JP2018056233A - Solar cell - Google Patents

Abstract

A solar cell having excellent durability at high temperature and high humidity is provided. A solar cell having a plurality of solar cells on a substrate, the plurality of solar cells being disposed between a lower electrode, an upper electrode, and a lower electrode and an upper electrode, respectively. A plurality of solar cells, the upper electrode is electrically connected by connecting to the lower electrode of the adjacent solar cell, and an electron microscope is used. In the observed cross-sectional view of a solar cell, a solar cell in which θ2 is less than 90 ° when the angle of the side surface of the photoelectric conversion layer in contact with the upper surface of the lower electrode is θ2. [Selection] Figure 3

Description

The present invention relates to a solar cell excellent in high temperature and high humidity durability.

Conventionally, a photoelectric conversion element including a stacked body in which an N-type semiconductor layer and a P-type semiconductor layer are arranged between opposing electrodes has been developed. In such a photoelectric conversion element, photocarriers are generated by photoexcitation, and an electric field is generated by electrons moving through an N-type semiconductor and holes moving through a P-type semiconductor.

Currently, most of the photoelectric conversion elements in practical use are inorganic solar cells manufactured using an inorganic semiconductor such as silicon. However, since inorganic solar cells are expensive to manufacture and difficult to increase in size, and the range of use is limited, organic solar cells manufactured using organic semiconductors instead of inorganic semiconductors are attracting attention. .

In organic solar cells, fullerene is almost always used. Fullerenes are known to work mainly as N-type semiconductors. For example, Patent Document 1 describes a semiconductor heterojunction film formed using an organic compound that becomes a P-type semiconductor and fullerenes. However, in organic solar cells manufactured using fullerenes, it is known that the cause of deterioration is fullerenes (see, for example, Non-Patent Document 1), and materials that replace fullerenes are required.

Therefore, in recent years, a photoelectric conversion material having a perovskite structure using lead, tin, or the like as a central metal, which is called an organic-inorganic hybrid semiconductor, has been discovered and shown to have high photoelectric conversion efficiency (for example, Non-Patent Document 2). .
However, when such an organic inorganic perovskite compound is used, there is a problem that the organic solar cell is inferior in durability at high temperature and high humidity.

JP 2006-344794 A

Reese et al. , Adv. Funct. Mater. , 20, 3476-3483 (2010) M.M. M.M. Lee et al. , Science, 338, 643-647 (2012)

An object of this invention is to provide the solar cell excellent in high temperature, high humidity durability.

The present invention is a solar cell having a plurality of solar cells on a substrate, wherein the plurality of solar cells are disposed between a lower electrode, an upper electrode, and the lower electrode and the upper electrode, respectively. A plurality of solar cells, wherein the upper electrode is electrically connected by connecting to the lower electrode of an adjacent solar cell, and an electron microscope In the cross-sectional view of the solar cell observed in (1), when the angle of the side surface of the photoelectric conversion layer in contact with the upper surface of the lower electrode is θ2, θ2 is less than 90 °.
The present invention is described in detail below.

FIG. 1 is a sectional view schematically showing an example of a conventional solar cell (organic solar cell).
As shown in FIG. 1, in general, a conventional solar cell 1 ′ has a plurality of solar cells on a substrate 2 ′, and each of the plurality of solar cells has a lower electrode 3 ′. And a laminated body having an upper electrode 4 ′ and a photoelectric conversion layer 5 ′ disposed between the lower electrode 3 ′ and the upper electrode 4 ′. The plurality of solar cells are electrically connected by connecting the upper electrode 4 ′ to the lower electrode 3 ′ of the adjacent solar cell. If necessary, a barrier layer 6 ′ that covers the upper electrode 4 ′ and seals the plurality of solar cells is formed.

When manufacturing a conventional solar cell (organic solar cell) as shown in FIG. 1, generally, after forming a lower electrode on the entire surface of the substrate, patterning the lower electrode (1), the substrate A step (2) of patterning the photoelectric conversion layer after forming a photoelectric conversion layer on the entire surface of the sample on which the lower electrode is provided, and a sample in which the lower electrode and the photoelectric conversion layer are provided on the substrate After forming the upper electrode on the entire surface, a step (3) of patterning the upper electrode is performed. The inventors of the present invention have studied the reason why the organic solar cell is inferior in the high temperature and high humidity durability when the organic / inorganic perovskite compound is used, and the organic solar cell is extremely thin compared to other solar cells. When the upper electrode is formed in the step (3), the upper electrode may not sufficiently cover the photoelectric conversion layer. As a result, the organic / inorganic perovskite compound deteriorates due to moisture permeation, and sufficient high temperature and humidity It was found that durability could not be obtained. In addition, since an organic-inorganic perovskite compound is very weak to moisture, an organic solar cell whose photoelectric conversion layer includes such an organic-inorganic perovskite compound has a higher temperature and humidity than other solar cells (for example, CIGS solar cells). Low durability tends to be a problem.
FIG. 2 is a cross-sectional view schematically showing an example of a conventional solar cell (organic solar cell) where the upper electrode cannot sufficiently cover the photoelectric conversion layer. In FIG. 2, the upper electrode 4 ′ does not sufficiently cover the photoelectric conversion layer 5 ′, and the side surface of the photoelectric conversion layer 5 ′ is exposed or the corner portion of the photoelectric conversion layer 5 ′ is exposed. doing.
In contrast, in the cross-sectional view of the solar cell observed with an electron microscope, the present inventors adjust θ2 to a specific range when the angle of the side surface of the photoelectric conversion layer in contact with the upper surface of the lower electrode is θ2. By making the angle gentle, the upper electrode can sufficiently cover the photoelectric conversion layer when forming the upper electrode, and as a result, it has been found that high high temperature and high humidity durability can be obtained, The present invention has been completed.

The solar cell of the present invention has a plurality of solar cells on a substrate.
The said board | substrate is not specifically limited, For example, transparent glass substrates, such as soda-lime glass and an alkali free glass, a ceramic substrate, a transparent plastic substrate, a metal substrate, etc. are mentioned.

Each of the plurality of solar cells is composed of a laminated body having a lower electrode, an upper electrode, and a photoelectric conversion layer disposed between the lower electrode and the upper electrode. The plurality of solar cells are electrically connected by the upper electrode being connected to the lower electrode of an adjacent solar cell.

In the solar cell of the present invention, in the cross-sectional view of the solar cell of the present invention observed with an electron microscope, θ1 is less than 90 ° when the angle of the side surface of the lower electrode in contact with the upper surface of the substrate is θ1. It is preferable.
By adjusting θ1 within the above range to a gentle angle, the photoelectric conversion layer can sufficiently cover the lower electrode when the photoelectric conversion layer is formed. As a result, it is possible to prevent the side surface of the lower electrode from being exposed and the corner portion of the lower electrode from being exposed, and the upper electrode and the lower electrode are in contact with each other, thereby causing variations in photoelectric conversion efficiency. It can be prevented from occurring. A more preferable upper limit of θ1 is 85 °. The lower limit of θ1 is not particularly limited, but a preferable lower limit is 10 °. When θ1 is 85 ° or less, the photoelectric conversion layer can more fully cover the lower electrode. A more preferable lower limit of θ1 is 20 °.

In the solar cell of the present invention, in the cross-sectional view of the solar cell of the present invention observed with an electron microscope, θ2 is less than 90 ° when the angle of the side surface of the photoelectric conversion layer in contact with the upper surface of the lower electrode is θ2. It is. When the solar cell of the present invention has an electron transport layer and / or a hole transport layer, the side surface of the layer including the electron transport layer, the photoelectric conversion layer, and the hole transport layer in contact with the upper surface of the lower electrode. Is defined as θ2.
By adjusting θ2 to the above range so as to have a gentle angle, the upper electrode can sufficiently cover the photoelectric conversion layer when the upper electrode is formed. As a result, it is possible to prevent the side surface of the photoelectric conversion layer from being exposed or the corner portion of the photoelectric conversion layer from being exposed, and even if the photoelectric conversion layer contains an organic-inorganic perovskite compound. It is possible to suppress deterioration of the organic / inorganic perovskite compound due to moisture permeation and to obtain high high temperature and high humidity durability. A preferable upper limit of θ2 is 85 °. The lower limit of θ2 is not particularly limited, but a preferable lower limit is 20 °. If θ2 is 85 ° or less, the upper electrode can more fully cover the photoelectric conversion layer.

In the cross-sectional view of the solar cell of the present invention observed with the electron microscope, the angle of the side surface of the upper electrode in contact with the upper surface of the photoelectric conversion layer may also be less than 90 °.

As a method of measuring θ1 and θ2, a cross section perpendicular to the horizontal plane of the solar cell of the present invention at an magnification of 50,000 to 500,000 times using an electron microscope (for example, S-4800, manufactured by HITACHI, etc.) A method of calculating θ1 and θ2 by observing the figure and using image analysis software from the obtained photograph can be adopted.
If the upper surface of the substrate, the side surface of the lower electrode, the upper surface of the lower electrode, the side surface of the photoelectric conversion layer, etc. are not smooth, for example, if they are wavy, correction by an approximate straight line is performed as follows: Yes, θ1 and θ2 can be measured as being smooth.
That is, when the upper surface of the substrate or the lower electrode is not smooth, arbitrary 10 points on the image corresponding to the upper portion of the substrate or the lower electrode are selected, and a straight line is approximated by the least square method. When the side surface of the lower electrode is not smooth, each of the quadrant of the average thickness of the lower electrode obtained from the approximate straight line obtained by the method and the boundary line between the lower electrode and the photoelectric conversion layer A straight line is approximated by the method of least squares using three points as intersections. Even when the side surface of the photoelectric conversion layer is not smooth, a straight line is approximated as in the case of the lower electrode.

As a method of adjusting θ1 and θ2 to the above range, for example, a method of selecting and adjusting a patterning method can be mentioned. Specifically, for example, when patterning the lower electrode and the photoelectric conversion layer by mechanical scribe, there are a method of adjusting by the type of scribe tool, a method of adjusting by scribe pressure, and the like. Moreover, when patterning the said lower electrode and the said photoelectric converting layer by laser scribe, the method etc. which adjust with processing speed, a shot pitch, a laser irradiation diameter, a pulse width, laser intensity, etc. are mentioned.

