JP2997538B2 - Polycrystalline silicon solar cell element - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polycrystalline silicon solar cell device, and more particularly, to a solar cell device having reduced surface reflection of incident light and enhanced light confinement inside the device. .

[Conventional technology]

In order to increase the conversion efficiency of the solar cell element, reduction of surface reflection of light and study of a light confinement structure are being studied.

With respect to surface reflection of light, in a single crystal solar cell element, etching (pyramid shape, V-groove structure) using a plane orientation by an alkali solution, a multilayer antireflection film structure, and the like are performed.

For the light confinement structure, use the plane orientation etch,
Although a double-sided V-groove structure is used, expensive techniques such as photolithography are required. These technologies are
For example, BLSopori, RAPryor, Optical characteristics
of taxtured (100) oriented siliconsurfaces applic
ations to solar cells, Conf.Record 15th IEEEPhotovo
ltaic specialist, 1981, p.468.

[Problems to be solved by the invention]

Although polycrystalline silicon solar cell elements are low cost, the plane orientation is not constant, and the plane orientation using an alkaline solution does not have uniform surface irregularities. Was difficult to form.

An object of the present invention is to provide a high-efficiency polycrystalline silicon solar cell element having less light reflection on the surface and having a light confinement effect.

[Means for solving the problem]

The above-mentioned object is to form a groove by a fluorine nitric acid etching method having no plane orientation and form an SiO ₂ film on the surface thereof, and on the light-receiving surface side, the thickness of the SiO ₂ film is set so that the reflectance is minimized. Is satisfied, and the thickness of the SiO ₂ film on the back surface side is achieved by satisfying the condition that the reflectance increases. The groove and the SiO ₂ film are provided on at least one of the light receiving surface and the back surface.

[Action]

The reflection of light having a wavelength λ that is perpendicularly incident on the light receiving surface of the solar cell is reflected at a reflectance R (λ) defined by the following equation.

_{R (λ) = (r 1} 2 + r 2 2 + 2r 1 r 2 cos2θ) / (1 + r 1 2 · r 2 2 + 2r 1 r 2 cos2θ) _{here, r 1 = (n 0 -n} 1) / (n 0 + N ₁ ), r ₂ = (n ₁ −n ₂ ) / (n ₁ + n ₂ θ = 2πn ₁ d ₁ / λ n ₀ is the refractive index of air, n ₁ is the refractive index of the SiO ₂ film, and n ₂ is silicon Where d ₁ is the thickness of the SiO ₂ film and λ is the wavelength, where the thickness of the SiO ₂ film on the light receiving surface satisfies the following formula, the reflectance of the light receiving surface is the minimum It has the value R _min (λ).

d ₁ = λ / 4n _{1 Further} , a part of the light reflected at the bottom of the groove on the light receiving surface hits the side surface of the groove, a part of which is incident, and a part is reflected. Further, a part of the light reflected on the side surface of the groove enters the bottom of the groove or the opposing surface. As described above, since a part of the light reflected on the bottom and side surfaces of the groove is more likely to be incident again, the overall reflectance is reduced.

The reflectance R ′ (λ) of light incident on the device and reaching the back surface while being absorbed by silicon is the reflectance R ′ of the light receiving surface.
The formula is the same as that of (λ), and the thickness of the back surface SiO ₂ film is different from that of the light receiving surface. The refractive index n ₀ is silicon, n ₁ is SiO ₂ film, n ₂ is air, and the SiO ₂ film thickness d ₁ Is made thinner or thicker than in the preceding case so that the reflectivity is increased. Since the light reflected at the bottom of the back surface is close to the junction of the light receiving surface, the light utilization efficiency increases. Further, a part of light reflected from the back surface and emitted from the side surface of the groove is more likely to be incident again on the bottom of the groove or on the opposing surface, so that the utilization rate of the incident light is increased.

Here, when the SiO ₂ film is formed on the light receiving surface and the back surface, the light receiving surface and the back surface are passivated. Experiments have confirmed that when the thickness of the SiO ₂ film is set to 100 mm or more, the surface passivation effect is enhanced.

