JP6321490B2 - Quantum dot solar cell - Google Patents

Description

  The present invention relates to a quantum dot solar cell.

  A solar cell provided with quantum dots (hereinafter referred to as “quantum dot solar cell”) has a quantum dot integrated portion inserted as a light detection layer between two pn-junction semiconductor layers.

  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.

  In this case, since the photoelectric conversion efficiency of the quantum dot solar cell is related to the total amount of carriers generated in the quantum dot integrated part, for example, the quantum dot integrated part may be thickened to increase the degree of integration of the quantum dots. This will lead to an improvement in power generation.

  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 hardly occurs and does not easily disappear.

  However, when a quantum dot integrated part is formed by integrating quantum dots, carriers generated in the quantum dot are likely to disappear by combining with defects existing in the quantum dot integrated part including the barrier layer. There is a problem that the density of carriers decreases, the amount of charge that can reach the electrode decreases, and the photoelectric conversion efficiency cannot be increased.

  In recent years, various structures for improving the current collection performance of carriers in the quantum dot integrated portion have been proposed for such problems. For example, Patent Document 1 shows an example in which a columnar carrier collection unit 101 called a nanorod is arranged in a quantum dot integration unit as shown in FIG.

Special table 2009-537994

The quantum dot solar cell of the present invention includes a quantum dot integrated portion, a bonding layer disposed on at least one main surface of the quantum dot integrated portion, and a root on the bonding layer side from the bonding layer into the quantum dot integrated portion. extend from parts in different directions, said and having a plurality of carrier collection section having an open end to the quantum dot integrated portion, before Symbol carrier collection portions are partially contact or bonding, the carrier collection unit The diameter is gradually reduced from the root side toward the open end side .
In addition, the quantum dot solar cell of the present invention has a quantum dot integrated portion, a bonding layer disposed on at least one main surface of the quantum dot integrated portion, and a columnar shape extending from the bonding layer into the quantum dot integrated portion. A plurality of carrier collecting units, and part of the carrier collecting units having different stretching directions are in contact with or joined to each other, and the quantum dot integration unit includes an n-type quantum dot and a p-type quantum dot. And n-type quantum dots are arranged on the side close to the carrier collecting section, and p-type quantum dots are arranged around the n-type quantum dots.

  Therefore, an object of this invention is to provide the quantum dot solar cell which can improve the conductivity to the joining layer of a carrier, and can improve photoelectric conversion efficiency by this.

The quantum dot solar cell of the present invention includes a quantum dot integrated portion, a bonding layer disposed on at least one main surface of the quantum dot integrated portion, and a plurality of columnar shapes extending from the bonding layer into the quantum dot integrated portion. And a carrier collecting part, and a part of the carrier collecting parts having different stretching directions are in contact with each other.

  ADVANTAGE OF THE INVENTION According to this invention, the quantum dot solar cell which can improve the electroconductivity to the joining layer of a carrier and can improve photoelectric conversion efficiency by this can be obtained.

(A) is a cross-sectional schematic diagram which partially shows one Embodiment of the quantum dot solar cell of this invention, (b) is the schematic diagram which expanded the inside of the dashed-dotted line in (a). (A) shows the other aspect of the quantum dot solar cell of this invention, (b) is the schematic diagram which expanded the inside of the dashed-dotted line circle | round | yen in (a). The other aspect of this embodiment is shown, the quantum dot is comprised from the n-type quantum dot and the p-type quantum dot, the n-type quantum dot is arrange | positioned at the carrier collection part side, and an n-type It is a cross-sectional schematic diagram which shows the state by which the p-type quantum dot is arrange | positioned around the quantum dot. The quantum dot solar cell of the other aspect of this embodiment is shown, The cross section which shows the structure which multilayered the photoelectric conversion layer which integrated the quantum dot integration | stacking part, the junction layer with which this was equipped, and the carrier collection part It is a schematic diagram. It is process drawing which shows the manufacturing method of the quantum dot solar cell of this embodiment. It is a cross-sectional schematic diagram which shows the conventional quantum dot solar cell.