In FIG. 3, sectional drawing which shows typically an example of the solar cell of this invention is shown.
As shown in FIG. 3, the solar cell 1 of the present invention has a plurality of solar cells on a substrate 2, and the plurality of solar cells are respectively a lower electrode 3, an upper electrode 4, It consists of a laminated body which has the photoelectric converting layer 5 arrange | positioned between the lower electrode 3 and the upper electrode 4. FIG. The plurality of solar cells are electrically connected by the upper electrode 4 being connected to the lower electrode 3 of the adjacent solar cell. If necessary, a barrier layer 6 that covers the upper electrode 4 and seals the plurality of solar cells is formed.
In the solar cell 1 of the present invention, when the angle of the side surface of the photoelectric conversion layer 5 in contact with the upper surface of the lower electrode 3 is θ2, θ2 is less than 90 °. Furthermore, when the angle of the side surface of the lower electrode 3 in contact with the upper surface of the substrate 2 is θ1, it is preferable that θ1 is less than 90 °.

In the cross-sectional view of the solar cell of the present invention observed with the electron microscope, the shape of the lower electrode and / or the shape of the photoelectric conversion layer is a trapezoidal shape in which the length of the upper base is shorter than the length of the lower base It is preferable that The upper base means the side opposite to the substrate, and the lower base means the side on the substrate side.
As a method for observing the shape of the lower electrode and the shape of the photoelectric conversion layer, the sun of the present invention is used at an magnification of 50,000 to 500,000 times using an electron microscope (for example, S-4800, manufactured by HITACHI). A method of observing a cross-sectional view perpendicular to the horizontal plane of the battery and observing the shape from the obtained photograph can be employed.
For example, in the case of the shape of the lower electrode, the length of the contact surface between the substrate and the lower electrode is the length of the lower base, and the contact surface between the lower electrode and the photoelectric conversion layer is parallel to the lower base. The length of the area is defined as the length of the upper base.

Either the lower electrode or the upper electrode may be a cathode or an anode. Examples of the material of the lower electrode and the upper electrode include FTO (fluorine-doped tin oxide), sodium, sodium-potassium alloy, lithium, magnesium, aluminum, magnesium-silver mixture, magnesium-indium mixture, aluminum-lithium alloy, Al / Al ₂ O ₃ mixture, Al / LiF mixture, metal such as gold, CuI, ITO (indium tin oxide), SnO ₂ , AZO (aluminum zinc oxide), IZO (indium zinc oxide), GZO (gallium zinc) Conductive transparent materials such as oxides) and conductive transparent polymers. These materials may be used alone or in combination of two or more.

The photoelectric conversion layer contains an organic inorganic perovskite compound represented by the general formula R-M-X ₃ (where R is an organic molecule, M is a metal atom, and X is a halogen atom or a chalcogen atom). preferable. By using the organic-inorganic perovskite compound for the photoelectric conversion layer, the photoelectric conversion efficiency of the solar cell can be improved.
In the present specification, “layer” means not only a layer having a clear boundary but also a layer having a concentration gradient in which the contained elements gradually change. In addition, the elemental analysis of a layer can be performed by performing the FE-TEM / EDS ray analysis measurement of the cross section of a solar cell, and confirming the element distribution of a specific element etc., for example. In addition, in this specification, a layer means not only a flat thin film-like layer but also a layer that can form a complicated and complicated structure together with other layers.

The R is an organic molecule, and is preferably represented by C ₁ N _m H _n (l, m, and n are all positive integers).
Specifically, R is, for example, methylamine, ethylamine, propylamine, butylamine, pentylamine, hexylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, dipentylamine, dihexylamine, trimethylamine, triethylamine, tripropyl. Amine, tributylamine, tripentylamine, trihexylamine, ethylmethylamine, methylpropylamine, butylmethylamine, methylpentylamine, hexylmethylamine, ethylpropylamine, ethylbutylamine, imidazole, azole, pyrrole, aziridine, azirine, Azetidine, azeto, imidazoline, carbazole, methylcarboxyamine, ethylcarboxyamine, propylcarboxyamine, butyl Rubokishiamin, pentyl carboxyamine, hexyl carboxyamine, formamidinium, guanidine, aniline, pyridine and these ions (e.g., 3 _{NH 3)} such as methyl ammonium (CH) and the like or phenethyl ammonium and the like. Of these, methylamine, ethylamine, propylamine, propylcarboxyamine, butylcarboxyamine, pentylcarboxyamine, formamidinium, guanidine and their ions are preferred, and methylamine, ethylamine, pentylcarboxyamine, formamidinium, guanidine and These ions are more preferred. Among these, methylamine, formamidinium, and these ions are more preferable because high photoelectric conversion efficiency can be obtained.

M is a metal atom, for example, lead, tin, zinc, titanium, antimony, bismuth, nickel, iron, cobalt, silver, copper, gallium, germanium, magnesium, calcium, indium, aluminum, manganese, chromium, molybdenum, Europium etc. are mentioned. Among these, lead or tin is preferable from the viewpoint of overlapping of electron orbits. These metal atoms may be used independently and 2 or more types may be used together.

