KR20130079759A - Thin-film typed solar cell comprising wo3 buffer layer - Google Patents

Abstract

PURPOSE: A thin film type solar cell including a WO3 buffer layer is provided to improve the efficiency of the thin film type solar cell by forming a buffer layer including WO3 between a p-type semiconductor layer and a first electrode. CONSTITUTION: A first electrode (120) is formed on the upper side of a substrate (110). A photoelectric conversion layer (140) is formed on the upper side of the first electrode. The photoelectric conversion layer includes a p-type semiconductor layer (141), an n-type semiconductor layer (143), and an i-type semiconductor layer (142). A second electrode (150) is formed on the upper side of the photoelectric conversion layer. A buffer layer (130) including WO3 is formed between the p-type semiconductor layer and the first electrode.

Description

Thin-film solar cell comprising a 3O3 buffer layer {THIN-FILM TYPED SOLAR CELL COMPRISING WO3 BUFFER LAYER}

The present invention relates to a thin film solar cell, and more particularly to a thin film solar cell comprising a WO ₃ buffer layer.

In general, a solar cell uses a diode composed of a p-n junction, and may be classified into various types according to a material used as a light absorption layer. For example, a solar cell using silicon as a light absorbing layer can be classified into a crystalline (monocrystalline, polycrystalline) wafer type solar cell and a thin film (crystalline, amorphous) solar cell.

However, in the case of the crystalline substrate type solar cell, the cost of the solar module is increasing due to the high price ratio of the silicon substrate. In recent years, a thin film on the low-cost substrate is deposited on a low-cost substrate instead of using a silicon substrate. Research into thin film solar cells that manufacture devices by depositing them in a form has been actively conducted.

Such thin film solar cells can be classified into various types according to the thin film deposition temperature, the type of substrate used, and the deposition method. The thin film solar cells are largely amorphous and crystalline silicon thin film solar cells depending on the crystal characteristics of the light absorbing layer. Can be classified.

1 and 2 are cross-sectional views schematically showing the structure of a conventional thin film solar cell.

1 and 2, the thin film solar cell may be classified into a nip substrate type and a pin superstrate type according to a deposition order.

 In the nip substrate type shown in FIG. 1, an n-type semiconductor layer 11, an i-type semiconductor layer 12, a p-type semiconductor layer 13, and a TCO layer 14 (transparent conductive oxide) are sequentially formed on the substrate 10. It is a structure deposited, and sunlight is incident from the TCO layer (14).

On the other hand, in the pin super-straight type shown in FIG. 2, the TCO layer 21, the p-type semiconductor layer 22, the i-type semiconductor layer 23, the n-type semiconductor layer 24, and the metal electrode layer on the substrate 20 ( 25 is a sequentially deposited structure, and sunlight is incident from the substrate 20.

In both structures, solar light has a common point of incidence through the TCO layer and the p-type semiconductor layer into the i-semiconductor layer due to the difference in drift mobility between electrons and holes generated by the incident light. Is due. In general, since the drift mobility of holes is lower than that of electrons, in order to maximize the collection efficiency of carriers due to incident light, most carriers should be generated at the pi interface to minimize hole movement distance.

Therefore, in both the substrate type and the superstrate type, sunlight is incident through the p-type semiconductor layer, and the characteristics of the window material such as the p-type semiconductor layer are changed to improve the efficiency of the thin film solar cell. There is a variety of research is going on.

Embodiments of the present invention are to provide a thin-film solar cell with improved short circuit current, filling rate and efficiency.

According to an aspect of the invention, the substrate; A first electrode disposed on the substrate; A photoelectric conversion layer disposed on the first electrode and formed by bonding at least one p-type semiconductor layer, at least one n-type semiconductor layer, and at least one i-type semiconductor layer; A second electrode disposed on the photoelectric conversion layer; And a buffer layer disposed between the p-type semiconductor layer and the first electrode, the buffer layer including WO ₃ .

At this time, the substrate may be characterized in that the glass substrate coated with Fluorine Tin Oxide (FTO).

In addition, the substrate may be a dual substrate including an indium tin oxide (ITO) coated substrate and a gallium zinc oxide (GZO) coated substrate.

In addition, the substrate may be a substrate coated with AZO (Aluminum Zinc Oxide).

The p-type semiconductor layer of the photoelectric conversion layer may be a p-type silicon thin film or silicon carbide (SiC), and the n-type semiconductor layer may be an n-type silicon thin film.

The i-type semiconductor layer of the photoelectric conversion layer may be formed of one selected from an amorphous silicon thin film, a microcrystalline silicon thin film, and a nanocrystalline silicon thin film.

On the other hand, the buffer layer may be formed including amorphous WO ₃ (Amophous WO ₃ , a-WO ₃ ).

In this case, the thickness of the buffer layer is 1 to 6nm, the thickness of the p-type semiconductor layer of the photoelectric conversion layer may be characterized in that 5 to 15nm.

Embodiments of the present invention can improve the efficiency of the thin-film solar cell by forming a buffer layer including WO ₃ between the p-type semiconductor layer and the first electrode.

In addition, by providing the optimum thickness of the buffer layer and the p-type semiconductor layer, it is possible to improve the efficiency of the thin film solar cell.

1 and 2 are cross-sectional views schematically showing the structure of a conventional thin film solar cell.
3 is a cross-sectional view schematically showing the structure of a thin film solar cell according to an embodiment of the present invention.
4 is a graph illustrating measurement of an open voltage, a short circuit current density, a filling rate, and an efficiency according to a thickness of a p-type semiconductor layer.
5 is a graph illustrating measurement of short circuit current density according to a thickness of a buffer layer.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

3 is a cross-sectional view schematically showing the structure of a thin film solar cell 100 according to an embodiment of the present invention.

Referring to FIG. 3, in the thin film solar cell 100, the first electrode 120, the buffer layer 130, the photoelectric conversion layer 140, and the second electrode 150 may be sequentially disposed on the substrate 110. . In this case, the first electrode 120 may be referred to as a front electrode, and the second electrode 150 may be referred to as a rear electrode. In addition, since the first electrode 120 has a property of transmitting incident light, the first electrode 120 may be referred to as a transparent electrode or a transparent conductive oxide (TCO) layer. However, in the present specification, the first electrode 120 and the second electrode 150 will be referred to for convenience of description.

The substrate 110 may be formed of a transparent material so that the incident light effectively reaches the photoelectric conversion layer 140. For example, the substrate 110 may be a glass substrate or a plastic substrate. In addition, the substrate 110 is a glass substrate coated with Fluorine Tin Oxide (FTO), or a dual substrate including a substrate coated with Indium Tin Oxide (ITO) and a substrate coated with Gallium Zinc Oxide (GZO), or It may be a substrate coated with aluminum zinc oxide (AZO). However, for convenience of explanation, hereinafter, the substrate 110 will be described based on the case where the glass substrate is coated with FTO.

The first electrode 120 may be formed of a transparent material to increase the transmittance of incident light, and may be formed of a material having electrical conductivity. For example, the first electrode 120 may be formed of a tin oxide (SnO ₂ , SnO ₂ : F, ITO), a double layer of ITO / GZO (Gallium Zinc Oxide), ZnO: Al, AgO, FTO ( Fluorine Tin Oxide) and mixtures thereof.

The size of the first electrode 120 is not limited, and for example, may be formed on the entire surface of the substrate 110. In addition, the first electrode 120 may be electrically connected to the photoelectric conversion layer 140 to collect and output one of the carriers generated by incident light (for example, holes).

Meanwhile, a plurality of irregularities (not shown) having an amorphous pyramid structure may be formed on one surface or both surfaces of the first electrode 120. That is, the first electrode 120 may have a texturing surface. The texturing surface provided on the first electrode 120 may reduce reflection of incident light and increase absorption of light, thereby contributing to improving efficiency of the solar cell. However, in the present specification, for convenience of description, the description will be made mainly on the case where the texturing surface is not formed on the first electrode.

The photoelectric conversion layer 140 converts light incident from the outside into electricity. The photoelectric conversion layer 140 may be formed by bonding at least one p-type semiconductor layer 141, at least one n-type semiconductor layer 142, and at least one i-type semiconductor layer 143. The photoelectric conversion layer 140 having such a structure may be formed using a plasma enhanced chemical vapor deposition (PECVD) method or a chemical vapor deposition (CVD) method.

The p-type semiconductor layer 141 may be a p-type silicon thin film or silicon carbide (SiC), and may be formed by using a gas containing a trivalent element such as boron, potassium, indium, or the like in a raw material gas containing silicon. . In addition, the p-type semiconductor layer 141 may be a hydrogenated amorphous silicon (a-Si: H) thin film. The p-type semiconductor layer 141 may have a thickness of 5 to 15 nm, and 12 nm is preferable when considering the relationship with the buffer layer 120. This will be described later.

The i-type semiconductor layer 142 includes an amorphous silicon thin film (a-Si: H), a microcrystalline silicon thin film (Micro-Crystalline Silicon, mc-Si: H), and a nanocrystalline silicon thin film (Nano-Crystalline Silicon, nc-Si: H) can be made of one selected. In addition, the i-type semiconductor layer 142 may be referred to as an intrinsic semiconductor layer, and may have a thickness of about 500 nm.

The n-type semiconductor layer 143 may be an n-type silicon thin film, using a gas containing impurity of pentavalent element such as phosphorus (P), arsenic (As), antimony (Sb), etc. as a source gas containing silicon. It is possible to form. In addition, the n-type semiconductor layer 143 may be a hydrogenated amorphous silicon (a-Si: H) thin film, it may have a thickness of about 25nm.

As described above, when light enters the p-type semiconductor layer 141 from the photoelectric conversion layer 140 having the pin junction structure, the inside of the i-type semiconductor layer 142 has a p-type semiconductor layer having a relatively high doping concentration ( Since the depletion is performed by the 141 and the n-type semiconductor layer 143, a flow current is generated and power can be generated.

The second electrode 150 is disposed on the photoelectric conversion layer 140, and may be formed of a metal material having excellent electrical conductivity in order to increase recovery efficiency of power generated by the photoelectric conversion layer 140. In addition, the second electrode 150 may be electrically connected to the photoelectric conversion layer 140 to collect and output one of the carriers generated by incident light (for example, electrons).

The thin film solar cell 100 according to the exemplary embodiment of the present invention may include a buffer layer 130 disposed between the p-type semiconductor layer 141 and the first electrode 120 of the photoelectric conversion layer 140. do.

The buffer layer 130 is formed to include tungsten trioxide (W0 ₃ ). In addition, the buffer layer 130 includes a first buffer layer (not shown) formed by including WO ₃ and a second buffer layer (not shown) formed by including a p-type metal oxide material such as Cu ₂ O. It is also possible.

Meanwhile, the WO ₃ may be amorphous WO ₃ (amophous WO ₃ , a-WO ₃ ), and a bandgap of 3 eV or more and a valence band of about 5 eV or more may be used. In the case where WO ₃ is crystalline, since grain boundaries are increased on the surface and hole mobility is limited, properties are degraded. Therefore, it is preferable to use amorphous WO ₃ as the buffer layer 130.

Applicants of the present invention can increase the efficiency of the thin film solar cell 100 by disposing a buffer layer 130 including WO ₃ between the p-type semiconductor layer 141 and the first electrode 120. Confirmed. This is because the optical bandgap of the buffer layer 130 including WO ₃ is wider than that of amorphous silicon. More specifically, the large band gap difference in the heterojunction between the interface of the first electrode 120 and the p-type semiconductor layer 141 is the cause of the decrease in efficiency of the thin film solar cell due to the hole recombination from the p-type semiconductor layer 141. Acts as. However, when the buffer layer 130 including WO ₃ is formed between the first electrode 120 and the p-type semiconductor layer 141, since the buffer layer 130 has a wide band gap, the first electrode ( The reduction of recombination at the 120 / p-type semiconductor layer 141 may be prevented and the efficiency may be improved.

In the case of the WO ₃ constituting the buffer layer 130, a dipole layer having conductivity (~ 6 * 10 ^-6 S / cm) suitable for OLEDs (Organic Light-Emitting Diodes) or solar cells and facilitating current injection. It is used as a dipole layer. In addition, since WO ₃ has a Fermi-Level pinning effect of correcting a work-function mismatch between the first electrode 120 and the p-type semiconductor layer 141, It is suitable for use as the buffer layer 130.

Meanwhile, a method of manufacturing the buffer layer 130 may use a conventional method such as thermal evaporation, ebeam evaporation, sputtering evaporation, or the like.

On the other hand, one embodiment of the present invention, to provide an optimum value of the thickness (t ₂₎ of the thickness of the buffer layer (130) (t ₁₎ and the p-type semiconductor layer 141. In an aspect. This is because the efficiency of the thin-film solar cell 100 can vary depending upon the thickness (t ₂₎ of the thickness (t ₁₎ and a p-type semiconductor layer 141 of the buffer layer 130.

Applicants of the present invention confirmed the optimum value of both thicknesses by experimenting by varying the thickness of the buffer layer 130 and the thickness of the p-type semiconductor layer 141, will be described below.

Specifically, in the thin film solar cell 100 according to an embodiment of the present invention, the thickness t ₁ of the buffer layer 130 may be 1 to 6 nm, and preferably 2 to 6 nm. In addition, the thickness t ₂ of the p-type semiconductor layer 141 of the photoelectric conversion layer 140 may be 5 to 15 nm, and preferably 9 to 15 nm.

In this regard, FIG. 4 illustrates an open circuit voltage (V _oc ), a short-circuit current density (J _sc ), and a fill factor (FF) according to the thickness of the p-type semiconductor layer 141. And a graph showing measurement of efficiency (Eff, conversion efficiency), and FIG. 5 is a graph illustrating measurement of short circuit current density according to the thickness of the buffer layer 130.

