KR20120137939A

KR20120137939A - Solar cell having excellent stability at high temperature

Info

Publication number: KR20120137939A
Application number: KR1020110057118A
Authority: KR
Inventors: 박영준; 김경보; 백제훈; 김종상
Original assignee: 주식회사 포스코
Priority date: 2011-06-13
Filing date: 2011-06-13
Publication date: 2012-12-24
Also published as: KR101294972B1

Abstract

PURPOSE: A solar cell having excellent stability at high temperatures is provided to reduce temperature changes in a semiconductor layer by including a phase change material having a high phase change enthalpy in a substrate. CONSTITUTION: A heat dissipation layer is adhered to an opposite surface of a semiconductor layer on a substrate(10). The heat dissipation layer comprises a phase change material(60) and a heat radiation resin. The phase transition material absorbs heat emitted from the substrate at high temperatures. The phase transition material releases the heat to the outside at low temperatures. The heat radiation resin fixes the phase change material.

Description

SOLAR CELL HAVING EXCELLENT STABILITY AT HIGH TEMPERATURE

The present invention relates to a solar cell excellent in high temperature stability, and more particularly, to a solar cell having good energy conversion efficiency and durability even in a high temperature external environment.

Traditional methods of collecting energy using fossil fuels are slowly reaching their limits due to global warming, depletion of fuel resources, and environmental pollution. In particular, petroleum fuels, though slightly different for every forecaster, are expected to bottom out not too long.

In addition, the Energy Climate Convention, represented by the Kyoto Protocol, requires compulsory reduction of the emissions of carbon dioxide produced by the burning of fossil fuels. Therefore, it is clear that the current consumption of fossil fuels will be limited not only in the present Contracting State but also in other countries around the world in the future.

The most representative energy source used to replace fossil fuels is nuclear power. Nuclear power has a high amount of energy that can be collected per unit weight of uranium or plutonium as a raw material, and does not generate greenhouse gases such as carbon dioxide, so it is a promising alternative energy source that can replace fossil fuels such as petroleum. Have been received.

However, the explosion of the former Soviet Chernobyl nuclear power plant and Japan's Fukushima nuclear power plant caused by the Great East Japan Earthquake led to a review of the safety of nuclear power, which has been regarded as an infinite clean energy source. The introduction of energy is more urgently needed than ever.

Hydrogen power may be used as an energy source that is widely used as other alternative energy, but the use of hydroelectric power may be limited because it is influenced by topographic and climatic factors. In addition, other alternative energy sources are also unlikely to be used as an alternative to fossil fuels due to their low power generation or largely limited use areas.

However, solar cells can be used anywhere as long as only a reasonable amount of sunshine is ensured, and the power generation capacity and equipment scale are almost linearly proportional to each other. Therefore, when used for small-capacity demands such as households, solar panels can be installed in small areas on the roof of buildings. The advantage of production is that not only is its use globally, but its research is also increasing.

The solar cell is based on the principle of a semiconductor. When a light having a certain level of energy is irradiated to a pn-bonded semiconductor, the solar cell is excited as an electronic device that can move freely. ) Is generated. The generated electrons and holes move to the electrode located on the opposite side to generate an electromotive force.

The general structure of the solar cell has a structure 50 having a lower electrode 20 / pn junction semiconductor layer 30 / upper electrode 40 layer on the substrate 10 as shown in FIG. Of course, if necessary, a transparent window or an anti-reflection film may be further included.

However, as shown in FIG. 2, the energy conversion efficiency of the semiconductor layer reacts sensitively with temperature. In other words, the conversion efficiency of the semiconductor layer generally decreases rapidly as the temperature increases, which results in a decrease in the amount of power generation due to the low energy conversion efficiency even in the solar-rich time. In addition, the high temperature operating environment adversely affects the durability of solar cells. This problem is particularly fatal for solar cells used in high temperature solar environments such as deserts.

The present invention is to solve the problems of the prior art, according to one aspect of the present invention is provided a solar cell including a substrate that does not change the temperature even in a high temperature environment.

