JPH03285360A - Solar cell - Google Patents

Abstract

PURPOSE:To prevent recombination of minority carrier of a base region and to improve a generating efficiency by holding a base region between a pair of layers each having high impurity concentration. CONSTITUTION:A P<+> type layer 7 having further high impurity concentration is provided at the surface side of a base region 1 made of P-type semiconductor, and the region 1 having lower concentration than those of FSF7 and BSF3 of P<+> type high concentration layers is held between the SFS7 and the BSF3 from the front and rear surfaces. For example, if the base 1 contains 1X10<17>cm<-3> of impurity concentration, the FSF1 and the BSF3 are set to 5X10<17>cm<-3> of impurity concentration. Thus, recombination of minority carrier in a boundary between the front and rear surfaces of the base region can be prevented by the BSF3 and the FSF7 having higher impurity concentration than that of the region 1, a collection efficiency in an emitter region 2 is improved, and a generating efficiency is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a solar cell in which recombination of minority carriers generated in a base region is prevented.

<Prior Art> Solar cells, which convert light energy into electrical energy through the photovoltaic effect, are actively being used as a clean and inexhaustible power generation system.

FIG. 4 shows an example of a conventional solar cell.

This solar cell has a highly concentrated N-type diffusion layer formed on the surface of a P-type semiconductor (Sl) substrate to form a P-type base region 1 and an N-type emitter region 2. Then, on the back surface of the substrate, a P' type layer (Pack Surf Ace Field F': BSF > 3) is provided by diffusing impurities at a high concentration, and on the surface of this BSF 3, an electrode 4 made of A1 or the like is provided. Further, an electrode 6 made of AI or the like is provided on the surface side of the substrate via an insulating film (Si02) 5, and this electrode 6 is connected to the emitter region 2.

According to this theory, when light hv whose photon energy is larger than the forbidden band width is removed from the surface side, electric power is generated between the electrodes 4 and 6 due to the photovoltaic effect of the PN junction. At this time, the BSF 3 reflects minority carriers (electrons in this case) in the base region 1 toward the emitter region 2 side to prevent recombination at the interface, thereby improving power generation efficiency.

<Problem to be solved by the invention> Conventionally, solar cells have been provided with BSF3 whose concentration is considerably higher than that of the base region 1, and the recombination of minority carriers on the back side of the substrate has been prevented to improve power generation efficiency. There is.

However, on the surface side of the substrate, there is no attempt to prevent minority carrier recombination at the interface between the base region 1 and the bashing film, buffer layer, light reflection film, etc., and sufficient improvement in power generation efficiency has not been achieved. could not.

The present invention was made in view of the above-mentioned conventional circumstances, and by sandwiching the base region between a pair of layers with high impurity concentration, recombination of minority carriers in the base region is completely prevented,
The aim is to provide solar cells that significantly improve power generation efficiency.

<Means for Solving the Problems> A solar cell according to the present invention has an emitter region made of a semiconductor of another conductivity type formed in contact with a base region made of a semiconductor of one conductivity type. It is characterized by providing layers of one conductivity type with high impurity concentration sandwiching the region.

Effect> By sandwiching the base region between a pair of layers of the same conductivity type with high impurity concentration, recombination of minority carriers in the base region at the interface is prevented and collection efficiency of the minority carriers in the emitter region is increased.

<Example> The solar cell of the present invention will be specifically described based on an example.

FIG. 1 shows a solar cell according to a first embodiment of the present invention. Incidentally, the same parts as those in the conventional example described above are given the same reference numerals and redundant explanations will be omitted.

The solar cell of this example has a base region 1 made of a P-type semiconductor.
A (P゛) layer ()a ant surface field (FSF) 7 with a higher impurity concentration is provided on the surface side of the .
3 and 3 sandwich the P-type base region 1 having a lower concentration than these from the front and back surfaces.

For example, if base region 1 is doped with impurity concentration lXl0''CT11
3, FSF7 and BSF3 have an impurity concentration of 5
Set to X 1019cyn-3.

