KR20170049359A - Perovskite based solar cells employing graphene as transparent conductive electrodes - Google Patents

Abstract

The present invention relates to a perovskite-based solar cell using graphene as a transparent conductive electrode which increases efficiency to the maximum level, and can represent a conversion efficiency value of 17% or more through a proper energy band combination of a graphene electrode/a hoe transfer layer/perovskite/an electron transfer layer/a metal electrode.

Description

[0001] PEROVSKITE BASED SOLAR CELLS EMPLOYING GRAPHENE AS TRANSPARENT CONDUCTIVE ELECTRODES USING GREPIN AS A CONDUCTIVE TRANSPARENT ELECTRODE [0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an energy device including a solar cell, and more particularly, to an energy device including a transparent ITO electrode and an FTO transparent conductive oxide electrode, Battery.

The organic / inorganic composite perovskite has a high absorption coefficient, a well-balanced electron / hole transport, low temperature treatment capability, small exciton binding energy and a long exciton diffusion length than the organic semiconductor material, It is a promising material used. High performance perovskite solar cells generally employ a nip architecture consisting of metal oxide / perovskite / hole transport materials such as TiO ₂ or Al ₂ O ₃ . However, the selection of the substrate is limited by the high-temperature process of 450 DEG C or more for the production of the metal oxide thin film, and the manufacturing cost is increased due to this limitation. The organic material used as an alternative to the metal oxide layer has been utilized not only in a general nip structure but also in a pin-structured perovskite solar cell. (PEDOT: PSS) and [6, 6] -phenyl C61-butyric acid methyl ester (PCBM), which can usually be subjected to solution treatment, are each composed of a hole transport layer (HTL) And an electron transport layer (ETL). Although _{PSS / CH 3 NH 3 PbI 3} (MAPbI 3) / PCBM / gold (Au) 18.1% by pin element PCE (power conversion efficiency), including the achieved: In recent years, an indium tin oxide (ITO) / PEDOT This is still a low value compared to nip devices that have more than 20% efficiency with the use of scaled metal oxides as the electron transport layer (ETL). Nonetheless, pin perovskite solar cells are being studied extensively due to their advantages such as low hysteresis behavior, low processing temperature and easy fabrication process.

Flexible perovskite substrate with pin structure using low-temperature process In the case of solar cell, PEN (polyethylene naphthalate) film is coated with ITO and used as an electrode. Up to now, efficiency of up to 12.2% has been shown. The reduction of the efficiency of the solar cell due to the mechanical brittleness of the ITO layer is reported to be caused by the cracking. On the other hand, in the organic solar cell field (OPV), as a substitute for a fragile transparent conducting oxide (TCO) applicable to a flexible solar cell, a flexible conductive electrode such as a graphene, a carbon nanotube, a metal grid and a conductive polymer Much has been studied. Of these, graphene and single layer 2D carbon materials, which are optically very transparent (about 97% in the visible region), mechanically rigid, flexible and stretchable, are the most promising candidates. In the prior art, there is an example in which graphene is used as a conductive transparent electrode in a fuel-responsive solar cell or an organic solar cell, and a solar cell using a graphene transparent electrode reported to date has obtained a maximum efficiency of 8.48% in a tandem polymer solar cell The corresponding structure in the tandem configuration is disadvantageous in terms of the number of constituent layers and is still lower than that of the TCO-preperovskite solar cell showing 11.0% PCE. Recent studies have used graphene electrodes in perovskite devices, but in these studies, graphene was not used as a replacement for conventional TCO electrodes, but only as an upper electrode.

Recently, a solar cell formed on a flexible substrate has been attracting attention as a major development field of the next generation solar cell technology. For stable operation of a flexible solar cell, it is necessary to form a constituent layer of the solar cell with a material having a low degree of cracking. Conductive transparent electrodes widely used in solar cells are conductive transparent oxides of ITO (indium tin oxide) and FTO (fluorine doped tin oxide). However, since the material is highly cracked, the solar cells are repeatedly warped to cause a decrease in the efficiency of the solar cell.

Graphene has lower conductivity than conductive transparent oxides, but is easily obtainable. Its properties such as light transmittance, mechanical strength, and flexibility are expected as substitutes for flexible transparent electrodes.

The organic metal halide perovskite material has a high light absorbance and high charge mobility, which has made a great leap in the recent increase in the efficiency of the third-generation solar cell (achieving an efficiency of more than 20%) and a flexible solar cell .

In order to overcome the disadvantages of the prior art as described above, the present invention provides a solar cell using perovskite as an absorber by replacing the conventional ITO and FTO transparent conductive oxide electrode having cracks with a flexible graphene electrode, And a manufacturing method thereof.

In order to achieve the above object, the present invention provides a perovskite-based solar cell comprising a graphene layer as a conductive transparent electrode.

The conductive transparent electrode made of the graphene layer may be a transparent front electrode.

In addition, the solar cell may have a transparent anode electrode, a hole transport layer, a perovskite layer, an electron transport layer, and a cathode electrode sequentially stacked on a substrate.

In addition, the solar cell may have a transparent cathode electrode, an electron transport layer, a perovskite layer, a hole transport layer, and an anode electrode sequentially stacked on a substrate.

In addition, the solar cell may further include a transparent anode electrode made of the graphene layer or a metal oxide layer deposited on the transparent cathode electrode.

Wherein the metal oxide layer comprises MoO₃, NiO, CoO and TiO₂ ≪ RTI ID = 0.0 > and / or < / RTI >

The thickness of the metal oxide layer may be about 0.5 nm to about 6 nm.

The perovskite may be a perovskite element using a halogenated lead-duct compound.

The halogenated lead duct compound may be represented by the following general formula (1).

[Chemical Formula 1]

A · PbY ₂ · Q

In the above formula,

A is an organic halide compound or an inorganic halide compound,

Y is a halogen ion of F ^- , Cl ^- , Br ^- or I ^-

Q is 1 ~ 10 cm from the compound of formula than the compound of the FT-IR formula (2) to the peak of the Lewis base and (Lewis base) compound, the functional group including a functional group to an atom having a lone pair pieces electron pair Note ^{- 1} by red shift,

(2)

PbY ₂ · Q

Wherein Y and Q are the same as defined for formula (1).

