KR20230091646A - Measuring method for recombination loss of silicon solar cell and designing method for silicon solar cell using the same - Google Patents

Abstract

An object of the present invention is to provide a method for measuring recombination loss of a silicon solar cell.
To this end, the present invention calculates metal induced gap states (MIGS) in the LDOS of silicon in the silicon-metal interface system calculated by applying the density functional theory to modeling of the interface between silicon and metal electrodes; Calculating dangling bond states (DBS) from the LDOS of silicon in the silicon unsaturated bond surface system calculated by applying the density functional theory to modeling of unsaturated bonds on the silicon surface; and comparing recombination by MIGS and recombination by dangling bond (DB) by comparing MIGS and DBS.
The present invention has an effect of comparing the proportions of recombination by MIGS and recombination by DB by comparing MIGS for the silicon-metal interface and DBS for the silicon surface.
In addition, by measuring the effect of recombination by MIGS and recombination by DB, there is an effect of reflecting information on recombination loss in the process of designing a silicon solar cell.

Description

Method for measuring recombination loss of silicon solar cell and design method of silicon solar cell using the same

The present invention relates to a method for measuring loss generated in a silicon solar cell, and more particularly, to a method for measuring recombination loss that reduces the efficiency of a solar cell.

Recently, the importance of developing next-generation clean energy is increasing due to serious environmental pollution problems and depletion of fossil energy. Among them, a solar cell is a device that directly converts solar energy into electrical energy, and is expected to be an energy source that can solve future energy problems because it has low pollution, unlimited resources, and a semi-permanent lifespan.

A solar cell is composed of a P-N junction diode and is an element that generates power through a photoelectric effect. The photoelectric effect is when an object receives energy greater than the bandgap, electrons are excited from the valence band to the conduction band, and electron-hole pairs are generated. It is separated and collected by the electrode, and current flows.

At this time, recombination of the separated electron-electron pairs is called recombination, and causes the power generation efficiency to be lowered. This recombination is a loss that occurs in the photovoltaic device itself, and even in the case of a very small recombination loss, the overall efficiency of a solar cell module including a plurality of solar cells is significantly lowered. Therefore, many technologies are being developed to increase the efficiency of photovoltaic power generation by reducing or preventing recombination occurring in solar cells.

On the other hand, recombination occurring in the solar cell appears for various reasons, and recombination may occur for different reasons depending on the structure of the solar cell. In recent years, as the quality of materials used in the manufacture of silicon solar cells has improved and the thickness of devices has become thinner, recombination on the surface of solar cells has become an important problem, and many technologies for solving this problem have been studied.

However, since the causes of recombination occurring in solar cells are very diverse, if the cause of recombination loss is not accurately identified, countermeasures that do not match the cause are applied, resulting in inability to reduce recombination loss.

Republic of Korea Patent Publication 10-2012-0067361 Korean Registered Patent No. 10-1195040

The present invention is to provide a method for comparatively measuring recombination loss due to contact between an emitter layer and a metal of a silicon solar cell and recombination loss due to silicon unsaturated bonds in the emitter layer.

In order to achieve the above object, the present invention provides a method for measuring recombination loss of a silicon solar cell having the following configuration.

In the present invention, the metal induced gap states (MIGS) in the LDOS (local density of states) of silicon in the silicon-metal interface system calculated by applying the density functional theory to the modeling of the interface between silicon and metal electrodes ) to calculate; Calculating dangling bond states (DBS) from the LDOS of silicon in the silicon unsaturated bond surface system calculated by applying the density functional theory to modeling of unsaturated bonds on the silicon surface; and comparing recombination by MIGS and recombination by dangling bond (DB) by comparing MIGS and DBS.

Modeling of the interface between the silicon and the metal electrode is performed by modeling so that a plurality of unit cells are included in the silicon lattice and a plurality of unit cells are included in the metal lattice so that the lattice mismatch rate between the silicon lattice and the metal lattice is 7% or less. it is desirable to be

It is preferable that modeling of the interface between the silicon and the metal electrode satisfies that the interface formation energy is less than zero.

Modeling of the interface between silicon and the metal electrode is preferably performed by reflecting lattice strain of silicon due to a dopant doped in silicon.

