base 5 and the quantum dot integrated portion 1. Can do. Thereby, a high gradient can be formed by the energy rays (L ₁ ) extending from the quantum dot integrated portion 1 to the current collecting base portion 5 side.

In the photoelectric conversion devices A ₁ , A ₂ , and A ₃ , the nanostructure layer 5 has the quantum particle 7aa diameter, the quantum wire 7bb diameter, and the quantum thin film 7cc thickness on the quantum dot integrated film 1 side. It is desirable that it is small and large on the current collector base 5 side. Here, the quantum wire 7bb has a wire diameter that decreases from the collector base 5 side toward the quantum dot integrated portion 1 side. The quantum thin film 7 cc is thinner from the current collector base 5 side toward the quantum dot integrated portion 1 side.

  For example, taking the quantum particle 7aa shown in FIG. 3A as an example, the diameter of the quantum particle 7aa constituting the nanostructure layer 7 is arranged so that the quantum dot integrated part 1 side is small and the current collecting base part 5 side is large. In this case, since the quantum particles 7aa constituting the nanostructure layer 7 can increase the energy level on the quantum dot integrated film 1 side, the energy level (Ec) of the conduction band between the quantum particles 7aa and the quantum particles 7aa on the current collecting base 5 side It can have a big difference. Similarly, the quantum wire 7bb and the quantum thin film 7cc may be similarly reduced in size (wire diameter, thickness) on the quantum dot integrated portion 1 side.

In addition, it is more desirable that the diameter of the quantum grains 7aa, the diameter of the quantum wires 7bb, and the thickness of the quantum thin film 7cc gradually increase from the quantum dot integrated film 1 side toward the current collecting base 5 side. When the diameter of the quantum grain 7aa, the diameter of the quantum wire 7bb, and the thickness of the quantum thin film 7cc gradually increase from the quantum dot integrated film 1 side toward the current collecting base 5 side, the thickness direction of the nanostructure layer 7 ( Since a gradient can be formed in the energy level (Ec) of the conduction band in the entire direction of D ₀ and D ₁ in FIG. 3, the mobility of the carrier C in the current collector 3 can be further increased.

  The quantum grains 7aa, the quantum wires 7bb, and the quantum thin film 7cc may be in contact with the current collector base 5 so as to have a low resistance. However, the gap between the nanostructure layer 7 and the current collector base 5 is greater. In terms of low resistance, the nanostructure layer 7 is preferably integrated with the current collector base 5 or has a structure grown from the current collector base 5.

  As a material for the current collector 3 (the current collector base 5 and the nanostructure layer 7), at least one selected from the group consisting of Ti, Zn, Ga, Ge, As, Sb, Sn, and In is preferable. When silicon (Si) or PbS (lead sulfide) is applied to the material of the quantum dots 1a constituting the quantum dot integrated portion 1, the energy gap (Eg) is larger than these and the conductor resistance can be lowered. Zn, Sn and Ti are more preferable.

FIG. 4 is a schematic cross-sectional view partially showing an embodiment of the photoelectric conversion device of the present invention. Figure 4 is a photoelectric conversion device B, and shows an example in which a photoelectric conversion layer A ₁ described above. The photoelectric conversion device B includes a lower transparent conductive film 9 on the side and the glass substrate 11 of the photoelectric conversion layer A _1, has an electrode layer 13 on the upper layer side of the photoelectric conversion layer A _1. In this case, the lower surface side of the glass substrate 11 becomes the light incident surface 15a, and the upper surface side of the electrode layer 9 becomes the light emitting surface 15b. Note that a protective layer, an antireflection material, or the like may be provided on the surface of the glass substrate 7 on the light incident surface 15a side or the upper surface of the electrode layer 9 on the light emitting surface 15b.

According to the photoelectric conversion device B of the present embodiment, the current collector 3 provided adjacent to the quantum dot integrated unit 1 is provided with the nanostructure layer 7 having the quantum effect made of the same material. The energy level (Ec) of the conduction band in the band structure in the current collector 3 can be high on the quantum dot integrated portion 1 side and low on the current collecting base 3 side opposite to the quantum dot integrated portion 1. Further, the energy ray can have a (L ₁ ) gradient in the thickness direction of the current collector 3. Thereby, the mobility of the carrier C in the current collection part 3 can be raised, and photoelectric conversion efficiency can be improved.

As described above, the photoelectric conversion layer A ₁ and the photoelectric conversion device B of the present embodiment have been described based on FIGS. 1 to 4, but the present invention is not limited to this, and instead of the photoelectric conversion layer A 1, nano The same effect can be obtained for the photoelectric conversion layers A ₂ and A _{3 in} which the quantum wire 7bb and the quantum thin film 7cc are applied to the structure layer 7.

Component analysis, shape determination, and size evaluation of the nanostructure layer 7 constituting the photoelectric conversion layers A ₁ , A ₂ , A ₃ and the photoelectric conversion device B described above are obtained by an electron microscope and an analyzer attached thereto.

  Various semiconductor materials are applied as the material of the quantum dots 1a constituting the quantum dot integrated portion 1, and those having an energy gap (Eg) of 0.15 to 2.50 ev are suitable. is there. Specific semiconductor materials include germanium (Ge), silicon (Si), gallium (Ga), indium (In), arsenic (As), antimony (Sb), copper (Cu), iron (Fe), sulfur ( It is desirable to use any one selected from S), lead (Pb), tellurium (Te), and selenium (Se), or a compound semiconductor thereof.

