JPS6112086A - Thin-film solar battery device - Google Patents

Abstract

PURPOSE:To decelerate the increase in the wire-connecting cost and to gain a required output voltage by a method wherein a plurality of solar batteries made of amorphous semiconductor is stacked up one upon the other through the intermediary of transparent conductive films. CONSTITUTION:On a glass substrate 1, the pattern of a grid electrode 2 is printed by using a silver-based electrode paste, to be followed by the formation of a transparent conductive film 3. Next, by using a glow discharge equipment, a first stage is grown of solar battery layers P<+>/N<->/N<+> 4, 5, 6 made of amorphous silicon. Next, through the intermediary of a transparent conductive film 7 capable of transmission of incident light, a second stage is grown of solar battery layers P<+>/N<->/N<+> 8, 9, 10 of amorphous silicon. Similarly, a third stage is grown, composed of a transparent electrode film 11 and P<+>/N<->/N<+> layers 12, 13, 14 to be followed by the formation of a rear-side electrode 15.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a solar cell capable of producing high output in a thin film solar cell.

<Prior art> As a method of reducing the cost of power solar cells, silicon single crystals have been used to reduce process costs.
The method of using large area wafers is progressing to inch and 6 inch wafers. In this case, the optimal operating voltage of the silicon solar cell element is constant at 0.4 to 0.5 μm, and the optimal operating current is 30 to 50 mA/cm2 per unit area, so for a 4-inch wafer or a 5-inch wafer, 2, 4.00-4,000mA/sheet, 3.
The current is extremely large, 800 to 6,300 A+A/sheet, and the power loss due to the series resistance cannot be ignored unless the series resistance of the element is made considerably small. If the series resistance is to be reduced, the ratio of the electrode area to the light-receiving area will actually increase, resulting in a decrease in the effective photoelectric substitution efficiency of the solar cell element. One possible solution to this problem is to take out a plurality of lead wires from the light-receiving surface and interconnect the solar cell elements, but this leads to an increase in connection wiring costs. Furthermore, in solar cells for sensors, since the operating voltage of a single solar cell element is constant, it is necessary to connect a plurality of solar cell elements in series in order to obtain an arbitrary output voltage.

<Object of the Invention> The present invention has been made in view of the problem of increased connection wiring cost and the problem of connections for obtaining a desired output voltage in the conventional device, and it is an object of the present invention to effectively utilize the advantages of the manufacturing process of amorphous semiconductors. By stacking solar cells in multiple stages and further reducing loss on the light-transmitting electrode side on the light-receiving surface side, a high-output voltage solar cell device can be obtained.

<Example> From the relationship of output = voltage x current, the output of the solar cell device is
Series resistance loss can be reduced by dividing the solar cell into a plurality of unit solar cells in the thickness direction from the light receiving surface, multiplying the voltage by the number of divisions, and relatively reducing the current by the number of divisions. In general, solar cell elements using an amorphous semiconductor material have extremely poor collection efficiency as the element thickness increases (carrier diffusion length is short), and output current is limited. On the other hand, the structure of the embodiment in which the solar cell is divided into a plurality of unit solar cells in the thickness direction increases the carrier collection efficiency deep from the light-receiving surface and contributes to improving the charge conversion efficiency of the solar cell element. In a sensor solar cell, by appropriately selecting the number of divisions, any output voltage can be obtained from one solar cell element. Furthermore, the low-temperature process characteristic of amorphous semiconductors can suppress autodoping during the growth of a thin film between a transparent conductive film and a semiconductor or between a semiconductor.

10-+ FIG. 1 shows a specific example of stacking three P/N/N amorphous silicon unit solar cells.

Reference numeral 1 denotes a glass substrate (Hooning 7059) covering the light-receiving surface, on which a pattern of grid electrodes 2 is printed using silver thread electrode paste, and baked at 500 to 850°C. The grid electrodes 2 are distributed on the glass substrate 1 at partial pitches, and collect current by compensating for the high resistance of the transparent electrodes to be formed next. Next 1. T.O.

