CN104201230A - Three-sub-node compound photovoltaic cell - Google Patents

Abstract

The invention relates to a triple junction compound photovoltaic cell, specifically an InAlAsP/InGaAs/Ge triple junction compound photovoltaic cell, which has an optimized 1.90ev/1.40ev/0.66ev energy band structure; the triple junction compound photovoltaic cell has two step convex structure, and the relationship between the n++InGaP/p++InGaAsP heterojunction tunneling diode and the thickness of the base region designed to configure the above-mentioned photovoltaic cell structure, the three-subjunction III-V compound photovoltaic cell has high photoelectricity Conversion efficiency and collection efficiency, especially effective confinement for natural light.

Description

A triple junction compound photovoltaic cell

technical field

The invention relates to a compound photovoltaic cell, especially a multi-subjunction compound photovoltaic cell. the

Background technique

III-V compound photovoltaic cells were first used in the space field, but with the advancement of technology, III-V compound photovoltaic cells are also increasingly used in non-space fields. Compared with silicon photovoltaic cells, III-V compound photovoltaic cells have greater energy conversion efficiency. The photoelectric conversion efficiency of III-V compound photovoltaic cells manufactured by advanced technology can exceed 25%, while silicon photovoltaic cells do not will exceed 20%. Compared with silicon photovoltaic cells, III-V compound photovoltaic cells can achieve maximum conversion of multiple solar radiation by using multiple sub-cells with different band gap energies;

For III-V compound photovoltaic cells, GaInP/GaAs/Ge is the most typical and mature III-V compound photovoltaic cell, and its photocurrent density can reach 25mA/cm2. However, the existing III-V The spectral absorption of natural sunlight by the group compound photovoltaic cells is not sufficient, and most of them are epitaxial to the semiconductor substrate layer by layer in the form of vertical and multi-junctions, and often cannot form confinement effects on light like silicon photovoltaic cells. Flocking surface, the existing III-V compound photovoltaic cells need to be further improved. the

Contents of the invention

In order to make up for the shortcomings of the existing III-V compound photovoltaic cells and further improve the utilization rate of light, the present invention provides an InAlAsP/IGaAs/Ge triple-junction compound photovoltaic cell. The InAlAsP/InGaAs/Ge triple-junction structure can effectively Improve the conversion efficiency of photovoltaic cells. At the same time, the InAlAsP/IGaAs/Ge triple junction compound photovoltaic cell also has a second-order raised structure that confines light. The second-order raised structure can effectively increase the light contact area. And it can effectively confine the light;

The three-junction III-V compound photovoltaic cell provided by the present invention comprises a Ge substrate; a Ge sub-cell is located on the Ge substrate; an InGaAs sub-cell is located on the Ge sub-cell; an InAlAsP sub-cell is located on the InGaAs sub-cell; Between the Ge substrate and the Ge sub-cell, include the back field layer on the n++ Ge contact layer and the n++ Ge contact layer; on the InAlAsP sub-cell, it is a window layer, and on the window layer is a p++ contact layer; the Ge sub-cell and InGaAs sub-cells, InGaAs sub-cells and InAlAsP sub-cells have lattice-matched n++/p++ tunneling diodes;

Further, the Ge sub-cell sequentially includes an n Ge base region, a p+ Ge emitter region in the direction away from the substrate, and has a band gap of about 0.66ev; the InGaAs sub-cell sequentially includes an n InGaAs base region in the direction away from the substrate region, p+ InGaAs emitter region, and has a bandgap of about 1.40ev; the InAlAsP subcell includes n InAlAsP base region, p+ InAlAsP emitter region, and has a bandgap of about 1.90ev in the direction away from the substrate;

Further, the shape of the illuminated surface on the upper part of the photovoltaic cell is a continuous two-stage convex structure, each of which has a first-stage convex structure and a second-stage convex structure, wherein the second-stage convex structure is formed from the first-stage convex structure. The raised upper surface is raised upwards;

