CN104900733B - A kind of InxGa1 xSb/GaSb strained quantum well intermediate band thermophotovoltaic based on GaSb and preparation method thereof - Google Patents

Abstract

The invention relates to a GaSb-based In _x Ga _1‑x Sb/GaSb strained quantum well intermediate band thermal photovoltaic cell and a preparation method thereof, which belong to the technical field of thermal photovoltaic cells. From top to bottom are top electrode, heavily doped p-type Al _x1 Ga _1-x1 As _y1 Sb _1-y1 window layer, p-type GaSb active region, intrinsic In _x Ga _1-x Sb/GaSb multi-quantum Well, n-type GaSb active region, heavily doped n-type Al _x2 Ga _1-x2 As _y2 Sb _1-y2 back electric field layer, n-type GaSb substrate and back electrode; where, intrinsic In _x Ga _1-x The number of Sb/GaSb multiple quantum wells is 4-5, and the area of the upper electrode accounts for 8-10% of the total area of the upper surface of the battery. The invention utilizes the low-pressure metal organic compound chemical vapor phase epitaxy technology to prepare the structure as each layer structure on the n-type GaSb substrate, and utilizes the electron beam evaporation technology to prepare the upper electrode and the back electrode. When the temperature of the radiator is 1050°C and the operating temperature of the battery is 25°C, the thermal photovoltaic cell of the present invention can achieve an energy conversion efficiency of 36.4%, and an output electric power density of 5.6W/cm ² .

Description

A GaSb-based InxGa1-xSb/GaSb strained quantum well intermediate band thermal photovoltaic Battery and its preparation method

technical field

The invention belongs to the technical field of thermal photovoltaic cells, and in particular relates to a GaSb-based In _x Ga _1-x Sb/GaSb strained quantum well intermediate band thermal photovoltaic cell and a preparation method thereof.

Background technique

Thermophotovoltaic (Thermphotovoltaic: TPV) technology is a photovoltaic conversion technology that uses the photovoltaic effect of semiconductor pn junctions under illumination to convert infrared photons radiated by thermal radiators into electrical energy. It has high output electric power density and energy under spectral control. It has the advantages of high conversion efficiency, quietness and portability. The two core components of the thermal photovoltaic cell system are the heat radiator and the TPV cell. The heat source of the thermal radiation body can come from industrial waste heat, waste incineration heat, fossil fuel combustion heat, nuclear heat energy, etc. Therefore, thermal photovoltaic power generation will be applied to environmental protection and energy-saving vehicles, waste incineration, thermoelectric dual-use and other occasions, forming a huge industry. The radiation characteristics of the thermal radiator meet Planck's radiation law, the temperature range is 950-1500°C, and the best band gap corresponding to semiconductor materials is between 0.3-0.7eV. The TPV battery system with low-temperature thermal radiation source has good stability, High security advantages. In addition, the heat radiator is very close to the TPV cell, and a high optical power input density of 5-30W/ ^cm2 can be obtained.

Antimonide materials are internationally recognized materials of choice for TPV devices. JX Crystal in the United States has commercialized GaSb TPV single-junction devices, and the thermal photovoltaic system efficiency is 24%. In addition, it is reported that the energy conversion efficiency of single-junction ternary In _x Ga _{1- x} Sb TPV is up to 13%. The highest energy conversion efficiency of single-junction quaternary Ga _x In _1-x As _y Sb _1-y is 28%. It can be seen that the conversion efficiency of a single thermal photovoltaic cell is low, mainly due to the low spectral utilization. However, multi-cell and quantum well TPV cells can make up for the shortcomings of single-cell TPV cells.

Multi-junction antimonide TPV devices are mainly binary GaSb top cells and quaternary Ga _x In _1-x As _y Sb _1-y bottom cells connected through heavily doped GaSb tunnel junctions to form stacked TPV devices. The top cell absorbs photons with high energy, and the bottom cell absorbs photons with low energy, which broadens the absorption range of the spectrum, thereby achieving the purpose of improving conversion efficiency. However, the conditions for GaSb and Ga _x In _{1- x} As _y Sb _1-y to form stacked TPV devices require the lattice matching of the two, so as to reduce the degradation of device performance caused by lattice defects such as misfit dislocations. Therefore, multi-junction photovoltaic cells are limited in the matching and selection of individual subcell materials and tunnel junction materials.

The quantum well battery is formed by introducing a quantum well structure material with a smaller band gap than the active region in the p-i-n structure instead of the material in the intrinsic region. This structure has two advantages: one is by changing the thickness of the material in the quantum well structure or components to change the effective band gap of the material to achieve the purpose of broadening the use of the spectrum. The device using this mechanism is a quantum well solar cell or a quantum well TPV battery. This concept was proposed by K.Barnham of the Royal College of London University; The second is to use the quantum size effect to form an intermediate energy band in the forbidden band of the active region, so that the electrons at the bottom of the valence band can not only absorb photons with high energy and jump to the conduction band, but also jump to the middle by absorbing photons with low energy. Energy band, and then transition to the conduction band by absorbing low-energy photons, which further broadens the utilization efficiency of the spectrum. The device using this mechanism is a quantum well intermediate band solar cell or a quantum well intermediate band TPV battery. This concept was developed by Madrid, Spain. Proposed by A.Luque and A.Martí of the Polytechnic University. No matter which kind of advantage it is, it breaks the bottleneck of multi-junction devices in terms of material selection, and increases the flexibility of material selection in device design. In addition, compared with general single-junction and multi-junction photovoltaic cells, another advantage of quantum well photovoltaic cells is that their short-circuit current and open-circuit voltage are basically determined separately by the well material and barrier material of the quantum well, so they can be optimized separately. For quantum well TPV devices, the photogenerated carriers generated in the well region can not only jump to the conduction band through the mechanism of photoexcitation, but also jump to the conduction band through thermionic emission, which reduces the temperature dependence of quantum well TPV devices. Sensitivity, so that it can work normally in a higher temperature environment.

At present, there are more reports in the literature on the application of quantum well structures in solar cells, and in the application of TPV, some units such as Imperial University London have reported quantum well TPV photovoltaic cells, but they mainly use the principle of strain balance, and Applications without intermediate energy bands, that is, they do not take advantage of the characteristics of intermediate energy bands.

Contents of the invention

In order to solve the deficiencies in the prior art, the present invention inserts the In _x Ga _1-x Sb/GaSb multi-quantum well structure in the pn junction structure of GaSb material, and utilizes the sufficiently thin well material In _x Ga _1-x Sb The quantum size effect of the barrier material GaSb confines the well material, and a bound state is generated in the well material to form an intermediate energy band.

