JPS62101081A - Tandem structure solar cell - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a tandem structure solar cell with improved light conversion efficiency of solar energy.

<Conventional technology and its problems> The 4T4 structure of solar cells using amorphous silicon (A-SI) includes one A-3L single-layer cell structure as shown in Figure 4, and a highly efficient solar cell. For example, a tandem structure with two a-si unit cells as shown in FIG. 5 is known.

However, in a tandem structure cell as shown in Figure 5,
An n-p junction surface is required, which was not possible in the conventional single-layer cell with a pin structure as shown in FIG. 4, and it is necessary to improve the structure peculiar to the tandem structure cell.

That is, conventionally, pl 11n1, p2!2n2 as shown in FIG.
Even if a cell with a two-layer structure of
Because the current generated in the 11n1 cell and the current generated in the 2'2n2 cell do not flow smoothly, the current-voltage curve suddenly changes as the voltage (V) increases, as shown in (I) in Figure 6. The required current-voltage curve (I
The characteristics were worse than I), and the disadvantage was that the output reaching the maximum output point was lower.

This is because when only the n1p2 junction is taken out, a rectifying effect occurs as shown in the curve in Figure 7, so DI! 1n1, p212n
This is thought to be because the nl p2 of the second diode is connected in the opposite direction.

In view of the above, the present inventors found that the current-voltage characteristics of the n1 layer 2 junction surface in tandem structure cells, for example, pl 11n1 and p212n2, do not exhibit any rectification characteristics, that is, the current (I) If the '1 p22 layer plane is a straight line almost close to the axis and has an extremely low resistance structure, then the n1 layer 2
This invention was developed based on the discovery that a highly efficient tandem structure solar cell can be obtained because no current loss occurs at the junction surface.

<Operation> That is, the present invention achieves the above object as follows.

■ When forming the n2 layer on the n1 layer, the high frequency output is set to 0.
．． The purpose is to increase the concentration to 1W/Cr7I or more to create a large number of junction surface units (defects) on the nID2 junction surface, thereby smoothing the bonding of electrons and holes and roughly promoting microcrystalization.

Also, as for (■), the sum of the activation energy of the n layer and the activation energy of the p2 layer can be made smaller or smaller.

In the case of (2), it is also effective and necessary to heavily dope the n1 layer and the second layer with an impurity such as phosphorus or boron.

In this way, both the generation of junction surface levels by high-frequency output and the doping of impurity substances may be adjusted as appropriate.

In short, this invention achieves the same result by lowering the resistance of the n1 layer 2 junction surface by providing many junction surface levels at the <n11)2 junction surface, performing microcrystalization, or doping with phosphorus, boron, etc., as described above. By smoothing the flow of current at the junction surface, it is extremely effective in preventing power loss at the '1p22 layer surface.

Thus, the tandem structure cell of the present invention can be used not only as a tandem structure solar cell, but also as an image sensor and photoreceptor having a tandem structure.

<Example> This invention will be explained below with reference to Examples.

When manufacturing a tandem structure cell sample with two a-si unit cells by a conventionally known method, the high frequency output of the n1 layer 2 bonding surface was set to 0.5 W/ci, and a large number of bonding surfaces were applied to the n1 layer 2 bonding surface. A cell sample A of the present invention in which a level was created and a cell sample B having a conventional structure in which the high frequency output of the n1 layer 2 junction surface was 0.05 W/CrII were made.

Current for these samples A and B under sunlight irradiation -
The voltage output characteristics are as shown in Figure 1.
In this case, there was no power loss at the n1 layer 2 junction surface, a normal current-voltage curve was exhibited, and the fill factor was 43%.

On the other hand, in the sample B made using the conventional method, the n1 layer 2 junction has rectifying characteristics, so power loss occurs at the n1 layer 2 junction, and sufficient output cannot be obtained, and the fill factor is 31. %
It was nothing more than The above example was carried out to show the characteristics of the np junction surface, and the output characteristics of each unit cell were not optimized, so the conversion efficiency was around 3%. After a rough study of each unit cell, one with a conversion efficiency of 8% was found.
It is being

Regarding A and B in FIG. 1, the current-voltage characteristics will be briefly explained by simulation.

In Fig. 2, if the output characteristics of the first layer of the tandem structure cell are <a) and the output characteristics of the 21st cell are (b), then if there is no output loss due to the n1 layer 2 junction, then n
Assuming that current flows without resistance at the one-layer, two-layer junction interface, the overall output exhibits a good output characteristic as shown in (C), and can reproduce the pattern shown in Fig. 1.

Next, in order to reproduce B in FIG. 1, it is necessary to add the output characteristics of the nl p22 layer plane as shown in (d) in FIG. 3, and then (e) can be simulated. This is because the n1 layer 2 junction surface of the conventional tandem structure cell has the output characteristic of the curve shown in (d> in Figure 3), resulting in the state shown in (e), where the fill factor becomes extremely large. Therefore, if (d> in Fig. 3 is
ll, in other words, eliminate the rectifying property, and reduce the resistance (resistance) to the end of the wood so that the current flows without resistance, making it easier for the electrons and balls that fall on the n1p2 junction to recombine. If this is done, the state shown in FIG. 2 will be achieved, and the output characteristics of the tandem structure cell can be improved.

<Effects of the Invention> As described above, according to the present invention, a tandem solar cell with high light conversion efficiency can be obtained, and its practical effects are very great.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the output characteristics of the tandem structure solar cell of the present invention, FIGS. 2 and 3 are simulation explanatory diagrams of the output characteristics of FIG. 1, and FIG. 5 is a sectional view showing an example of a tandem structure solar cell, and FIG. 6 is a sectional view showing an example of a tandem structure solar cell.
The output characteristics of the layered solar cell (I) and the proper solar cell (II) are shown, and FIG. 7 is an explanatory diagram showing the current-voltage characteristics of the np junction surface of the conventional two-layer structure solar cell.

Claims (2)

[Claims] (1) In a tandem solar cell in which the junction between unit cells is an np junction, the current-voltage output characteristic of the np junction surface is almost linear, and the light conversion efficiency is improved by reducing the sheet resistance of the np junction surface. A tandem structure solar cell characterized by increased height. (2) The tandem structure solar cell according to claim 1, characterized in that a large number of junction surface levels are provided on the np junction surface.