KR20130093319A - Quantum dot-sensitized solar cell - Google Patents

Abstract

PURPOSE: A quantum dot-sensitized solar cell is provided to increase the light absorption rate of a quantum dot and to efficiently transmit electrons and holes without recombination. CONSTITUTION: A counter electrode faces a photocathode. The photocathode includes a transparent conductive substrate, a photosensitive quantum dot layer, and a ZnS capping layer. The photocathode is thermally processed after the ZnS capping layer is formed. The transparent conductive substrate is a fluorine-doped tin oxide substrate. An electrolyte is interposed between the counter electrode and the photocathode. [Reference numerals] (AA) Quantum dot; (BB) Thermal process

Description

Quantum Dot-Sensitized Solar Cell

The present invention relates to a method for manufacturing a quantum dot-sensitized solar cell and a photoanode for a quantum dot-sensitized solar cell.

Recently, due to the depletion of fossil fuels and various environmental problems, there is a growing interest in environmentally friendly energy that can replace fossil energy. Among them, solar cells using solar energy, which is an alternative energy source having an infinite energy source and having no pollution, is attracting much attention.

Generally, a solar cell refers to a cell that generates a current-voltage using a photovoltaic effect in which a semiconductor absorbs light to generate electrons and holes. Although n-p diodes of inorganic semiconductors such as silicon or gallium arsenide (GaAs) have been mainly used as semiconductors of early solar cells, their manufacturing costs have been high, which has been a hindrance to practical use of solar cells.

In order to solve such a problem, much attention has been focused on a dye (or quantum dot nanoparticle) sensitive solar cell in which a low cost titania is used as a main component of a solar cell. A conventional dye-sensitized solar cell has a structure in which a transparent substrate, a transparent electrode layer, a titania layer, a photosensitive dye layer (or a quantum dot nanoparticle layer), an electrolyte layer, an electrode layer, and a substrate are laminated. At this time, the titania layer has a porous structure so that the dye can easily be colored, and becomes a movement path of electrons generated by electron and hole separation reactions.

Therefore, in order to manufacture a dye-sensitized solar cell with high efficiency (or quantum dot nanoparticle), titania having a dye layer formed must have a high specific surface area, and the electron transfer characteristic of titania itself must be excellent. Further, Layer and a photo-sensitive dye layer should have excellent electron transfer characteristics and have high photoelectric conversion efficiency.

Currently, the most urgent problem to be solved for the high efficiency of dye (or quantum dot nanoparticle) sensitized solar cell is to increase the amount of light absorption and to transfer electrons and holes generated by light absorption rapidly to the cathode and anode without recombination . Therefore, there is a need for research on techniques for increasing the light absorption rate of quantum dots and transferring electrons and holes without recombination.

SUMMARY OF THE INVENTION Accordingly, the present invention is directed to a technique for manufacturing a photocathode capable of increasing the light absorption rate of quantum dots and transferring electrons and holes with high efficiency without recombination, and a quantum dot-sensitized solar cell including the same.

In order to solve the above problems, the present invention provides a light-emitting device comprising a photoanode and a counter electrode opposed to the photo-cathode, and an electrolyte interposed therebetween, the photo-cathode comprising a transparent conductive substrate, the porous titanium dioxide formed in the (TiO ₂₎ layer, said porous contains ZnS capping layer formed on the light-sensitive quantum dot layer and the light-sensitive quantum dot layer provided in contact with the titanium dioxide layer, a negative electrode the light is then formed ZnS capping layer Heat treatment And a quantum dot-sensitized solar cell.

The present invention also provides a method of fabricating a semiconductor light emitting device, comprising the steps of: immersing a porous titanium dioxide (TiO ₂ ) layer formed on a transparent conductive substrate in a photosensitized quantum dot precursor solution to form photosensitive sensitized quantum dots in the porous titanium dioxide layer; Immersing the substrate on which the photo sensitive quantum dot is formed in a ZnS precursor solution including a zinc precursor and a sulfur precursor to form a ZnS lid layer; And a step of heat-treating the photocathode of the photocathode for a quantum dot-sensitized solar cell.

The quantum dot-sensitized solar cell after the formation of the ZnS liner layer according to the present invention increases the light absorption amount due to the increase in the size of the photo-sensitive quantum dots due to the increase in the size of the photo-sensitive quantum dots, thereby increasing the connection between the photo- sensitized quantum dots and titanium dioxide And the recombination of the electron holes is reduced due to the ZnS lid layer. As a result, the photoelectric conversion efficiency due to the increase of the short-circuit current is obtained.