A GaSb-based In _x Ga _1-x Sb/GaSb strained quantum well intermediate band thermal photovoltaic cell according to the present invention has the following structure from top to bottom: top electrode, heavily doped p-type Al _x1 Ga _{1 -x1} As _y1 Sb _1-y1 window layer, p-type GaSb active region, intrinsic In _x Ga _1-x Sb/GaSb multiple quantum wells, n-type GaSb active region, heavily doped n-type Al _x2 Ga _{1 -x2} As _y2 Sb _1-y2 back electric field layer, n-type GaSb substrate and back electrode, wherein the number of intrinsic In _x Ga _1-x Sb/GaSb multiple quantum wells is 4-5.

Furthermore, the aforementioned n-type GaSb substrate is obtained through purchase. It is a Te-doped n-type GaSb polished single wafer with a net donor Te doping concentration of about 4.7×10 ¹⁷ /cm ³ and a thickness of 500± 25μm, the crystal orientation is 2° from (100) to (110) direction.

The previously mentioned heavily doped n-type Al _x2 Ga _1-x2 As _y2 Sb _1-y2 back electric field layer and the heavily doped p-type Al _x1 Ga _{1- x1} As _y1 Sb _1-y1 window layer are both GaSb Al _x0 Ga _1-x0 As _y0 Sb _1-y0 quaternary alloy material with substrate lattice matching, its components x ₀ , x ₁ , x ₂ and y ₀ , y ₁ , y ₂ satisfy the relationship: y ₀ =0.093 x ₀ /(1+0.061x ₀ ), y ₁ =0.093x ₁ /(1+0.061x ₁ ), y ₂ =0.093x ₂ /(1+0.061x ₂ ), x ₀ , x ₁ , x ₂ are all Take 0.05~0.35, y ₀ , y ₁ , y ₂ take 0.005~0.03, the corresponding band gap is 0.807~1.22eV, heavily doped n-type Al _x2 Ga _1-x2 As _y2 Sb _1-y2 on the back The thickness and doping concentration of the electric field layer and the heavily doped p-type Al _x1 Ga _1-x1 As _y1 Sb _1-y1 window layer are both 45-60nm and 1×10 ¹⁹ ˜2×10 ¹⁹ /cm ³ . The role of the heavily doped p-type Al _x1 Ga _1-x1 As _y1 Sb _1-y1 window layer is to block photogenerated electrons, reduce surface recombination, and thereby increase the open circuit voltage; heavily doped n-type Al _x2 Ga _1-x2 As _y2 The function of the electric field layer on the back of Sb _1-y2 is to block the interfacial recombination of photogenerated holes and increase the open circuit voltage.

In the aforementioned In _x Ga _1-x Sb/GaSb multiple quantum wells, the number of quantum wells is 4-5, the barrier material is intrinsic GaSb, its thickness is 10-15nm, and the well material is intrinsic In _x Ga _{1- x} Sb, the thickness of which is 5.5-6.5nm, and the component x is between 0.25-0.3.

The aforementioned n-type GaSb active region has a thickness of 6-8 μm and a doping concentration of 9.5×10 ¹⁷ to 2×10 ¹⁸ /cm ³ , and the p-type GaSb active region has a thickness of 0.2-0.4 μm and a doping concentration of 0.2-0.4 μm. The concentration is 9.5×10 ¹⁷ to 2×10 ¹⁸ /cm ³ .

The above-mentioned heavily doped n-type Al _x2 Ga _1-x2 As _y2 Sb _1-y2 back electric field layer and the dopant of the n-type GaSb active region are both Te, and the heavily doped p-type Al _x1 Ga _1- The dopant of the _x1 As _y1 Sb _1-y1 window layer and the p-type GaSb active region is Zn.

The material of the upper electrode mentioned above is a double-layer Au-Pb/Au material, the alloy mass ratio is Au:Pb=6:4, the thickness of the first layer of Au-Pb alloy layer is 40-60nm, and the second layer of Au metal layer The thickness is 100-150nm; the area of the upper electrode accounts for 8-10% of the total area of the upper surface of the battery; the material of the back electrode is a double-layer Au-Ge-Ni/Au material, and the alloy mass ratio is Au:Ge:Ni=84 :14:2, the thickness of the first Au-Ge-Ni alloy layer is 20-40nm, and the thickness of the second Au metal layer is 200-300nm.

The invention utilizes low-pressure metal organic chemical vapor phase epitaxy (LP-MOCVD) technology to prepare an n-type GaSb substrate/n ⁺ type Al _x2 Ga _1-x2 As _y2 Sb _1-y2 back electric field layer on an n-type GaSb substrate /n-type GaSb active layer/4~5 intrinsic In _x Ga _1-x Sb/GaSb multiple quantum wells/p-type GaSb active layer/p ⁺ type Al _x1 Ga _1-x1 As _y1 Sb _1-y1 window Layer GaSb-based In _x Ga _1-x Sb/GaSb strained quantum well intermediate band thermal photovoltaic cells.

Both the metal-organic source and the source bottle doped with organic source are placed in a high-precision temperature-controlled cold trap, the pressure is controlled by each pressure controller (PC), and the flow rate of the carrier gas passing into the source bottle is controlled by each mass flow controller (MFC). ) control, the amount of material taken out of the source bottle by the carrier gas per minute is a function of the above three quantities. The organic sources of Al, Ga, In, As and Sb used for growth are triethylaluminum (TEAl), trimethylgallium (TMGa), trimethylindium (TMLn), arsine (AsH ₃ ) and triethyl Antimony (TESb), _H2 as carrier gas, p-type dopant source and n-type dopant source are diethylzinc (DEZn) and diethyltellurium (DETe), respectively. The pre-programmed In _x Ga _1-x Sb/GaSb strained quantum well intermediate energy band TPV photovoltaic cell growth program is run by MOCVD equipment, and the epitaxial growth of each layer of material is carried out, and then the TPV structure is prepared through the device process.

A kind of preparation method of GaSb-based In _x Ga _1-x Sb/GaSb strained quantum well intermediate energy band thermal photovoltaic cell of the present invention, its specific steps are as follows:

1) Cleaning and corrosion of the substrate: put the n-type GaSb substrate in the mixed solution of nitric acid, hydrochloric acid and glacial acetic acid (the dosage range of HNO ₃ , HCl, CH ₃ COOH is 1~3mL: 5~15mL: 40~60mL) After medium corrosion for 10-15 minutes, immediately wash with deionized water, blow dry with high-purity nitrogen and put it into the reaction chamber of LP-MOCVD equipment;

2) Growth program setting: the materials of each layer of the device to be prepared (n ⁺ type Al _x2 Ga _1-x2 As _y2 Sb _1-y2 back electric field layer/n-type GaSb active layer/4-5 intrinsic In _x Ga _1-x Sb/GaSb multiple quantum wells/p-type GaSb active layer/p ⁺ type Al _x1 Ga _{1- x1} As _y1 Sb _1-y1 window layer) growth parameters are set, including the material of each layer Growth temperature, the flow rate of each organic source and dopant and the flow rate of carrier gas hydrogen (H ₂ ) when growing each layer of material;

