KR20180024870A - Hole transport material for perovskite structure solar cell - Google Patents

Abstract

The present invention relates to a solar cell. The solar cell according to the present invention includes: a first electrode; a light absorbing layer which is formed on the first electrode and includes a perovskite material; a hole transporting layer formed on the light absorbing layer; and a second electrode formed on the hole transporting layer. The hole transporting layer is made of composite materials of a polymer layer and a single-walled carbon nanotubes (SWNT) layer and the polymer layer includes 4-tert-butylpyridine. Accordingly, the present invention can obtain high power conversion efficiency and high steady-state performance.

Description

[0001] HOLE TRANSPORT MATERIAL FOR PEROVSKITE STRUCTURE SOLAR CELL [0002]

The present invention relates to a solar cell, and more particularly, to the development of a hole transport material for improving the efficiency of a perovskite solar cell.

As the need for renewable eco-friendly energy development has arisen due to the depletion of fossil fuels and environmental pollution, there is a growing interest in solar cells, which supply infinite clean energy to change electrical energy directly from sunlight.

Although silicon solar cells currently commercialized have a power generation efficiency of 20% or more, it is not easy to lower the process cost for producing high-purity crystalline silicon. As a result, it has become urgent to develop an ultra-low-cost, high-efficiency solar cell capable of competing with conventional fossil fuels in order to use solar cells as a universal energy source.

In recent years, silicon-based, organic dye-based, and newly perovskite-based solar cells have been competing in the development of solar cells, among which perovskite-based solar cells are attracting attention as the most promising photovoltaic technology .

Perovskite solar cell is a device that converts light energy into electric energy by absorbing light by using perovskite, which is a metal oxide of special structure that shows superconductivity phenomenon together with non-conductor, semiconductor and conductor properties as a photoactive layer.

Perovskite solar cells have reported efficiencies up to 20.1% and are capable of low temperature solution processes. Perovskite solar cells are emerging as next-generation solar cells to replace silicon solar cells due to their high efficiency and low manufacturing costs.

Despite these advantages, perovskite solar cells suffer from poor stability of perovskite and lack of materials for hole transport layer, making them difficult to commercialize.

In recent years, the development of a retrostructured perovskite solar cell that reverses the position of an electron carrier and a hole transport layer has solved the long-term stability problem, which is a hindrance to commercialization of a perovskite solar cell.

However, PEDOT: PSS (poly (3,4-ethylenedioxythiophene) polystyrene sulfonate), which is widely used as a hole transport layer of a reverse-structured perovskite solar cell, exhibits excellent device efficiency. However, since it is strongly acidic, the perovskite- Thereby shortening the lifetime of the device.

Therefore, it is necessary to continue research on new structures and new materials that can satisfy the characteristics of long-term stability, life span and efficiency of perovskite solar cells.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a solar cell having high power conversion efficiency and excellent steady-state performance.

The present invention provides a light emitting device comprising: a first electrode; A light absorbing layer formed on the first electrode and including a perovskite material; A hole transporting layer formed on the light absorbing layer; And a second electrode formed on the hole transport layer, wherein the hole transport layer is formed of a composite material of a single-walled carbon nanotube (SWNT) layer and a polymer layer, (4-tert-butylpyridine). ≪ / RTI >

In the above, the concentration of 4-tertiary-butylpyridine is 2 wt% to 10 wt%.

In the above, the polymer layer is characterized by comprising poly (methylmethacrylate) (poly (methylmethacrylate)) or polycarbonate.

In the above, the single-walled carbon nanotube layer is characterized in that its surface is enclosed by a single sheath of P3HT material.

In the above, the perovskite substance is characterized by being represented by the following general formula (1).

≪ Formula 1 > ABX ₃

Wherein A is an organic cation containing CH ₃ NH ₃ ⁺ or HC (NH) ₂ ⁺ , B is a metal cation containing Pb ^{2 +} or Sn ²⁺ , X is Cl ^-, Br ^- and I ^- It is a halogen anion including one.)