1 is a schematic view of a photocathode surface before and after a heat treatment according to the present invention.
FIG. 2 is a graph showing an experimental result of measuring the energy conversion efficiency of the solar cell manufactured in Comparative Examples 1 and 2. FIG.
FIG. 3 is a graph of an experiment result of measuring the energy conversion efficiency of the solar cell manufactured in Comparative Example 1, Comparative Example 3, and Example 1. FIG.

The present invention includes a photoanode and a counter electrode opposing the photo cathode and an electrolyte interposed therebetween,

The photocathode includes a transparent conductive substrate, a porous titanium dioxide (TiO ₂ ) layer formed on the transparent conductive substrate, a photo sensitive quantum dot layer provided in contact with the porous titanium dioxide layer, and a ZnS lid layer formed on the photo- Including,

Wherein the photocathode is subjected to a heat treatment after formation of a ZnS lid layer, thereby providing a quantum dot-sensitized solar cell.

The inventors of the present invention have been studying a photocathode manufacturing technology for a solar cell which can increase the light absorption rate of quantum dots and transfer electrons and holes with high efficiency without recombination. The photocathode quantum dots are chemically deposited on the porous titanium dioxide layer , And ZnS is further chemically deposited and annealed. As a result, the size of the photo-sensitive quantum dots increases and the band gap decreases. As a result, the photoabsorption amount increases and the electron transfer characteristics are increased due to the better connection between the photo- sensitized quantum dots and titanium dioxide , And ZnS liner layer can reduce the recombination of the electron holes, thereby increasing the photoelectric conversion efficiency of the solar cell. Thus, the present invention has been completed.

In one embodiment of the present invention, the transparent conductive substrate may be a transparent conductive film or a laminated substrate in which a transparent conductive film and a transparent substrate are laminated. The transparent conductive film may be formed of indium tin oxide (ITO), indium zinc oxide (IZO) And may contain indium oxide or fluorine-doped tin oxide (FTO, SnO ₂ : F). In addition, the counter electrode may be a transparent conductive substrate on which a platinum group material is coated. More specifically, the counter electrode may be, for example, FTO (Fluorine-doped Tin Oxide, SnO ₂ : F)

More specifically, the transparent conductive substrate of the photocathode is FTO (Fluorine-doped Tin Oxide, SnO ₂ : F), and the counter electrode is a FTO (Fluorine-doped Tin Oxide, SnO ₂ : F) have.

In another embodiment of the present invention, the photo sensitive quantum dots absorb ultraviolet-near-infrared light in the 200 to 1100 nm region of the sunlight spectrum and the quantum dots include II-IV, III-IV, V- .

Specifically, the quantum dots include, CdS, CdSe, CdTe, PbS , PbSe, ZnS, ZnSe, ZnTe, HgS, HgSe, HgTe, GaN, GaP, GaAs, Bi 2 S 3, Bi 2 Se 3, InP, InAs, InCuS SnS _x (1? _X ? 2), NiS, CoS, FeS _y (1? _Y ? ₂ ), In ₂ S ₃ , MoS ₂ , In (CuGa) Se ₂ , Sb ₂ S ₃ , Sb ₂ Se ₃ , MoSe, and alloys thereof, but is not limited thereto. In some cases, a mixture of two or more of the quantum dots listed above may be used. For example, a quantum dot mixture in which two or more quantum dots exist in a simple mixed state, or a crystal having a crystal structure having a core-shell structure or a crystal structure having a gradient structure, Mixed crystals in which crystals are partially separated, or alloys of two or more kinds of nanocrystalline compounds may be used.

In still another embodiment of the present invention, the anode which is the opposite electrode is located opposite to the photo cathode, wherein the photo cathode and the anode are spaced apart from each other by a predetermined distance to form a closed space. The sealed space is filled with an electrolyte. The electrolyte injected into the sealed space may be an ordinary electrolyte solution serving to provide electrons to the photocathode, and may be more specifically polysulfide. It is not.

The present invention also provides a method of fabricating a semiconductor light emitting device, comprising the steps of: immersing a porous titanium dioxide (TiO ₂ ) layer formed on a transparent conductive substrate in a photosensitized quantum dot precursor solution to form photosensitive sensitized quantum dots in the porous titanium dioxide layer; Immersing the substrate on which the photo sensitive quantum dot is formed in a ZnS precursor solution including a zinc precursor and a sulfur precursor to form a ZnS lid layer; And a step of heat-treating the photocathode of the photocathode for a quantum dot-sensitized solar cell.