3) Vacuumize the reaction chamber: set the pressure to the value required for growth of 20 to 50 mbar, start the mechanical pump to evacuate the reaction chamber, and at the same time pass in hydrogen to replace the nitrogen in the reaction chamber, and pass in rotating gas to rotate the substrate;

4) Heat treatment of the substrate: set the temperature at 580-620°C, start the intermediate frequency furnace to heat the substrate, and when the temperature rises to 330-360°C, feed TESb to protect the substrate surface, because the Sb in the GaSb substrate is in the At high temperature, it will dissociate from the surface of the substrate. The introduction of TESb inhibits the dissociation of Sb atoms. When the temperature reaches the set value and stabilizes, the high-temperature download gas hydrogen will react with the oxide on the substrate surface, and the reaction product Take it out of the reaction chamber with hydrogen to achieve the purpose of desorption treatment of oxides on the substrate surface, and the treatment time is 10 to 20 minutes;

5) Growing each epitaxial layer: After the substrate is heat-treated, lower the temperature and enter the epitaxial layer growth program to grow each epitaxial layer;

6) Cooling and sampling: after the growth is over, after the temperature drops to room temperature and the reaction chamber returns to normal pressure, take out the device prepared in the reaction chamber;

7) Cleaning: ultrasonically clean the prepared n-type GaSb substrate/n ⁺ type Al _x2 Ga _{1- x2} As _y2 Sb _1-y2 back electric field layer/n-type GaSb active layer/4 with CCl ₄ , acetone and alcohol respectively Devices with ~5 intrinsic In _x Ga _1-x Sb/GaSb quantum wells/p-type GaSb active layer/p ⁺ type Al _x1 Ga _1-x1 As _y1 Sb _1-y1 window layer 2~3 times, each time 5-10 minutes, then dry with high-purity _N2 ;

8) Baking: Baking the prepared device in an oven at 75-85°C for 20-25 minutes;

9) Fabrication of the upper electrode: Au-Pb (50-60nm)/Au (80-90nm) on the upper surface of the p ⁺ type Al _x1 Ga _1-x1 As _y1 Sb _1-y1 window layer by electron beam evaporation electrode, as shown in Figure 5. First, make a mask made of copper sheet, the shape and area of which are the same as the upper surface of the device, and then dig out a rectangular hole in the center of the mask, the dug area accounts for 8% to 10% of the mask area %, and overlap and press the mask plate and the upper surface of the device, put the mask plate and the device into the evaporation chamber of the electron beam evaporation equipment, fix the device and let the upper surface of the device face the crucible; then, place the customized A good mass ratio is prepared for the alloy target of Au:Pb=6:4, put it into the crucible in the evaporation chamber, and then adjust the ratio of the material deposited on the surface of the device by setting the speed of the electron beam; then, Use a molecular pump to evacuate the cavity, and the vacuum degree is below 6×10 ^-4 Pascal. After completion, turn on the electron beam switch to start the electron beam evaporation, and turn off the electron beam switch after 5 to 10 minutes; fill with nitrogen, and then evacuate. Then flush nitrogen until the pressure returns to normal pressure. After the alloy target is cooled, open the chamber door, take out the alloy target and replace it with an Au metal target, and then repeat the above steps of electron beam evaporation alloy to evaporate the Au metal. The evaporation time is 10~ After 15 minutes, turn off the electron beam switch, wait for the target to cool down, and the pressure in the chamber returns to normal pressure, open the evaporation chamber door to take out the device, remove the mask, and prepare the upper electrode on the upper surface of the device;

10) Substrate thinning: First, use coarse sand (280-320 mesh) to grind the back of the n-type GaSb substrate of the above-mentioned TPV cell to 350-380um, and then use fine sand (2000-2500 mesh) for grinding To 230 ~ 260um, finally polished with emery;

11) Fabrication of the back electrode: Au-Ge-Ni (20-40nm)/Au (200-300nm) back electrode is fabricated on the back of the n-type GaSb substrate of the above device by means of electron beam evaporation. First, put the device into the evaporation chamber, fix the device and let the lower surface face the crucible; then, prepare the customized alloy target with a mass ratio of Au:Ge:Ni=84:14:2, and put it into the evaporation chamber. In the crucible in the cavity, the thickness of the material deposited on the surface of the device can be adjusted by setting the speed of the electron beam; then, the cavity is evacuated with a molecular pump, and the vacuum degree is below 6×10 ^-4 Pascals. Turn on the electron beam switch to start electron beam evaporation, turn off the electron beam switch after 4 to 6 minutes; fill with nitrogen, then evacuate, and then flush nitrogen until the pressure returns to normal pressure. After the alloy target cools down, open the chamber door and take out the alloy Replace the target with an Au metal target, and then repeat the above steps of electron beam evaporation alloy to evaporate Au metal. The evaporation time is 15 to 20 minutes. After completion, turn off the electron beam switch, wait for the target to cool down, and the pressure in the cavity returns to normal pressure , open the evaporation chamber door and take out the device, so as to complete the preparation of the back electrode of the device;

12) Annealing: Put the TPV device prepared above into an annealing furnace, pass nitrogen gas, and carry out alloying treatment for 1 to 2 minutes at 250-295 ° C to form an ohmic-contact upper electrode and a back electrode, thereby completing the invention. Preparation of GaSb-based In _x Ga _1-x Sb/GaSb strained quantum well intermediate band thermal photovoltaic cells.

Description of drawings

Figure 1: The relationship curve between fine balance efficiency and energy in the intermediate energy band;

As shown in Figure 1, when T _b = 1050°C and T _c = 25°C, the energy conversion efficiency of _IBTPV is 45.4%. The energy intervals E _IV are 0.13eV and 0.58eV, respectively.

Figure 2: The relationship between the thickness of the well material and the bound energy level of the conduction band;

As shown in Figure 2, as the thickness of the well material increases, the quantum size effect gradually weakens, and the binding energy gradually decreases. When _Lw is 10nm, the quantum size effect is very weak, and the binding energy is almost negligible.