Here, in this embodiment, the FSF 7 is not in contact with the emitter region 2 and a gap d is provided between the two, but even if this is done, if the gap d is about the width of the depletion layer of the PN junction, it will be small. There is no problem in preventing carrier recombination. It goes without saying that the FSF 7 may be provided in contact with the emitter region 2.

According to the solar cell having the above configuration, BSF3 and FSF7, which have a higher impurity concentration than the base region 1, prevent minority carriers in the base region from recombining at the front and back interfaces, improving the collection efficiency in the emitter region 2. Improved power generation efficiency can be achieved.

Comparing the power generation efficiency between the conventional structure shown in Figure 4 and the one shown in Figure 1, it was found that the conventional structure shown in Figure 4 had a power generation efficiency of 15.0%. The power generation efficiency was 16.1% higher than that of the structure shown in Figure 1, and the power generation efficiency was improved by 1.1% by applying the present invention.

FIG. 2 shows a solar cell according to a second embodiment of the invention.

In the solar cell to which the present invention is applied in this embodiment, the picture electrode 4.6 is set on one surface of the substrate, and light is emitted from the surface opposite to the surface on which these HBs are provided. In addition to improving the absorption efficiency of optical energy, the highly concentrated P-type collector region 8 and emitter region 2 are formed inside the base region 1 to prevent minority carriers from recombining beyond the interface of the power generation region. This is an attempt to expand the power generation area. Note that 9.10 in the figure is an insulating film.

The solar cell of this example also has a structure in which the base region 1 is sandwiched between the FSF 7 and the BSF 3 from the front and back surfaces, and as in the above example, recombination of minority carriers is prevented to improve power generation efficiency. There is.

When we compared the power generation efficiency between the system shown in Figure 2 and the system without FSF7, we found that the system without FSF7 was 23%
．． The power generation efficiency was 8%, but by applying Fig. 2, the power generation efficiency was improved by 1.1%.

FIG. 3 shows a solar cell according to a third embodiment of the present invention.

This embodiment is a further improvement on the second embodiment described above, in which the paths of the electrodes 6 and 4 to the emitter region 2 and collector region 8 are also covered with the FSF 7, and thereby,
Recombination of minority carriers in this path portion is prevented.

When we compared the power generation efficiency between the system shown in Figure 3 and the system without FSF7, we found that the system without FSF7 was 23.
．． While it was 8%, it was 25.3% for the structure shown in FIG. 3, and the power generation efficiency was improved by 1.5% by applying the present invention.

Incidentally, in the present invention, the PN relationship of the conductivity type may be reversed from that shown in each of the above embodiments, and if the minority carriers in the base region are electrons as in the above embodiments, BSF and FS
F! , tP'' type, and if the minority carriers in the base region are holes, then it is assumed to be BSF and FSF!, tN'' type.

<Effects> According to the solar cell according to the present invention, since the layers with high impurity concentration sandwiching the base region are provided, it is possible to prevent minority carriers in the base region from recombining at the front and back interfaces,
Improving the collection efficiency of the minority carriers in the emitter region,
Significant improvements in power generation efficiency can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a solar cell according to a first embodiment of the present invention, FIG. 2 is a perspective view of a solar cell according to a second embodiment of the present invention, and FIG. 3 is a perspective view of a solar cell according to a third embodiment of the present invention. FIG. 4 is a perspective view of a solar cell according to an example. FIG. 4 is a perspective view of a solar cell according to a conventional example. 1 is a base region, 2 is an emitter region, 3 is a pack surf ace field, 4.6ζ is an electrode, 5.9.10 is an insulating layer, and 7 is a front surf ace field.

Claims (1)

[Claims] In a solar cell in which an emitter region made of a semiconductor of another conductivity type is formed in contact with a base region made of a semiconductor of one conductivity type, a layer of the first conductivity type with a high impurity concentration sandwiching the base region is provided. A solar cell featuring: