JPH05206493A - Solar cell - Google Patents

Abstract

PURPOSE:To obtain a low-cost solar cell which provides high energy conversion efficiency by laminating a transparent lower electrode, solid solutions as a plurality of window layers, a semiconductor layer as an absorption layer and an upper electrode layer on a transparent substrate one after another. CONSTITUTION:There is formed a solid solution layer, such as a Cd0.4Mn0.6Te thin film 3 (n-type semiconductor) for a first semiconductor and a second semiconductor as a window layer at the thickness of around 0.5mum on a transparent lower electrode 2 formed on a glass substrate 1. As for the second semiconductor, for example, a CdTe thin film (p-type semiconductor) 4 is formed as an absorption layer at the film thickness of around 5mum. What is more, there is formed an upper electrode 5 on the CdTe thin film 4. At that time, the lattice constants for the Cd0.4Mn0.6Te and the CdTe are substantially matched to each other. Furthermore, the band gap of the Cd0.4Mn0.6Te is virtually identical to that of Cds, thereby improving their release voltage and enhance their energy conversion efficiency.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solar cell having high energy conversion efficiency.

[0002]

2. Description of the Related Art Solar cells using conventional compound thin films are
As shown in FIGS. 2 (a) and 2 (b), the compound semiconductor thin film 3 having a wide band gap (functions as a window layer) and the compound thin film thin film 4 having a narrow band gap (functions as an absorption layer) are formed by a heterojunction. Has been done.

The most necessary condition for obtaining high energy conversion efficiency is to form a high quality heterojunction without carrier recombination at the interface. The high-quality hetero interface is closely related to the manufacturing method and the order of film formation. In the CdS / CdTe system, as shown in FIG. 2, the transparent electrode 2, the window layer 3 (CdS), and the absorption layer 4 are formed. (Cd
It is better to form Te) / electrode 5 in that order. This can be seen, for example, in the Thin-Film Cadmium Tellurite Solar Cells (Thin-Fil) published in the US DOE Rep (1988).
m Cadmium Telluride Solar Cells) from P30 onward, and as a partner of CdTe heterojunction, C
It is also stated that dS is most suitable. The reason for this is considered to be an excellent hetero interface because the solid solution layer of CdS and CdTe at the junction interface alleviates the lattice mismatch of about 8%.

[0004]

As a method that has been conventionally used for improving the efficiency of a CdTe-based thin film solar cell, an attempt to make CdS thinner (0.1 μm or less) or a semiconductor having a wider bandgap. , For example, CdZ
nS or transparent conductive oxide film (SnO2, ITO, ZnO)
Etc.), the sensitivity of short wavelength light of sunlight is improved. However, in the former case, CdS and Cd required to obtain an excellent hetero interface
Since the solid solution layer at the interface with Te is formed at the interface by mutual diffusion in the process using a temperature of 600 ° C. or higher, it is necessary to sufficiently consider the thickness of each of the semiconductor layers. Therefore, the thickness of CdS should be 0.1 μm.
It is very difficult to manufacture by controlling the following. Further, in the latter attempt, a hetero interface property with CdTe has not been obtained so far as compared with CdS / CdTe under the present circumstances, and as a result, high efficiency of a solar cell is not expected so much. From the above viewpoints, an object of the present invention is to solve the above-mentioned drawbacks and realize a solar cell with higher efficiency.

[0005]

A transparent lower electrode, a solid solution layer of a first semiconductor layer and a second semiconductor layer as a window layer, and a second semiconductor as an absorption layer are formed on a transparent substrate. The layers and the upper electrode are sequentially stacked.

Alternatively, a lower electrode, a second semiconductor layer as an absorption layer, a solid solution layer of the first semiconductor layer and the second semiconductor layer as a window layer, and a translucent upper electrode are provided on a substrate. Stack in sequence.

[0007]

According to the above construction, by matching the lattice constants of the solid solution layers of the first semiconductor and the second semiconductor and the second semiconductor layer, it is possible to improve the quality of the hetero interface between the two semiconductors. it can. In the conventional CdS / CdTe solar cell, there is a lattice mismatch of 8% between CdS and CdTe, but the presence of both solid solution layers improves the quality of the heterojunction. Then, the solid solution layer has a degree of freedom in the lattice constant, and the solar cell is constructed by a combination of matching lattice constants. With such a configuration, the saturation current at the time of reverse bias in the current-voltage characteristics of the heterojunction can be further reduced as compared with the conventional one, and carrier recombination at the hetero interface at the time of light irradiation can be suppressed and the output voltage and the solar voltage can be reduced. The fill factor in the battery characteristics can also be improved. In addition, the fact that the heterojunction of the present invention can be formed steeply increases the degree of freedom in setting the film thickness of the two semiconductor layers used in device design. For example, the semiconductor layer on the light incident side has a thickness of about 0.1 μm. And can be designed so that more light can be taken into the depletion layer generated near the hetero interface.

[0008]

EXAMPLES Examples of the present invention are shown below. FIG. 1 shows one configuration of the solar cell of the present invention. That is, Cd _0.4 Mn _0.6 T as a solid solution layer of the first semiconductor and the second semiconductor is formed on the transparent lower electrode 2 formed on the glass substrate 1.
A structure in which an e thin film 3 (n-type semiconductor) is formed to a thickness of about 0.5 μm, a CdTe thin film (p-type semiconductor) is formed to a thickness of about 5 μm as a second semiconductor, and an upper electrode is formed on the CdTe thin film. Is. Cd _0.4 Mn _0.6 Te and the lattice constant of CdTe is 0.00 approximately aligned, Cd _{0. 4} Mn _0.6 T
The bandgap of e is almost the same as CdS. Figure 1
The characteristics of the solar cell of the present invention shown in FIG. 2 and the conventional solar cell shown in FIG. 2 are shown in A and B of FIG. 3, respectively. The characteristics are summarized in the table below.

[0009]

[Table 1]

From the above, the open circuit voltage Voc is remarkably improved as compared with the conventional one, and as a result, a solar cell having a conversion efficiency of about 13% can be realized by the structure of the present invention.

[0011]

According to the present invention, it is possible to provide a low cost solar cell structure having high energy conversion efficiency.

[Brief description of drawings]

FIG. 1 is a perspective view showing a solar cell according to an embodiment of the present invention.

FIG. 2 is a perspective view showing the configuration of a conventional solar cell.

FIG. 3 is a graph showing the characteristics of the conventional solar cell and the characteristics of the solar cell of the present invention shown in FIG.

[Explanation of symbols]

 1 substrate 2 lower electrode 2a translucent lower electrode 3 window layer 4 absorption layer 5 upper electrode 5a translucent upper electrode

Claims (3)

[Claims] 1. A transparent lower electrode, a solid solution layer of a first semiconductor layer and a second semiconductor layer as a window layer, a second semiconductor layer as an absorption layer, and an upper portion on a transparent substrate. A solar cell comprising an electrode and a laminated layer. 2. A lower electrode and a second absorbing layer on the substrate.
2. A solar cell comprising: a semiconductor layer, a solid solution layer of a first semiconductor layer and a second semiconductor layer as a window layer, and a translucent upper electrode, which are sequentially laminated. 3. The solar cell according to claim 1, wherein the first semiconductor is MnTe and the second semiconductor is CdTe.