In one embodiment of the present invention, the transparent conductive substrate may be a transparent conductive film or a laminated substrate in which a transparent conductive film and a transparent substrate are laminated. The transparent conductive film may be formed of indium tin oxide (ITO), indium zinc oxide (IZO) And may contain indium oxide or fluorine-doped tin oxide (FTO, SnO ₂ : F). More specifically, the transparent conductive substrate may be FTO (Fluorine-doped Tin Oxide, SnO ₂ : F), but is not limited thereto.

In one embodiment of the present invention, the porous titanium dioxide (TiO ₂ ) layer formed on the transparent conductive substrate may be formed through a process of applying and heat-treating the titanium dioxide paste. In order to form a porous titanium dioxide layer, the paste may contain a polymer material, and the polymer material may be used as long as it can be removed by the heat treatment. In addition to the purpose of pore formation, the polymer material contained in the paste can also be used to improve dispersibility, viscosity, and adhesion to a substrate.

The porous titanium dioxide layer formed on the transparent conductive substrate is immersed in the photo sensitive quantum dot precursor solution to form photo sensitive quantum dots on the porous titanium dioxide layer.

More specifically, the substrate having the porous titanium dioxide layer is immersed and recovered in the photo sensitive quantum dot precursor solution, and the immersion and separation and recovery processes can be repeated, and each immersion time is 1 to 10 minutes or 3 to 7 Min, and the number of repetitions may be 3 to 15, but is not limited thereto. The number of photo sensitive quantum dots formed in contact with the surface of the porous titanium dioxide layer can be easily controlled by repeating the immersion process.

In one embodiment of the present invention, the photo sensitive quantum dots absorb ultraviolet-near-infrared rays in the range of 200 to 1100 nm in the sunlight spectrum, and the quantum dots include II-IV, III-IV, and V- .

Specifically, the quantum dots include, CdS, CdSe, CdTe, PbS , PbSe, ZnS, ZnSe, ZnTe, HgS, HgSe, HgTe, GaN, GaP, GaAs, Bi 2 S 3, Bi 2 Se 3, InP, InAs, InCuS SnS _x (1? _X ? 2), NiS, CoS, FeS _y (1? _Y ? ₂ ), In ₂ S ₃ , MoS ₂ , In (CuGa) Se ₂ , Sb ₂ S ₃ , Sb ₂ Se ₃ , MoSe, and alloys thereof, but is not limited thereto. In some cases, a mixture of two or more of the quantum dots listed above may be used. For example, a quantum dot mixture in which two or more quantum dots exist in a simple mixed state, or a crystal having a crystal structure having a core-shell structure or a crystal structure having a gradient structure, Mixed crystals in which crystals are partially separated, or alloys of two or more kinds of nanocrystalline compounds may be used.

In one embodiment of the present invention, the photo sensitive quantum dot is CdS and the photo sensitive quantum dot precursor is a cadmium precursor such as Cd (NO ₃ ) ₂ , CdSO _4, CdCl ₂ Or a mixture thereof. As the sulfur precursor, Na ₂ S, thiourea, or a mixture thereof may be used, but the present invention is not limited thereto. At this time, the immersion process may be performed in a precursor solution containing both a cadmium precursor and a sulfur precursor, and the process of immersion and separation into a cadmium precursor solution and the process of immersion and separation and recovery into a sulfur precursor solution may be performed independently.

Then, the substrate on which the photo sensitive quantum dots are formed is dipped in a ZnS precursor solution containing a zinc precursor and a sulfur precursor to form a ZnS cap layer.

In one embodiment of the present invention, as the zinc precursor is _{Zn (NO 3) 2, Zn} (CH 3 COO) , and _2, or to use a mixture of these, the sulfur precursor is Na ₂ S, thiourea (thiourea) or Mixtures of these may be used, but are not limited thereto. At this time, the immersion process may be performed in a precursor solution containing both the zinc precursor and the sulfur precursor, and the immersion and separation of the precursor solution into the zinc precursor solution and the immersion and separation and recovery of the precursor solution into the sulfur precursor solution may be performed independently.

Thereafter, heat treatment of the substrate is performed.

In one embodiment of the present invention, the heat treatment may be performed at 200 to 500 DEG C or 300 to 400 DEG C, but is not limited thereto.

More specifically, the heat treatment can be performed by heating under inert gas conditions, and the temperature raising rate can be maintained at 1 to 3 ° C per minute and maintained at the final temperature for 10 to 60 minutes or 20 to 40 minutes.