The solar cell of the present invention for solving the above problems is a solar cell for converting sunlight into electrical energy by a semiconductor layer formed on a substrate, the material of the substrate is a metal, the heat radiation on the opposite surface of the semiconductor layer of the metal substrate A layer is attached, and the heat dissipation layer is a capsule-shaped phase change medium that absorbs heat emitted from the substrate at a high temperature and releases heat to the outside at a low temperature, and a heat dissipation resin that fixes the phase change medium and releases heat to the outside. The heat dissipation resin comprises at least one heat dissipating pigment selected from the group consisting of carbon black, graphite, iron oxide, phosphoric acid oxide, alumina, zirconia, diamond, and carbon nanotubes (CNT) to facilitate heat dissipation to the outside. It is done.

At this time, the heat radiation layer is preferably attached to the substrate so that the total thickness is 0.5 ~ 10㎛.

In addition, the phase change medium is advantageously included in the range of 1 to 40 parts by weight per 100 parts by weight of the resin composition.

As the phase change medium, it is effective to use a phase change at a temperature between room temperature and 75 ° C.

Further, the phase change medium may be n-octacoic acid, n-heptacoic acid, n-hexacoic acid, n-tetracoic acid, n-tricoic acid, n-docoic acid, n-heneicoic acid, n-acoic acid, n -It is preferable that it is 1 type, or 2 or more types chosen from nonadecane, n-octadecane, n-heptadecane, n-hexadecane, n-pentadecane, n-tetradecane, and n-tridecane.

In addition, the particle size of the phase change medium is preferably 5 ~ 500nm.

In addition, the phase change medium in the form of a capsule is advantageous to have a form in which a polymer is coated on the surface of the phase change medium.

Moreover, it is preferable that the said board | substrate is a steel substrate.

As described above, the solar cell of the present invention emits heat to the outside through the substrate and also includes a phase change medium having a high phase change enthalpy in the substrate. By slowing down, it has high energy conversion efficiency and excellent durability.

1 is a schematic cross-sectional view showing a solar structure,
2 is a graph conceptually illustrating a phenomenon in which energy conversion efficiency of a solar cell is changed according to temperature change, and
Figure 3 is a schematic cross-sectional view showing a form of a phase change medium attached to the lower portion of the substrate in the solar cell of the present invention.

Hereinafter, the present invention will be described in detail.

In order to solve the problems of the prior art, the inventors of the present invention use a metal material having high thermal conductivity as a substrate of a solar cell, and use a high phase change enthalpy to absorb heat conducted through the metal substrate. When the medium having the heat dissipation layer contacts the opposite surface of the substrate on which the semiconductor layer of the solar cell is formed, it is found that the temperature change of the solar cell can be minimized even if the external temperature change is extreme. It came.

That is, as shown in FIG. 3, the solar cell of the present invention includes a metal substrate 10 and a phase change material 60 attached to the substrate 10. It is common for the medium to undergo a phase change at a constant temperature or at a constant temperature range. At this time, during the phase change, high calories are emitted or required. This can be expressed as follows.

s (solid) → l (liquid), ΔH _s _{→ l} = H _l -H _s

In other words, when changing from a solid to a liquid, the ΔH (enthalpy change) indicates a positive value, which means that heat absorption occurred during the reaction. If the reaction is assumed to occur at a temperature of T2, and the medium is heated from T1 (<T2) to T3 (> T2), the enthalpy change of the medium is as follows.

ΔH ₁ _{→ 3} = H _l3 -H _l2 + _ΔH _s _{→ l} + H _s2 -H _s1

That is, the enthalpy change of each enthalpy is the change in enthalpy (H _s2 -H _s1 ) according to the temperature change from T1 to T2 of the solid medium, the enthalpy change (ΔH _s _{→ l} ) when the solid medium phase changes to liquid, and the liquid medium. It is expressed as the sum of enthalpy changes (H _l3 -H _l2 ) with temperature changes from T2 to T3. However, the enthalpy change according to the temperature change of each solid or liquid is represented by a value obtained by multiplying the heat capacity by the temperature change (= mCpΔT). In general, the enthalpy change according to the temperature change is the amount of heat emitted from the solar cell. It is not high enough to absorb enough, which is insufficient to slow down the temperature change of the solar cell.