In the above, the perovskite material is characterized in that methyl ammonium iodide Pb _{(CH 3 NH 3 PbI 3)} .

In the above, the perovskite material is characterized in that it is impregnated on a mesoporous support.

In the above, the mesoporous support is characterized by containing mesoporous alumina (Al ₂ O ₃ ).

In the above, an electron transport layer is further included between the first electrode and the light absorption layer.

In the above, the electron transport layer is characterized by including a titanium dioxide (TiO ₂ ) layer.

In this case, a capping layer containing a perovskite material is further provided between the light absorbing layer and the hole transporting layer.

The perovskite material of the capping layer is represented by the following general formula (2).

≪ Formula 2 > ABX ₃

Wherein A is an organic cation containing CH ₃ NH ₃ ⁺ or HC (NH) ₂ ⁺ , B is a metal cation containing Pb ^{2 +} or Sn ²⁺ , X is Cl ^-, Br ^- and I ^- It is a halogen anion including one.)

In the above, a perovskite material of the capping layer is characterized in that methyl ammonium iodide Pb _{(CH 3 NH 3 PbI 3)} .

In the above, the first electrode is a transparent conductive electrode.

In the above, 4-tertbutylpyridine is characterized by causing band bending at the interface with the perovskite material favorably for hole extraction.

According to the present invention, by including the hole transporting layer to which tBP is added, The direct chemical interaction between tBP and perovskite can improve the overall performance of the perovskite solar cell, including power conversion efficiency and steady-state performance.

1 is a cross-sectional view of a solar cell according to an embodiment of the present invention.
2 is an exploded perspective view of FIG.
3 is an electron microscope (SEM) photograph of a section of a solar cell according to Example 1 of the present invention.
4 is a graph showing current-voltage characteristics of a solar cell according to Comparative Example 1 of the present invention.
5 is a graph showing current-voltage characteristics of a solar cell according to Example 1 of the present invention.
6 is a graph showing photoelectric conversion efficiency (PCE) characteristics of a solar cell according to Comparative Example 1 of the present invention.
7 is a graph showing PCE characteristics of a solar cell according to Example 1 of the present invention.
8 is a graph showing current-voltage characteristics of a solar cell according to Example 2 and Comparative Example 2 of the present invention.
9 is a graph showing PCE characteristics of a solar cell according to Example 2 and Comparative Example 2 of the present invention.
10 is a graph showing current-voltage characteristics of positive and negative biases under the light of the solar cell according to Experimental Example 1 and Comparative Experimental Example 1 of the present invention.
11 is a graph showing current-voltage characteristics of positive and negative biases in a solar cell according to Experimental Example 1 and Comparative Experimental Example 1 of the present invention under dark current.
12 is a schematic view for explaining a mechanism of a solar cell according to Experimental Example 2 of the present invention.
13 shows the SPO of the solar cell according to Experimental Example 2 of the present invention.

Brief Description of the Drawings The advantages and features of the present invention, and how to accomplish them, will become apparent with reference to the embodiments and experiments described below in conjunction with the accompanying drawings. It is to be understood, however, that the same is by way of illustration and example only and is not to be construed in a limiting sense. The contents not described here are sufficiently technically inferior to those skilled in the art, and a description thereof will be omitted.

Hereinafter, a solar cell according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a cross-sectional view of a solar cell according to an embodiment of the present invention, and FIG. 2 is an exploded perspective view of FIG.

1 and 2, a solar cell 100 according to the present invention includes a first electrode 110, an electron transport layer 120, a light absorption layer 130, a hole transport layer 140, and a second electrode 150, And may include a gapping layer 160 in addition to the above.

The first electrode 110 may be a transparent conductive electrode for ohmic junction with the electron transport layer 120 to enhance transmission of light.

For example, the transparent conductive electrode may include FTO (fluorine doped tin oxide) or ITO (indium doped tin oxide), but the present invention is not limited thereto. The first electrode 110 is used as an anode electrode.

The solar cell 100 may further include a transparent substrate 105 under the first electrode 110. The transparent substrate 105 serves as a support for supporting the first electrode 110, and can be used without limitation as long as it is a substrate through which light is transmitted.