Wherein A is may be a _{CH 3 NH 3 I, CH (} NH 2) 2 I or CsI.

The perovskite may be prepared by heating and drying the adduct compound to remove the Lewis base compound contained in the adduct compound.

The present invention has successfully implemented a perovskite-based solar cell using graphene as a conductive transparent electrode and has achieved the highest efficiency by combining appropriate energy bands of graphene electrode / hole transport layer / perovskite / electron transport layer / metal electrode And 17.1% respectively. This is the highest efficiency among the graphene electrode-based solar cell efficiencies reported so far, and other transparent conductive electrodes (metal thin films or conductive organic materials such as PEDOT: PSS) for replacing transparent conductive oxide electrodes such as ITO and FTO, Is the highest efficiency among the solar cell cases. In addition, when the structure of the present invention is formed on a polymer substrate such as PET or PEN coated with graphene, it is expected that reduction in efficiency will be small even in repetitive warpage unlike existing ITO electrodes as well as a high efficiency flexible solar cell. It is expected to be applicable to the development of flexible devices in optoelectronic devices (for example, optical sensors and light emitting diodes) and perovskite-based memory devices.

FIG. 1 is a graph showing the conversion efficiency (PCE) of a perovskite-based solar cell using graphene as a conductive transparent electrode according to the present invention.
2 is a schematic view of a perovskite-based solar cell using graphene as a conductive transparent electrode.
Each of FIG. 3 (a) graphene, (b) 1 nm MoO ₃ deposited graphene, (c) 2 nm MoO deposited to ₃ graphene, (d) ITO, (e ) UVO treated ITO and (f) UVO PEDOT: PSS droplets on ITO covered with 1 nm MoO ₃ after treatment.
Figure 4 shows a graphical representation of the results of (a) graphene (b) graphene / 1 nm MoO ₃ (c) SEM image of graphene / 2 nm MoO ₃ (scale bar 100 nm).
Figure 5 shows (a) graphene / 2 nm MoO ₃ Electrode and (b) ITO / 1 nm MoO ₃ (Left) and BSE mode (right) of the cross section of the element having the electrode.
6 is a graph showing the relationship between the thickness of MoO ₃ and the average PCE of the graphene electrode and the ITO electrode, (c) the JV curve showing the best performance of the device of Example 2 and (d) Comparative Example 2, (e) Relation between sheet resistance of graphene and ITO and MoO ₃ thickness, (f) 2 nm thick MoO ₃ Lt; RTI ID = 0.0 > ITO < / RTI > with or without a layer.
7 shows the JV curves of (a) Example 1 and (b) Example 2 measured.
8 shows a PCE histogram of the electrodes of Example 2 and Comparative Example 2;
FIG. 9 shows the EQE spectrum (black line) and J _sc (blue line) at the highest performance of (a) Example 2 and (b) Comparative Example 2 electrode.
FIG. 10 shows a comparison of the 2 nm thick MoO ₃ / Glass < / RTI > and glass / ITO with or without a layer.
Fig. 11 is a graph _{showing the relationship between} (A) ITO and (b) graphene, including the layer, of the structure, and (c) the approximate energy level of the structure.
PEDOT: PSS, (d) Comparative Example 1, (e) Comparative Example 2, and (f) Comparative Example 2 / PEDOT: The AFM images (3 μm × 3 μm) of PSS are shown.
13 shows a planar SEM image of the MAPbI ₃ perovskite film produced on (a) Example 2 / PEDOT: PSS and (b) Comparative Example 2 / PEDOT: PSS. (c) and (d) show high magnification images of (a) and (b).
Figure 14 (a) is DMSO (solution), PbI ₂ · DMSO (powder) and MAI · PbI ₂ · a FT-IR spectrum of a DMSO (powder), (b) MAI · PbI 2 · DMSO ( powder) and FAI · And the FT-IR spectrum of PbI _2. DMSO (powder).
15 is an FT-IR spectrum of PbI ₂ · TU (powder) and FAI · PbI ₂ · TU (powder).

BRIEF DESCRIPTION OF THE DRAWINGS The present invention is capable of various modifications and various embodiments, and specific embodiments are illustrated in the drawings and will be described in detail in the detailed description. It should be understood, however, that the invention is not intended to be limited to the particular embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

Hereinafter, the present invention will be described in detail.

The present invention provides a perovskite-based solar cell comprising a graphene layer as a conductive transparent electrode.

According to a preferred embodiment, the conductive transparent electrode made of the graphene layer may be a transparent front electrode.

In addition, the solar cell may have a transparent anode electrode, a hole transport layer, a perovskite layer, an electron transport layer, and a cathode electrode sequentially stacked on a substrate.

In addition, the solar cell may have a transparent cathode electrode, an electron transport layer, a perovskite layer, a hole transport layer, and an anode electrode sequentially stacked on a substrate.

According to an embodiment of the present invention, there is provided a solar cell in which a transparent anode electrode, a hole injection layer (metal oxide layer), a hole transport layer, a perovskite layer, an electron transport layer and a cathode electrode are sequentially laminated on a substrate.

Here, graphene is a two-dimensional carbon isotope, and methods for producing it include a peeling method in which a physically graphene layer is separated from graphite, a chemical oxidation in which graphite is dispersed in a dispersion and chemically reduced to obtain graphene , A pyrolysis method in which a graphene layer is obtained through pyrolysis at a high temperature in a silicon carbide (SiC) substrate, and a chemical vapor deposition method. Among them, a chemical vapor deposition method can be exemplified as a method capable of synthesizing high quality graphene . Although not limited thereto, graphene produced by a chemical vapor deposition method is preferable. Although single-layer graphene is used in this embodiment, it is not limited thereto, and multi-layer graphene can be used

The thickness of the graphene layer may be from 0.01 to 35 nm, preferably from 0.01 to 3.5 nm, and more preferably from 0.01 to 0.35 nm.

According to one embodiment, the graphene may exhibit a shape aspect ratio of not more than 0.1, a number of graphene layers of not more than 100, and a specific surface area of 300 m ² / g or more. The graphene refers to a single mesh web of carbon (C) SP ² bonds in the hcp structure of graphite. Recently, a graphene composite layer having a plurality of layers has been broadly classified into graphene.

The method of transferring the graphene to the substrate is not particularly limited and is not described in detail because it is a general method known in the art.

