CN110534607A - A GaInP/GaAs/μ c-Si: h three-junction laminated solar cell - Google Patents

Abstract

The present invention relates to a GaInP/GaAs/μc‑Si:H triple junction tandem solar cell. The present invention belongs to the technical field of solar cells. A GaInP/GaAs/μc‑Si:H triple junction tandem solar cell, characterized in that: the GaInP/GaAs/μc‑Si:H triple junction tandem solar cell adopts MOCVD technology to epitaxially grow lattice-matched solar cell materials on a Ge substrate, including two sub-cells: a GaInP top cell and a GaAs middle cell; the GaAs middle cell and the μc‑Si:H bottom cell prepared by PECVD are bonded together by a low-temperature bonding process, and the GaAs substrate is peeled off by chemical etching; the GaInP/GaAs/μc‑Si:H triple junction tandem solar cell sequentially connects the GaInP top cell, the tunnel junction, the GaAs middle cell, and the μc‑Si:H bottom cell. The present invention has the advantages of significantly improving the conversion efficiency of the battery, effectively reducing the battery cost, and greatly improving the application prospects of the triple junction tandem solar cell.

Description

A GaInP/GaAs/μc-Si:H Triple Junction Laminated Solar Cell

technical field

The invention belongs to the technical field of solar cells, in particular to a GaInP/GaAs/μc-Si:H triple-junction laminated solar cell.

Background technique

At present, forward lattice-matched triple-junction GaAs has been widely used in space power systems due to its high photoelectric conversion efficiency and good radiation resistance. The conversion efficiency of forward-matched triple-junction cascaded GaInP/GaAs/Ge solar cells is close to 30.0% under the AM0 spectrum, but the photocurrent density of the cell is usually limited by the top cell, and the redundant photocurrent density on the bottom cell cannot be controlled. Effective utilization makes it impossible to realize full-spectrum absorption and utilization; at the same time, a considerable part of the energy of the triple-junction cascaded GaAs solar cell that is greater than the forbidden band width of the corresponding sub-cell is lost in the form of heat energy. Therefore, a cell with a bandgap ~1.1eV is needed to replace the Ge bottom cell. An inverse lattice mismatch (IMM) triple-junction GaAs solar cell can achieve an ideal match between the cell band gap and the spectrum through a graded buffer layer, but The process of IMM battery is difficult and costly.

The research on silicon-based thin-film solar cells began in the late 1960s, and it is the thin-film solar cell technology that achieved industrialization technology earlier. In 1980, the efficiency of amorphous silicon (a-Si:H) solar cells was increased to 8%, which was a sign of industrialization. With the development of silicon-based materials such as silicon germanium (a-SiGe:H) and microcrystalline silicon (μc-Si:H), a-Si:H/a-SiGe:H/μc-Si:H triple junction solar The initial efficiency of the small-area battery reaches 16.3%, but the light-induced attenuation effect of a-Si:H and a-SiGe:H restricts the highest stable efficiency that silicon-based thin-film solar cells can achieve. Due to its narrow energy gap and light stability, μc-Si:H can be used as a bottom cell and other wide band gap semiconductor materials to form a hybrid tandem solar cell.

Hybrid tandem cells are a hot spot in the research of multi-junction solar cells in recent years. Different semiconductor materials (III-V, CIGS, Si, perovskite, etc.) are combined according to the principle of "cell band gap and spectrum matching" to realize High efficiency, low cost and other purposes.

Contents of the invention

The invention provides a GaInP/GaAs/μc-Si:H triple-junction laminated solar cell to solve the technical problems in the known technology.

The purpose of the present invention is to provide a GaInP/GaAs/μc-Si:H triple-junction stack with the characteristics of significantly improving the conversion efficiency of the battery, effectively reducing the cost of the battery, and greatly improving the application prospects of the triple-junction stack solar cell. layer solar cells.

The technical scheme adopted by the GaInP/GaAs/μc-Si:H triple junction solar cell of the present invention is:

A GaInP/GaAs/μc-Si: H triple-junction stacked solar cell, which is characterized by: GaInP/GaAs/μc-Si: H triple-junction stacked solar cell, using MOCVD technology to epitaxially grow the crystal lattice on the Ge substrate Matched solar cell materials, including two sub-cells: GaInP top cell, GaAs middle cell; GaAs middle cell and μc-Si:H bottom cell prepared by PECVD are bonded together by low-temperature bonding process, and GaAs substrate is bonded by chemical Etching and stripping; GaInP/GaAs/μc-Si:H triple-junction stacked solar cells are sequentially connected to GaInP top cell, tunnel junction, GaAs middle cell, and μc-Si:H bottom cell.