X is a halogen atom or a chalcogen atom, and examples thereof include chlorine, bromine, iodine, sulfur, and selenium. These halogen atoms or chalcogen atoms may be used alone or in combination of two or more. Among these, the halogen atom is preferable because the organic / inorganic perovskite compound becomes soluble in an organic solvent and can be applied to an inexpensive printing method by containing halogen in the structure. Furthermore, iodine is more preferable because the energy band gap of the organic-inorganic perovskite compound becomes narrow.

The organic / inorganic perovskite compound preferably has a cubic structure in which a metal atom M is disposed at the body center, an organic molecule R is disposed at each vertex, and a halogen atom or a chalcogen atom X is disposed at the face center.
FIG. 4 shows an example of a crystal structure of an organic / inorganic perovskite compound having a cubic structure in which a metal atom M is arranged at the body center, an organic molecule R is arranged at each vertex, and a halogen atom or a chalcogen atom X is arranged at the face center. It is a schematic diagram. Although details are not clear, since the orientation of the octahedron in the crystal lattice can be easily changed by having the structure described above, the mobility of electrons in the organic-inorganic perovskite compound is increased, and the photoelectric properties of the solar cell are increased. It is estimated that the conversion efficiency is improved.

The organic / inorganic perovskite compound is preferably a crystalline semiconductor. The crystalline semiconductor means a semiconductor capable of measuring the X-ray scattering intensity distribution and detecting a scattering peak.
If the organic / inorganic perovskite compound is a crystalline semiconductor, the mobility of electrons in the organic / inorganic perovskite compound is increased, and the photoelectric conversion efficiency of the solar cell is improved. In addition, if the organic / inorganic perovskite compound is a crystalline semiconductor, it is easy to suppress a decrease in photoelectric conversion efficiency (photodegradation) caused by continuing to irradiate light on a solar cell, particularly a photodegradation due to a decrease in short-circuit current. .

In addition, the degree of crystallization can be evaluated as an index of crystallization. The degree of crystallinity is determined by separating the crystalline-derived scattering peak detected by the X-ray scattering intensity distribution measurement and the halo derived from the amorphous part by fitting, obtaining the respective intensity integrals, Can be obtained by calculating the ratio.
A preferable lower limit of the crystallinity of the organic-inorganic perovskite compound is 30%. If the crystallinity is 30% or more, the mobility of electrons in the organic / inorganic perovskite compound is increased, and the photoelectric conversion efficiency of the solar cell is improved. Moreover, if the said crystallinity is 30% or more, it will become easy to suppress the photodegradation resulting from the fall (photodegradation) of photoelectric conversion efficiency by continuing irradiating a solar cell with light, especially the fall of a short circuit current. A more preferred lower limit of the crystallinity is 50%, and a more preferred lower limit is 70%.
Examples of a method for increasing the crystallinity of the organic / inorganic perovskite compound include thermal annealing (heat treatment), irradiation with intense light such as a laser, and plasma irradiation.

The crystallite diameter can also be evaluated as another crystallization index. The crystallite diameter can be calculated by the holder-Wagner method from the half-value width of the scattering peak derived from the crystalline substance detected by the X-ray scattering intensity distribution measurement.
When the crystallite diameter of the organic / inorganic perovskite compound is 5 nm or more, a decrease in photoelectric conversion efficiency (photodegradation) caused by continuing to irradiate light to the solar cell, particularly a photodegradation due to a decrease in short-circuit current is suppressed. . Further, the mobility of electrons in the organic / inorganic perovskite compound is increased, and the photoelectric conversion efficiency of the solar cell is improved. A more preferred lower limit of the crystallite diameter is 10 nm, and a more preferred lower limit is 20 nm.

The photoelectric conversion layer may further contain an organic semiconductor or an inorganic semiconductor in addition to the organic / inorganic perovskite compound as long as the effects of the present invention are not impaired.
Examples of the organic semiconductor include compounds having a thiophene skeleton such as poly (3-alkylthiophene). In addition, for example, conductive polymers having a polyparaphenylene vinylene skeleton, a polyvinyl carbazole skeleton, a polyaniline skeleton, a polyacetylene skeleton, and the like can be given. Further, for example, a compound having a porphyrin skeleton such as a phthalocyanine skeleton, a naphthalocyanine skeleton, a pentacene skeleton, or a benzoporphyrin skeleton, a spirobifluorene skeleton, or the like, or a carbon-containing material such as a carbon nanotube, graphene, or fullerene that may be surface-modified. Also mentioned.

Examples of the inorganic semiconductor include titanium oxide, zinc oxide, indium oxide, tin oxide, gallium oxide, tin sulfide, indium sulfide, zinc sulfide, CuSCN, Cu ₂ O, CuI, MoO ₃ , V ₂ O ₅ , WO ₃ , _{MoS 2, MoSe 2, Cu 2} S , and the like.

In the case where the photoelectric conversion layer includes the organic-inorganic perovskite compound and the organic semiconductor or the inorganic semiconductor, the photoelectric conversion layer is a laminated body in which a thin-film organic semiconductor or an inorganic semiconductor portion and a thin-film organic-inorganic perovskite compound portion are stacked. Alternatively, a composite film in which an organic semiconductor or inorganic semiconductor part and an organic / inorganic perovskite compound part are combined may be used. A laminated body is preferable in that the production method is simple, and a composite film is preferable in that the charge separation efficiency in the organic semiconductor or the inorganic semiconductor can be improved.