However, the inventors of the present invention, when the medium causes a phase change in the temperature change section and the enthalpy due to the phase change is very large, not only sufficiently absorbs heat emitted from the solar cell, but also absorbs the heat to cause a phase change. In the meantime, since there is no change in the temperature of the medium or it becomes very slow, the present inventors have discovered that the temperature change of the solar cell can be slowed down. In the case of using the phase change medium as described above, it is possible to obtain relatively constant, high energy conversion efficiency and high durability by absorbing heat without changing the temperature in a high temperature environment such as day and releasing heat in a low temperature environment such as night. have. The medium causing the phase change (or simply, the 'phase change medium') is usually preferable to cause phase change between room temperature (25 ° C) and 75 ° C. If the temperature is too low or too high, the phase change does not occur in the temperature range of the solar cell, it is preferable to cause the phase change in the temperature range.

Phase-change media meeting these conditions include n-octacoic acid, n-heptacoic acid, n-hexacoic acid, n-tetracoic acid, n-tricoic acid, n-docoic acid, n-heneicoic acid, n-aiko Acids, n-nonadecane, n-octadecane, n-heptadecane, n-hexadecane, n-pentadecane, n-tetradecane and n-tridecane, and the like. It is adjustable by adjusting the length. However, the length or molecular weight of the suitable chain is not particularly limited in the present invention because any one having ordinary skill in the art can be selected and applied from a simple experiment or known results.

The phase change medium is preferably present in the form of a capsule. A number of such phase-change media in the form of capsules are already known in the art, but one preferred example thereof is 100 parts by weight of the phase change material in a mixture of 70 to 120 parts by weight of a polymer monomer and 60 to 100 parts by weight of an emulsifier. After dissolving, it may be added to 600 to 1000 parts by weight of water containing 1 to 5 parts by weight of an emulsifier and emulsified, and then 0.5 to 2 parts by weight of an initiator may be added, followed by polymerization.

As the polymer monomer, any polymer monomer commonly used to coat a phase change material in the art may be used, and preferably, melamine resin, urea resin, gelatin, cellulose, epoxy, polyurethane, polyamide, polyethylene, At least one polymer selected from the group consisting of polymethylmethacrylate, polyester, polystyrene and polyvinyl alcohol can be used.

When the amount of the polymer monomer is insufficient, it is difficult to sufficiently encapsulate the phase change material. On the contrary, the polymer monomer is added in an amount of 70 to 120 parts by weight based on 100 parts by weight of the phase change material. It is desirable to.

In addition, the emulsifying adjuvant is added in order to maintain a stable emulsified state, it is applicable to those commonly used in the art. Long-chain alcohols such as cetyl alcohol or stearyl alcohol may be used as the emulsification aid, and more preferably cetyl alcohol may be used.

The emulsifying aid is used 60 to 100 parts by weight with respect to 100 parts by weight of the phase change material, when the amount is less than 60 parts by weight of the capsule size increases the problem that the stability is reduced, the amount is 100 parts by weight If exceeded, the latent heat characteristic is deteriorated.

The emulsifier may be any one generally used in the art, and preferably anionic surfactants are used. The anionic surfactant may be selected and used in general, for example, those selected from carboxylate, sulfonate, sulfate ester salt and phosphate ester salt may be used. The carboxylates include higher fatty acid alkali salts, N-acrylic amino acid salts, alkyl ether carbonates, and acylated peptides, and sulfonate salts include alkyl sulfonates, alkylbenzenes and alkylamino acid salts, alkylnaphthalene sulfonate salts, and sulfo pumpkin salts. The sulfuric ester salts include alkyl sulfates, alkyl ether sulfates, alkylaryl ether sulfates, alkylamide sulfates, and the like, and phosphate ester salts include alkyl phosphates, alkyl ether phosphates, and alkylaryl ether phosphates.

The emulsifier will be used in 1 to 5 parts by weight based on 100 parts by weight of the phase change material. If the amount of the emulsifier is less than 1 part by weight, the particles of the capsules are large, and if the amount is more than 5 parts by weight, the latent heat characteristic is deteriorated.

Water does not limit the amount used, but in consideration of workability, it is preferable to use 600 to 1000 parts by weight based on 100 parts by weight of phase change material.

The emulsification method is not necessarily limited, and various methods may be applied when emulsifying the above-described phase change material in the polymer monomer and the emulsion adjuvant mixture in water containing the emulsifier. For example, a homogenizer or an ultrasonic wave can be used. In the case of using a homogenizer, it can be stirred at 5,000 to 12,000 rpm for 5 to 30 minutes, and in the case of using an ultrasonic wave, it can be emulsified by treating at an amplitude of 50 to 500 watts for 5 to 30 minutes.

An initiator is added to enable encapsulation of the phase change material as the polymer monomer polymerizes. As the initiator, an initiator commonly used in the art may be used. For example, potassium percellate (KPS), aminopropanesulfonic acid (APS), Azobismethylpropionitrile (AIBN) ) May be used. It is preferable to use potassium persulfate.

The initiator is added to 0.5 to 2 parts by weight based on 100 parts by weight of the phase change material, when the addition amount is less than 0.5 parts by weight polymerization of the monomer is not made smoothly occurs a problem that can not be encapsulated, the addition amount 2 If it exceeds the weight part, it is preferable to add it within the above range because it causes a problem of stability due to a faster polymerization rate than necessary.

The reaction temperature in the polymerization reaction is 60 to 80 ℃, preferably about 70 ℃ 2 to 6 hours, preferably about 4 hours to obtain a nano-encapsulated phase change material. Suitable particle sizes of the obtained capsules are about 5 nm to 500 nm. If the capsule is excessively large, it adversely affects the surface condition of the product after coating, and most importantly, liquid dispersion for preparing the coating material is not easy and disadvantageous. Therefore, it is preferable that the fine capsule is dispersed and distributed, but it is difficult to manufacture to 5 nm or less, so the lower limit of the particle size of the capsule is limited to 5 nm.

The obtained phase change medium is attached to the opposite side of the battery structure 50 of the metal substrate as shown in FIG. Here, the opposite side of the battery structure 50 refers to the opposite side of the surface on which the structure 50 for generating electrical energy from sunlight, such as an electrode or a semiconductor layer, is formed.

In this case, the phase change medium may be mixed with the resin and attached to the substrate. The resins may be used as long as they can fix the phase change medium. However, in order to obtain a better effect, it is preferable to use a heat radiation resin as the resins. That is, the heat dissipation resin is a resin having excellent properties in releasing heat to the outside due to excellent thermal conductivity and radiation property, and can easily transfer heat transferred from the substrate to the phase change medium. The heat dissipating resin may be used as long as it is commonly referred to as a heat dissipating resin in the related art, but one more preferable example is as follows.

One example of the heat dissipating resin used in the present invention is formed of a heat dissipating resin composition containing a main resin and a heat dissipating pigment.

In the heat dissipating resin composition, the main resin includes a main resin containing at least one selected from the group consisting of polyester resins, epoxy resins, acrylic resins, urethane resins, and alkyd resins. It includes. The main resin is not particularly limited to a resin commonly used in the art, but in the case of polyester crab resin, the acid value is 5 mgKOH / g or less, and the base value is 5 to 20 by addition polymerization of bisphenol A and ethylene oxide. Preference is given to mgKOH / g.

In addition, the solvent used in the resin composition serves to easily dissolve the main resin, specifically, aromatic hydrocarbon-based, aromatic naphtha-based, isobutyl alcohol-based, dipropylene glycol monoethyl ether may be used alone or mixed. have. The solvent is preferably used 30 to 90 parts by weight based on 100 parts by weight of the main resin. In the final cured heat dissipating layer, it will be obvious to a person skilled in the art without mentioning that the solvent may not exist or the content or form may be changed by the reaction.

In the present invention, the heat dissipating pigment may be one or more selected from the group consisting of carbon black, graphite, iron oxide, phosphoric acid oxide, alumina, zirconia, diamond, and carbon nanotubes (CNT) to facilitate heat release to the outside. This is not restrictive.

The heat dissipating pigment is preferably 0.1 to 30 parts by weight, more preferably 5 to 20 parts by weight based on 100 parts by weight of the main resin. When the content thereof is less than 0.1 part by weight, there is a problem that the effect of improving the heat dissipation is not effective, and when it exceeds 30 parts by weight, the increase of the heat dissipation improvement effect is insufficient, the price is high, and the dispersing force is lowered, thereby deteriorating the solution stability. In addition, the heat-dissipating pigment may be a powder in its present form, and the particle size is not particularly limited as long as it is a powder.

The heat dissipating resin composition includes additives such as lubricants, color separation stabilizers, antifoaming agents, leveling agents, slip agents, acid catalysts, wetting agents, adhesion promoters, quenchers, dispersants, curing agents, and crosslinking agents, in addition to the main resin, solvent, and heat dissipating pigment. The present invention may be used by appropriately mixing in an amount commonly used in the art.

The phase change medium capsule may be mixed with the resin composition to form a resin and then coated and cured onto the substrate to be attached. In this case, the mixing of the phase change medium and the heat dissipating resin composition may be made by various methods known in the art, for example, physical dispersion or chemical dispersion. Moreover, as said hardening method, any method, such as thermosetting and photocuring, can be used.

At this time, the phase change medium capsule is preferably included in the range of 1 to 40 parts by weight, more preferably 3 to 40 parts by weight per 100 parts by weight of the resin composition. When the amount of the capsule is small, the endothermic amount due to the phase change is reduced, which does not meet the object of the present invention, on the contrary, when the amount of the capsule is excessively large, the ratio of the resin is low to provide sufficient adhesion to the substrate, and the viscosity of the resin It is difficult to use as a coating due to the rise.

In addition, the mixture of the phase change medium capsule and the resin composition needs to be attached so as to have a thickness of 0.5 to 10 μm after curing. In other words, when the thickness of the resin composition is too thin, the amount of phase change medium capsules contained therein is also reduced, which is not preferable. When the thickness is 10 µm or more, it is difficult to expect an increase in effect any more, and causes a cost increase. Not desirable

Since metal generally has good thermal conductivity, the substrate used in the solar cell of the present invention is not limited as long as it is made of metal. However, in consideration of manufacturing costs and the like, it is preferable that steel (carbon steel, stainless steel, etc.) be used. Among them, using stainless steel is more advantageous for securing corrosion resistance.

Claims

In a solar cell that converts sunlight into electrical energy by a semiconductor layer formed on a substrate,
The material of the substrate is a metal,
A heat dissipation layer is attached to the opposite side of the semiconductor layer of the metal substrate,
The heat dissipation layer is composed of a phase change medium in the form of a capsule that absorbs heat emitted from the substrate at high temperature and releases heat to the outside at a low temperature, and a heat dissipation resin which fixes the phase change medium and releases heat to the outside.
The heat dissipating resin has a high temperature stability solar including one or more heat dissipating pigments selected from the group consisting of carbon black, graphite, iron oxide, phosphoric acid, alumina, zirconia, diamond and carbon nanotubes (CNT) to facilitate heat dissipation to the outside battery.

The solar cell of claim 1, wherein the heat dissipation layer is attached to a substrate such that its total thickness is 0.5 to 10 μm.

The solar cell of claim 2, wherein the phase change medium is included in the range of 1 to 40 parts by weight based on 100 parts by weight of the resin composition.

The solar cell of claim 1, wherein the phase change medium has a high temperature stability that causes a phase change at a temperature between room temperature and 75 ° C.

The method of claim 4, wherein the phase change medium is n-octacoic acid, n-heptacoic acid, n-hexacoic acid, n-tetracoic acid, n-tricoic acid, n-docoic acid, n-heneicoic acid, n- One or two or more kinds of high temperature stability selected from among icosane, n-nonadecan, n-octadecane, n-heptadecane, n-hexadecane, n-pentadecane, n-tetradecane and n-tridecane battery.

The solar cell of claim 7, wherein the phase change medium has a particle size of 5 nm to 500 nm.

The solar cell of claim 1, wherein the phase change medium in the form of a capsule is formed by coating a polymer on a surface of the phase change medium.

The solar cell of claim 1, wherein the substrate is a steel substrate.