According to the present invention, the electron transport layer can be formed directly on the transparent cathode electrode (graphene layer), or the hole transport layer can be formed directly on the transparent anode electrode (graphene layer), but the deposition of the metal oxide layer on the graphene layer It is possible. At this time, when the graphene layer is a transparent anode electrode, the metal oxide layer functions as a hole injection layer, and when the graphene layer is a transparent cathode electrode, the metal oxide layer may serve as an electron injection layer.

According to one embodiment, a metal oxide layer may be deposited to render the graphene layer wettable. The metal oxide layer may include MoO ₃ , NiO, CoO, and TiO ₂ But not limited to, at least one selected from the group consisting of the following materials, and any materials known in the related art may be used without limitation. The thickness of the metal oxide layer may be about 0.5 nm to about 6 nm.

Preferably from about 1 nm to about 6 nm, more preferably from about 1 nm to about 4 nm, and even more preferably from about 2 to 3 nm.

On the other hand, the hole transport layer may be formed of poly (3,4-ethylenedioxythiophene) polystyrenesulfone (PEDOT: PSS); Tetrafluoro-tetracyanoquinodimethane (CuPc: F ₄ -TCNQ); (WO _x ), graphene oxide (GO), carbon nanotubes (CNT), molybdenum oxide (MoO _x ), vanadium oxide (V ₂ O ₅ ) and nickel oxide (NiO _x ) in PEDOT: PSS , But the present invention is not limited thereto. Any material may be used as long as it is used in the industry. For example, it may include a hole transporting molecular material or a hole transporting polymer material. As the hole transporting molecular material, spiro-MeOTAD [2,2 ', 7,7'-tetrakis- (N, N-di-p-methoxyphenyl-amine) -9,9'- spirobifluoren] As the hole transporting polymer material, P3HT [poly (3-hexylthiophene)] may be used. In addition, the hole transporting layer may include a doping material. The doping material may be selected from the group consisting of a Li-based dopant, a Co-based dopant, and combinations thereof, but is not limited thereto. For example, a mixture of spiro-MeOTAD, 4-tert-butyl pyridine (tBP), and Li-TFSI may be used as the material constituting the hole transport layer.

PEDOT: PSS used as a hole transporting layer used in a preferred embodiment of the present invention is prepared by dispersing poly (3,4-ethylenedioxythiophene) having 5 to 10 thiophenes on polystyrene sulfonic acid (PSS) The electron transporting layer is at least one selected from the group consisting of fullerene, bathocuproine (BCP) and fullerene derivatives, or a mixture of at least one selected from the group consisting of TiO ₂ , ZnO, SrTiO ₃ , WO ₃ , Metal oxides. Any material used in the industry can be used without limitation.

Examples of fullerene derivatives include, but are not limited to, phenyl-C61-butyric acid methyl ester (PCBM). According to a preferred embodiment, C60 / BCP can be used. The metal electrode or the rear electrode used as the cathode or the anode may be formed of a material selected from the group consisting of Pt, Au, Al, Ni, Cu, Ag, In, Ru, Pd, Rh, Ir, Os and C, But are not limited to, and can be used without limitation as long as it is a substance known in the related art.

According to another embodiment of the present invention, the perovskite may be a halogenated lead duct compound.

The halogenated lead duct compound may be represented by the following general formula (1).

[Chemical Formula 1]

A · PbY ₂ · Q

In the above formula,

A is an organic halide compound or an inorganic halide compound,

Y is a halogen ion of F ^- , Cl ^- , Br ^- or I ^-

Q is 1 ~ 10 cm from the compound of formula than the compound of the FT-IR formula (2) to the peak of the Lewis and the base (Lewis base) compound, the functional group including a functional group to an atom having a lone pair pieces electron pair Note ^{- 1} by red shift,

(2)

PbY ₂ · Q

Wherein Y and Q are the same as defined for formula (1).

Wherein A is may be a _{CH 3 NH 3 I, CH (} NH 2) 2 I or CsI.

The perovskite may be prepared by heating and drying the adduct compound to remove the Lewis base compound contained in the adduct compound.

The preparation of perovskite using the above-mentioned adduct compound can be referred to other patent applications of the present inventors, Korean Patent Application Nos. 2015-0090139 and 2015-0164744, the entire contents of which are incorporated herein by reference.

According to one embodiment, A in the formula (1) is an organic or inorganic compound consisting of a combination of an organic cation or a Cs ⁺ cation represented by the following Chemical Formula 3 or 4 and a halogen ion selected from F ^- , Cl ^- , Br ^- and I ^- Halide compound.

 (3)

(R ₁ R ₂ N = CH-NR ₃ R ₄ ) ⁺

In the above formula,

R ₁ , R ₂ , R ₃ and R ₄ are independently selected from hydrogen and unsubstituted or substituted C 1 -C 6 alkyl,

[Chemical Formula 4]

_{(R 5 R 6 R 7 R} 8 N) +

In the above formula,

R ₅ , R ₆ , R ₇ and R ₈ are hydrogen, unsubstituted or substituted C 1 -C 20 alkyl or unsubstituted or substituted aryl.

More specifically, A may be selected from CH ₃ NH ₃ I (MAI, Methyl Ammonium Iodide), CH (NH ₂ ) ₂ I (FAI, Formamidinium Iodide, formamidinium iodide) have.

Q is a Lewis base compound having a functional group that functions as a pair of electrons by nitrogen (N), oxygen (O), or sulfur (S) atoms. More specifically, Q represents a nitrogen, oxygen, Thioester group, thioacetamide group, carbonyl group, aldehyde group, carboxyl group, ether group, thioamide group, thioamide group, thiocyanate group, thioether group, thioketone group, thiol group, thiophene group, An amide group, an amine group, an amide group, an imide group, an imine group, an azide group, a pyridine group, a pyrrolyl group, a nitro group, a nitro group, May be a Lewis base compound containing at least one functional group selected from the group consisting of a nitro group, a nitro group, a cyano group, a nitro group, and an isocyano group, and may be a thioamide group in which an S atom is a pair of electrons, Nate A compound containing at least one functional group selected from the group consisting of a thioether group, thioether group, thioketone group, thiol group, thiophene group, thiourea, thioacetamide group and thiosulfate group has stronger bond with lead halide And can be more preferable to the present invention.