FIG. 1 is a schematic view of the photocathode surface before and after the heat treatment.

The heat treatment increases the size of the quantum dots to reduce the band gap, increasing the light absorption amount, and the bonding of the titanium dioxide and the quantum dot become close to each other to increase the electron conductivity. Since the ZnS liner layer is uniformly formed on the quantum dots, the recombination of electrons and holes due to the direct contact between the electrolyte and the quantum dots is reduced and the shortcircuit current is increased.

The photoanode manufactured by the above method can be usefully used in a quantum dot-sensitive solar cell. More specifically, the quantum dot-sensitive solar cell can be manufactured through the step of positioning the counter electrode facing the photocathode, then injecting and sealing the electrolyte.

More specifically, the spacer is disposed between the photo cathode and the counter electrode to produce the sealed space, and then the electrolyte solution is injected into the sealed space through the hole of the anode using a pressure difference, A battery cell may be manufactured, but is not limited thereto.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to the following examples. However, the following examples are intended to illustrate the contents of the present invention, but the scope of the present invention is not limited to the following examples. Embodiments of the present invention are provided to more fully describe the present invention to those skilled in the art.

< Example  1> ZnS After layer formation Heat-treated Photo cathode  And production of solar cell using the same

9 g of TiO ₂ (P-25, Degussa), 1.5 g of ethyl cellulose (# 46070) as an organic binder, 1.5 g of ethyl cellulose (# 46080), 20 g of terpineol as a solvent and 20 g of ethyl alcohol were mixed. The resulting paste was screen printed to form a 7.5 μm thick film on a FTO (Fluorine-doped Tin Oxide, SnO ₂ : F) substrate, followed by heat treatment at 500 ° C. for 30 minutes in air to prepare a porous titanium dioxide layer.

0.5 M Cd (NO ₃ ) ₂ solution and 0.5 M Na ₂ S solution were prepared, and the FTO substrate on which the titanium dioxide layer was formed was immersed in each solution for 5 minutes. The above method is referred to as one cycle and has been cycled eight times. CdS photo sensitive quantum dots were formed on the porous titanium dioxide layer.

After the rotation of the S ² of the 0.5M Zn (NO ₃₎ Zn ^{2 +} ₂ in the precursor and 0.5M Na ₂ S ^- using the precursor to form a ZnS capping layer. The photocathode substrate formed up to the cover layer was flowed with Ar gas in a tube-shaped electric furnace, and the temperature was raised at a rate of 2 DEG C per minute, and the resultant was subjected to heat treatment at 350 DEG C for 30 minutes to manufacture a photocathode for a solar cell of the present invention .

After the surface was plated with a Pt-treated FTO counter electrode (anode) and a spacer (surlyn 1702, Dupont), the electrolyte was injected through the hole of the FTO anode through a Vaccum back filling method, .

As the electrolyte, a polysulfide solution was used. The solvent was methanol: water 7: 3 (volume ratio), and the solutes were 0.5M Na ₂ S, 2M S, and 0.2M KCl.

< Comparative example  1>

In Example 1, after the formation of the CdS photosensitive quantum dots on the porous titanium dioxide layer, the ZnO cover layer formation and the heat treatment were not performed, and the surface was treated with the Pt-treated FTO counter electrode (anode) and a spacer (surlyn 1702, Dupont) Then, the same electrolyte as in Example 1 was injected through a hole of an FTO anode through a Vaccum back filling method, and then sealed to manufacture a solar cell.

< Comparative example  2>

After the formation of the CdS photosensitivity quantum dots in the porous titanium dioxide layer in Example 1, after the heat treatment was performed, the surface was plated with a Pt-treated FTO counter electrode (anode) and a spacer (surlyn 1702, Dupont) The same electrolyte as that in Example 1 was injected through a hole of a hole-injection-hole-filling-hole (Vaccum back filling) method, and the solar cell was fabricated by sealing.

< Comparative example  3>

The CdS photo-sensitized quantum dots and the ZnS lid layer were formed on the porous titanium dioxide layer in Example 1, and then the adhesion was performed using a FTO counter electrode (anode) whose surface had been treated with Pt and a spacer (surlyn 1702, Dupont) Thereafter, the same electrolyte as in Example 1 was injected through a hole in the FTO anode and then sealed using a Vaccum back filling method to manufacture a solar cell.

FIG. 2 is a graph showing an experimental result of measuring the energy conversion efficiency of the solar cell manufactured in Comparative Examples 1 and 2. FIG. Referring to FIG. 2, the photoelectric conversion efficiency of Comparative Example 1 was generally low, and the short circuit current was increased by the heat treatment (Comparative Example 2), but the photoelectric conversion efficiency was decreased due to the decrease of the open- I could.