4 and 5, first, a thin film solar cell was manufactured as shown in FIG. 3. FTO glass was used as the substrate 110, and the first electrode 120 and the buffer layer 130 were deposited. Next, the p-type semiconductor layer 141, the i-type semiconductor layer 142, and the n-type semiconductor layer 143 are sequentially deposited by using a PECVD device, and then a second process is performed using a deposition process through a hard mask. The electrode 150 was formed. Finally, after scribing with a diamond pencil, the first electrode 120 measurement joint (pad end) was bonded by ultrasonic pharyngeal bonding. In the thin film solar cell 100 manufactured as described above, the efficiency was measured by varying the thicknesses of the p-type semiconductor layer 141 and the buffer layer 130. The measurement results are summarized in FIG. 4 and Table 1 below.

1st buffer layer
(Thickness, nm) Open-circuit voltage
(V _oc , V) Short-circuit current
(J _sc , mA / cm ² ) Filling rate efficiency(%) Comparative Example 1 × 0.814 12.821 0.744 7.780 Example 1 ○ (4 nm) 0.807 13.398 0.738 7.990 Example 2 ○ (8 nm) 0.811 12.860 0.735 7.676 Example 3 ○ (12 nm) 0.800 12.613 0.740 7.476

All the measurement results summarized in Table 1 correspond to the case where the thickness of the p-type semiconductor layer 141 is 12 nm. This is because, as shown in FIG. 4, the efficiency is the highest when the thickness of the p-type semiconductor layer 141 is 12 nm. In addition, when the thicknesses of the first buffer layer 130 are 8 nm and 12 nm, the efficiency is lower than that when the thickness of the first buffer layer 130 is 4 nm. Therefore, the optimal thickness of the first buffer layer 130 is 4 nm. It was confirmed that the optimum thickness range accordingly was 1nm to 6nm.

As described above, the embodiments of the present invention can improve the efficiency of the thin film solar cell by forming a buffer layer including WO ₃ between the p-type semiconductor layer and the first electrode. In addition, by providing the optimum thickness of the buffer layer and the p-type semiconductor layer, it is possible to improve the efficiency of the thin film solar cell.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit of the invention as set forth in the appended claims. The present invention can be variously modified and changed by those skilled in the art, and it is also within the scope of the present invention.

10: substrate 11: n-type semiconductor layer
12: i-type semiconductor layer 13: p-type semiconductor layer
14: TCO layer 20: substrate
21: TCO layer 22: p-type semiconductor layer
23: i-type semiconductor layer 24: n-type semiconductor layer
25: metal electrode layer 100: thin film solar cell
110: substrate 120: first electrode
130: buffer layer 140: photoelectric conversion layer
141: p-type semiconductor layer 142: i-type semiconductor layer
143: n-type semiconductor layer 150: second electrode

Claims (8)

Board;
A first electrode disposed on the substrate;
A photoelectric conversion layer disposed on the first electrode and formed by bonding at least one p-type semiconductor layer, at least one n-type semiconductor layer, and at least one i-type semiconductor layer;
A second electrode disposed on the photoelectric conversion layer; And
A thin film type solar cell, disposed between the p-type semiconductor layer and the first electrode, comprising a buffer layer including WO ₃ . The method of claim 1,
The substrate is a thin film solar cell, characterized in that the glass substrate coated with Fluorine Tin Oxide (FTO). The method of claim 1,
The substrate is a thin film solar cell, characterized in that the dual substrate comprising a substrate coated with indium tin oxide (ITO) and a gallium zinc oxide (GZO) coated. The method of claim 1,
The substrate is a thin-film solar cell, characterized in that the substrate is coated with AZO (Aluminum Zinc Oxide). The method of claim 1,
The p-type semiconductor layer of the photoelectric conversion layer is a p-type silicon thin film or silicon carbide (SiC), the n-type semiconductor layer is a thin-film solar cell, characterized in that the n-type silicon thin film. The method of claim 1,
The i-type semiconductor layer of the photoelectric conversion layer is a thin film solar cell, characterized in that made of one selected from amorphous silicon thin film, microcrystalline silicon thin film and nanocrystalline silicon thin film. The method of claim 1,
The buffer layer is a thin film solar cell, characterized in that it comprises an amorphous WO ₃ (Amophous WO ₃ , a-WO ₃ ). The method according to claim 6,
The thickness of the buffer layer is 1 to 6nm,
The thickness of the p-type semiconductor layer of the photoelectric conversion layer is a thin film type solar cell, characterized in that 5 to 15nm.

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