〔Example〕

Hereinafter, an embodiment of the present invention will be described with reference to FIG. The solar cell element 1 is composed of a p-type (0.5 to 1.5 Ω · cm) polycrystalline substrate 11 and has a thin thickness of approximately 250 μm. On this substrate, a pattern is printed on both sides by a screen printing method using an acid-resistant resist, and hydrofluoric / nitric acid (hydrofluoric acid: nitric acid = 1: 4) having no plane orientation is etched to form a groove 21 on the light receiving surface side. , A groove 22 on the back surface side is formed. Phosphorus oxyhydrochloride (PO
Cl ₃ ) n ⁺ with a sheet resistance of 90Ω / □ and a depth of 0.25 μm by diffusion method
A mold conductive layer 31 is formed. 1000 in oxygen gas atmosphere
℃, dry oxidation for 80 minutes, SiO ₂ film 41 on the light-receiving surface, SiO ₂ on the back
_Two films 42 are formed. Thereby, the SiO ₂ film 4 on the light receiving surface
The film thickness of 1 is formed to be 1000 °, which satisfies the condition of the smallest surface reflectivity obtained from the above equation. On the other hand,
The thickness of the O ₂ film 42 is such that the reflectivity is large because the n ⁺ -type conductive layer is removed by etching, and the concentration is low for the p-layer.
700-800Å is formed. The back busbar electrode 51, the finger electrode 52, and the Ag-Al paste are printed and fired by screen printing. Light-receiving busbar electrode
61, finger electrodes 62 are formed by printing and baking Ag paste by a screen printing method.

FIG. 2 shows wavelengths of the light receiving surface provided with the groove and the SiO ₂ film according to the present invention (C), the light receiving surface provided with only the groove (B), and the light receiving surface provided with neither the groove nor the SiO ₂ film (A). The reflectance for 300 nm to 1200 nm is shown. Here, the dimensions of the groove are 110 μm in width, 30 μm in depth, and 250 μm in pitch. According to this figure, by providing the groove, the reflectance is reduced by 5% as a whole, and the groove and the SiO ₂ film are formed.
It can be seen that the reflectance is greatly reduced by providing 1000 °. In addition, the back side has the same
By providing the SiO ₂ film having a thickness of 0 °, the reflectance on the long wavelength side is reduced as shown in FIG.

FIG. 4 shows the conversion efficiency of each solar cell element without the grooved SiO ₂ film (A), without the grooved SiO ₂ film (B), and with the grooved SiO ₂ film (C) on the light receiving surface and the back surface. Si on the light receiving surface
The thickness of the O ₂ film was 1000 mm, and the thickness of the SiO ₂ film on the back surface was 700 mm. As shown in the figure, by providing grooves, the conversion efficiency is improved,
It can be seen that the conversion efficiency is further improved by providing the SiO ₂ film.

In the present invention, the substrate thickness is 250 μm, the sheet resistance of the n ⁺ type conductive layer is 90Ω / □, the depth is 0.25 μm, and the thickness of the SiO ₂ film on the light receiving surface is
1000 Å, the rear surface of the SiO ₂ film with a thickness 700～800A, the width of the groove 110μ
m, a depth of 30 μm, and a pitch of 250 μm are examples,
It does not limit the scope of the invention.

〔The invention's effect〕

According to the present invention, a solar cell element having high conversion efficiency can be realized by an easy and inexpensive manufacturing method, and its economic effect is extremely large.

[Brief description of the drawings]

FIG. 1 is a partially enlarged view showing one embodiment of the solar cell element of the present invention, FIG. 2 is a characteristic diagram showing the relationship between the light receiving surface side structure and the reflectance, and FIG. FIG. 4 is a characteristic diagram showing the relationship between the reflectances, and FIG. 4 is a characteristic diagram showing the relationship between the light receiving surface side structure and the conversion efficiency. 1 ... solar cell element, 11 ... substrate, 21 ... light receiving surface side groove,
22 ... back side groove, 31 ... n ^{+ type} conductive layer, 41 ... light receiving side oxide film, 42 ... back side oxide film, 51 ... back bus bar electrode,
52: Back side fin bar electrode, 61: Light receiving surface bus bar electrode, 62: Light receiving surface finger electrode.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tadao Nemoto 3-1-1, Sachimachi, Hitachi-shi, Ibaraki Pref. Hitachi, Ltd. Hitachi Plant (72) Inventor Minoru Uchiyama 3-1-1, Sachimachi, Hitachi-shi, Ibaraki No. 1 Hitachi, Ltd. Hitachi Plant (56) References JP-A-57-143873 (JP, A) JP-A-63-234567 (JP, A) JP-A-62-179164 (JP, A) JP 57-17184 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 31/04-31/078

Claims (1)

(57) [Claims] 1. A polycrystalline silicon solar cell element, wherein a groove having an SiO ₂ film is formed on the light receiving surface and the back surface, and the thickness of the SiO ₂ film on the light receiving surface satisfies a condition that the reflectance is minimum; A polycrystalline silicon solar cell element, wherein the thickness of the SiO ₂ film on the back surface is different from the thickness of the SiO ₂ film on the light receiving surface.