Modeling of the unsaturated bond of the silicon surface is preferably modeled by reflecting the lattice deformation of the silicon by the dopant doped in the silicon.

A method of designing a silicon solar cell according to another aspect of the present invention is a method of designing a silicon solar cell by reflecting recombination loss, and includes a process of verifying the recombination loss of the designed solar cell, and a process of verifying the recombination loss. Calculating the MIGS in the LDOS of silicon in the silicon-metal interface system calculated by applying the density functional theory to the modeling of the interface between the silicon and the metal electrode; Calculating DBS from the LDOS of silicon in the silicon unsaturated bond surface system calculated by applying the density functional theory to modeling of unsaturated bonds on the silicon surface; and comparing recombination by MIGS and recombination by DB by comparing MIGS and DBS.

The present invention configured as described above has an effect of comparing the proportions of recombination by MIGS and recombination by DB by comparing MIGS for the silicon-metal interface and DBS for the silicon surface.

In addition, by measuring the effect of recombination by MIGS and recombination by DB, there is an effect of reflecting information on recombination loss in the process of designing a silicon solar cell.

1 is a diagram showing a unit lattice structure of silicon and silver.
2 is a diagram for explaining modeling for reducing lattice mismatch between silicon and silver.
FIG. 3 is an LDOS result of silicon in a silicon-silver interface system derived for the modeling of FIG. 2 .
4 is a diagram for explaining modeling of a silicon unsaturated bond surface.
FIG. 5 is an LDOS result of silicon in a silicon unsaturated bond surface system derived for the modeling of FIG. 4 .
6 is a graph comparing MIGS and DBS derived from FIGS. 3 and 4 .

Hereinafter, the present invention will be described in detail through preferred embodiments with reference to the drawings. However, the embodiments of the present invention can be modified in many different forms, and the scope of the present invention is not limited only to the embodiments described below. The shapes and sizes of elements in the drawings may be exaggerated for clearer description, and elements indicated by the same reference numerals in the drawings are the same elements.

And throughout the specification, when a part is said to be “connected” to another part, this includes not only the case of being “directly connected” but also the case of being “electrically connected” with another element interposed therebetween. In addition, when a part "includes" or "includes" a certain component, it means that it may further include or include other components, not excluding other components unless otherwise specified. .

In addition, terms such as "first" and "second" are used to distinguish one component from another, and the scope of rights should not be limited by these terms. For example, a first element may be termed a second element, and similarly, a second element may be termed a first element.

In a silicon solar cell, an emitter layer doped in an opposite type is formed on a silicon substrate doped with a P-type or N-type, and a metal electrode constituting a grid electrode is in contact with the emitter layer.

At this time, recombination by MIGS occurs at the silicon-metal contact portion. MIGS is known to be induced near the Fermi level by chemical bonding with metals, resulting in a higher Schottky barrier height and increased recombination of electron-hole pairs. As such, recombination by MIGS is one of the causes of lowering the efficiency of silicon solar cells.

In addition, surface recombination occurs due to a discontinuous structure in which an end of silicon constituting the emitter layer is unsaturated. Recombination caused by dangling bonds in silicon is one of the main causes of lowering the efficiency of silicon solar cells.

At this time, recombination by MIGS and recombination by DB are simultaneously applied in an actual silicon solar cell. In order to reduce loss due to recombination, when a technique capable of reducing one of them is applied, the desired effect cannot be obtained unless the effect on the recombination loss is taken into account. For example, a technology for reducing or preventing recombination by DB is applied to a solar cell with high recombination by MIGS and little by recombination by DB, or conversely, to a solar cell with high recombination by DB and little recombination by MIGS. In the case of applying a technique for reducing or preventing recombination by MIGS, there will be no significant difference in loss due to recombination despite the application of the technique.

In order to solve this problem, the inventors of the present invention developed a method for comparatively measuring recombination by MIGS and recombination by DB.

Specifically, the inventors of the present invention calculated a factor representing recombination by MIGS and a factor representing recombination by DB through density functional theory, and compared and measured recombination by MIGS and recombination by DB by comparing them. developed.