For example, there may be mentioned dimethylsulfoxide (DMSO), N, N-dimethylacetamide (DMA), N-methyl-2-pyrrolidione MPLD), N-methyl-2-pyridine (MPD), 2,6-dimethyl-γ-pyrone (DMP) N, N-dimethylthioacetamide (DMTA), thioacetamide (TAM), ethylene diamine (NAD), and the like. Ethylenediamine (EN), tetramethylethylenediamine (TMEN), 2,2'-bipyridine (BIPY), 1,10-piperidine, At least one compound selected from the group consisting of aniline, pyrrolidine, diethylamine, N-methylpyrrolidine, n-propylamine, (Thiourea (TU)) comprising an S-pair of electrons, N, N'- N-dimethylthioacetamide (DMTA), and thioacetamide (TAM).

The FT-IR peak corresponding to the functional group of the electron pair trapping atom in which the Lewis base compound represented by Q bonds with Pb is red-shifted by 10 to 30 cm ^-1 in the compound represented by Formula 2 from the Q compound (red shift).

The Lewis base compound may be in the form of a liquid, preferably nonvolatile or low-volatile, and has a boiling point of 120 ° C or higher, for example, a boiling point of 150 ° C or higher.

In the method for producing the halogenated lead duct compound represented by the above formula (1)

Preparing a precursor solution by dissolving a Lewis base compound containing a halogenated lead, an organic halide compound or an inorganic halide compound and a nitrogen (N), oxygen (O) or sulfur (S) atom as a pair of electrons in a first solvent;

And a step of adding a second solvent to the precursor solution to filter out the resulting precipitate, thereby producing a halogenated lead duct compound.

The halogenated lead, a halogenated compound containing a divalent cation, and an organic material including a ligand can be mixed in a molar ratio of 1: 1: 1 to 1: 1: 1.5, and the molar ratio of 1: 1: 1 Most preferred.

According to one embodiment, the first solvent comprises an organic material comprising the halogenated lead, an organic halide compound or an inorganic halide compound, and a functional group which electron pairs the nitrogen (N), oxygen (O) or sulfur (S) (PD), ethylene carbonate (EC), diethylene glycol, propylene carbonate (PC), propylene carbonate (PC), hexamethylphosphoric triamide (HMPA ), Ethyl acetate, nitrobenzene, formamide, gamma -butyrolactone (GBL), benzyl alcohol, N-methyl-2-pyrrolidone (NMP), acetophenone, ethylene glycol, trifluoro phosphate, BN), valeronitrile (VN), acetonitrile (AN), 3-methoxypropionitrile (MPN), dimethylsulfoxide (DMSO), dimethylsulfate, aniline, N-methylformamide 1,2-dichlorobenzene, tri-n-butyl phosphate, o-di (DMEA), 3-methoxypropionone nitrile (MPN), diglyme, cyclohexane, cyclohexane, chlorobenzene, selenium oxychloride, ethylene sulfate, benzene thiol, dimethylacetamide, diethylacetamide, But are not limited to, hexanol, bromobenzene, cyclohexanone, Anisole, diethylformamide (DEF), dimethylformamide (DMF), 1-hexanethiol, hydrogen peroxide, bromoform, ethyl chloroacetate, But are not limited to, 1-dodecanethiol, di-n-butyl ether, dibutyl ether, acetic anhydride, m-xylene, p- xylene, chlorobenzene, morpholine, diisopropyletheramine , Diethyl carbonate (DEC), 1-pentanediol, n-butyl acetate 1-hexadecanethiol, and the like. These organic solvents may be used singly or in combination of two or more.

The first solvent may be added in an excess amount, and may be preferably added in a weight ratio of 1: 1 to 1: 3 (lead halide: first solvent) based on the weight of the halogenated lead.

According to one embodiment, the second solvent may be a non-polar or weak polar solvent for selectively removing the first solvent. For example, it may be an acetone solvent, a C1-C3 alcohol solvent, an ethyl acetate solvent, Based, alkylene chloride-based, cyclic ether-based, and mixtures thereof.

According to one embodiment, perovskite produced from a halogenated lead duct compound may exhibit low reproducibility when using toluene and chlorobenzene, which are common volatile solvents, In the case of using a volatile solvent, it can be largely influenced by the amount of dripping and / or the spinning speed of the washing liquid and the difference in solubility between the washing liquid and the precursor solution. However, when a second solvent, preferably a diethyl ether solvent, according to the present invention is used, the second solvent completely dissolved in the completely dissolved first solvent is used regardless of the spin coating condition, A skate membrane can be obtained.

According to a preferred embodiment of the present invention, the adduct compound contains peaks each located in the range of 2? Values of the XRD diffraction peaks ranging from 7 to 8.5 and 9.8 to 10.5. Specifically, the 2? Values of the XRD diffraction peaks range from 6 to 7 , 7 to 8.5, and 9.8 to 10.5, respectively, or include peaks each having a 2θ value of the XRD diffraction peak in the range of 7 to 8.5, 9.8 to 10.5, 11 to 12.5, and 13 to 14, respectively (See Figs. 14 and 15). These peaks do not appear in the compounds prepared by other methods and may be characteristic peaks that appear in the adduct compound.

According to one embodiment, the halogenated lead duct compound thin film prepared as described above can form a transparent thin film as shown in FIG. 2 (a).

The halogenated lead duct compound formed from the thin film may be subjected to a heating process at a temperature of 30 캜 or higher and preferably heated at a temperature of 40 캜 or higher or higher than 50 캜, It is possible to form perovskite by heating in the following temperature range. Further, the heating process may be heated in a stepwise manner by heating at a temperature of 30 ° C to 80 ° C and then at 90 ° C to 150 ° C, and by a further heating process, a perovskiy Can be obtained. In the annealing process, the ligand organic substance represented by Q in the formula (1) is removed from the crystalline structure of the halogenated lead duct compound to form perovskite. According to one embodiment, the perovskite thin film produced is dark brown A thin film having a dark color can be formed.

Meanwhile, the solar cell according to the present invention

Transferring graphene onto the substrate to form a transparent anode electrode;

Optionally, depositing a metal oxide on the graphene transferred onto the substrate;

Forming a hole transport layer (HTL) on the deposited metal oxide;

Forming a perovskite layer as an absorber on the hole transport layer formed above;

Forming an electron transport layer (ETL) on the perovskite layer; And

And forming a cathode electrode on the electron transporting layer.