Further, the thickness from the top surface of the second-stage protrusion to the bottom surface of the Ge substrate is 300-400um, and the thickness from the top of the first-stage protrusion to the bottom surface of the first-stage protrusion is 50-80um; and the second-stage protrusion The thickness from the top of the first-stage protrusion to the top of the first-level protrusion is at least twice the thickness from the top of the first-level protrusion to the bottom of the first-level protrusion; the interval between every two second-level protrusion structures is less than the first The thickness from the top of the step protrusion to the bottom surface of the first step protrusion;

Further, the thickness of the n Ge base region is greater than the thickness of the n InGaAs base region, the thickness of the n InGaAs base region is greater than the thickness of the n InAlAsP base region, the thickness of the n Ge base region is about 2.5 microns, and the thickness of the n InGaAs base region The thickness of the n InAlAsP base region is about 2.2 microns, and the thickness is about 1.8-2.0 microns; the thickness of the p+ Ge emitter region, p+ InGaAs emitter region, and p+ InAlAsP emitter region is 80-100 nanometers;

Further, the lattice-matched n++/p++ tunneling diode is a heterojunction tunneling diode;

Further, the lattice-matched n++/p++ tunneling diode is an n++ InGaP/p++ InGaAsP heterojunction tunneling diode; its total thickness is 30-45 nanometers;

Description of drawings

Fig. 1 is according to the structure schematic diagram of triple junction compound photovoltaic cell of the present invention;

FIG. 2 is an enlarged view of area A in FIG. 1 , that is, a schematic diagram of each sub-junction material layer of the photovoltaic cell of the present invention. the

Detailed ways

The present invention will be further described below in conjunction with the best embodiment, and the beneficial effects of the present invention will become clear in the detailed description;

Referring to Figs. 1-2, Fig. 1 is a schematic structural view of a three-subjunction photovoltaic cell of the present invention, and Fig. 2 is an enlarged view of area A in Fig. 1, which shows details of a photovoltaic cell of the present invention; for an aspect of the present invention, see Fig. 2 The compound photovoltaic cell of the present invention has a multi-junction InAlAsP/InGaAs/Ge structure, wherein the band gap of the InAlAsP sub-cell (300) is about 1.9 eV, the band gap of the InGaAs sub-cell (200) is about 1.40 eV, and the Ge sub-cell The bandgap of the cell (100) is about 0.66ev. The optimized structure of the bandgap of the triple-junction photovoltaic cell of the present invention can match the wavelength structure of the natural solar spectrum, make full use of the photon energy of each wavelength band of photovoltaics, and optimize overall Absorption of the solar spectrum improves cell efficiency. And, referring to Fig. 1, the shape of the upper illuminated surface of the compound photovoltaic cell of the present invention is a continuous second-order convex structure (a, b), and each second-order convex structure (a, b) has a first-order protrusion (b ) and a second-stage protrusion (a), wherein the second-stage protrusion (a) protrudes upward from the upper surface of the first-stage protrusion (b);