The GaInP/GaAs/μc-Si:H triple junction solar cell of the present invention can also adopt the following technical solutions:

The GaInP/GaAs/μc-Si:H triple-junction stacked solar cell is characterized in that the band gaps of the three sub-cells of the triple-junction cascaded solar cell are 1.86±0.05eV, 1.40±0.05eV, 1.05 ±0.05eV.

The GaInP/GaAs/μc-Si:H triple junction solar cell is characterized by:

The first junction GaInP battery: sequentially grown into an n-type doped AlGaInP back field layer with a thickness of 100-200nm, an n-type doped GaInP base region with a thickness of 500-1000nm, a p-type doped GaInP emitter region with a thickness of 50-100nm, and a thickness of 30-100nm p-type doped AlInP window layer, in which: the doping concentration of the n-type doped AlGaInP back field layer is 1×10 ¹⁷ -1×10 ¹⁹ cm ^-3 , the doping concentration of the n-type doped GaInP base region The concentration is 1×10 ¹⁶ -1×10 ¹⁷ cm ^-3 , the doping concentration of the p-type doped GaInP emission region is 1×10 ¹⁷ -1×10 ¹⁹ cm ^-3 , the doping concentration of the p-type doped AlInP window layer The concentration is 1×10 ¹⁷ -1×10 ¹⁹ cm ^-3 ;

Tunneling junction: sequentially grown into an n-type GaInP layer with a thickness of 10-100nm and a p-type Al _0.4 Ga _0.6 As with a thickness of 10-100nm: where: the doping concentration of the n-type GaInP layer is 1×10 ¹⁸ -1×10 ²⁰ cm ^-3 , the doping concentration of p-type Al _0.4 Ga _0.6 As is 1×10 ¹⁸ -1×10 ²⁰ cm ^-3 ;

The second junction GaAs cell: grow in turn an n-type doped AlxGa1-xAs back field layer with a thickness of 100-200nm, an n-type doped GaAs base region with a thickness of 1000-2000nm, and a p-type doped GaAs emission region with a thickness of 50-200nm , a p-type doped AlxGa1-xAs window layer with a thickness of 30-100nm; wherein: the doping concentration of the n-type doped AlxGa1-xAs back field layer is 1×10 ¹⁷ -1×10 ¹⁹ cm ^-3 , and the n-type doped The doping concentration of the GaAs base region is 1×10 ¹⁶ -1×10 ¹⁷ cm ^-3 , the doping concentration of the p-type doped GaAs emitter region is 1×10 ¹⁷ -1×10 ¹⁹ cm ^-3 , the p-type doping The doping concentration of the AlxGa1-xAs window layer is 1×10 ¹⁷ -1×10 ¹⁹ cm ^-3 , 0.3≤x≤0.5;

The third junction μc-Si:H battery: sequentially grow Ag with a thickness of 1-2 μm as the back electrode, a ZnO:Al(AZO) layer with a thickness of about 1-2 μm, and an n-type doped layer with a thickness of 10-100 nm in sequence μc-Si:H, intrinsic μc-Si:H of 2-4um, p-type doped a-Si:H of 10-100nm, AZO window layer with a thickness of 0.5-1.5μm.

The GaInP/GaAs/μc-Si:H triple-junction cascaded solar cell of the present invention should ensure good light transmittance, mechanical strength and low resistivity of the bonding surface between the GaAs sub-cell and the μc-Si:H sub-cell.

This bandgap combination can basically match the bandgap of the subcell with the AM0 solar spectrum, and the theoretical photoelectric conversion efficiency is consistent with that of the IMM triple-junction GaAs solar cell.

The preparation process of the GaInP/GaAs/μc-Si:H triple-junction cascaded solar cell of the present invention:

Step 1. Epitaxial reverse growth to prepare GaInP and GaAs sub-cells

Place the Ge substrate in the MOCVD operating chamber, set the growth temperature at 500°C to 800°C, and epitaxially grow a GaAs buffer layer with a thickness of 0.1-0.3 μm and a GaInP etch stop layer with a thickness of 0.1-0.3 μm on the Ge substrate. , a p-type doped GaAs cap layer with a thickness of 100-500nm, a GaInP battery as the top battery, a tunnel junction, a GaAs battery as the middle battery, and an AlGaAs or GaInAs sacrificial layer with a thickness of 50-100nm;

Step 2. Preparation of μc-Si:H sub-battery by PECVD growth

Stainless steel foil and other materials are used as the substrate, after surface cleaning, Ag with a thickness of 1-2 μm is deposited by evaporation process as the back electrode, AZO with a thickness of about 1-2 μm is deposited by DC magnetron sputtering, and N-i-P silicon substrate is deposited sequentially by PECVD Semiconductor film, AZO or ITO window layer with a thickness of 0.5-1.5 μm is deposited by DC magnetron sputtering;

Step 3. Bond the batteries prepared in steps 1 and 2 together

The surface roughness of AlGaAs or GaInAs sacrificial layer and AZO window layer is reduced to less than 1nm by CMP process. After surface cleaning, the surface of the battery is activated by plasma, and the GaAs sub-battery and μc-Si:H sub-battery are bonded together; put into the bonding chamber of the bonding machine, and the bonding chamber is filled with N ₂ , when the temperature of the bonding chamber is raised to 80-120°C, preheat the battery for 60-120 seconds; Raise the temperature to 150-250°C, maintain a constant temperature, and perform bonding for 1-2 hours, and then lower the temperature in the bonding chamber to room temperature at a cooling rate of 3°C/min to achieve low-temperature bonding;

Step 4, peel off the Ge substrate

Use HF:H2O2:H2O=2:1:1 etchant to etch the Ge substrate, use 1:1 ammonia water and hydrogen peroxide to etch the GaAs buffer layer, after the Ge substrate and GaAs buffer layer are stripped off from the battery, use HCl: H2O=1:1 etching solution corrodes the GaInP etch stop layer, the GaInP etch stop layer is peeled off from the battery, and the peeling of the Ge substrate is completed;

Step 5. Finally, the preparation of the GaInP/GaInAs/μc-Si:H triple-junction cascaded solar cell is completed according to the device process of the gallium arsenide solar cell.

The advantages and positive effects that the present invention has are:

The GaInP/GaAs/μc-Si:H triple-junction stacked solar cell adopts the brand-new technical solution of the present invention. Compared with the prior art, the present invention has the following obvious features:

1. The present invention adopts epitaxial growth lattice-matched top battery and middle battery, and adopts PECVD to grow μc-Si:H bottom battery; and then bonds two kinds of semiconductor materials through low-temperature bonding technology, which overcomes the last problem of IMM battery. Growth of a lattice-mismatched InGaAs bottom cell results in higher domain defects.

2. The present invention uses μc-Si:H to replace the Ge sub-cell, which can significantly improve the theoretical conversion efficiency of the cell, effectively reduce the cost of the cell, and greatly improve the application prospect of the triple-junction stacked solar cell.

Description of drawings

Fig. 1 is a schematic diagram of the cell structure in which the epitaxial layer is grown reversely during the preparation process of the present invention;

Fig. 2 is a schematic diagram of the μc-Si:H battery structure in the preparation process of the present invention;

Fig. 3 is a schematic structural diagram of a GaInP/GaAs/μc-Si:H triple-junction cascaded solar cell prepared by the present invention.

The labels in the figure are divided into: 4-GaInP top cell; 5-tunnel junction; 6-GaAs middle cell; 8-AZO window layer; 9-μc-Si:H bottom cell; 10-AZO layer; 11-A back Electrode; 12 - Substrate.

Detailed ways

In order to further understand the invention content, characteristics and effects of the present invention, the following examples are given, and detailed descriptions are as follows in conjunction with the accompanying drawings:

Refer to accompanying drawing 1, Fig. 2 and Fig. 3.

Example 1

GaInP/GaAs/μc-Si: H triple-junction tandem solar cell, its structure and preparation process:

Step 1. GaInP/GaAs double junction solar cell prepared by reverse growth of epitaxial layer

(1) Select an n-type doped Ge sheet as the Ge substrate 1, the thickness of the Ge sheet is 180 μm, and the doping concentration is 1×10 ¹⁷ cm ⁻³ (the preferred doping concentration in the present invention is 1×10 ¹⁸ cm ^{−3 3} ):

Using MOCVD equipment, epitaxially grow GaAs buffer layer 2, GaInP corrosion stop layer 3, p-type doped GaAs cap layer, first junction GaInP cell 4 as the top cell, and tunnel junction on the Ge substrate in (1). 5. The growth temperature of the second junction GaAs battery 6 used as the medium battery, AlGaAs or GaAs sacrificial layer 7 is 600°C;

in:

1) The GaAs buffer layer is used as a nucleation layer for growing GaAs-based materials, with a thickness of 0.2 μm;

2) The GaInP etch stop layer is used as the corrosion control layer for peeling off the epitaxial growth substrate, with a thickness of 0.2 μm;

3) The p-type doped GaAs cap layer (not marked in the figure) is used as a heavily doped epitaxial layer forming ohmic contact with the metal electrode, with a thickness of 100-500nm and a doping concentration of 1×10 ¹⁸ cm ^-3 ;

4) The first junction GaInP cell as the top cell grows in turn into an n-type doped AlGaInP back field layer, an n-type doped GaInP base region, a p-type doped GaInP emitter region, and a p-type doped AlInP window layer ;

in:

The thickness of the n-type doped AlGaInP back field layer is 150nm, and the doping concentration is 1×10 ¹⁸ cm ^-3 ;

The n-type doped GaInP base region has a thickness of 800nm and a doping concentration of 1×10 ¹⁶ cm ^-3 ;

The thickness of the p-type doped GaInP back field layer is 100nm, and the doping concentration is 1×10 ¹⁸ cm ^-3 ;

The thickness of the p-type doped AlInP window layer is 70nm, and the doping concentration is 1×10 ¹⁸ cm ^-3 ;

5) The tunnel junction grows an n-type GaInP layer and a p-type AlGaAs layer in sequence;

in:

The growth temperature of the n-type GaInP layer is 500-800°C, the doping concentration is 1×10 ¹⁹ cm ^-3 , and the thickness range is 60nm;

The growth temperature of the p-type AlGaAs layer is 500-800°C, the doping concentration is 1×10 ¹⁹ cm ^-3 , and the thickness range is 60nm;

6) The second-junction GaAs battery as the middle battery is sequentially grown into an n-type AlGaAs back field layer, an n-type doped GaAs base region, a p-type doped GaAs emitter region, and a p-type doped AlGaAs window layer;

in:

The thickness of the n-type doped AlGaAs back field layer is 150nm, and the doping concentration is 1×10 ¹⁸ cm ^-3 ;

The thickness of the n-type doped GaAs base region is 1500nm, and the doping concentration is 1×10 ¹⁶ cm ^-3 ;

The thickness of the p-type doped GaAs back field layer is 70nm, and the doping concentration is 1×10 ¹⁸ cm ^-3 ;

The thickness of the p-type doped AlGaAs window layer is 60nm, and the doping concentration is 1×10 ¹⁸ cm ^-3 ;

7) The thickness of the n-type doped AlGaAs or GaAs sacrificial layer is 70nm, and the doping concentration is 1×10 ¹⁸ cm ^-3 ;

Step 2. Preparation of μc-Si:H solar cells by PECVD growth

(2) Materials such as stainless steel foil are selected as the substrate 12, and the substrate is ultrasonically cleaned with deionized water and dried with N gas _;

On the substrate in (2), grow Ag back electrode 11, AZO layer 10, μc-Si:H bottom cell 9, AZO window layer 8 sequentially;

in:

The Ag back electrode is grown by evaporation or sputtering, with a thickness of 1μm and a sheet resistance of 0.2Ω/sq;

The AZO layer is grown by sputtering, with a thickness of 1 μm and a sheet resistance of 15Ω/sq. The surface is etched with 0.5% HCl solution for 30s to form a textured surface;

n-type doped μc-Si:H is grown by RF-PECVD with a thickness of 50nm and a doping concentration of 1×10 ¹⁸ cm ^-3 ;

Intrinsic μc-Si:H is grown by VHF-PECVD with a thickness of 3um;

p-type doped a-Si:H is grown by RF-PECVD with a thickness of 10-100nm and a doping concentration of 1×10 ¹⁸ cm ^-3 ;

The AZO window layer is grown by sputtering, with a thickness of 1μm and a sheet resistance of 15Ω/sq;

Step 3. Bond the batteries prepared in steps 1 and 2 together

The surface roughness of AlGaAs or GaAs sacrificial layer and AZO window layer is reduced to less than 1nm by CMP process. The surface of the battery after surface cleaning is treated with plasma for surface activation, and the GaAs sub-battery μc-Si:H sub-battery is bonded together by van der Waals force; it is placed in the bonding chamber of the bonding machine, and the bonding chamber is filled with N _2. When the temperature of the bonding chamber is raised to 100°C, preheat the battery for 90 seconds; then apply a bonding pressure of 3KN, and raise the temperature inside the bonding chamber to 200°C at a rate of 15°C/min. Maintain a constant temperature for 1.5 hours of bonding, and then lower the temperature in the bonding chamber to room temperature at a rate of 3°C/min to achieve low-temperature bonding;

Step 4, peel off the Ge substrate

Use HF:H ₂ O ₂ :H ₂ O=2:1:1 etchant to etch the Ge substrate, use 1:1 ammonia water and hydrogen peroxide to etch the GaAs buffer layer, the Ge substrate and GaAs buffer layer are peeled off from the battery Finally, corrode the GaInP etch-stop layer with HCl:H ₂ O=1:1 etchant, the GaInP etch-stop layer is peeled off from the battery, and the peeling of the Ge substrate is completed; finally, the battery is ultrasonically cleaned with deionized water for 5 minutes and taken out After that, a GaInP/GaAs/μc-Si:H triple-junction cascaded solar cell as shown in FIG. 3 is fabricated.

This embodiment has positive effects such as significantly improving the conversion efficiency of the battery, effectively reducing the cost of the battery, and greatly improving the application prospect of the triple-junction stacked solar battery.

Claims (3)

1. a kind of GaInP/GaAs/ μ c-Si:H three-knot laminated solar cell, it is characterized in that: tri- knot of GaInP/GaAs/ μ c-Si:H Stacked solar cell, cascade solar cell, using the solar cell material of MOCVD technology epitaxial growth Lattice Matching on Ge substrate, including two sons Battery: GaInP pushes up battery, GaAs intermediate cell；GaAs intermediate cell and the bottom the μ c-Si:H battery for using PECVD to prepare pass through The bonding of low-temperature bonding technique is connected together, and GaAs substrate is removed by chemical etching；GaInP/GaAs/ μ c-Si:H three-knot laminated Solar cell is sequentially connected the top GaInP battery, tunnel junctions, GaAs intermediate cell, the bottom μ c-Si:H battery.

2. GaInP/GaAs/ μ c-Si:H three-knot laminated solar cell according to claim 1, it is characterized in that: three knots cascade The forbidden bandwidth of three sub- batteries of solar cell is respectively 1.86 ± 0.05eV, 1.40 ± 0.05eV, 1.05 ± 0.05eV.

3. GaInP/GaAs/ μ c-Si:H three-knot laminated solar cell according to claim 1 or 2, it is characterized in that:

First knot GaInP battery: n-type doping AlGaInP back surface field layer, the thickness 500- of thickness 100-200nm are successively grown to The base area n-type doping GaInP of 1000nm, the p-type doping GaInP emitter region of thickness 50-100nm, the p-type of thickness 30-100nm are mixed Miscellaneous AlInP Window layer, wherein: the doping concentration of n-type doping AlGaInP back surface field layer is 1 × 10¹⁷-1×10¹⁹cm^-3, n-type doping The doping concentration of the base area GaInP is 1 × 10¹⁶-1×10¹⁷cm^-3, the doping concentration of p-type doping GaInP emitter region is 1 × 10¹⁷-1 ×10¹⁹cm^-3, the doping concentration of p-type doping AlInP Window layer is 1 × 10¹⁷-1×10¹⁹cm^-3；

Tunnel junctions: GaInP layers of the N-shaped of thickness 10-100nm and the p-type Al of thickness 10-100nm are successively grown to_0.4Ga_0.6As: its In: the doping concentration that GaInP layers of N-shaped is 1 × 10¹⁸-1×10²⁰cm^-3, p-type Al_0.4Ga_0.6The doping concentration of As is 1 × 10¹⁸-1 ×10²⁰cm^-3；

Second knot GaAs battery: n-type doping AlxGa1-xAs back surface field layer, the thickness 1000- of thickness 100-200nm are successively grown to The base area n-type doping GaAs of 2000nm, the p-type doping GaAs emitter region of thickness 50-200nm, the p-type doping of thickness 30-100nm AlxGa1-xAs Window layer；Wherein: the doping concentration of n-type doping AlxGa1-xAs back surface field layer is 1 × 10¹⁷-1×10¹⁹cm^-3,n The doping concentration that type adulterates the base area GaAs is 1 × 10¹⁶-1×10¹⁷cm^-3, the doping concentration of p-type doping GaAs emitter region is 1 × 10¹⁷-1×10¹⁹cm^-3, the doping concentration of p-type doping AlxGa1-xAs Window layer is 1 × 10¹⁷-1×10¹⁹cm^-3、0.3≤x≤ 0.5；

Third knot μ c-Si:H battery: the Ag with a thickness of 1-2 μm is successively grown to as about 1-2 μm of back electrode, thickness of ZnO:Al (AZO) layer, thickness are followed successively by the μ c-Si:H of the n-type doping of 10-100nm, are the intrinsic μ c-Si:H of 2-4um, are 10-100nm P-type doping a-Si:H, with a thickness of 0.5-1.5 μm of AZO Window layer.