Density functional theory is a computational quantum mechanical model methodology, and is a theoretical method for calculating the shape and energy of electrons in atoms, molecules, and materials through quantum mechanics. This density functional theory can be applied anywhere to a many-body problem with a similar structure, and the inventors of the present invention use the density range as a method of deriving the LDOS of silicon in a silicon-metal interface system and the LDOS of silicon in a silicon unsaturated bond surface system. Functional theory was applied.

MIGS at the silicon-metal interface can be derived through the LDOS analysis result of silicon in the silicon-metal interface system, and DBS of the silicon unsaturated bond surface can be derived through the LDOS analysis result of silicon in the silicon unsaturated bond surface system. there is.

By comparing MIGS and DBS derived through LDOS, it is possible to compare the proportions of recombination by MIGS and recombination by DB in the current system.

First, the process of deriving MIGS will be described.

In this embodiment, silver (Ag), which is widely used as a metal electrode, will be described.

1 is a diagram showing a unit lattice structure of silicon and silver.

Calculated lattice constants for silicon and silver having a unit cell structure as shown are 5.4467 Å and 4.0877 Å, respectively, and the lattice mismatch rate between them reaches 24.951%.

When the silver electrode is formed on the surface of silicon (emitter), the unit cell-to-unit interface is not formed because the unit cell mismatch is large, and the number of unit cells disposed between bonds is controlled.

In order to reflect the adjustment of the number of unit cells, modeling is performed to adjust the number of unit cells of silicon and silver so that the lattice mismatch rate is less than a predetermined value (7% or less).

2 is a diagram for explaining modeling for reducing lattice mismatch between silicon and silver.

When the (111) plane of silicon and the (111) plane of silver are targeted, the lattice constant of the new lattice consisting of three silicon unit lattices is 11.554Å, and the lattice constant of the new lattice consisting of four silver unit lattices is 11.562Å Because of this, the lattice mismatch rate for the new lattice of silicon and silver is reduced to 0.06546%, and a desired degree of lattice mismatch rate can be obtained. Accordingly, the interface system of silicon and silver can be modeled in a form in which three silicon unit cells and four silver unit cells are bundled.

In order to confirm the legitimacy of these modeling results, the interface formation energy is calculated for the modeled structure.

The interface formation energy can be calculated by the following formula, and if the interface formation energy is less than 0, it can be determined that the interface is formed in the form of modeling as a thermodynamically stable state.

Conversely, if the interface formation energy is greater than zero, it is a thermodynamically unstable state and other modeling should be sought.

On the other hand, when a dopant is included in silicon, the effect thereof must be reflected, and in the case of silicon doped with P, the formation energy can be calculated by the following formula.

The previously determined modeling of three silicon unit cells and four silver unit cells was confirmed to be suitable modeling because the interface formation energy was less than zero.

The MIGS of the silicon-silver interface is derived by calculating the LDOS of silicon in the silicon-silver interface system formed by modeling three silicon unit cells and four silver unit cells by density functional theory.

FIG. 3 is an LDOS result of silicon in a silicon-silver interface system derived for the modeling of FIG. 2 .

For the calculation according to the density functional theory, generalized gradient approximation using the Perdew-Burke-Ernzerhof function was used in the case of exchange-correlation energy. Spin-polarized calculations were performed, and the Tkatchenko-Scheffler method was used for van der Waals correction. The orbital cut-off distance was set to 4.6 Å, and the gamma k -point was used with a Monkhorst-Pack grid.

In FIG. 3 , a red dotted line represents the maximum value of the valence band and the minimum value of the conduction band of the silicon crystal lattice, and the interval between them is the MIGS region.

MIGS for the interface formed between a specific metal and silicon can be calculated by the method described above.

Next, the process of deriving the DBS will be described.

As in the previous case, modeling of the silicon unsaturated bond surface is performed to calculate the LDOS by density functional theory.

4 is a diagram for explaining modeling of a silicon unsaturated bond surface.

As in the previous modeling of the silicon-silver interface, if the lattice connection relationship of silicon is reflected on the (111) plane, modeling in which unsaturated bonded silicon is dispersed on the surface can be derived.

The DBS of the silicon surface is derived by calculating the LDOS of silicon in the silicon unsaturated bond surface system for the shown silicon surface modeling by density functional theory.