The substrate may be a flexible substrate made of polymer or a non-flexible substrate such as glass.

According to a preferred embodiment, the transparent anode electrode is made of graphene, the metal oxide layer is made of molybdenum trioxide (MoO ₃ ), the hole transporting layer is made of PEDOT: PSS, the perovskite layer is made of MAPbI ₃ (Methyl Ammonium Lead Iodide) A high efficiency TCO-preperovoked-base solar cell is provided, which includes a fullerene / BCP (bathocuproine) ₆₀ and a cathode electrode is lithium fluoride (LiF) / aluminum (aluminum). Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the scope of the present invention is not limited thereto, and various modifications are possible.

MoO ₃ formed to a thickness of several nanometers  Layer is formed between the graphene and the PEDOT: PSS layer to provide hydrophilicity to the graphene surface and raise the low work function (4.23 eV) to a high level (4.71 eV) through hole doping. The wettability and the physical properties of the PEDOT: PSS are affected by the thickness of the MoO ₃ layer. According to a more preferred embodiment, a conversion efficiency of up to about 17.1% can be achieved by introducing a MoO ₃ interface layer about 2 nm thick (see FIG. 1).

The structure of a solar cell device according to an embodiment of the present invention is schematically shown in Fig. In a MAPBI ₃ perovskite based solar cell structure using graphene as a conductive transparent electrode, PEDOT: PSS and C ₆₀ / BCP were used as a hole transport layer (HTL) and an electron transport layer (ETL), respectively. The above structure is suitable for the next generation application which is applicable to a flexible plastic substrate because a low temperature process is possible.

Single-layer graphene grown by chemical vapor deposition (CVD) increases the work function (~4.3 eV) by P-type doping and, as a result, not only improves the conductivity, but also increases the peak occupancy of the desired hole transport layer It is preferable to use it as a transparent anode electrode since the energy level of the highest occupied molecular orbital (HOMO) level (for example, about 5.2 eV for PEDOT: PSS) is derived. However, the present invention is not limited thereto, and graphene may be doped n-type to be used as a cathode if necessary. In the present invention, by vacuum thermal deposition, MoO ₃ between the graphene and the PEDOT: PSS layer  Layer was deposited and then heat-treated at 150 캜 on a hot plate to prevent loss during the spin coating process. In the present invention, MoO ₃ By varying the thickness of the layer from 0 to 4 nm, the interface characteristics of the graphene electrode such as wettability and doping level of PEDOT: PSS were controlled. The wettability of PEDOT: PSS on graphene is a very important factor in the fabrication of high performance devices.

Hereinafter, the perovskite-based solar cell using the graphene according to the present invention as a conductive transparent electrode will be described in more detail with reference to Examples and Experimental Examples. However, the following examples are merely illustrative of the present invention and should not be construed to limit the scope of protection of the present invention.

< Example  1 to 3> Grapina  Based Perovskite  Manufacture of solar cell

A single-layer graphene-coated glass substrate (Graphene Square Inc.> 1 k? Cm ² , 15 x 15 mm ² ), on which CVD-grown graphene was transferred onto a cleaned glass substrate (AMG, 25 x 25 mm ² )  ) Was used to fabricate a graphene-based perovskite solar cell.

Thin layer of MoO ₃ having various thicknesses of 1 nm, 2 nm and 4 nm on a single-layer graphene-coated glass substrate was subjected to vacuum thermal deposition at a deposition rate of 0.1 Ås ^-1 using a vacuum heat evaporator, and then heated at 150 ° C. for 10 minutes Heat treated. During the deposition, the deposition rate and thickness were monitored using a quartz crystal sensor. The MoO ₃ layer was intended to change the hydrophobic graphene surface to hydrophilic.

Then, the substrate was first dipped in deionized water, and 50 의 of PEDOT: PSS solution (Clevios P VP Al 4083) was spin-coated at 5000 rpm for 30 seconds and then heat-treated at 150 캜 for 20 minutes to form a hole transport layer Respectively.

A perovskite layer was formed as an absorber on the hole transport layer. The perovskite layer may comprise MAI, PbI ₂ And DMSO were mixed in a molar ratio of 1: 1: 1 and dissolved in 50 wt% DMF solution without heating. Then, 50 μl of completely dissolved MAI · PbI ₂ · DMSO solution was spin-coated at 3500 rpm for 20 seconds, After 8 seconds from the start, 0.3 ml of diethyl ether (DE, Diethyl ether) was slowly dropped to remove excess dimethylformamide to remove CH ₃ NH ₃ I · PbI ₂ After forming a DMSO adduct compound film, the CH ₃ NH ₃ I · PbI ₂ The DMSO adduct compound film was heat-treated at 65 ° C for 1 minute and at 100 ° C for 4 minutes to form a dark brown perovskite film.

After that, the substrate in the vacuum thermal deposition of less than 10 ^-6 Torr C ₆₀ (20 nm), BCP (10 nm), LiF (0.5 nm), and Al (150 nm). All of the above spin coatings were performed at atmospheric conditions.

< Comparative Example  1 to 4> ITO-based Perovskite  Manufacture of solar cell

In the fabrication of ITO-based perovskite solar cells, the ITO devices used were made on commercially available ITO-coated glass substrates (AMG, 9.5 Ω cm ² , 25 × 25 mm ² ).

The ITO-coated glass substrate was washed with acetone, isopropanol and deionized water for 15 minutes each using an ultrasonic bath, dried with nitrogen gas, and stored in an oven at 120 ° C.

The ultra-thin MoO ₃ layer with various thicknesses of 0 nm, 1 nm, 2 nm and 4 nm was vacuum deposited on the cleaned and dried ITO-coated glass substrate using a vacuum thermal evaporator at a deposition rate of 0.1 Å s ¹ And then heat-treated at 150 ° C for 10 minutes. During the deposition, the deposition rate and thickness were monitored using a quartz crystal sensor.

Subsequently, the substrate was first dipped in deionized water, and 50 P of PEDOT: PSS solution was spin-coated at 5000 rpm for 30 seconds and then heat-treated at 150 캜 for 20 minutes to form a hole transport layer.