Figure 3: The relationship between the thickness of the well material and the binding energy level of the valence band;

Figure 3 uses the Kronig-Penney model to calculate the difference between the bound energy level of the valence band in the quantum well and the top of the valence band of the well material, and the energy at the top of the valence band is 0. It can be seen from the calculation that there are multiple bound energy levels, where n is taken as positive integer. However, because the transition of the quantum well is limited by the selection rule, the energy level of ΔE _hh1 is generally taken, because the transition of the energy level E _hh1 and E _c1 conforms to the selection rule. It can be seen that when the thickness L _w of the well material is 6nm, ΔE _c1 is 0.084eV, |ΔE _hh1 | is 0.022eV, and when the ln composition x is 0.3, the band gap E _g0 of In _0.3 Ga _0.7 Sb is 0.47eV, and after considering the quantum size effect, the band-limit width of In _0.3 Ga _0.7 Sb well material E _g =E _g0 +ΔE _c1 +|ΔE _hh1 |, so E _g can be obtained as 0.578eV, which is consistent with the detailed balance theory The obtained E _IV = 0.58eV is basically the same, and the energy difference of the conduction band bound energy level of the well material and the barrier material is 0.2-0.084 = 0.116eV, which is not much different from the E _CI = 0.13eV obtained by the detailed balance theory , and the thickness L _w of the well material can be further determined to be 6nm.

Figure 4: The relationship between In composition and critical thickness;

As shown in Figure 4, the smaller the composition x of In, the smaller the mismatch _f and the larger the critical thickness hc. Because the number of In _x Ga _1-x Sb/GaSb multi-quantum wells will change with the change of x, and the number of wells will decrease as the value of x increases. When x=0.3, the critical thickness h _c takes a value of 28nm, therefore, it can be estimated that the number of In _0.3 Ga _0.7 Sb/GaSb quantum wells does not exceed 5 at most.

Figure 5: Schematic diagram of the structure of the In _x Ga _1-x Sb/GaSb strained quantum well intermediate band TPV cell;

As shown in Figure 5, from top to bottom, the names of the components are: thermal radiation source 8 that radiates photons to the surface of the battery, the upper electrode 9 of the battery, heavily doped p ⁺ type Al _x1 Ga _1-x1 As _y1 Sb _{1- y1} window layer 10, p-type GaSb active layer 11, intrinsic In _x Ga _1-x Sb/GaSb multiple quantum wells 12, n-type GaSb active layer 13, heavily doped n ⁺ type Al _x2 Ga _1-x2 As _y2 Sb _1-y2 back electric field layer 14, n-type GaSb substrate 15, back electrode 16 of battery.

Figure 6: The energy band diagram of the In _x Ga _1-x Sb/GaSb strained quantum well intermediate band TPV battery in thermal equilibrium;

Figure 6 is the energy band diagram of In _x Ga _1-x Sb/GaSb strained quantum well TPV battery in thermal equilibrium state, from left to right are heavily doped p ⁺ type Al _x1 Ga _1-x1 As _y1 Sb _1-y1 window Energy band 1 of the p-type GaSb active region, energy band 2 of the p-type GaSb active region, energy band 3 of the intrinsic In _x Ga _1-x Sb well material of In _x Ga _1-x Sb/GaSb multiple quantum wells, and In _x Ga ₁ Energy band 4 of intrinsic GaSb barrier material of _x Sb/GaSb multiple quantum wells, energy band 5 of n-type GaSb active region, heavily doped n ⁺ type Al _x2 Ga _1-x2 As _y2 Sb _1-y2 back electric field The energy band of the layer is 6, and the energy band of the n-type GaSb substrate is 7. It can be seen from the energy band diagram that the p ⁺ type Al _x1 Ga _1-x1 As _y1 Sb _1-y1 window layer does have the effect of blocking electrons, reducing the recombination of electrons on the surface; the n ⁺ type Al _x2 Ga _1-x2 As _y2 The electric field layer on the back of Sb _1-y2 does have the effect of blocking holes and avoiding the recombination of holes at the interface.

Figure 7: Enlarged view of the band structure of the quantum well region of the In _x Ga _1-x Sb/GaSb strained quantum well intermediate band TPV cell;

Figure 7 is an enlarged diagram of the energy bands of the multiple quantum well region, and a bound state is generated in the well material region, forming an intermediate band, and its position is also consistent with the intermediate band discussed in the detailed balance theory.

Figure 8: IV characteristic curve of In _0.3 Ga _0.7 Sb/GaSb strained quantum well intermediate band TPV cell;

For the device with the above structure, the simulation of IV characteristics is carried out by SILVACO TCAD software, that is, the material of each layer structure of the device designed above, and the physical parameters of each material include forbidden band width, intrinsic carrier concentration, electron affinity, The effective density of states of the conduction band and valence band are input into the device simulation interface of the software for simulation. The optimized simulation results are shown in Figure 8, and the results are basically consistent with the values calculated by the careful balance calculation of the middle energy band TPV battery, indicating that Rationality of In _0.3 Ga _0.7 Sb/GaSb strained quantum well intermediate band TPV cell design. In addition, the In _0.3 Ga _0.7 Sb/GaSb strained quantum well intermediate band TPV cells prepared by LP-MOCVD technology have achieved high energy conversion efficiency and high power density output, which further proves the advantages of device design and theoretical simulation. rationality.

detailed description

Example 1

As shown in Figure 1, in order to calculate the energy conversion efficiency of the GaSb-based In _x Ga _1-x Sb/GaSb strained quantum well intermediate band thermal photovoltaic cell, first calculate the detailed balance efficiency of the cell and determine the radiation temperature T _b of the heat source and the operating temperature _Tc of the battery. Generally, the device works at room temperature, so _Tc is set at 25°C, while the temperature of the practical heat radiation source is in the range of 1000-1500°C, and the lower the temperature, the better the stability of the TPV system and The higher the security, considering the utilization efficiency of the light spectrum of the device, set T _b to 1050°C, the radiation energy spectrum can be approximated according to the Planck black body radiation law, the total output power density is 15.4W/cm ² , and the maximum output power density The corresponding wavelength is 2.2 μm. According to the detailed balance theory model of the middle energy band, the conversion efficiency can be calculated as 45.4% by using MATLAB, and the energy interval E _CI between the middle band and the bottom of the conduction band and the energy interval E _IV between the middle band and the top of the valence band are 0.13eV respectively. and 0.58eV. This result is consistent with the simulation optimization result of In _x Ga _1-x Sb/GaSb strained quantum well intermediate band thermal photovoltaic cells using SILVACO TCAD. Therefore, it provides a theoretical reference for the preparation of the following In _0.3 Ga _0.7 Sb/GaSb strained quantum well intermediate band thermal photovoltaic cells.

The energy conversion efficiency of the GaSb-based In _x Ga _1-x Sb/GaSb strained quantum well intermediate band thermal photovoltaic cell theoretically provided by the present invention can reach 45.4%, which is higher than that of a single solar cell with a forbidden band width of 1.31 The maximum efficiency corresponding to eV is 31%, which also exceeds the maximum efficiency of 40.8% corresponding to the maximum concentration of a single solar cell when the band gap becomes 1.11eV.

In order to maximize the conversion efficiency, the intermediate band should be matched with the generated bound state, so it is necessary to determine the forbidden band width of the well material In _x Ga _1-x Sb and select its thickness.