FIG. 5 is an LDOS result of silicon in a silicon unsaturated bond surface system derived for the modeling of FIG. 4 .

In the same way as described above, the LDOS of silicon in the silicon unsaturated bond surface system was calculated through the calculation according to the density functional theory. am.

Finally, if MIGS and DBS calculated according to the density functional theory are converted into cumulative values, the effects of recombination by MIGS at the silicon-silver interface and recombination by DB at the silicon surface can be compared.

6 is a graph comparing MIGS and DBS derived from FIGS. 3 and 4 .

As shown, it can be seen that recombination loss due to DB on the silicon surface has a greater effect than recombination loss due to MIGS between the silver electrode and emitter in a general silicon solar cell, which is consistent with generally known results.

From the above results, it can be confirmed that the effects of recombination by MIGS at the silicon-metal interface and recombination by DB on the silicon surface can be theoretically compared.

On the other hand, considering the difference in the material of the metal electrode used in the silicon solar cell and the lattice deformation due to the doping of silicon, a new modeling different from the above form should be performed, and finally the silicon-calculated silicon- Comparative results of recombination by MIGS at the metal interface and recombination by DB at the silicon surface may be different.

Therefore, if the comparison of recombination by MIGS at the silicon-metal interface and recombination by DB on the silicon surface as described above is applied to solar cell design, it is possible to design a solar cell with reduced loss due to recombination.

Furthermore, in order to improve the performance of previously designed solar cells, even when a new technology is applied, a method with a higher performance improvement effect by applying a comparison of recombination by MIGS at the silicon-metal interface and recombination by DB on the silicon surface will be able to find

The present invention has been described above through preferred embodiments, but the above-described embodiments are only illustrative of the technical idea of the present invention, and various changes are possible within a range that does not depart from the technical idea of the present invention. Anyone with ordinary knowledge will be able to understand. Therefore, the protection scope of the present invention should be construed by the matters described in the claims, not the specific examples, and all technical ideas within the scope equivalent thereto should be construed as being included in the scope of the present invention.

Claims (6)

Calculating metal induced gap states (MIGS) in the LDOS of silicon in the silicon-metal interface system calculated by applying the density functional theory to the modeling of the interface between the silicon and the metal electrode;
Calculating dangling bond states (DBS) from the LDOS of silicon in the silicon unsaturated bond surface system calculated by applying the density functional theory to modeling of unsaturated bonds on the silicon surface; and
A method for measuring recombination loss of a silicon solar cell, comprising the step of comparing recombination by MIGS and recombination by DB (dangling bond) by comparing MIGS and DBS.
The method of claim 1,
Modeling of the interface between silicon and metal electrodes,
Recombination loss of a silicon solar cell characterized in that the modeling is performed so that a plurality of unit cells are included in the silicon lattice and a plurality of unit cells are included in the metal lattice so that the lattice mismatch between the silicon lattice and the metal lattice is 7% or less. measurement method.
The method of claim 1,
Modeling of the interface between silicon and metal electrodes,
A method for measuring recombination loss of a silicon solar cell, characterized in that the interface formation energy is modeled to satisfy that it is less than zero.
The method of claim 1,
Modeling of the interface between silicon and metal electrodes,
A method for measuring recombination loss of a silicon solar cell, characterized in that it is modeled by reflecting the lattice strain of silicon by a dopant doped in silicon.
The method of claim 1,
Modeling of the unsaturated bond on the silicon surface,
A method for measuring recombination loss of a silicon solar cell, characterized in that it is modeled by reflecting the lattice strain of silicon by a dopant doped in silicon.
As a method of designing a silicon solar cell by reflecting recombination loss,
Including the process of verifying the recombination loss for the designed solar cell,
The process of verifying the recombination loss,
Calculating metal induced gap states (MIGS) in the LDOS of silicon in the silicon-metal interface system calculated by applying the density functional theory to the modeling of the interface between the silicon and the metal electrode;
Calculating dangling bond states (DBS) from the LDOS of silicon in the silicon unsaturated bond surface system calculated by applying the density functional theory to modeling of unsaturated bonds on the silicon surface; and
A method for designing a silicon solar cell comprising the step of comparing recombination by MIGS and recombination by dangling bond (DB) by comparing MIGS and DBS.

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