For example, the transparent substrate 105 may be a rigid substrate including a glass substrate, or a substrate such as a polyethylene terephthalate (PET), a polyethylene naphthalate (PEN), a polyimide (PI), a polycarbonate and may be a flexible substrate including a polymer such as polycarbonate (PC), polypropylene (PP), triacetyl cellulose (TAC), polyethersulfone (PES)

The electron transport layer 120 is formed on the first electrode 110 and provides a smooth path for electrons.

The electron transport layer 120 may be an n-type layer, and may include a metal oxide such as titanium dioxide (TiO ₂ ). The electron transport layer 120 has a hole-blocking effect to prevent holes from migrating to the first electrode 110.

Although the thickness of the electron transporting layer 120 is not particularly limited, it is preferable that the electron transporting layer 120 is formed of a thin film having a thickness of 50 nm to 100 nm in order to improve the efficiency.

If the thickness of the electron transporting layer 120 is less than 50 nm, the contact area with the light absorbing layer 130 may be reduced and the efficiency may be lowered. On the other hand, when the thickness exceeds 100 nm, the moving distance of the photocurrent increases, .

Meanwhile, The electron transport layer 120  However, Electrically  It is more preferable to form it in order to form a device having excellent performance.

The light absorption layer 130 is interposed between the electron transport layer 120 and the hole transport layer 140 and absorbs light to generate an exciton.

The light absorbing layer 130 includes a perovskite material, which is a metal oxide having a special structure, which has a non-conductor, semiconductor, and conductor properties as well as a superconducting phenomenon.

The perovskite material has a structure represented by the following formula (1).

≪ Formula 1 >

ABX ₃

(Where A and B are cations and X is an anion bonding to them).

(1) Perovskite  In material A cation AX12 is combined with 12 X anions to form a cubic octahedral structure, and B cation BX6 is combined with 6 X anions and octahedral structure.

As a specific example, Perovskite  The material may be an organic cation (e.g., CH ₃ NH ₃ ⁺  Or HC (NH) ₂ ⁺ ), And a metal cation (e.g., Pb ^{2 +}  or Sn ^{2 +} ), And a halogen anion (Cl ^- . Br ^-  And I ^-  Or a combination of three-dimensional structure including any one of them) Perovskite  Material.

Preferably, the perovskite material may be mentioned methyl ammonium iodide, lead of the three-dimensional structure _{(CH 3 NH 3 PbI 3)} . CH ₃ NH ₃ PbI ₃ is suitable as a light absorbing material for solar cells because the band gap energy is as low as about 1.5 eV.

These perovskite materials can accumulate holes themselves and contribute to the performance improvement of perovskite solar cells. In addition, the perovskite material has a high absorbance in the visible light region of the perovskite light absorbing layer, so that it absorbs sufficient light even at a thickness of 500 nm or less and generates a large amount of electric charge.

The perovskite material is completely impregnated on a support such as mesoporous alumina (Al ₂ O ₃ ) to constitute the light absorbing layer 130.

The light absorbing layer 130 is interposed between the electron transport layer 120 and the hole transport layer 140 to form a heterojunction interface between the electron transport layer 120 and the hole transport layer 140 to make interface contact .

The light absorption layer 130  Although the thickness is not particularly limited, it is preferably formed of a thin film having a thickness of 200 nm to 400 nm.

At this time, The light absorption layer 130  If the thickness is less than 200 nm, the absorption of light is insufficient and the current density is low and the efficiency can be reduced. On the other hand, if the thickness exceeds 400 nm, the distance to the pn interface becomes far away and the resulting exciton migrates to the pn interface, The efficiency can be reduced.

The light absorption layer 130 may be formed by applying a support solution on the electron transport layer 120 and then drying it without performing a high temperature heating or a high vacuum process, and then applying a perovskite solution on the support and drying .

For example, CH ₃ NH ₃ PbI ₃ may be formed by spin coating and heat treatment of a mixed solution of CH ₃ NH ₃ I and PbI ₂ , or by spin coating PbI ₂ and reacting with CH ₃ NH ₃ I .