The preferable lower limit of the thickness of the thin-film organic / inorganic perovskite compound site is 5 nm, and the preferable upper limit is 5000 nm. If the thickness is 5 nm or more, light can be sufficiently absorbed, and the photoelectric conversion efficiency is increased. If the said thickness is 5000 nm or less, since it can suppress that the area | region which cannot carry out charge separation generate | occur | produces, it will lead to the improvement of photoelectric conversion efficiency. The more preferable lower limit of the thickness is 10 nm, the more preferable upper limit is 1000 nm, the still more preferable lower limit is 20 nm, and the still more preferable upper limit is 500 nm.

When the photoelectric conversion layer is a composite film in which an organic semiconductor or an inorganic semiconductor part and an organic / inorganic perovskite compound part are combined, a preferable lower limit of the thickness of the composite film is 30 nm, and a preferable upper limit is 3000 nm. If the thickness is 30 nm or more, light can be sufficiently absorbed, and the photoelectric conversion efficiency is increased. If the said thickness is 3000 nm or less, since it becomes easy to reach | attain an electrode, a photoelectric conversion efficiency becomes high. The more preferable lower limit of the thickness is 40 nm, the more preferable upper limit is 2000 nm, the still more preferable lower limit is 50 nm, and the still more preferable upper limit is 1000 nm.

The photoelectric conversion layer is preferably subjected to thermal annealing (heat treatment) after the photoelectric conversion layer is formed. By performing thermal annealing (heat treatment), the degree of crystallinity of the organic-inorganic perovskite compound in the photoelectric conversion layer can be sufficiently increased, and the decrease in photoelectric conversion efficiency (photodegradation) due to continued irradiation with light is further increased. Can be suppressed. When such thermal annealing (heating treatment) is performed on a solar cell using a flexible base material made of a conventional heat-resistant polymer material as the substrate, due to the difference in linear expansion coefficient between the flexible base material and the photoelectric conversion layer, etc. Distortion may occur during annealing, and as a result, it may be difficult to achieve high photoelectric conversion efficiency. In contrast, by using a metal substrate (for example, a metal foil such as an aluminum foil) as the substrate, even if thermal annealing (heat treatment) is performed, distortion is minimized and high photoelectric conversion efficiency is achieved. Can be obtained.

When performing the thermal annealing (heat treatment), the temperature for heating the photoelectric conversion layer is not particularly limited, but is preferably 100 ° C. or higher and lower than 200 ° C. When the heating temperature is 100 ° C. or higher, the crystallinity of the organic / inorganic perovskite compound can be sufficiently increased. If the said heating temperature is less than 200 degreeC, it can heat-process, without thermally degrading the said organic-inorganic perovskite compound. A more preferable heating temperature is 120 ° C. or higher and 170 ° C. or lower. The heating time is not particularly limited, but is preferably 3 minutes or longer and 2 hours or shorter. When the heating time is 3 minutes or longer, the crystallinity of the organic-inorganic perovskite compound can be sufficiently increased. If the heating time is within 2 hours, the organic inorganic perovskite compound can be heat-treated without causing thermal degradation.
These heating operations are preferably performed in a vacuum or under an inert gas, and the dew point temperature is preferably 10 ° C or lower, more preferably 7.5 ° C or lower, and further preferably 5 ° C or lower.

The solar cell of this invention may have an electron carrying layer between the electrode used as the cathode of the said lower electrode and the said upper electrode, and the said photoelectric converting layer.
The material of the electron transport layer is not particularly limited. For example, N-type conductive polymer, N-type low molecular organic semiconductor, N-type metal oxide, N-type metal sulfide, alkali metal halide, alkali metal, surface activity Specific examples include, for example, cyano group-containing polyphenylene vinylene, boron-containing polymer, bathocuproine, bathophenanthrene, hydroxyquinolinato aluminum, oxadiazole compound, benzimidazole compound, naphthalene tetracarboxylic acid compound, perylene derivative, Examples include phosphine oxide compounds, phosphine sulfide compounds, fluoro group-containing phthalocyanines, titanium oxide, zinc oxide, indium oxide, tin oxide, gallium oxide, tin sulfide, indium sulfide, and zinc sulfide.

The electron transport layer may consist of only a thin film electron transport layer (buffer layer), but preferably includes a porous electron transport layer. In particular, when the photoelectric conversion layer is a composite film in which an organic semiconductor or an inorganic semiconductor part and an organic / inorganic perovskite compound part are combined, a more complex composite film (a more complicated structure) is obtained, and the photoelectric conversion efficiency Therefore, the composite film is preferably formed on the porous electron transport layer.

The preferable lower limit of the thickness of the electron transport layer is 1 nm, and the preferable upper limit is 2000 nm. If the thickness is 1 nm or more, holes can be sufficiently blocked. If the said thickness is 2000 nm or less, it will become difficult to become resistance at the time of electron transport, and photoelectric conversion efficiency will become high. The more preferable lower limit of the thickness of the electron transport layer is 3 nm, the more preferable upper limit is 1000 nm, the still more preferable lower limit is 5 nm, and the still more preferable upper limit is 500 nm.