For convenience, the In _x Ga _1-x Sb/GaSb quantum well is approximated by a one-dimensional finite deep square potential well, then the height of the potential barrier is the difference between the electron affinity of the barrier material and the well material, and the ternary barrier material The electron affinity of can be obtained by interpolation of two binary materials by Vegard's law, namely:

Q(In _x Ga _1-x Sb)=xQ(InSb)+(1-x)Q(GaSb) (1)

Q represents the general term for binary alloy parameters. Since the bound state is generated in the potential well, the value of the barrier height should be greater than 0.13eV, and x>0.241 is obtained, but the value of x should not be too large, because when the value of x increases, The lattice mismatch between In _x Ga _1-x Sb and GaSb becomes larger, which first increases the difficulty of process realization, and secondly, the strain caused by the mismatch increases, and when it exceeds a certain value, it will be released in the form of dislocations , which eventually leads to degraded device performance. Based on the above considerations, x is set to 0.3. And because the forbidden band width of In _x Ga _1-x Sb has a one-to-one correspondence with the In composition x, the forbidden band width is determined when the composition is determined.

Further, the conditions for generating the quantum size effect are as follows,

On the premise that the In composition is determined, each parameter of the well material can be obtained through equation (1) using the binary parameters in Table 1. Through equation (2), it can be obtained that the thickness of the well material should be less than 9.8nm, where m is the electron effective mass of the well material, Δx is the thickness of the well material, k _B is the Boltzmann constant, As the approximated Planck's constant, the temperature T = 25 ℃.

Table 1: Binary alloy parameters

Since the In _x Ga _1-x Sb/GaSb quantum well can be approximated by a one-dimensional finite-depth square potential well, the bound energy level in the square potential well can be calculated by the Kronig-Penney model. Therefore, the energy level distribution can be solved by the solution of (3) Obtained, for the case of E<V ₀ :

Where E is the energy, V ₀ is the height of the potential barrier, K and Q are L _w and L _b are the thicknesses of the well material and the barrier material respectively, because it is a quantum well structure, therefore, L _b >L _w , and according to the above The condition of the quantum size effect is L _w <10 nm, so L _b =15 nm is set. m _w and m _b are the electron effective mass of the well material and the barrier material respectively, which can be estimated by Vegard's law. When the value of L _w ranges from 2 to 10 nm, the Kronig-Penney model is used to calculate the difference between the bound energy level of the conduction band in the quantum well and the bottom of the conduction band of the well material, and the energy of the bottom of the conduction band is set to 0, as shown in Figure 2 It is shown that with the increase of the thickness of the well material, the quantum size effect is gradually weakened, and the binding energy is gradually reduced. When L _w is 10nm, the quantum size effect is very weak, and the binding energy is almost negligible.

As we all know, in the In _x Ga _1-x Sb/GaSb multi-quantum well structure, the well material and the barrier material are lattice-mismatched, and the lattice constant of the well material is larger than that of the barrier material. GaSb substrates are generally used in epitaxial growth. Therefore, the barrier material is not subject to stress, but the well material is subjected to compressive stress. When the number of quantum wells increases, the compressive stress will gradually accumulate. When the critical value is exceeded, the stress will be released by forming dislocations. , which will inevitably degrade the performance of the device. Therefore, the number of quantum wells is limited. According to the energy balance theory proposed by R.People and JCBean, the critical thickness of the In _x Ga _1-x Sb/GaSb quantum well can be calculated, as shown in equation (4),

where h _c is the critical thickness of the well material In _x Ga _1-x Sb, ν is the Poisson's ratio of the well material, b is the Burgers vector, a(x) is the lattice constant of the ternary well material, ν and a (x) can be obtained by interpolation method. The relevant binary alloy parameters are listed in Table 1. f is the mismatch degree between the well material and the substrate material. Its calculation method is shown in equation (5), and the required data are brought into In equation (4),

f=[a(In _x Ga _1-x Sb)-a(GaSb)]/a(In _x Ga _1-x Sb) (5)

The relationship between the critical thickness h _c and the In composition x can be obtained, as shown in Figure 4. It can be seen that the smaller the composition x of In, the smaller the mismatch _f and the larger the critical thickness hc. When x=0.3, the critical thickness h _c takes a value of 28nm, therefore, it can be estimated that the number of In _x Ga _1-x Sb/GaSb quantum wells does not exceed 5.

According to the above theoretical analysis and numerical calculation, the structure of the designed In _x Ga _1-x Sb/GaSb strained quantum well intermediate band thermal photovoltaic cell is shown in Figure 5. Through SILVACO TCAD device simulation software, the parameter optimization and IV characteristic simulation of the device are carried out, and the energy conversion efficiency of the device is obtained as 45.3%, which is consistent with the calculation of the detailed balance theory. The optimized parameters of the materials of each layer of the device are shown in Table 2.

The significance of previous theoretical calculations and device simulations is: firstly, it is proposed that the In _x Ga _1-x Sb/GaSb strained quantum well intermediate band thermal photovoltaic cell is a high-efficiency energy conversion device with great potential development value; secondly, the design The simulated results of the In _0.3 Ga _0.7 Sb/GaSb strained quantum well intermediate band thermal photovoltaic cell are consistent with the theoretical calculation, which not only shows the rationality and correctness of the theoretical calculation, but also shows the rationality and feasibility of the design of the device; finally , due to the high cost of materials prepared by MOCVD, the theoretical calculations and device simulation optimization in the early stage provide a theoretical basis for the preparation of materials for each layer of the device.

Table 2: Optimum parameters of materials for each layer of In _x Ga _1-x Sb/GaSb strained quantum well intermediate band thermal photovoltaic cells

Example 2

Te-doped n-type GaSb polished single wafer is used as the substrate, the net donor concentration is 4.7×10 ¹⁷ cm ^-3 , the crystal orientation is 2° from (100) to (110), and the prepared structure is n-type GaSb substrate/ n ⁺ type Al _0.1 Ga _0.9 As _0.01 Sb _0.99 back electric field layer/n type GaSb active layer/5 intrinsic In _0.3 Ga _0.7 Sb/GaSb quantum wells/p type GaSb active layer/p ⁺ type Al _0.1 Ga _0.9 In _0.3 Ga _0.7 Sb/GaSb strained quantum well intermediate band TPV cell with As _0.01 Sb _0.99 window layer.