The hole transport layer 140 is formed on the light absorbing layer 130 and serves to transmit holes generated by solar light absorbed in the solar cell 100 to the first electrode 110 which is a transparent conductive electrode. In addition, the hole transport layer 140 is a p-type layer having an electron-blocking effect.

The hole transport layer 140 of the present invention may be formed of a polymer layer 144 to which a single-walled carbon nanotubes (SWNT) layer 142 and a 4-tert butylpyridine (tBP) Composites, i.e., SWNT-polymer composites.

The SWNT-polymer composite material has a structure in which a SWNT layer 122 is embedded in a matrix-type polymer layer 144 to which tBP is added, and the SWNT layer 122 is highly interconnected with the polymer layer 144 Network. In this case, charge extraction occurs through the SWNT through the polymer layer 144.

The SWNT, which is the active part of the hole transport layer 140, has a surface covered with a single sheath of P3HT material to prevent formation of discrete dispersions and bundles and clusters.

The tBP added to the hole transport layer 140 is a hole transporting material (HTM), and the addition of only a small amount of the hole transporting material (HTM) can improve the power conversion efficiency and the steady- It has a beneficial effect.

When tBP is added to the SWNT layer 122, tBP is added to the SWNT-polymer composite material at a very low concentration to cause SWNT cluster formation and degradation of the perovskite material, 124).

Such tBP 2wt%  To 10wt%  It is preferable that it is added to the polymer layer 144 at a high concentration. At this time, of tBP  Concentration 2wt%  , The effect may be insufficient. On the contrary, when the content is more than 10 wt% Without effect  It may only increase the manufacturing cost.

On the other hand, a concrete effect of adding tBP to the hole transporting layer 140 will be described later.

In addition, the polymer layer 144 of the SWNT-polymer composite minimizes the shunting path due to the direct contact between the perovskite absorber and the metal electrode, and does not directly contribute to charge extraction, It affects extraction.

Since the polymer layer 144 is independent of the performance change of the device due to the interaction with the tBP, the material thereof is not particularly limited. For example, poly (methylmethacrylate) (PMMA) or polycarbonate and polycarbonate.

Although the thickness of the polymer layer 144 is not particularly limited, it is preferably formed to a thickness of about 300 nm. If the thickness of the polymer layer 144 is too thin to be less than 300 nm, it may lead to an increase in recombination and a reduction in shunt resistance. Conversely, if the thickness is excessively larger than 300 nm, the series resistance and charge collection efficiency may increase.

The tBP added to the hole transporting layer 140 having such a configuration forms a heterojunction interface between three layers, namely, the SWNT layer 142, the polymer layer 144, and the perovskite of the light absorbing layer 130, .

The second electrode 150 is formed on the hole transport layer 140 and is used as a cathode electrode. The second electrode 150 may be formed of a metal such as Cu, Au, Al, Ca, Ag, Pt, Zn, And may be one or more, and is not particularly limited as long as it can be used as a cathode electrode.

Meanwhile, a capping layer 160 may be further interposed between the light absorption layer 130 and the hole transporting layer 140 for the purpose of improving the efficiency.

The capping layer 160 preferably includes a perovskite material capable of accumulating holes therein. Since the characteristics of the perovskite material are the same as those described in the description of the light absorbing layer 130, The description is omitted.

In this case, the capping layer 160 may be used as an entire light absorbing layer (not shown) together with the light absorbing layer 130. In addition, the perovskite of the capping layer 160 may interface with the tBP added to the hole transporting layer 140, forming a heterojunction interface.

The thickness of the capping layer 160 can be appropriately selected in consideration of the thickness of the entire light absorbing layer from the viewpoint of efficiency improvement.

The solar cell 100 having such a configuration can operate with the following mechanism. The electrons in the valence band of the perovskite of the light absorbing layer 130 are excited by the sunlight to the conduction band and the excited electrons are emitted from the TiO ₂ nanoparticles of the electron transport layer 120 It is injected into a conduction band. The injected electrons are moved to the first electrode 110 by diffusion and the holes generated in the valence band move to the second electrode 150 through the hole transporting material HTM of the hole transport layer 140 do.