A perovskite layer was formed as an absorber on the hole transport layer. The perovskite layer may comprise MAI, PbI ₂ And DMSO were mixed at a molar ratio of 1: 1: 1 and dissolved in 50 wt% DMF solution without heating. Then, 50 μl of completely dissolved MAI · PbI ₂ · DMSO solution was spin-coated at 3500 rpm for 20 seconds, After 8 seconds from the start, 0.3 ml of diethyl ether (DE, Diethyl ether) was slowly dropped to remove excess dimethylformamide to remove CH ₃ NH ₃ I · PbI ₂ After forming the DMSO adduct compound film, the CH ₃ NH ₃ I · PbI ₂ The DMSO adduct compound film was heat-treated at 65 ° C for 1 minute and at 100 ° C for 4 minutes to form a dark brown perovskite film. Then, the substrate inside a vacuum thermal deposition of less than 10 ^-6 Torr C ₆₀ (20 nm), BCP (10 nm), LiF (0.5 nm), and Al (150 nm). All of the above spin coatings were performed at atmospheric conditions.

< Experimental Example  1> Characterization of solar cell

The SEM image, the J- V curve, the external quantum efficiency (EQE) spectrum, the sheet resistance, and the resistivity of the perovskite-based solar cells of Examples 1 to 3 and Comparative Examples 1 to 4 were measured in the following manner. Transmittance, UPS and AFM images were analyzed.

The SEM image was analyzed using a field emission scanning electron microscope (AURIGA, Zeiss), and the Oriel Sol3A solar simulator calibrated to 100mWcm ^-2 using a standard Si solar cell (RC-1000-TC-KG5-N, VLSI Standards) The photovoltaic simulation was performed with the AM 1.5G daylight produced by.

The J- V curves were recorded by a Keithley 2400 source meter and the forward and reverse scan rates were set at 200 ms per 20 mV and the active area of the device was 1.77 mm ² .

The EQE spectrum was measured with a Newport IQE200 system equipped with a 300 mW xenon light source and a lock-in amplifier.

The sheet resistance was measured using a 4-well method (CMT-SERIES, Advanced Instrument Technology).

The transmittance was measured using UV-vis spectroscopy (Cary 5000, Agilent).

The UPS measurements were made using a helium discharge lamp (He I 21.2 eV, AXIS-NOVA, Kratos) and AFM images were taken using a contactless mode XE-100 (Park Systems) scanning probe microscope.

MoO ₃  Deposition of layers PEDOT: PSS  Wettability and Grapina  Improved hydrophilicity of electrode

The wettability of PEDOT: PSS in graphene-based and ITO-based devices is very important in the manufacture of high performance devices and the difference in wettability with and without MoO ₃ layer was measured through contact angle measurement.

3 shows an optical microscope image of a PEDOT: PSS layer obtained by dropping water droplets onto the surface of graphene and ITO. As shown in FIG. 3A, MoO ₃ The contact angle of the PEDOT: PSS on the layerless graphene surface was measured to be 90.4 ± 0.3 °. As a result, the continuous PEDOT: PSS / MAPbI ₃ layer is unlikely to be formed by the spin-coating process ). However, as shown in FIGS. 3B and 3C, when the 1 nm thick MoO ₃ layer is present on the graphene, the contact angle decreases to 46.6 ± 1.3 °, and when the 2 nm thick MoO ₃ layer is present, the contact angle is 30.0 ± 1.6 ° Respectively. It can be seen from the inset of FIG. 3B and FIG. 3C that the wettability is improved as well as the contact angle is decreased.

As shown in FIG. 3C, dark brown MAPBI ₃ The film was formed in a rectangular shape at the center of the glass substrate of the pre-thermally deposited MoO ₃ layer. In particular, the square-shaped MAPBI ₃ The film was formed on a 2 nm thick MoO ₃ layer and the PEDOT: PSS showed better wettability over the thick MoO ₃ layer.

Figure 4 is a SEM image, it is not sufficiently covered with a 1nm thick MoO ₃ layer, and clearly shows the hydrophobic graphene surface is completely covered with a 2nm thick MoO ₃ layer.

For comparison, the contact angle of PEDOT: PSS on the ITO surface is shown in Figs. 3d to 3f as UV / ozone (UVO) treatment and MoO ₃ Was measured before and after the combination treatment of the deposition. As a result, similar to graphene. The ITO surface did not exhibit wettability to PEDOT: PSS forming a continuous film by spin coating, and the contact angle on the ITO surface treated with UVO was considerably increased to 84.9 ± 1.3 ° (FIG. 3D) and 16.9 ± 1.8 ° (FIG. 3E) And decreased slightly by 9.3 ± 0.6 ° (FIG. 3f) by 1 nm thick MoO ₃ layer, which means that the wettability of the ITO surface is improved.

FIG. 5 is a graph _{showing the results of a &lt;} (Fig. 5A) and 1 nm-thick MoO ₃ Fig. 2 shows an SEM image of a cross section of the device manufactured using the ITO electrode of Fig. The left image of FIG. 5 was measured in a secondary electron (SE) mode and the right image was measured in a back-scattered electron (BSE) mode. The hydrophilicity of the PEDOT: PSS layer formed by similar thickness (~ 50 nm) and spin coating of the morphology on the graphene and ITO was MoO ₃ And can be maintained smoothly and continuously by the interface layer. In addition, as shown in Figure 5, the surface of the perovskite film on both graphene and ITO based substrates was observed to be very smooth with a uniform thickness (~ 510 nm).

The smooth and dense perovskite film described above contains PbI ₂ And a highly reproducible nip perovskite solar cell with a maximum conversion efficiency of 19.7% was recently developed by the present inventors. A manufacturing method can be referred to Korean Patent Application No. 2015-0164744. MAI and PbI ₂ The DMSO adduct film was formed by spin coating with dropping diethyl ether (DE) to wash excess dimethylformamide (DMF) solvent and then converted to perovskite film by heat treatment.