The growth of each layer material structure in the In _0.3 Ga _0.7 Sb/GaSb strained quantum well intermediate band TPV cell can be realized by using low pressure metal organic chemical vapor phase epitaxy (LP-MOCVD) technology. The MOCVD equipment used for material growth is self-assembled by our research group. The organic sources of Al, Ga, In, As and Sb used for growth are triethylaluminum (TEAl), trimethylgallium (TMGa), trimethylindium (TMLn), arsine (AsH ₃ ) and triethyl Antimony (TESb), _H2 as carrier gas, p-type dopant source and n-type dopant source are diethylzinc (DEZn) and diethyltellurium (DETe), metal-organic source and source of doped organic source, respectively The bottles are all placed in a high-precision temperature-controlled cold trap, the pressure is controlled by each pressure controller (PC), the flow rate of the carrier gas into the source bottle is controlled by each mass flow controller (MFC), and it is carried out by the carrier gas every minute The amount of substance sourced in the source bottle is a function of the above three quantities. Pre-program the growth program of each layer of In _0.3 Ga _0.7 Sb/GaSb strained quantum well intermediate band TPV battery, and import it into the software that controls the growth of MOCVD materials, and finally carry out the epitaxial growth of each layer of materials, that is, the GaSb substrate Bottom-on epitaxy n ⁺ type Al _0.1 Ga _0.9 As _0.01 Sb _0.99 back electric field layer/n type GaSb active layer/5 intrinsic In _0.3 Ga _0.7 Sb/GaSb quantum wells/p type GaSb active layer/p ⁺ type Al _0.1 Ga _0.9 As _0.01 Sb _0.99 window layer.

A method for preparing a GaSb-based In _x Ga _1-x Sb/GaSb strained quantum well intermediate band thermal photovoltaic cell, the specific steps of which are as follows:

1) Cleaning and etching of the substrate: corrode the purchased n-type GaSb substrate in a mixed solution of nitric acid, hydrochloric acid and glacial acetic acid (HNO ₃ : HCl: CH ₃ COOH = 1mL: 10mL: 50mL) for 10 minutes, Immediately wash with deionized water, blow dry with high-purity nitrogen and put it in the reaction chamber.

2) Growth program setting: the materials of each layer of the device to be prepared (n ⁺ type Al _x2 Ga _1-x2 As _y2 Sb _1-y2 back electric field layer/n-type GaSb active layer/5 intrinsic In _x Ga _1-x Sb/GaSb multiple quantum wells/p-type GaSb active layer/p ⁺ -type Al _x1 Ga _{1- x1} As _y1 Sb _1-y1 window layer) growth parameters are set, including the growth temperature of each layer of material , the flow rate of each organic source and dopant and the flow rate of carrier gas hydrogen (H ₂ ) when growing each layer of material.

3) Vacuumize the reaction chamber: set the pressure to the value required for growth, start the mechanical pump to evacuate the reaction chamber, and at the same time pass in hydrogen to replace the nitrogen in the reaction chamber, and pass in rotating gas to rotate the substrate.

4) Heat treatment of the substrate: set the temperature to 600°C, start the intermediate frequency furnace to heat the substrate, and when the temperature rises to 350°C, feed TESb to protect the substrate surface, because the Sb in the GaSb substrate will be removed from the The dissociation of the substrate surface, the introduction of TESb is to inhibit the dissociation of Sb atoms, when the temperature reaches the set value and stabilizes, the surface oxide desorption treatment is performed on the substrate, and the treatment time is 10 minutes;

5) Growth of each epitaxial layer: After the substrate is heat-treated, the temperature is lowered, and the epitaxial layer growth program is entered to grow each epitaxial layer. The process parameters of each layer of material growth are shown in Table 3;

6) Cooling and sampling: After the growth is over, after the temperature drops to room temperature and the reaction chamber returns to normal pressure, take out the device in the reaction chamber;

7) Cleaning: ultrasonically clean the prepared n-type GaSb substrate/n ⁺ type Al _x2 Ga _{1- x2} As _y2 Sb _1-y2 back electric field layer/n-type GaSb active layer/5 with CCl ₄ , acetone and alcohol respectively Intrinsic In _x Ga _1-x Sb/GaSb quantum well/p-type GaSb active layer/p ⁺ -type Al _x1 Ga _1-x1 As _y1 Sb _1-y1 window layer device 2 times, 8 minutes each time, and then Blow dry with high-purity _N2 ;

8) Baking: put the prepared material in an oven at 80°C for 20 minutes;

9) Fabrication of the upper electrode: Au-Pb (50nm)/Au (120nm) upper electrode is fabricated on the upper surface of the p ⁺ type Al _x1 Ga _1-x1 As _y1 Sb _1-y1 window layer by electron beam evaporation, as shown in the figure 5, and the process parameters are shown in Table 5. First, make a mask made of copper sheet, the shape and area are the same as the upper surface of the device (1×1cm ² ), and a rectangular hole is dug in the center of the mask. 8% to 10% of the area, and the mask plate and the upper surface of the device are overlapped and pressed tightly, and they are put into the evaporation chamber together, and the device is fixed so that the upper surface faces the crucible; then, the customized mass ratio Prepare the alloy target material of Au:Pb=6:4, put it into the crucible in the evaporation chamber, and then adjust the thickness of the material deposited on the surface of the device by setting the speed of the electron beam; then, use the molecular pump to Vacuum the chamber with a vacuum degree below 6×10 ^-4 Pascals. After completion, turn on the electron beam switch to start electron beam evaporation, and turn off the electron beam switch after about 5 minutes; fill with nitrogen, then vacuumize, and then flush nitrogen to reach the pressure Return to normal pressure. After the alloy target cools down, open the chamber door, take out the alloy target and replace it with an Au metal target, then repeat the above steps of electron beam evaporation alloy to evaporate the Au metal. The evaporation time is about 10 minutes, and then close it after completion. Switch on the electron beam, wait for the target to cool down, the pressure in the cavity returns to normal pressure, open the cavity door to take out the device, remove the mask, and the upper electrode is completed.

10) Substrate thinning: use coarse sand (mesh number 280-320) to grind the back of the GaSb substrate of the above-mentioned TPV battery to 360 μm, use fine sand (mesh number 2000-2500) to grind to about 250 μm, and then use emery polishing;

11) Fabrication of back electrode: Au-Ge-Ni (30nm)/Au (220nm) back electrode was evaporated by electron beam on the back of the GaSb substrate of the above-mentioned device, and the process parameters are shown in Table 5. First, put the device into the evaporation chamber, fix the device and let the lower surface face the crucible; then, prepare the customized alloy target with a mass ratio of Au:Ge:Ni=84:14:2, and put it into the evaporation chamber. In the crucible in the cavity, the thickness of the material deposited on the surface of the device can be adjusted by setting the speed of the electron beam; then, the cavity is evacuated with a molecular pump, and the vacuum degree is below 6×10 ^-4 Pascals. Turn on the electron beam switch, start the electron beam evaporation, and turn off the electron beam switch after about 5 minutes; fill with nitrogen, then evacuate, and then flush nitrogen until the pressure returns to normal pressure. After the alloy target cools down, open the chamber door and take out the alloy target Replace the target material with Au metal target, and then repeat the above steps of electron beam evaporation alloy to evaporate Au metal. The evaporation time is about 15 minutes. After the completion, turn off the electron beam switch, wait for the target material to cool down, and the pressure in the cavity returns to normal pressure. The device is taken out from the evaporation chamber door to complete the back electrode preparation of the device.