Specifically, the compound photovoltaic cell of the present invention includes a Ge substrate (001) with continuous second-order raised structures (a, b), wherein each second-order raised structure (a, b) includes a first-order raised The protrusion (b) and the second-level protrusion (a), wherein the second-level protrusion (a) protrudes upward from the upper surface of the first-level protrusion (b). Ge sub-cells (100), InGaAs sub-cells (200), and InAlAsP sub-cells (300) are located on the Ge substrate (001) in order to form a triple-junction cell with a band structure of 1.90ev/1.40ev/0.66ev. The bandgap of each subcell gradually increases in the direction away from the substrate, which is very conducive to the improvement of the photocurrent density, and the Ge subcell (100) has a bandgap of about 0.66ev and in the direction away from the substrate The n Ge base region (101) and the p+ Ge emitter region (102) are sequentially, the thickness of the n Ge base region (101) is preferably 2.5 microns, the thickness of the p+ Ge emitter region (102) is preferably 80-100 nanometers; the InGaAs sub-cell ( 200) has a bandgap of about 1.40ev, and in the direction away from the substrate, there are n InGaAs base region (201) and p+ InGaAs emitter region (202) sequentially, and the thickness of n InGaAs base region (201) is preferably 2.2 microns, The thickness of the p+ InGaAs emitter region (202) is preferably 80-100 nanometers; the InAlAsP sub-cell (300) has a band gap of about 1.90ev, and in the direction away from the substrate, there are n InAlAsP base region (301), p+ InAlAsp In the emitting region (302), the thickness of the n InAlAsP base region (301) is preferably 1.8-2.0 microns, and the thickness of the p+ InAlAsp emitting region (302) is preferably 80-100 nanometers. Between the Ge substrate (001) and the n Ge base region (101) also includes an n++ Ge contact layer (002) and a back field layer (003); on the InAlAsP subcell (300) is a window layer (006), the window Layer (006) is a p++ contact layer (007). In the present invention, the optimization of the base thickness of each sub-cell is that the sub-cell with a large energy gap close to the illuminated surface is smaller than the sub-cell with a small energy gap far away from the illuminated surface; specifically In other words, the thickness of the n InAlAsP base region (301) is smaller than the thickness of the n InGaAs base region (201), and the thickness of the n InGaAs base region (201) is smaller than the thickness of the n Ge base region (101), which is beneficial to the natural photovoltaic spectrum maximize the use of

Lattice-matched n++/p++ tunneling diodes (004, 005) between each sub-cell layer; in this InAlAsP/InGaAs/Ge band system multi-junction photovoltaic cell, lattice-matched n++/p++ tunneling The diode needs to use a heterojunction structure, which is beneficial to provide a high interjunction barrier, especially the tunneling diode (005) between the InAlAsP and InGaAs subcells. In our experiments, it was observed that this pair of light passes through the upper InAlAsP The sub-cell (300) and the reduction of minority carrier diffusion between junctions play a favorable role. In the experiment, we used n++ InGaP/p++ InGaAsP heterojunction tunneling diodes, which improved the photocurrent efficiency of the cell to the greatest extent. Of course, as for For epitaxially grown multi-junction III-V photovoltaic cells, the thickness of the tunneling diode is very important and sensitive. When selecting n++ InGaP/p++ InGaAsP heterojunction tunneling diode as the sub-cell of the multi-junction photovoltaic cell InAlAsP and InGaAs When the tunneling diode (005) in between, the total thickness of the experimentally optimized n++ InGaP/p++ InGaAsP heterojunction tunneling diode (005) is 30-45 nanometers;

Next, we will focus on the second-order convex structure of the InAlAsP/InGaAs/Ge triple-junction photovoltaic cell of the present invention. First of all, the second-order raised structure (a, b) of the InAlAsP/InGaAs/Ge triple-junction photovoltaic cell of the present invention is built on the Ge substrate of the second-order raised structure, and each sub-cell and other functional layers are sequentially covered on the Ge substrate. on the substrate. The thickness d1 from the top surface of the second-stage protrusion (b) to the bottom surface of the Ge substrate is about 300-400um, and the thickness d2 from the top of the first-stage protrusion (b) to the bottom surface of the first-stage protrusion (b) is preferably 50~80um, that is, the height d2 of the first-stage protrusion (b) is 50-80um; the thickness d3 between the top of the second-stage protrusion (a) and the top of the first-stage protrusion (a) is at least greater than that of the first-stage protrusion (a) Twice the height d2 of the first-order protrusion (b), preferably 150-200um, that is, the height d3 of the second-order protrusion (a) is preferably 150-200um; the interval between every two second-order protrusion structures less than the height of the first-order protrusion (b); the width of each second-order protrusion structure is preferably 150-200um. Through the optimization of the above parameters, when the incident light hits the surface of the photovoltaic cell at a certain angle, a part of it is firstly absorbed by the battery on the surface of the second-stage raised structure, and a part of the unabsorbed part irradiated on the side of the second raised structure is reflected to the second-order raised structure. The surfaces of the first-order bumps are absorbed by the first-order bumps, and part of the light that is not absorbed by the surface of the first-order bump structures is reflected to the surface of the battery between the second-order bump structures. In this way, only the light irradiated on the upper surface of the battery can be used originally, but the light irradiated on the upper surface can not be used through the second-order convex structure, and the light irradiated to the side can also be used through the reflection of the side. Light, this part of light is the added extra light. To some extent, the structure makes systematic use of light, so the incident light from the sun can be maximized. What is more noteworthy is that the light reflected from the surface of the cell between the second-level bump structures will hit the surface of the first-level bump structure and/or the surface of the second-level bump structure, so that the photovoltaic light is maximized. On the surface of the photovoltaic cell with the second-order bump structure, the use of solar light by the battery is greatly improved; the above-mentioned limiting effect is inseparable from the above-mentioned parameter selection. If the second-order bump structure If the raised height is less than the height of the first-order raised structures or the distance between the second-order raised structures is too large, it will not limit the sunlight or will greatly weaken the limited effect;