  As shown in FIG. 1A, the quantum dot solar cell of this embodiment includes a quantum dot integrated portion 1 and a bonding layer 3 disposed on at least one main surface of the quantum dot integrated portion 1.

  Further, this quantum dot solar cell has a plurality of columnar carrier collecting portions 5 extending from the bonding layer 3 into the quantum dot integrated portion 1.

  Furthermore, the plurality of carrier collecting units 5 are in a state where a part of the carrier collecting units 5 in different extending directions are in contact with each other. In FIG. 1A, the contacted portion is the tip of the carrier collecting unit 5 or the center of the carrier collecting unit 5.

  Here, the state in which the carrier collection parts 5 (5A, 5B) are in contact with each other means that the carrier collection parts 5A, 5B are in contact with each other at a part of the surface, as shown in FIG. It means a state in which the contact surfaces of the carrier collecting units 5A and 5B are electrically connected.

  In FIG. 1A, a glass substrate 9 is provided on the lower layer side of the bonding layer 3 via a transparent conductive film 7, and an electrode layer 11 is disposed on the upper surface side of one quantum dot integrated portion 1. In this case, the glass substrate 9 side is the light incident side, and the electrode layer 11 side is the light emitting side.

  When a plurality of carrier collection units 5 are provided in the quantum dot integration unit 1, some carrier collection units 5 may have lower conductivity than other carrier collection units 5. For example, in FIG. 1A, the conductivity of the carrier collecting unit 5A is lower than the conductivity of the carrier collecting unit 5B, and the quantum dot 13 having the carrier C is in contact with the carrier collecting unit 5A having low conductivity. It has become a state.

When the quantum dots 13, the carrier collecting units 5A and 5B, and the bonding layer 3 have a structure as shown in FIG. 1A, the carrier collecting unit 5A and the carrier collecting unit 5B start from the quantum dots 13 and the bonding layer The parallel circuit is terminated with 3.

  When the plurality of carrier collecting units 5A and 5B are connected to the bonding layer 3 in a parallel circuit, the conductivity of the carrier collecting unit (in this case, the carrier collecting unit 5A) in contact with the quantum dots 13 is low. Even in this case, the carrier C generated in the quantum dot 13 can be quickly moved from the carrier collecting unit 5A having low conductivity to the bonding layer 3 through the carrier collecting unit 5B having high conductivity. Thereby, the collection efficiency of the carrier C produced | generated in the quantum dot integration | stacking part 1 can be raised, and the photoelectric conversion efficiency of a quantum dot solar cell can be improved.

  2A and 2B show an example of a state in which the carrier collection unit 5A and the carrier collection unit 5B are joined as another aspect of the quantum dot solar cell of the present embodiment. Similarly to the quantum dot solar cell shown in FIGS. 1A and 1B, the quantum dot solar cell shown in FIGS. 2A and 2B is also at least one of the quantum dot integrated unit 1 and the quantum dot integrated unit 1. And a plurality of columnar carrier collecting units 5 extending from the bonding layer 3 into the quantum dot integration unit 1. Here, the difference from the quantum dot solar cell shown in FIG. 1 is that a part of the carrier collecting parts 5 having different stretching directions are joined.

  Like the quantum dot solar cell shown in FIGS. 2 (a) and 2 (b), when the carrier collectors 5 (5A, 5B) are partially joined together, the two carrier collectors 5A, 5B are The interface resistance formed by the contact of the surfaces of these carrier collecting portions 5A and 5B is removed. Accordingly, the interface resistance between the carrier collecting unit 5A and the carrier collecting unit 5B is reduced, and the mobility of the carrier C from the carrier collecting unit 5A to the carrier collecting unit 5B can be increased.

  In addition, when the carrier collection units 5 (5A, 5B) are in a partially joined state, the carrier collection unit 5 can be a skeleton connected in the quantum dot integration unit 1, and thus the carrier collection unit 5 The mechanical strength of the carrier collecting unit 5 and the quantum dot integrated unit 1 including the same can be increased by coupling (5A, 5B). In this case, the carrier collecting unit 5A and the carrier collecting unit 5B are in a state in which a neck portion 15 is formed between the carrier collecting units 5A and 5B, as shown in FIG.