12) Annealing: put the TPV device prepared above into an annealing furnace, pass through nitrogen, and carry out an alloying treatment at 275° C. for 2 minutes to form an ohmic-contact upper electrode and a back electrode, thereby completing the GaSb-based Preparation of In _x Ga _{1- x} Sb/GaSb strained quantum well intermediate band thermal photovoltaic cells.

Table 3: Process parameters of each layer material in In _0.3 Ga _0.7 Sb/GaSb strained quantum well intermediate band TPV cells

According to the previous device preparation process, the prepared device was prepared for electrode preparation, and finally an In _0.3 Ga _0.7 Sb/GaSb strained quantum well intermediate band TPV battery was obtained. In a thermophotovoltaic system with a filter, when the reflectance of the filter is 97% for photons with energy below the forbidden band width, 15% for photons with energy higher than the forbidden band width, and the absorption rate is 2%, the present Invented In _x Ga _1-x Sb/GaSb strained quantum well intermediate band TPV battery. When the temperature of the radiator is 1050°C and the operating temperature of the battery is 25°C, the energy conversion efficiency can reach 36.4%, and the output power density can reach 5.6W /cm ² . There are some differences between the modified value and that obtained by device simulation. The main reason may be that there are defects in the prepared material and other factors that reduce the performance of the device. Table 4 shows the material parameters of each layer of the GaSb-based In _0.3 Ga _0.7 Sb/GaSb strained quantum well intermediate band TPV cell.

Table 4: Material parameters of each layer of In _0.3 Ga _0.7 Sb/GaSb strained quantum well intermediate band TPV cells

Table 5: Process parameters for preparing device electrodes

Claims (10)