(In203-8nO2) transparent conductive film 3 at substrate temperature 25
0.100 by electron beam evaporation equipment at 0-450℃
．． Deposit to a thickness of 15 μm. Next, a mixed gas (SiH
=/H2) as raw material, amorphous silicon + unit solar cell layer P/N/N (Fig. 1, 4, 5
゜6) Growth is carried out. In this case, the gas pressure is 1 to 5 to
The rr growth rate was 60 to 180 A/min, and the substrate temperature was +250 to 300 °C. Only S i H= / H2 gas is used, and the N+ layer is formed by adding phosphine (PH) to SiH4/H2 gas.
, /H2) gas is added in a small amount for growth.

Regarding the glass substrate 1 on which the first-stage unit solar cells are formed, amorphous silicon unit solar cell layers P /N /N+ second stage solar cell and similar transparent conductive films 11.12, 13.1
4 amorphous silicon unit solar cell layer P+/N
/N+ third-stage unit solar cells are formed, and then the back electrode 15 is formed using a combination of nickel electroless plating method and electrolytic plating method.

The thickness of each of the above unit solar cells was determined as follows from the equivalent circuit shown in FIG. 2 and the calculation example of the absorption current of amorphous silicon shown in FIG. In other words, the photocurrent i1 of each unit solar cell in FIG. i2. Since the minimum value of i3 determines the value of the output current 1 of the solar cell element, the output current i becomes maximum when the condition of 1 and 12=i3. In this example, the thickness of each unit solar cell is set to 0.063 μIII and 0.03μ from the light-receiving surface side, respectively, so that 11=i2=i3 from the calculation example of the absorbed current of amorphous silicon in FIG.
They were 127 μm and 0.560 μm. In this case, ITO
Although it is assumed that the transmittance of the transparent conductive film is 100%, in reality, it is necessary to take this transmittance and the carrier diffusion length into consideration when determining the thickness of each unit solar cell.

In short, in thin-film solar cells stacked in multiple stages in the direction of light incidence, the layer thickness is adjusted in the process of growing the solar cell layers so that the light output current obtained from each stacked unit solar cell is approximately equal. controlled.

10−+ Above, we have described a specific example in which three stages of P /N /N amorphous silicon unit solar cells are stacked.
It can be easily inferred that a stainless steel plate or the like may be used for the back electrode 15 shown in the figure, and that each layer may be sequentially formed from the back side, contrary to this specific example, and then the glass substrates may be stacked.

In addition to these, by arbitrarily selecting the layer structure and the number of stacked layers of the unit solar cell according to the present invention according to the purpose, the photoelectric conversion efficiency of the solar cell element using an amorphous semiconductor material can be improved. The output voltage can be obtained and the range of applications will be expanded dramatically. When the unit solar cell structure is a Schottky junction solar cell, it can be easily inferred that the metal film of the Schottky junction also serves as the transparent conductive film of the embodiment, that is, the transparent conductive film can be omitted.

<Effects> According to the present invention, high output can be achieved with a simple configuration by taking advantage of the manufacturing process of thin-film solar cells and configuring solar cell elements in multiple stages in the direction of light incidence. By taking out the output, the loss of the light-transmitting electrode on the light-receiving surface side is reduced and the output is taken out, so a thin-film solar cell device with high utilization efficiency can be obtained.

[Brief explanation of drawings]

+-+ Fig. 1 is a cross-sectional view of a solar cell element in which three stages of P /N /N amorphous silicon unit solar cells are stacked according to the present invention, Fig. 2 is an equivalent circuit of Fig. 1, and Fig. 3 is a diagram showing the relationship between the element thickness of amorphous silicon and the absorption current when the incident light is assumed to be AM2 75 mw/cm2. 1 Nigel glass substrate, 2 Nigellid electrode, 3.7
．． 11: Transparent conductive film, +4.8, 12: P amorphous silicon layer, 5
．． 9.13: N amorphous silicon layer, + 6.10.14: N amorphous silicon layer, 15
: Back electrode,

Claims (1)

[Claims] 1) A plurality of unit thin film solar cells each comprising a plurality of amorphous semiconductor layers are formed between a light-transmitting front electrode formed on the light-receiving surface side and an electrode formed on the back side, A thin film solar cell device characterized in that a current collecting electrode is formed on a front electrode. 2) Each unit thin film solar cell is P^+/N^-/N^+
The thin film solar cell device according to claim 1, characterized in that the thin film solar cell device comprises an amorphous silicon layer having a structure.