  In addition, the above-described quantum dot 1a may have a barrier layer (barrier layer) on the surface of the quantum dot 1a because the electron confinement effect can be enhanced. The barrier layer is preferably a material having an energy gap 2 to 15 times that of the semiconductor material to be the quantum dots 1a, and preferably has an energy gap (Eg) of 1.0 to 10.0 ev. When the quantum dot 1a has a barrier layer on the surface, the material of the barrier layer is a compound containing at least one element selected from Si, C, Ti, Cu, Ga, S, In and Se ( Semiconductors, carbides, oxides, nitrides) are preferred.

  FIG. 5 is a process diagram showing the method for manufacturing the photoelectric conversion device of this embodiment. First, as shown to Fig.5 (a), the glass substrate 11 used as a support body is prepared. Next, a transparent conductive film 9 is formed on one main surface of the glass substrate 11 using a conductive material such as ITO.

Next, as shown in FIG. 5 (b), a zinc oxide bulk body to be the current collector base 5 is formed in a film shape on the surface of the transparent conductive film 9 by sputtering or the like. Next, the nanostructure layer 7 is formed on the surface of the current collector base 5. The quantum grains 7aa constituting the nanostructure layer 7 are produced as follows. For example, lithium hydroxide is added to an ethanol solution of zinc acetate, and the temperature is below room temperature (
For example, colloidal quantum particles 7aa are formed by mixing at −5 to 5 ° C. By mixing hexane and heptane with this mixed solution, only colloidal quantum particles 7aa are precipitated, and the residue of lithium and acetic acid is removed. Thereafter, the colloidal quantum particles 7aa are redispersed in an ethanol solution.

  Next, the produced quantum particles 7aa are applied to the surface of the current collecting base portion 5 by a film forming method such as spin coating, and the current collecting portion having the nanostructure layer 7 is performed by performing a drying treatment or a densification treatment by pressure heating. 3 is formed.

  When the quantum wire 7bb or the quantum thin film 7cc is formed in the current collector 3, it is formed by applying a solution containing zinc acetate to the surface of the transparent conductive film 7 and then heating to a temperature of about 350 ° C. In the case of forming the quantum thin film 7cc, the temperature, pressure, and holding time are set higher than the conditions for growing the quantum wire 7bb. In this case, the solution containing zinc acetate is obtained, for example, by adding an aqueous solution containing an element (a cation) as a secondary component to a solution obtained by mixing 500 mM (mmol) of zinc nitrate and 250 mM (mmol) of hexamethylenetetramine. Prepare.

Next, as shown in FIG. 5D, the upper surface of the formed current collector 3 is filled with semiconductor particles to be the quantum dots 1a, and the quantum dot integrated portion 1 is formed by performing a densification process. As a method for filling the semiconductor particles, a solution containing the semiconductor particles is preferably selected from a spin coating method and a precipitation method. For the densification treatment, heating or pressurization, or a method of performing these simultaneously is employed. The thickness of the quantum dot integrated portion 1 is adjusted by the amount of semiconductor particles to be deposited. When multi-layered photoelectric conversion layer A ₁ including quantum dots stacking unit 1 repeats the process of FIG. 5 (b) ~ (d) .

  Finally, a conductive material such as gold is vapor-deposited on the upper surface side of the quantum dot integrated portion 1 to form a conductive film to be the electrode layer 13, and then a protective layer is formed on the surface of the conductive film as necessary. Thereafter, it is covered with a glass film or the like.

A ₁ , A ₂ , A ₃ ... photoelectric conversion layer B ... photoelectric conversion device C ... carrier 1 ...・ ・ ・ ・ ・ ・ Quantum dot integration part 1a ・ ・ ・ ・ ・ ・ ・ ・ Quantum dot 3 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Current collection part 5 ・ ・ ・ ・ ・ ・Current collecting base 7 (7a, 7b, 7c), nanostructure layer 7aa, ... quantum grain 7bb, ... quantum wire 7cc, ... quantum Thin film 9 ... Transparent conductive film 11 ... Glass substrate 13 ... Electrode layer

Claims (6)

A photoelectric conversion layer comprising: a quantum dot integrated portion having a plurality of quantum dots; and a current collector disposed on at least one main surface of the quantum dot integrated portion,
The current collector is a current collector base made of a bulk body having a higher conductivity than the quantum dot integrated part, and a nanostructure layer made of the same material as the current collector base and having a larger energy gap than the current collector base; The photoelectric conversion layer is characterized in that the nanostructure layer is disposed between the quantum dot integrated portion and the current collecting base portion.   The photoelectric conversion layer according to claim 1, wherein the nanostructure layer is any one of a quantum grain, a quantum wire, and a quantum thin film.   The nanostructure layer is characterized in that the diameter of the quantum grain, the diameter of the quantum wire, or the thickness of the quantum thin film is small on the quantum dot integrated part side and large on the current collecting base part side. 2. The photoelectric conversion layer according to 2.   In the nanostructure layer, the diameter of the quantum grains, the diameter of the quantum wires, or the thickness of the quantum thin film is gradually increased from the quantum dot integrated part side toward the current collecting base part side. The photoelectric conversion layer according to claim 2 or 3.   The material of the said current collection part is at least 1 sort (s) chosen from the group of Ti, Zn, Ga, Ge, As, Sb, Sn, and In, In any one of Claims 1 thru | or 4 characterized by the above-mentioned. Photoelectric conversion layer.   6. A photoelectric conversion device, wherein the photoelectric conversion layer according to claim 1 is disposed between two conductor layers.

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