  Here, when the carrier collection unit 5 (5A, 5B) is in contact with or joined, the cross section of the quantum dot integration unit 1 having the carrier collection unit 5 (5A, 5B) is observed by, for example, a transmission electron microscope. Determine by doing. In this case, it is assumed that the carrier collecting units 5 (5A, 5B) are in contact with each other when a boundary line due to these contours is seen, and these contours are not confirmed between the carrier collecting units 5A, 5B. The case where the neck portion 15 is formed is assumed to be in a joined state.

Further, the quantum dot solar cell of the present embodiment, the carrier collection unit 5 (5A, 5B) is extending from the bonding layer 3 side of the root portion 5a, and has an open Hotan 5b to the quantum dot stacking section 1 cage, it is desirable in contact or joined with open Hotan 5b vicinity. If the opposite end of the base portion 5a of the carrier collection unit 5 is in the open Hotan 5b, it is possible to contact the quantum dots 13 to the end face on which it is open Hotan 5b, quantum dots 13 and the carrier collection The contact area with the part 5 can be increased. Thereby, the number of carriers that can be collected in the carrier collecting unit 5 is increased, and the photoelectric conversion efficiency can be improved.

Also, release when at least two carrier collection unit 5 (5A in Figure 1 and Figure 2, 5B) is or joined in contact with a portion, the portion is or joined in contact opens when in the vicinity of the end 5b is open Hotan 5b side locations carrier collection unit 5 that generates the carrier C, even when the distance to the bonding layer 3 is far, towards the carrier lower carrier C conductivity It is possible to move quickly to the collection unit 5 (the carrier collection unit 5B in the case of FIG. 1). Thereby, the disappearance of the carrier C can be suppressed, and the collection efficiency can be increased.

  Furthermore, when the tips of at least two carrier collecting units 5 are in contact with each other or are joined, the space around the root portion 5a of the carrier collecting unit 5 is widened. The filling rate increases, and a region with a high integration density of the quantum dots 13 can be formed in a region close to the bonding layer 3. As a result, more carriers can be generated in a region close to the bonding layer 3 and carriers are difficult to disappear. Therefore, the amount of carriers collected in the bonding layer 3 can be increased, and the photoelectric conversion efficiency can be further increased. Can be increased.

In this case, the quantum dot solar cell of the present embodiment, the diameter D of the carrier collection unit 5, it is desirable to open Hotan 5b side is smaller than the base portion 5a side. In FIG. 1A, the relation of D1> D2 is shown. If the diameter D2 of the opening Hotan 5b side of the carrier collection unit 5 is thinner than the diameter D1 of the base portion 5a side, at least two carrier collection unit 5A, or by joining 5B contacts originally Quantum even when filled the area of the dots 13 is narrowed, the open Hotan 5b side can be integrated more quantum dots 13. As a result, the light absorption rate is increased, and the photoelectric conversion efficiency can be improved.

The diameter D1 of the carrier collection unit 5 of the base portion 5a side, which is larger than the diameter D2 of the opening Hotan 5b side, as the carrier collecting unit 5 is rigidly connected on the bonding layer 3, durability High quantum dot integrated portion 1 can be formed. In this case, the diameter D of the carrier collection unit 5, when gradually becomes smaller toward the root portion 5a side opening Hotan 5b side, when the quantum dots 13 is filled in the quantum dot stacking unit 1, the quantum dot A structure in which the number of 13 gradually changes in the thickness direction can be formed. Thereby, it becomes easy to control the photoelectric conversion efficiency by the thickness of the quantum dot integrated portion 1.

  FIG. 3 shows another aspect of the present embodiment. The quantum dot 13 is composed of an n-type quantum dot 13n and a p-type quantum dot 13p, and n closer to the carrier collecting unit 5 is shown. FIG. 5 is a schematic cross-sectional view showing that a type quantum dot 13n is arranged and a p-type quantum dot 13p is arranged around the n-type quantum dot 13n.