FIG. 3 is a graph of an experiment result of measuring the energy conversion efficiency of the solar cell manufactured in Comparative Example 1, Comparative Example 3, and Example 1. FIG. Referring to FIG. 3, the photoelectric conversion efficiency is low even in the case of the comparative example 3, but the photocurrent density and the voltage are both increased in the case of the example 1 in which the heat treatment is performed after forming the cover layer.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that such detail is solved by the person skilled in the art without departing from the scope of the invention. will be. Accordingly, the actual scope of the present invention will be defined by the appended claims and their equivalents.

Claims (9)

A photoanode and an opposing electrode facing the photocathode and an electrolyte interposed therebetween,
The photocathode includes a transparent conductive substrate, a porous titanium dioxide (TiO ₂ ) layer formed on the transparent conductive substrate, a photo sensitive quantum dot layer provided in contact with the porous titanium dioxide layer, and a ZnS lid layer formed on the photo- Including,
The photocathode is quantum dot-sensitized solar cell, characterized in that the heat treatment after forming the ZnS cover layer. The method of claim 1,
The transparent conductive substrate of the photocathode is a FTO (Fluorine-doped Tin Oxide, SnO ₂ : F), the counter electrode is a quantum dot sensitive type that is a PTO stacked FTO (Fluorine-doped Tin Oxide, SnO ₂ : F) (Quantum Dot-Sensitized) Solar Cells. The method of claim 1,
The photosensitive quantum dots are CdS, CdSe, CdTe, PbS, PbSe, ZnS, ZnSe, ZnTe, HgS, HgSe, HgTe, GaN, GaP, GaAs, Bi ₂ S ₃ , Bi ₂ Se ₃ , InP, InAs, InCuS ₂ , In (CuGa) Se ₂ , Sb ₂ S ₃ , Sb ₂ Se ₃ , SnS _x (1 ≦ _x ≦ 2), NiS, CoS, FeS _y (1 ≦ _y ≦ ₂ ), In ₂ S ₃ , MoS, MoSe and A quantum dot-sensitized solar cell comprising one or more materials selected from the group consisting of alloys thereof. Forming a photosensitive quantum dot on the porous titanium dioxide layer by immersing the porous titanium dioxide (TiO ₂ ) layer formed on the transparent conductive substrate in the photosensitive quantum dot precursor solution;
Immersing the substrate on which the photo sensitive quantum dot is formed in a ZnS precursor solution including a zinc precursor and a sulfur precursor to form a ZnS lid layer; And
Method of manufacturing a photoanode for a quantum dot-sensitized solar cell comprising the step of heat treatment. 5. The method of claim 4,
The transparent conductive substrate is a FTO (Fluorine-doped Tin Oxide, SnO ₂ : F) substrate is a method of manufacturing a photoanode for a quantum dot-sensitized solar cell (photoanode). 5. The method of claim 4,
The photosensitive quantum dots are CdS, CdSe, CdTe, PbS, PbSe, ZnS, ZnSe, ZnTe, HgS, HgSe, HgTe, GaN, GaP, GaAs, Bi ₂ S ₃ , Bi ₂ Se ₃ , InP, InAs, InCuS ₂ , In (CuGa) Se ₂ , Sb ₂ S ₃ , Sb ₂ Se ₃ , SnS _x (1 ≦ _x ≦ 2), NiS, CoS, FeS _y (1 ≦ _y ≦ ₂ ), In ₂ S ₃ , MoS, MoSe and Method for producing a photoanode for a quantum dot-sensitized solar cell comprising at least one material selected from the group consisting of a mixture thereof. 5. The method of claim 4,
The photosensitive quantum dot is CdS,
The photosensitive quantum dot precursor is Cd (NO ₃ ) ₂ , CdSO ₄ , CdCl ₂ or a mixture thereof, and the sulfur precursor is Na ₂ S, thiourea or a mixture thereof. 5. The method of claim 4,
Wherein the zinc precursor is Zn (NO ₃ ) ₂ , Zn (CH ₃ COO) ₂ or a mixture thereof, and the sulfur precursor is Na ₂ S, thiourea or a mixture thereof. (Method for manufacturing photocathode for solar cell). 5. The method of claim 4,
The heat treatment in the heat treatment step is performed at 200 to 500 ℃ method of manufacturing a photoanode for a quantum dot-sensitized solar cell (photoanode).

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