The solar cell 100 of the present invention can improve the power conversion efficiency and the steady state performance of the solar cell 100 by including the hole transport layer 140 to which tBP is added.

This performance improvement is due to the direct chemical interaction between tBP and perovskite, which increases the charge selectivity of the perovskite-hole transport layer (140) interface and results in improved steady-state performance .

That is, the tBP added to the hole transport layer 140 may affect the normal-state charge collection efficiency of the solar cell by creating a more selective hole transport layer (HTL, 140) -perovskite interface to the hole It goes crazy. This shows that the charge selective interface plays a crucial role in normal-state charge extraction.

In addition, tBP is polar and can be regarded as a suitable strong base. This may be thought to be the deprotonation of methylammonium at the interface that produces a local negative space charge. This in turn facilitates hole extraction and suppresses electron extraction at this interface, resulting in slightly upper band bending. This band bend is the result of the acid-base reaction between tBP and perovskite.

The present invention is important for the development of new hole transport materials that must exhibit efficient charge extraction under steady-state conditions. The effect of tBP can be taken into account when comparing new materials to established standards in such areas as spiro-OMeTAD, especially when it includes both Li-TFSI and tBP.

Claims (15)

A first electrode;
A light absorbing layer formed on the first electrode and including a perovskite material;
A hole transporting layer formed on the light absorbing layer; And
And a second electrode formed on the hole transport layer,
Wherein the hole transport layer is formed of a composite material of a single-walled carbon nanotube layer and a polymer layer, and the polymer layer comprises 4-tert butylpyridine.
The method according to claim 1,
The concentration of 4-tertbutylpyridine is
2 wt% to 10 wt%.
The method according to claim 1,
The polymer layer
A solar cell comprising poly (methylmethacrylate) (poly (methylmethacrylate)) or polycarbonate.
The method according to claim 1,
The single-walled carbon nanotube layer
A solar cell whose surface is enclosed by a single sheath of P3HT material.
The method according to claim 1,
Wherein the perovskite material is represented by the following formula (1).
≪ Formula 1 > ABX ₃
Wherein A is an organic cation containing CH ₃ NH ₃ ⁺ or HC (NH) ₂ ⁺ , B is a metal cation containing Pb ^{2 +} or Sn ²⁺ , X is Cl ^-, Br ^- and I ^- It is a halogen anion including one.)
6. The method of claim 5,
The perovskite material is methyl ammonium iodide, lead (CH ₃ NH ₃ PbI ₃₎ of the solar cell.
The method according to claim 1,
Wherein the perovskite material is impregnated on a mesoporous support.
8. The method of claim 7,
Wherein the mesoporous support comprises mesoporous alumina (Al ₂ O ₃ ).
The method according to claim 1,
Between the first electrode and the light absorbing layer
A solar cell further comprising an electron transport layer.
10. The method of claim 9,
The electron transport layer is a solar cell including a titanium dioxide (TiO ₂₎ layer.
The method according to claim 1,
And a capping layer including a perovskite material between the light absorption layer and the hole transporting layer.
11. The method of claim 10,
Wherein the perovskite material of the capping layer is represented by the following formula (2).
≪ Formula 2 > ABX ₃
Wherein A is an organic cation containing CH ₃ NH ₃ ⁺ or HC (NH) ₂ ⁺ , B is a metal cation containing Pb ^{2 +} or Sn ²⁺ , X is Cl ^-, Br ^- and I ^- It is a halogen anion including one.)
13. The method of claim 12,
The perovskite material of the capping layer
Methyl ammonium iodide, lead (CH ₃ NH ₃ PbI ₃₎ of the solar cell.
The method according to claim 1,
The first electrode
A solar cell which is a transparent conductive electrode.
The method according to claim 1,
The 4-tertbutylpyridine
Wherein the upper band bending favorably occurs in the hole extraction at the interface with the perovskite material.

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