  Normally, the quantum dots 13 receive the energy of light, so that electrons existing in the quantum dots 13 are excited to a conductive level, and at the same time, holes are formed and these become carriers. Photoelectric conversion occurs. At this time, as shown in FIG. 3, a layer constituted by n-type quantum dots 13n and a layer constituted by p-type quantum dots 13p are stacked from the carrier collecting unit 5 side in the quantum dot integration unit 1. With this configuration, when electrons and holes that can move to each of the n-type quantum dot 13n and the p-type quantum dot 13p are generated, the electrons and holes are converted into the n-type quantum dot 13n and the p-type quantum dot, respectively. It becomes easier to move by the direction of the dot 13p, and this can further improve the current collecting property of the carrier.

  FIG. 3 shows a configuration in which n-type quantum dots 13n are arranged on the carrier collecting unit 5 side. In this case, the configuration in which p-type quantum dots 13p are arranged on the carrier collecting unit 5 side is the same. Photoelectric conversion characteristics can be obtained.

Although various semiconductor materials are applied as the material of the quantum dots 13, the carrier collection unit 5, and the bonding layer 3 constituting the quantum dot integrated unit 1, the energy gap (Eg) is 0.15 to Those having 2.50 ev are preferred. 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.

  The quantum dots 13 described above may have a barrier layer (barrier layer) on the surface of the quantum dots 13 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 13, and preferably has an energy gap (Eg) of 1.0 to 10.0 ev. In addition, when the quantum dot 13 has a barrier layer on the surface, as a material of the barrier layer, 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. 4 shows a quantum dot solar cell according to another aspect of the present embodiment, and is a cross section showing a configuration in which a quantum dot integrated portion, a carrier collecting portion provided in the quantum dot integrated portion, and a bonding layer are integrated into a multilayer structure. It is a schematic diagram.

  As described above, the quantum dot solar cell of the present embodiment has been described based on FIGS. 1 to 3, but the quantum dot solar cell of the present invention includes the quantum dot integrated unit 1 having the carrier collecting unit 5, and this The photoelectric conversion layer 14 integrated with the bonding layer 3 provided in is not limited to a single layer, and a plurality of photoelectric conversion layers 14 may be multilayered as shown in FIG. In this case, a quantum dot solar cell exhibiting higher photoelectric conversion efficiency can be obtained.

  In addition, when the thickness of the quantum dot integrated portion 1 constituting the photoelectric conversion layer 14 and the band gap of the quantum dots 13 are changed, the wavelength range of light that can be absorbed can be made wider and higher. A quantum dot solar cell exhibiting photoelectric conversion efficiency can be obtained.

  Next, the manufacturing method of the quantum dot solar cell of this embodiment is demonstrated. FIG. 5 is a process diagram showing a method for manufacturing the quantum dot solar cell of this embodiment. First, as shown to Fig.5 (a), the glass substrate 9 used as a support body is prepared. Next, the transparent conductive film 7 is formed on one main surface of the glass substrate 9 using a conductive material such as ITO. At this time, it is preferable to use a glass substrate 9 whose surface is processed into a shape having chevron irregularities. When the glass substrate 9 processed into a shape having a chevron-like unevenness on the surface is used, even when the transparent conductive film 7 is formed on the surface of the glass substrate 9, the chevron-like unevenness is left on the surface of the transparent conductive film 7. be able to.

  Next, as shown in FIG. 5B, a zinc oxide nanoparticle layer 21 is formed on the surface of the transparent conductive film 7 having chevron irregularities. The nanoparticle layer 21 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.

  Next, the glass substrate 9 on which the transparent conductive film 7 and the nanoparticle layer 21 are formed is immersed in a mixed solution of zinc nitrate and hexamethylenetetramine and left in a temperature environment of about 90 ° C. By placing the nanoparticle layer 21 in such an environment, as shown in FIG. 5 (c), a zinc oxide columnar crystal 23 serving as the carrier collecting portion 5 is formed on the upper surface of the nanoparticle layer 21 made of zinc oxide. can do. At this time, the lower layer side of the nanoparticle layer 21 remains as the bonding layer 3.

