JPH04309270A - Manufacture of tandem type solar cell - Google Patents

Abstract

PURPOSE:To provide a method which can efficiently manufacture a tandem type solar cell having a GaP/GaAsP structure or a structure which includes the structure. CONSTITUTION:This tandem type solar cell manufacturing method forms a p-type GaP compound semiconductor on the surface of an n-type GaP semiconductor substrate after a p-type GaAsP compound semiconductor and n-type GaAsP compound semiconductor are successively formed by epitaxial growth on the surface of the substrate opposite to the p-type GaP compound semiconductor.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to GaP cells and GaAs cells.
The present invention relates to a method for manufacturing a tandem solar cell having a stacked structure of P cells.

0002

[Prior art] In order to achieve ultra-high efficiency in solar cells,
It is necessary to utilize energy effectively across the spectrum of sunlight. To this end, a tandem solar cell with a structure in which solar cells with different forbidden band widths are stacked has been proposed, and research and development is underway. Table 1 shows examples of materials for three-layer tandem solar cells. Among these materials, the GaP/GaAsP/Si structure is known to have the forbidden band width shown in Table 2 as one of the combinations that can obtain an efficiency of η = 30% or more, and is a suitable combination of materials. (M.E. Nell et al. “GaAsPh
right-efficiency tandem sol
ar cell”18th IEEE PVSC, 19
85).

[Table 1]

[Table 2]

0003

[Problem to be solved by the invention] Although Si cells have been widely developed and some have been put into practical use,
Research on GaP cells and GaAsP cells is currently underway. These compound semiconductor cells are generally formed by epitaxial growth. When forming a GaP cell by epitaxial growth, there are the following problems. In other words, since the GaP compound semiconductor has an indirect transition type band structure, its absorption coefficient is much smaller than that of a direct transition type compound semiconductor such as GaAs, as shown in Figure 3, so it can effectively absorb sunlight. It is necessary to make the cell thickness sufficiently thick. For example, in order to obtain absorption of 99.9% or more for the peak wavelength of sunlight 0.5 μm, a thickness of about 1 μm is sufficient for direct transition type AlGaAs compound semiconductors, whereas GaP
The compound semiconductor needs to have a thickness of 10 to 20 μm or more.

On the other hand, a GaP cell with the above thickness is OMVP
When formed using the E method, the growth rate is generally 1 to 2 μm/h.
Since the growth time is about 5 to 20 hours, it is practically difficult. Furthermore, since the growth time directly affects the manufacturing cost, shortening the growth time is an essential issue. Therefore, the present invention solves the above problems and provides GaP/G
The present invention aims to provide a method for efficiently manufacturing a tandem solar cell having an aAsP structure or a structure including this.

[0005]

Means for Solving the Problems The present invention provides a method for manufacturing a tandem solar cell having a GaP cell and a GaAsP cell, in which a p-type GaAsP compound semiconductor and an n-type GaAsP compound semiconductor are sequentially epitaxially grown on an n-type GaP substrate. After that, p-type GaP is placed on the opposite side of the substrate.
A method for producing a tandem solar cell characterized by forming a compound semiconductor, and a method for producing the tandem solar cell described above, characterized by stacking another solar cell on a stacked structure of GaP cells and GaAsP cells. It's a method.

[0006]

[Operation] FIGS. 1(a) to 1(c) are sectional views showing the steps for manufacturing a tandem solar cell having a GaP/GaAsP structure. (a) is a stage in which a p-GaAsP layer and an n-GaAsP layer are epitaxially grown on an n-GaP substrate. GaAsP has a P composition (
When x:GaAs1-xPx) is 0.45 or less, it becomes a direct transition type, and the forbidden band width 1 is suitable for tandem solar cells.
．． Since the P composition to ensure 6 eV is x=0.14, the GaAsP cell can sufficiently absorb sunlight even if it is thin. The thickness of this cell is the p-type layer and n
The total thickness of the mold layers is only 5 μm, and when grown by the OMVPE method, it can be grown within 5 hours. (b) is a stage in which a pn junction is formed on the back surface of an n-GaP substrate by a diffusion method or the like after forming a GaAsP cell. The n-GaP substrate used here may have a thickness suitable for forming solar cells, or a GaAsP substrate may be used from the beginning.
The thickness may be adjusted by etching, polishing, etc. after cell formation, but the latter is more desirable since the thickness of a GaP cell is generally several tens of micrometers. Furthermore, since these processes can be performed on a large number of wafers at once, there is no major problem in terms of cost. (c) shows the stage at which p-electrodes and n-electrodes are formed on a wafer with a GaP/GaAsP structure;
A tandem solar cell having a stacked structure of P cells is manufactured. FIG. 2 is a cross-sectional view of a three-layer tandem solar cell in which separately manufactured Si cells are stacked on the GaP/GaAsP structure of FIG. 1(b) to form a p-electrode and an n-electrode.

[0007]

[Example] (Example 1) First, an S-doped n-type
G
aAsP cells were formed. Raw material is arsine (AsH3)
, phosphine (PH3), trimethyl gallium (TMG)
), and the growth temperature was adjusted to 700°C. The P composition of the cell was x = 0.14, dimethyl zinc (DMZ) was used as the dopant for the p-type, and tellurium hydride was used for the n-type, and the p-type layer was grown in the order of n-type layer. Ta. The thickness of the GaAsP cell thus obtained was 5.2 μm, and the growth time was 2.8 hours. The GaP substrate portion of the obtained wafer was selectively etched to a thickness of 22 μm.
GaP is thinned to 800°C in a diffusion furnace heated to
A GaP cell was obtained by diffusing Zn from the surface to form a pn junction. Next, a comb-shaped electrode and an antireflection film were formed on the p-type GaP side of this wafer, and a full-surface electrode was formed on the n-type GaAsP side to obtain a two-layer tandem solar cell. When this solar cell was irradiated with standard sunlight of AM1.5 using a solar simulator, the photoelectric conversion efficiency was 26%.

(Example 2) GaP/Ga obtained in Example 1
Separately prepared Si cells were mechanically bonded to a wafer having an AsP structure, and electrodes were formed in the same manner as in Example 1 to obtain a three-layer tandem solar cell. When this solar cell was irradiated with standard sunlight of AM1.5 using a solar simulator, a photoelectric conversion efficiency of 32% could be obtained.

[0009]

[Effects of the Invention] By adopting the above configuration, the present invention provides a GaP/GaAsP structure or a Si
It has become possible to efficiently manufacture tandem solar cells in which cells are further stacked, making it possible to reduce costs.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing a procedure for manufacturing a two-layer tandem solar cell by the method of the present invention.

FIG. 2 is a cross-sectional view of a three-layer tandem solar cell.

FIG. 3 is a graph showing absorption coefficients of various semiconductors.

Claims (2)

[Claims] Claim 1. In a method for manufacturing a tandem solar cell having a GaP cell and a GaAsP cell, n-type GaP
P-type GaAsP compound semiconductor and n-type GaA on the substrate
After epitaxially growing the sP compound semiconductor,
A method for manufacturing a tandem solar cell, comprising forming a p-type GaP compound semiconductor on the opposite side of the substrate. 2. The method for manufacturing a tandem solar cell according to claim 1, wherein another solar cell is stacked on the stacked structure of the GaP cell and the GaAsP cell.