Through the description of the above specific embodiments, the concept of the present invention has been fully disclosed, and those skilled in the art should be able to understand the advantages of the present invention; the understanding of the application should not be limited to the above embodiments, and the present invention Obviously modified implementations with the same spirit should also belong to the concept of the present invention.

Claims (7)

1. three son knot compound photovoltaic cells, comprise Ge substrate; Ge battery, is positioned on Ge substrate; The sub-battery of InGaAs, is positioned on Ge battery; The sub-battery of InAlAsP, is positioned on the sub-battery of InGaAs; At the back surface field layer comprising between described Ge substrate and Ge battery on n++ Ge contact layer and n++ Ge contact layer; On the sub-battery of InAlAsP, being Window layer, is p++ contact layer in Window layer; The sub-battery of Ge battery and InGaAs, the sub-battery of InGaAs and the sub-battery of InAlAsP have the n++/p++ tunneling diode of Lattice Matching before.

2. photovoltaic cell as claimed in claim 1, described Ge battery comprises successively n Ge base in the direction away from substrate, p+ Ge emitter region, and there is the band gap about 0.66ev; The sub-battery of described InGaAs comprises successively n InGaAs base on away from substrate direction, p+ InGaAs emitter region, and there is the band gap about 1.40ev; The sub-battery of the InAlAsP that tells of institute comprises successively n InAlAsP base on away from substrate direction, p+ InAlAsP emitter region, and there is the band gap about 1.90ev.

3. the photovoltaic cell as described in claim 1-2, be shaped as continuous second order bulge-structure at this photovoltaic cell top plane of illumination, each second order bulge-structure has the first rank projection and second-order projection, and wherein second-order projection raises up from the upper surface of the first rank projection.

4. photovoltaic cell as claimed in claim 3, is 300～400um from the end face of second-order projection to the bottom thickness of Ge substrate, and the top of the first rank projection is 50 ~ 80um to the thickness of the first projection bottom surface, rank; And the top of second-order projection is at least greater than the top of the first rank projection to the twice of the thickness of the first projection bottom surface, rank to the thickness at the top of the first rank projection; Interval between every two second order bulge-structures is less than the top of the first rank projection to the thickness of the first projection bottom surface, rank.

5. the photovoltaic cell as described in claim 1-4, the thickness of described n Ge base is greater than the thickness of n InGaAs base, the thickness of n InGaAs base is greater than the thickness of n InAlAsP base, and the thickness of n Ge base is that approximately 2.5 microns, the thickness of n InGaAs base are that approximately 2.2 microns, the thickness of n InAlAsP base are about 1.8-2.0 micron; The thickness of p+ Ge emitter region, p+ InGaAs emitter region, p+ InAlAsP emitter region is 80-100 nanometer.

6. photovoltaic cell as claimed in claim 5, the n++/p++ tunnel-through diode of described Lattice Matching is heterojunction tunnel-through diode.

7. photovoltaic cell as claimed in claim 6, the n++/p++ tunnel-through diode of described Lattice Matching is n++ InGaP/p++ InGaAsP heterojunction tunnel-through diode; Its gross thickness is 30-45 nanometer.