  Here, the state in which at least two columnar crystals 23 are in contact with each other or the state in which the columnar crystals 19 are joined changes the height of the mountain-shaped irregularities formed on the surface of the glass substrate 9, Adjust by changing the growth direction. In this case, if the height of the mountain-shaped irregularities is made higher, the columnar crystals 23 grow so as to cross three-dimensionally, and therefore the number of joined columnar crystals 21 can be increased.

  In the present invention, since the mountain-shaped irregularities are formed in advance on the surface of the glass substrate 9 on which the nanoparticle layer 21 is to be formed, the obtained columnar crystals 23 have different stretching directions. The carrier collection part 5 in which the parts are in contact with or bonded to each other can be formed. Here, the position at which the zinc oxide columnar crystals 23 that serve as the carrier collecting portion 5 contact (or join) can also be adjusted by the height of the chevron-shaped irregularities formed in advance on the surface of the glass substrate 9. The chevron-shaped irregularities formed on the surface of the glass substrate 9 and the height thereof are adjusted according to the conditions for polishing or etching the surface of the glass substrate 9. In addition, in the quantum dot solar cell of this embodiment mentioned above, the thing in the state in which the carrier collection part 5 contacted, and the state in which it was joined may be mixed.

  Next, as shown in FIG. 5 (d), the quantum dots are integrated by filling the semiconductor particles 25 that become the quantum dots 13 around the columnar crystals 23 that become the formed carrier collecting portions 5 and performing a densification process. 1 is formed. As a method for filling the semiconductor particles 25, a solution containing the semiconductor particles 25 is preferably selected from a spin coating method, a precipitation method, and the like. For the densification treatment, a method in which the semiconductor particles 25 are filled around the columnar crystals 23 and then heated or pressurized, or these are simultaneously performed. The thickness of the quantum dot integrated portion 1 is adjusted by the amount of semiconductor particles 25 to be deposited. When the photoelectric conversion layer 14 including the quantum dot integration unit 1 is multi-layered, the steps of FIGS. 5B to 5D are repeated.

  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 that becomes the electrode layer 11, 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.

  The quantum dot solar cell obtained as described above includes the carrier collection unit 5 in which the carrier collection units 5 having different stretching directions are partially in contact with or bonded to each other in the quantum dot integrated unit layer 1. The conductivity to the bonding layer 3 increases, and the photoelectric conversion efficiency can be increased.

1 .... Quantum dot integration unit 3 ... Junction layers 5, 5A, 5B ... Carrier collection unit 5a ... ································································································ Glass substrate 11 ··········································································· n Type quantum dot 15 ... neck part 21 ... nanoparticle layer 23 ... columnar crystal 25 ...・ ・ ・ ・ ・ Semiconductor particle C ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Carrier

Claims (5)

A quantum dot integrated portion, a bonding layer disposed on at least one main surface of the quantum dot integrated portion, and extending from the bonding layer into the quantum dot integrated portion in a different direction from a root portion on the bonding layer side, and having a plurality of carrier collection section having an open end to the quantum dot integrated portion, before Symbol carrier collection portions is partially in contact or joined, the diameter of the carrier collection unit, from the root portion The quantum dot solar cell, which gradually becomes smaller toward the open end side . The quantum dot integration unit includes an n-type quantum dot and a p-type quantum dot, and an n-type quantum dot is disposed on a side closer to the carrier collection unit, and the periphery of the n-type quantum dot 2. The quantum dot solar cell according to claim 1, wherein p-type quantum dots are arranged on the first electrode.   The quantum dot integration unit, a bonding layer disposed on at least one main surface of the quantum dot integration unit, and a plurality of columnar carrier collecting units extending from the bonding layer into the quantum dot integration unit, and extending A part of the carrier collecting units in different directions are in contact with or joined to each other, and the quantum dot integrated unit has n-type quantum dots and p-type quantum dots, and is close to the carrier collecting unit An n-type quantum dot is arranged on the side, and a p-type quantum dot is arranged around the n-type quantum dot. The carrier collection unit, quantum dot solar cell of claim 3 which extends from the root portion of the bonding layer side, characterized by Tei Rukoto has an open Hotan to said quantum dot integrated portion. Diameter of the carrier collection unit, quantum dot solar cell according to claim 4, wherein the opening Hotan side is smaller than said root portion.

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