The solar cell of the present invention may have a hole transport layer between the photoelectric conversion layer and an electrode serving as an anode of the lower electrode and the upper electrode.
The material of the hole transport layer is not particularly limited, and examples thereof include a P-type conductive polymer, a P-type low molecular organic semiconductor, a P-type metal oxide, a P-type metal sulfide, and a surfactant. Examples include compounds having a thiophene skeleton such as poly (3-alkylthiophene). In addition, for example, conductive polymers having a triphenylamine skeleton, a polyparaphenylene vinylene skeleton, a polyvinyl carbazole skeleton, a polyaniline skeleton, a polyacetylene skeleton, and the like can be given. Further, for example, compounds having a porphyrin skeleton such as phthalocyanine skeleton, naphthalocyanine skeleton, pentacene skeleton, benzoporphyrin skeleton, spirobifluorene skeleton, etc., molybdenum oxide, vanadium oxide, tungsten oxide, nickel oxide, copper oxide, tin oxide, sulfide Examples thereof include molybdenum, tungsten sulfide, copper sulfide, tin sulfide, etc., fluoro group-containing phosphonic acid, carbonyl group-containing phosphonic acid, copper compounds such as CuSCN and CuI, and carbon-containing materials such as carbon nanotubes and graphene.

A part of the hole transport layer may be immersed in the photoelectric conversion layer, or may be disposed in a thin film shape on the photoelectric conversion layer. The thickness when the hole transport layer is in the form of a thin film has a preferred lower limit of 1 nm and a preferred upper limit of 2000 nm. If the thickness is 1 nm or more, electrons can be sufficiently blocked. If the said thickness is 2000 nm or less, it will become difficult to become resistance at the time of hole transport, and a photoelectric conversion efficiency will become high. The more preferable lower limit of the thickness is 3 nm, the more preferable upper limit is 1000 nm, the still more preferable lower limit is 5 nm, and the still more preferable upper limit is 500 nm.

The solar cell of the present invention may further have a barrier layer that covers the upper electrode and seals the plurality of solar cells.
The material of the barrier layer is not particularly limited as long as it has a barrier property, and examples thereof include a thermosetting resin, a thermoplastic resin, and an inorganic material.

Examples of the thermosetting resin or thermoplastic resin, epoxy resin, acrylic resin, silicone over emissions resins, phenol resins, melamine resins, urea resins, butyl rubber, polyester, polyurethane, polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyvinyl alcohol , Polyvinyl acetate, ABS resin, polybutadiene, polyamide, polycarbonate, polyimide, polyisobutylene and the like.

When the material of the barrier layer is a thermosetting resin or a thermoplastic resin, the barrier layer (resin layer) has a preferable lower limit of 100 nm and a preferable upper limit of 100,000 nm. A more preferable lower limit of the thickness is 500 nm, a more preferable upper limit is 50000 nm, a still more preferable lower limit is 1000 nm, and a still more preferable upper limit is 20000 nm.

Examples of the inorganic material include Si, Al, Zn, Sn, In, Ti, Mg, Zr, Ni, Ta, W, Cu, or an oxide, nitride, or oxynitride of an alloy containing two or more of these. . Among these, in order to impart water vapor barrier properties and flexibility to the barrier layer, oxides, nitrides, or oxynitrides of metal elements including both metal elements of Zn and Sn are preferable.

When the material of the barrier layer is an inorganic material, the barrier layer (inorganic layer) has a preferable lower limit of 30 nm and a preferable upper limit of 3000 nm. When the thickness is 30 nm or more, the inorganic layer can have a sufficient water vapor barrier property, and the durability of the solar cell is improved. If the thickness is 3000 nm or less, even if the thickness of the inorganic layer is increased, the generated stress is small, and therefore, the peeling between the inorganic layer and the laminate can be suppressed. The more preferable lower limit of the thickness is 50 nm, the more preferable upper limit is 1000 nm, the still more preferable lower limit is 100 nm, and the still more preferable upper limit is 500 nm.
The thickness of the inorganic layer can be measured using an optical interference film thickness measuring device (for example, FE-3000 manufactured by Otsuka Electronics Co., Ltd.).

Of the materials for the barrier layer, a method for sealing the plurality of solar cells with the thermosetting resin or thermoplastic resin is not particularly limited. For example, the plurality of the plurality of the solar cells using a sheet-shaped barrier layer material. A method of sealing solar cells, a method of applying a solution obtained by dissolving a material of a barrier layer in an organic solvent to the plurality of solar cells, and after applying a liquid monomer to be a barrier layer to the plurality of solar cells, Examples thereof include a method of crosslinking or polymerizing a liquid monomer with heat or UV, a method of cooling the material of the barrier layer by applying heat to the material, and then cooling.

Of the materials for the barrier layer, vacuum deposition, sputtering, gas phase reaction (CVD), and ion plating are preferred as methods for covering the plurality of solar cells with the inorganic material. Of these, the sputtering method is preferable for forming a dense layer, and the DC magnetron sputtering method is more preferable among the sputtering methods.
In the sputtering method, an inorganic layer made of an inorganic material can be formed by depositing a raw material on the plurality of solar cells and forming a film using a metal target and oxygen gas or nitrogen gas as a raw material. it can.
The barrier layer material may be a combination of the thermosetting resin or thermoplastic resin and the inorganic material.