1. A GaSb-based In _x Ga _1-x Sb/GaSb strained quantum well intermediate energy band thermal photovoltaic cell, characterized in that: from top to bottom is an upper electrode, heavily doped p-type Al _x1 Ga _{1- x1} As _y1 Sb _1-y1 window layer, p-type GaSb active region, intrinsic In _x Ga _{1- x} Sb/GaSb multiple quantum wells, n-type GaSb active region, heavily doped n-type Al _x2 Ga _{1- x2} As _y2 Sb _1-y2 back electric field layer, n-type GaSb substrate and back electrode; among them, the number of intrinsic In _x Ga _1-x Sb/GaSb multiple quantum wells is 4 to 5, and x takes 0.25 to 0.3 , x ₁ and x ₂ both take 0.05-0.35, both y ₁ and y ₂ take 0.005-0.03, and the area of the upper electrode accounts for 8-10% of the total area of the upper surface of the battery. 2. a kind of In _x Ga _1-x Sb/GaSb strained quantum well intermediate band thermal photovoltaic cell based on GaSb as claimed in claim 1, is characterized in that: n-type GaSb substrate is the n-type GaSb polishing of Te doping For a single wafer, the net donor Te doping concentration is 4.7×10 ¹⁷ /cm ³ , the thickness is 500±25 μm, and the crystal orientation is 2° from (100) to (110). 3. A kind of GaSb-based In _x Ga _1-x Sb/GaSb strained quantum well intermediate energy band thermal photovoltaic cell as claimed in claim 1, characterized in that: heavily doped n-type Al _x2 Ga _1-x2 As _y2 Sb _1-y2 back electric field layer and heavily doped p-type Al _x1 Ga _{1- x1} As _y1 Sb _1-y1 window layer are Al _x0 Ga _1-x0 As _y0 Sb _{1- y0} quaternary alloy material, its composition satisfies the relationship y ₀ =0.093x ₀ /(1+0.061x ₀ ), y ₁ =0.093x ₁ /(1+0.061x ₁ ), y ₂ =0.093x ₂ /(1 +0.061x ₂ ), x ₀ , x ₁ , x ₂ all take 0.05~0.35, y ₀ , y ₁ , y ₂ take 0.005~0.03, the corresponding band gaps are all 0.807~1.22eV, heavily doped The thickness and doping concentration of the n-type Al _x2 Ga _1-x2 As _y2 Sb _1-y2 back electric field layer and the heavily doped p-type Al _x1 Ga _1-x1 As _y1 Sb _1-y1 window layer are both 45-60nm and 1×10 ¹⁹ to 2×10 ¹⁹ /cm ³ . 4. A kind of GaSb-based In _x Ga _1-x Sb/GaSb strained quantum well intermediate energy band thermal photovoltaic cell as claimed in claim 1, characterized in that: in In _x Ga _1-x Sb/GaSb multiple quantum wells The barrier material is intrinsic GaSb with a thickness of 10-15 nm, and the well material is intrinsic In _x Ga _1-x Sb with a thickness of 5.5-6.5 nm. 5. A kind of GaSb-based In _x Ga _1-x Sb/GaSb strained quantum well intermediate band thermal photovoltaic cell as claimed in claim 1, characterized in that: the thickness of the n-type GaSb active region is 6-8 μm, The doping concentration is 9.5×10 ¹⁷ -2×10 ¹⁸ /cm ³ , the thickness of the p-type GaSb active region is 0.2-0.4 μm, and the doping concentration is 9.5×10 ¹⁷ -2×10 ¹⁸ /cm ³ . 6. A kind of GaSb-based In _x Ga _1-x Sb/GaSb strained quantum well intermediate band thermal photovoltaic cell as claimed in claim 1, characterized in that: heavily doped n-type Al _x2 Ga _1-x2 As The dopant of _y2 Sb _1-y2 back electric field layer and n-type GaSb active region is Te, heavily doped p-type Al _x1 Ga _1-x1 As _y1 Sb _1-y1 window layer and p-type GaSb active region The dopant is Zn. 7. A kind of GaSb-based In _x Ga _1-x Sb/GaSb strained quantum well intermediate band thermal photovoltaic cell as claimed in claim 1, characterized in that: the material of the upper electrode is double-layered Au-Pb/Au The material, the alloy mass ratio is Au:Pb=6:4, the thickness of the first layer of Au-Pb alloy layer is 40-60nm, the thickness of the second layer of Au metal layer is 100-150nm; the material of the back electrode is double-layer Au- Ge-Ni/Au material, the alloy mass ratio is Au:Ge:Ni=84:14:2, the thickness of the first layer of Au-Ge-Ni alloy layer is 20-40nm, and the thickness of the second layer of Au metal layer is 200-300nm . 8. the preparation method of a kind of GaSb-based In _x Ga _1-x Sb/GaSb strained quantum well intermediate energy band thermal photovoltaic cell according to claim 1, its steps are as follows: 1) Cleaning and corrosion of the substrate: corrode the n-type GaSb substrate in a mixture of nitric acid, hydrochloric acid and glacial acetic acid for 10 to 15 minutes, then immediately wash it with deionized water, dry it with high-purity nitrogen and put it into LP-MOCVD In the reaction chamber of the equipment; among them, the dosage range of nitric acid, hydrochloric acid and glacial acetic acid is 1-3mL: 5-15mL: 40-60mL; 2) Growth program setting: heavily doped n-type Al _x2 Ga _1-x2 As _y2 Sb _1-y2 back electric field layer/n-type GaSb active layer/4~5 intrinsic In _x Ga _1-x Sb /GaSb multiple quantum wells/p-type GaSb active layer/heavily doped p-type Al _x1 Ga _1-x1 As _y1 Sb _1-y1 window layer growth parameters are set, including the growth temperature of each layer of material, growth The flow rate of each organic source and dopant and the flow rate of carrier gas hydrogen for each layer of material; 3) Vacuumize the reaction chamber: set the pressure to the value required for growth of 20 to 50 mbar, start the mechanical pump to evacuate the reaction chamber, and at the same time pass in hydrogen to replace the nitrogen in the reaction chamber, and pass in rotating gas to rotate the substrate; 4) Heat treatment of the substrate: set the temperature at 580-620°C, start the intermediate frequency furnace to heat the substrate, and when the temperature rises to 330-360°C, feed TESb to protect the substrate surface, because the Sb in the GaSb substrate is in the At high temperature, it will dissociate from the surface of the substrate. The introduction of TESb inhibits the dissociation of Sb atoms. When the temperature reaches the set value and stabilizes, the high-temperature download gas hydrogen will react with the oxide on the substrate surface, and the reaction product Take it out of the reaction chamber with hydrogen to achieve the purpose of desorption treatment of oxides on the substrate surface, and the treatment time is 10 to 20 minutes; 5) Growing each epitaxial layer: After the substrate is heat-treated, lower the temperature and enter the epitaxial layer growth program to grow each epitaxial layer; 6) Cooling and sampling: after the growth is over, after the temperature drops to room temperature and the reaction chamber returns to normal pressure, take out the device prepared in the reaction chamber; 7) Cleaning: ultrasonically clean the prepared n-type GaSb substrate/heavily doped n-type Al _x2 Ga _1-x2 As _y2 Sb _1-y2 back electric field layer/n-type GaSb active layer with CCl ₄ , acetone and alcohol respectively Layer/4～5 intrinsic In _x Ga _1-x Sb/GaSb quantum wells/p-type GaSb active layer/heavily doped p-type Al _x1 Ga _1-x1 As _y1 Sb _1-y1 window layer device 2 ~3 times, 5~10 minutes each time, and then blow dry with high-purity _N2 ; 8) Baking: Baking the prepared device in an oven at 75-85°C for 20-25 minutes; 9) Fabrication of the upper electrode: Au-Pb/Au upper electrode is fabricated on the upper surface of the p ⁺ type Al _x1 Ga _1-x1 As _y1 Sb _1-y1 window layer by means of electron beam evaporation; 10) Thinning of the substrate: First, use coarse sand with a mesh number of 280-320 to grind the back of the n-type GaSb substrate of the thermal photovoltaic cell to 350-380um, and then use fine sand with a mesh number of 2000-2500 to grind to 230～260um, finally polished with emery; 11) Fabrication of the back electrode: Au-Ge-Ni/Au back electrode is produced by electron beam evaporation on the back of the n-type GaSb substrate of the thermal photovoltaic cell prepared above; 12) Annealing: put the thermal photovoltaic cell prepared above into an annealing furnace, pass nitrogen gas, and carry out alloying treatment at 250-295 °C for 1-2 minutes to form an ohmic-contact upper electrode and a back electrode, thereby completing the process based on Preparation of GaSb In _x Ga _1-x Sb/GaSb strained quantum well intermediate band thermal photovoltaic cells. 9. a kind of preparation method based on GaSb In _x Ga _1-x Sb/GaSb strained quantum well intermediate energy band thermal photovoltaic cell as claimed in claim 8, is characterized in that: the preparation of upper electrode, at first is to make a material The mask plate is a copper sheet, the shape and area are the same as the upper surface of the device, and then a rectangular hole is dug in the center of the mask plate, and the dug area accounts for 8% to 10% of the mask plate area, and the mask The mask plate and the upper surface of the device are overlapped and pressed tightly, and the mask plate and the device are put into the evaporation chamber of the electron beam evaporation equipment, and the device is fixed so that the upper surface of the device faces the crucible; then, the customized mass ratio is The alloy target of Au:Pb=6:4 is ready, put it into the crucible in the evaporation chamber, and then adjust the ratio of materials deposited on the surface of the device by setting the speed of the electron beam; Vacuum inside, the vacuum degree is below 6×10 ^-4 Pascals, turn on the electron beam switch after completion, start the electron beam evaporation, turn off the electron beam switch after 5 to 10 minutes; fill with nitrogen, then vacuumize, and then flush nitrogen to reach the pressure Return to normal pressure. After the alloy target is cooled, open the chamber door, take out the alloy target and replace it with an Au metal target, and then repeat the above steps of electron beam evaporation alloy to evaporate the Au metal. The evaporation time is 10 to 15 minutes. Turn off the electron beam switch, wait for the target to cool down, the pressure in the chamber returns to normal pressure, open the door of the evaporation chamber to take out the device, remove the mask, and prepare the upper electrode on the upper surface of the device. 10. a kind of preparation method based on GaSb In _x Ga _1-x Sb/GaSb strained quantum well intermediate band heat photovoltaic cell as claimed in claim 8, is characterized in that: the preparation of back electrode, at first is to put device Put it into the evaporation chamber, fix the device and let the lower surface face the crucible; then, prepare the customized alloy target with a mass ratio of Au:Ge:Ni=84:14:2, and put it into the crucible in the evaporation chamber , and then by setting the speed of the electron beam to achieve the purpose of adjusting the thickness of the material deposited on the device surface; then, use a molecular pump to evacuate the cavity, and the vacuum degree is below 6×10 ^-4 Pascals. After completion, turn on the electron beam switch, Start electron beam evaporation, turn off the electron beam switch after 4 to 6 minutes; fill with nitrogen, then vacuumize, and then flush nitrogen until the pressure returns to normal pressure. After the alloy target cools down, open the chamber door, take out the alloy target and replace it with Au Metal target, and then repeat the above steps of electron beam evaporation alloy to evaporate Au metal. The evaporation time is 15-20 minutes. After completion, turn off the electron beam switch, wait for the target to cool down, the pressure in the chamber returns to normal pressure, and open the evaporation chamber door The device is taken out to complete the preparation of the back electrode of the device.