Element In terms of performance MoO ₃ Influence of layer thickness

MoO ₃ in device performance In order to investigate the effect of layer thickness, various thicknesses of MoO ₃ The open circuit voltage ( V _oc ), the short-circuit current ( J _sc ), the charging rate (FF), the conversion efficiency (PCE) for the perovskite solar cells of Examples 1 to 3 and Comparative Examples 1 to 4, And the maximum conversion efficiency are shown in Table 1. &lt; tb &gt;&lt; TABLE &gt;

electrode MoO ₃ Thickness
[nm] V _oc
[V] J _sc
[mA cm ² ] FF
PCE
[%] Best PCE
[%] Example 1
(G-M1) Grapina One 0.72 ± 0.36 17.6 ± 6.3 0.45 ± 0.09 6.7 ± 4.2 12.1 Example 2
(G-M2) 2 1.03 0.02 21.9 ± 0.4 0.72 + 0.02 16.1 ± 0.6 17.1 Example 3
(G-M4) 4 1.00 + - 0.01 22.9 ± 0.4 0.70 + 0.02 15.9 ± 0.5 16.2 Comparative Example 1
(ITO-M0) ITO 0 0.96 ± 0.01 21.4 ± 0.5 0.83 0.02 17.0 + - 0.4 17.6 Comparative Example 2
(ITO-M1) One 0.97 ± 0.01 22.6 ± 0.4 0.83 ± 0.01 18.2 ± 0.5 18.8 Comparative Example 3
(ITO-M2) 2 0.95 + - 0.01 22.2 ± 0.4 0.76 ± 0.01 16.1 ± 0.4 16.9 Comparative Example 4
(ITO-M4) 4 0.94 + - 0.01 21.0 ± 0.4 0.74 ± 0.01 14.7 ± 0.6 15.7

The relationship between average PCE and MoO ₃ layer thickness is shown in Figures 6A and 6B.

As shown in FIG. 6, in the case of a graphene-based device, since the surface of the hydrophobic graphene is not wetted with the MoO ₃ layer, the PEDOT: PSS solution or the perovskite solution forms a film after spin coating And PCE could not be assessed (see also Fig. 3a insertion). As well as the case of Example 1 by depositing the MoO ₃ layer of thickness 1nm irregular PEDOT: PSS were by irregular coating of PCE represents a large change in the 0% ~ 12.1%, 1nm thick These results MoO ₃ Layer can not completely cover the hydrophobic graphene surface. As a result, current density and voltage (JV) characteristics between devices were not constant (Fig. 7A).

However, MoO _{3 &lt; RTI ID = 0.0} &gt;  The devices of Examples 2 and 3 having the layer had the average PCE values of 16.1% and 15.9%, respectively, and the performance deviation between the devices was greatly reduced (Figs. 6A and 7B). In particular, the highest PCE of 17.1% was achieved in Example 2, which is not only the first time for a graphene electrode perovskite-based solar cell replacing the normal TCO electrode, but also the highest conversion efficiency Lt; / RTI &gt;

As shown in FIG. 6B, in the comparative examples, which are ITO-based devices, PCE was significantly affected by MoO ₃ thickness variations. The average PCE of Comparative Example 1 and Comparative Example 2 increased from 17.0% to 18.2%, and the average PCE of Comparative Example 3 and Comparative Example 4, which had a MoO ₃ layer thicker than 1 nm, were 16.1% And 14.7%, respectively.

8 shows a histogram of PCE for each of the electrode types of Example 2 and Comparative Example 2. Fig.

The maximum performance JV curves for Example 2 and Comparative Example 2 at 100 mW cm ² of AM 1.5 G solar irradiation, measured through reverse and forward bias sweep, are shown in Figures 6c and 6d, respectively. Both Example 2 and Comparative Example 2 did not show meaningful hysteresis according to the scanning direction.

In addition, compared to Comparative Example 2, Example 2 exhibited high series resistance and low shunt resistance. To understand the electrical properties of MoO ₃ -modified graphene and ITO electrodes, sheet resistance was measured via a four-point probe. 6E shows the relationship between the sheet resistance in graphene and ITO and the thickness of the MoO ₃ layer. As shown, the initial high sheet resistance (> 2 k? Cm ² ) of graphene was significantly reduced to ~ 780? Cm ² by deposition of a 0.5 nm thick MoO ₃ layer, and the thickness of the MoO ₃ layer And further decreased to ~ 500 Ω cm ² as it increased to 2 nm. The initial sheet resistance of ITO was measured to be 9.5 Ω cm ² , which was slightly reduced to 9.2 Ω cm ² by deposition of 1 and 2 nm MoO ₃ layers. The MoO ₃ doping over 4 times significantly reduced the sheet resistance of the initial single-layer graphene, but it was still much higher than ITO. Thus, Example 2 exhibited high series resistance, low shunt resistance and low fill factor (FF) for Comparative Example 2.

Transparency of device

As shown in FIG. 6F, single-atom-thick-layer single-layer graphene (~ 97% transmittance) exhibited high transparency compared to ITO (~ 89% transmittance) in the visible wavelength range. The short circuit current J _sc ) Levels.

8 shows the external quantum efficiency (EQE) spectra of Example 2 and Comparative Example 2. FIG. In the integrated photo current is 20.2 mA and 21.0 cm, ^respectively was calculated from the ^1. The EQE of the graphene- and TIO-based devices is similar (Figures 6F and 9), because the low carrier capture efficiency of the graphene anode is compensated by higher light transmittance as compared to the ITO anode. In addition, despite the much lower conductance of graphene than ITO, Example 2 shows a higher open-circuit voltage (V _oc ) level as compared to Comparative Example 2, and the results contribute to the higher PCE of Example 2 90% or more than Comparative Example 2).

Difference in work function of device

Although the same device structure is given, V 　 _oc Is related to the work function difference of the electrode. In the work function of ITO and graphene electrodes, ultra-thin MoO ₃ To investigate the effect of the layer, ultraviolet photoelectron spectroscopy (UPS) measurements were performed.

10 is MoO ₃ The UPS spectrum of the ITO and graphene electrodes with varying layer thickness is shown. As shown in FIG. 10A, a 0.5 nm thick MoO ₃ Deposition of the layer was rapidly transferred to high kinetic energy due to the interruption of the secondary battery of ITO. As a result, the work function increased from 4.29 eV to 4.65 eV. MoO ₃ Further deposition of the layers to a thickness of 1 nm and 2 nm increased the work function to 4.69 eV and 4.72 eV, respectively. Therefore, it is desirable to minimize the energy barrier between the anode and the hole transport layer (HTL) for efficient hole collection. As shown in Table 1, the higher J _sc and PCE of Comparative Example 2 as compared with Comparative Example 1 are attributed to an increase in the work function of the center electrode leading to improved hole collection efficiency. Meanwhile, MoO ₃ As the layer thickness increased to 2 nm and 4 nm, PCE decreased. Thin MoO ₃ between ITO and organic semiconductors in device structure  Layer behaves like an insulating layer and the holes are tunneled by a gradual decrease in the film thickness of ~ 3 nm. MoO ₃ Lt; / RTI &gt; layer. The hole collection efficiencies of Comparative Example 3 and Comparative Example 4 may be improved by increasing the number of workings of the electrode, but may be reduced by reducing the tunneling probability of the field due to a sudden decrease in FF and PCE as compared with Comparative Example 2. [

UPS spectrum of graphene based devices Also, MoO ₃ Layer structure of the ITO device. As shown in Figure 10b, a 0.5 nm thick MoO ₃ The rapid change of photoelectron initiation in the layer showed an increase in work function from 4.23 eV to 4.61, and MoO ₃ It was confirmed that further deposition of the layers to 1 nm and 2 nm thickness increased the work function to 4.67 eV and 4.71 eV, respectively. As shown in Fig. 10C, the ultra-thin MoO ₃ layer deposited on the graphene not only promoted the hole collection from the hole transport layer to the graphene anode by reducing the energy barrier at the interface, To enable successful spin coating of the PEDOT: PSS film on the surface.

When comparing the UPS data of ITO and graphene electrodes, the same MoO ₃ The work function for thickness was found to be approximately the same. The work function values of Comparative Example 2 and Example 2 were not significantly different. This means that the high V _oc of Example 2 is not explained in terms of the energy barrier difference at the anode / HTL interface than that of Comparative Example 2.

Also, V _oc  Can be influenced by the interface quality. Therefore, by atomic force microscopy (AFM) measurement, MoO₃And the parent polymer of the electrode after the formation of the PEDOT: PSS film.

As shown in Figs. 11A to 11F, the rms roughnesses of Comparative Example 1, Comparative Example 2 and Comparative Example 2 / PEDOT: PSS were 2.06, 1.95 and 1.2, respectively. (Root-mean-square) surface roughness of 0.29 nm, which is 6 times lower than that of the surface roughness (1.95 nm rms roughness). Here, the comparative example 2 / PEDOT: PSS has a MoO ₃ layer having the same thickness as the comparative example 2 and further has a PEDOT: PSS layer. Example 2 / PEDOT: PSS can be interpreted in the same sense.

Generally, the surface roughness of the underlying layer is smaller and therefore V _oc It is known that a better interface can be created between stacks. In this regard, the high V _oc of Example 2  , The electrode of Example 2 appears to have established a better PEDOT: PSS interface than the Comparative Example 2 / PEDOT: PSS interface.

Further, as shown in FIGS. 12 and 13, the SEM image of the perovskite surface on Example 2 / PEDOT: PSS and Comparative Example 2 / PEDOT: PSS showed that the particle size of Example 2 was smaller than the particle size of Comparative Example 2 .

Since the nano-scale edge of the surface can serve as nucleation sites, the surface roughness of the underlying layer in this study plays an important role in determining the particle size of PEDOT: PSS. Thus, the particles of the perovskite film on the smooth surface of Example 2 / PEDOT: PSS can grow to a larger size than the particles of the Comparative Example 2 / PEDOT: PSS surface. The larger particles of Example 2 reduced voltage loss due to charge recombination at the grain boundaries. Thus, compared to Comparative Example 2, the higher V _oc . &Lt; / RTI &gt;

The present invention not only uses graphene as a transparent conductive anode, but also provides a high efficiency TCO-free solar cell. MoO ₃ introduced into the anode surface of the solar cell of the present invention  Layer to form a better interface and allow alignment of the desired energy level between the anode and the major transport layer. Particularly, graphene has MoO ₃ The deposition makes a better role as a conductive electrode, and the optimal MoO ₃ At layer thicknesses, the highest PCE was achieved at 17.1% and 18.8% in graphene-based devices and ITO-based devices, respectively. The graphene electrode has lower conductivity compared to the ITO electrode, but similar J _sc , High V 　 _oc And high transparency and low surface roughness.

Claims (11)

A perovskite based solar cell comprising a graphene layer as a conductive transparent electrode. The method according to claim 1,
Wherein the conductive transparent electrode is a transparent front electrode. The method according to claim 1,
A transparent anode electrode comprising a graphene layer, a hole transport layer, a perovskite layer, an electron transport layer and a cathode electrode sequentially laminated on a substrate. The method according to claim 1,
A transparent cathode electrode made of a graphene layer, an electron transporting layer, a perovskite layer, a hole transporting layer, and an anode electrode are sequentially laminated on a substrate. The method according to claim 3 or 4,
And a metal oxide layer deposited on the transparent anode electrode or the transparent cathode electrode made of the graphene layer. 6. The method of claim 5,
The metal oxide layer may include MoO ₃ , NiO, CoO, and TiO ₂ &Lt; RTI ID = 0.0 &gt; and / or &lt; / RTI &gt; 6. The method of claim 5,
Wherein the thickness of the metal oxide layer is from about 0.5 nm to about 6 nm. The method according to claim 1,
Wherein the perovskite is produced using a halogenated lead duct compound. 9. The method of claim 8,
Wherein the halogenated lead duct compound is represented by the following formula 1:
[Chemical Formula 1]
A · PbY ₂ · Q
In the above formula,
A is an organic halide compound or an inorganic halide compound,
Y is a halogen ion of F ^- , Cl ^- , Br ^- or I ^-
Q is 1 ~ 10 cm from the compound of formula than the compound of the FT-IR formula (2) to the peak of the Lewis base and (Lewis base) compound, the functional group including a functional group to an atom having a lone pair pieces electron pair Note ^{- 1} by red shift,
(2)
PbY ₂ · Q
Wherein Y and Q are the same as defined for formula (1). 10. The method of claim 9,
Wherein A is _{CH 3 NH 3 I, CH (} NH 2) ₂ I of the solar cell or CsI. 10. The method of claim 9,
Wherein the perovskite is prepared by heating and drying an adduct compound to remove the Lewis base compound contained in the adduct compound.

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