In the solar cell of the present invention, the barrier layer may be covered with another material such as a resin film, a resin film coated with an inorganic material, or a metal foil. That is, the solar cell of the present invention may be configured such that the space between the plurality of solar cells and the other material is sealed, filled, or adhered by the barrier layer. Thereby, even if there is a pinhole in the barrier layer, water vapor can be sufficiently blocked, and the durability of the solar cell can be further improved.

The method for producing the solar cell of the present invention is not particularly limited. For example, after forming the lower electrode on the entire surface of the substrate, patterning the lower electrode (1), a sample in which the lower electrode is provided on the substrate After forming the photoelectric conversion layer on the entire surface of the substrate, the step (2) of patterning the photoelectric conversion layer, and after forming the upper electrode on the entire surface of the sample provided with the lower electrode and the photoelectric conversion layer on the substrate And a method having a step (3) of patterning the upper electrode. Furthermore, you may perform the process (4) of forming the barrier layer which covers an upper electrode and seals the said several photovoltaic cell.
As a method for adjusting θ1 and θ2 within the above ranges in the steps (1) and (2), for example, as described above, when patterning the lower electrode and the photoelectric conversion layer by mechanical scribing, scribing is performed. The method of adjusting by the kind of tool of this, the method of adjusting by scribe pressure, etc. are mentioned. Moreover, when patterning the said lower electrode and the said photoelectric converting layer by laser scribe, the method etc. which adjust with processing speed, a shot pitch, a laser irradiation diameter, a pulse width, laser intensity, etc. are mentioned.

ADVANTAGE OF THE INVENTION According to this invention, the solar cell excellent in high temperature, high humidity durability can be provided.

It is sectional drawing which shows an example of the conventional solar cell typically. It is sectional drawing which shows typically an example when the upper electrode has not fully covered the photoelectric converting layer in the conventional solar cell. It is sectional drawing which shows typically an example of the solar cell of this invention. It is a schematic diagram which shows an example of the crystal structure of an organic inorganic perovskite compound.

Hereinafter, embodiments of the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

Example 1
(1) Manufacture of solar cell An FTO film having a thickness of 1000 nm was formed as a cathode on a glass substrate, ultrasonically washed with pure water, acetone, and methanol in this order for 10 minutes each and then dried. At this time, masking tape was used to mask the portions other than the etched portion, and zinc powder was placed on the exposed portion, and further a 10% diluted hydrochloric acid aqueous solution was applied to perform patterning of the cathode (patterning method: etching).

A titanium isopropoxide ethanol solution adjusted to 2% was applied on the surface of the FTO film by a spin coating method, followed by baking at 400 ° C. for 10 minutes to form a thin-film electron transport layer having a thickness of 20 nm. Further, a titanium oxide paste containing polyisobutyl methacrylate as an organic binder and titanium oxide (a mixture of an average particle size of 10 nm and 30 nm) is applied onto the thin film electron transport layer by a spin coat method, and then heated to 500 ° C. Was fired for 10 minutes to form a porous electron transport layer having a thickness of 500 nm.

Next, lead iodide as a metal halide compound was dissolved in N, N-dimethylformamide (DMF) to prepare a 1M solution, and a film was formed on the porous electron transport layer by a spin coating method. Further, methylammonium iodide as an amine compound was dissolved in 2-propanol to prepare a 1M solution. A sample containing CH ₃ NH ₃ PbI ₃ which is an organic / inorganic perovskite compound was immersed in this solution to immerse the sample formed with the above lead iodide, and annealed at 120 ° C. for 30 minutes. Processed.

Next, a solution was prepared by dissolving 68 mM Spiro-OMeTAD (having a spirobifluorene skeleton), 55 mM t-butylpyridine, and 9 mM bis (trifluoromethylsulfonyl) imide / silver salt in 25 μL of chlorobenzene. This solution was applied onto the photoelectric conversion layer by a spin coating method to form a hole transport layer having a thickness of 150 nm.

Then, patterning of the combined electron transport layer, photoelectric conversion layer, and hole transport layer ((patterning method: mechanical scribe) was performed with a mechanical scriber. In patterning, the type of scribe tool and the scribe pressure were adjusted. As a result, the angle θ2 of the side surface of the layer including the electron transport layer, the photoelectric conversion layer, and the hole transport layer in contact with the upper surface of the cathode was adjusted.

On the obtained hole transport layer, an ITO film having a thickness of 100 nm was formed by vacuum deposition as an anode. At this time, patterning of the anode was performed using a tool having a tool width of 40 μm and a land of 150 μm in a mechanical scribing machine.

A barrier layer made of ZnSnO with a thickness of 100 nm was formed on the obtained anode by a sputtering method to obtain a solar cell.

(2) Observation of solar cell by electron microscope Using a scanning electron microscope (S-4800, manufactured by HITACHI) at a magnification of 50,000 times, a cross-sectional view perpendicular to the horizontal plane of the obtained solar cell was observed and obtained. Θ1 and θ2 were calculated from the obtained photographs using image analysis software. Further, the shape of the cathode (in Table 1, the shape of the lower electrode) and the shape of the layer including the electron transport layer, the photoelectric conversion layer, and the hole transport layer (in Table 1, the shape of the photoelectric conversion layer) were observed. The results are shown in Table 1. In addition, about the shape, it described in Table 1 as trapezoid shape or non-trapezoid (thing which is not trapezoid shape).

(Example 2)
On a glass substrate, an aluminum film having a thickness of 100 nm as a cathode and a titanium film having a thickness of 100 nm as an electron transport layer were formed by vapor deposition, and patterning (patterning method: mechanical scribe) between the cathode and the electron transport layer was performed by a mechanical scriber. Except for this, a solar cell was obtained in the same manner as in Example 1.

(Example 3)
A solar cell was obtained in the same manner as in Example 2 except that an anodized aluminum base material (in Table 1, an aluminum base material) was used instead of the glass substrate.

Example 4
A FTO film having a thickness of 1000 nm as a cathode on a glass substrate was covered with a mask simulating patterning and formed by the spray pyrolysis deposition method (patterning method: mask film formation), as in Example 1. Thus, a solar cell was obtained.

(Example 5)
Example 2 except that patterning (patterning method: laser scribing) was performed with a laser scribing machine at a processing speed of 1200 mm / s and a shot pitch of 5 μm in patterning the layer including the electron transport layer, the photoelectric conversion layer, and the hole transport layer. In the same manner, a solar cell was obtained.

(Comparative Example 1)
In the patterning of the layer including the electron transport layer, the photoelectric conversion layer, and the hole transport layer, except that the shape of the tool of the mechanical scriber was scooped (patterning method: mechanical scribe), the same as in Example 4 A solar cell was obtained.

(Comparative Example 2)
Example 2 except that patterning (patterning method: laser scribing) was performed with a laser scribing machine at a processing speed of 400 mm / s and a shot pitch of 1 μm in the patterning of the layer including the electron transport layer, the photoelectric conversion layer, and the hole transport layer. In the same manner, a solar cell was obtained.

<Evaluation>
The following evaluation was performed about the solar cell obtained by the Example and the comparative example. The results are shown in Table 1.

(1) Variation in photoelectric conversion efficiency A power source (manufactured by KEITHLEY, 236 model) is connected between the electrodes of the solar cell, and a solar simulation (manufactured by Yamashita Denso Co., Ltd.) with an intensity of 100 mW / cm ² is used and an exposure area of 0.01 cm ^2. The photoelectric conversion efficiency was measured. Ten samples were prepared and measured, σ was obtained by the following formula, and variations in photoelectric conversion efficiency were determined.

The case where the above value was less than 0.3 was marked with ◯, and the case where the value was 0.3 or more was marked with Δ.

(2) power between a high-temperature and high-humidity durability solar cell electrodes (KEITHLEY Co., 236 model) connected to, using a solar simulation of intensity 100 mW / cm ² (manufactured by Yamashita Denso Corporation), exposure area 0.01 cm ² The photoelectric conversion efficiency was measured by using the obtained photoelectric conversion efficiency as the initial conversion efficiency. Thereafter, the solar cell was placed in an environment of 85 ° C. and a humidity of 85% for 100 hours to conduct a high temperature and high humidity durability test. Similarly to the initial conversion efficiency, the photoelectric conversion efficiency after the high temperature and high humidity durability test was measured, and the value of the photoelectric conversion efficiency / initial conversion efficiency after the high temperature and high humidity durability test was determined.
○: The value of photoelectric conversion efficiency / initial conversion efficiency after high-temperature and high-humidity durability test is 0.8 or more ×: The value of photoelectric conversion efficiency / initial conversion efficiency after high-temperature and high-humidity durability test is less than 0.8

ADVANTAGE OF THE INVENTION According to this invention, the solar cell excellent in high temperature, high humidity durability can be provided.

DESCRIPTION OF SYMBOLS 1 Solar cell 1 'of this invention Conventional solar cell 2, 2' Substrate 3, 3 'Lower electrode 4, 4' Upper electrode 5, 5 'Photoelectric conversion layer 6, 6' Barrier layer

Claims (5)

A solar cell having a plurality of solar cells on a substrate,
Each of the plurality of solar cells comprises a laminate having a lower electrode, an upper electrode, and a photoelectric conversion layer disposed between the lower electrode and the upper electrode,
The plurality of solar cells are electrically connected by connecting the upper electrode to the lower electrode of an adjacent solar cell,
In the cross-sectional view of the solar cell observed with an electron microscope, when the angle of the side surface of the photoelectric conversion layer in contact with the upper surface of the lower electrode is θ2, θ2 is less than 90 °. 2. The solar cell according to claim 1, wherein in a cross-sectional view of the solar cell observed with an electron microscope, θ <b> 1 is less than 90 °, where θ <b> 1 is an angle of a side surface of the lower electrode that is in contact with the upper surface of the substrate. In the cross-sectional view of the solar cell observed with an electron microscope, the shape of the lower electrode and / or the shape of the photoelectric conversion layer is a trapezoidal shape in which the length of the upper base is shorter than the length of the lower base. The solar cell according to claim 1 or 2. The photoelectric conversion layer includes an organic inorganic perovskite compound represented by the general formula R-M-X ₃ (where R is an organic molecule, M is a metal atom, and X is a halogen atom or a chalcogen atom). The solar cell according to claim 1, 2, or 3. Furthermore, it has a barrier layer which covers a top electrode and seals a several photovoltaic cell, The solar cell of Claim 1, 2, 3 or 4 characterized by the above-mentioned.

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