CN106129165B - A heterojunction solar cell with double-sided field-assisted effect - Google Patents

Abstract

The invention discloses a kind of heterojunction solar battery for helping effect containing bilateral field, wide bandgap material area, low bandgap material area and Window layer region that the battery sets gradually.Wide bandgap material area includes the broad-band gap base and undoped p area for setting gradually.Broad-band gap base uses Al_yGa_1‑yAs, 0.24≤y≤0.3, thickness is 10 ~ 3000nm.Low bandgap material area uses Al_xGa_1‑xAs, x≤0.2, thickness is 10 ~ 40nm.Window layer region uses Al (Ga) InP or Al_zGa_1‑zAs, z >=0.4, thickness is 10 ~ 50nm.Wide bandgap material area and low bandgap material area form the second hetero-junctions, there is i/p types field and help in the hetero-junctions both sides and help structure with n+/n types.Therefore, the carrier transport of the hetero-junctions of solar cell second and the ability across potential barrier of heterogenous junction are improved, so as to improve the utilization rate of solar cell.

Description

A heterojunction solar cell with double-sided field-assisted effect

technical field

The invention relates to a solar cell, in particular to a heterojunction solar cell with a bilateral field-assisted effect.

Background technique

III-V compound solar cells are recognized as a new generation of high-performance and long-life space main power sources due to their high conversion efficiency, strong radiation resistance, and good temperature characteristics. With the continuous improvement of compound semiconductor growth technology (such as metal organic compound vapor phase epitaxy - MOCVD), the efficiency of III-V solar cells has been greatly improved. At present, the efficiency of single-junction GaAs cells has exceeded 29%, and the efficiency of bonded five-junction III-V solar cells has reached 36%. One of the key points to achieve high-efficiency five-junction-six-junction solar cells is to obtain the second junction with a band gap of 1.7-1.8eV, that is, a wavelength of 690nm-730nm. Usually, the material for this absorption band is AlGaAs with an Al composition of 20-28%. It is well known that compounds with high Al composition usually have relatively low carrier effective lifetime, especially the DX center defect formed by n-type doping is a very serious recombination center.

In a typical heterojunction solar cell, as shown in Figure 1, no field-assisted structure is used in the narrow bandgap emission region, or as shown in Figure 2, a field-assisted structure with an undoped layer is used, while in the wide bandgap base The field-assisted structure is not used in the region, which reduces the transport capacity of carriers, especially the transition of holes from the narrow-bandgap emitter region to the wide-bandgap base region.

Contents of the invention

The purpose of the present invention is to provide a heterojunction solar cell with double-sided field-assisted effect, which overcomes the low transport capacity of the existing technology carriers, especially the holes from the narrow bandgap material region to the wide bandgap base region For the problem of low transition ability, the double-field-assisted structure can improve the carrier transport ability and transition ability, and improve the utilization rate of solar cells.

In order to achieve the above purpose, the present invention provides a heterojunction solar cell with double-sided field-assisted effect, which includes a wide bandgap material region, a narrow bandgap material region and a window layer region arranged in sequence.

Wherein, the wide bandgap material region includes a wide bandgap base region and an undoped region arranged in sequence.

Wherein, the wide bandgap base region and the undoped region form a first homojunction, and the first homojunction has a field-assisted structure.

Wherein, the narrow bandgap material region and the window layer region form a first heterojunction, and the first heterojunction has a field-assisted structure.

Wherein, the wide bandgap material region and the narrow bandgap material region form a second heterojunction.

Wherein, the wide bandgap base region adopts i/p-/p+ type Al _y Ga _1-y As, 0.24 ≤ y ≤ 0.3, the thickness is 10~3000nm, and the p-type doping concentration is from 10 ¹⁶ to 10 ¹⁸ cm ^{- 3} .

Wherein, the narrow band gap material region adopts n+/n- type Al _x Ga _1-x As, x ≤ 0.2, the thickness is 10~100nm, and the n-type doping concentration is 10 ¹⁶ cm ^-3 to 10 ¹⁸ cm ^-3 .

Wherein, the window layer region is made of n-type Al(Ga)InP or Al _z Ga _1-z As, z≥0.4, a thickness of 10-50 nm, and an n-type doping concentration of 10 ¹⁷ ~10 ¹⁸ cm ^{- 3} .

The narrow bandgap material region includes a weakly n-type doped region and a heavily n-type doped region arranged in sequence, and the n-type doping concentrations of the weakly n-type doped region and the heavily n-type doped region are different.

The thicknesses of the weakly n-type doped region and the heavily n-type doped region are both 10-50 nm.

The weakly n-type doped region and the heavily n-type doped region form a second homojunction, and the second homojunction has a field-assisted structure.

The field aid structures of the second homojunction and the first heterojunction are both n+/n-type field aid.

The field-assisted structure of the first homojunction is an i/p-type field-assisted structure.

The doping concentration distribution function of the wide bandgap base region and the narrow bandgap material region is any one of gradient, linear, polynomial or exponential form.

The undoped region is made of Al _y Ga _1-y As, 0.24 ≤ y ≤ 0.3, the thickness is 10-100nm, and it is not doped.

The solar cell also includes a back field arranged on the side of the wide bandgap base region.

The back field adopts n-type AlzGa1 _- zAs, _z≥0.4 , thickness is 10-50mm, and p-type doping concentration is 10 ¹⁷ -10 ¹⁸ cm ^-3 .

A heterojunction solar cell with bilateral field-assisted effect provided by the present invention solves the problems of low carrier transport capacity and transition capacity in the prior art, and has the following advantages:

The wide bandgap material region and the narrow bandgap material region of the solar cell form a second heterojunction, and i/p-type field aids and n+/n-type field aids are formed on both sides of the second heterojunction, so that the The solar cell has a double field assist effect, so that the efficiency of the cell is improved; by reasonably setting the positions of different material regions of the solar cell, the concentration of p-type or n-type doping in the material, and the thickness of different regions, the narrow-bandgap material region and the wide-bandgap material region The formed heterojunction accelerates the carriers through the electric field in the field-assisted structure on both sides, which improves the transport capacity of the carriers, and at the same time enhances the ability of the carriers to cross the heterojunction barrier; The doping concentration distribution function of the region and the narrow bandgap material region is in gradient, linear, polynomial or exponential form, so that the concentration of homojunction and heterojunction changes slowly, and the carrier transport efficiency can be improved.

Description of drawings

Figure 1 is an energy band diagram of a heterojunction solar cell without a field-assisted structure in the narrow bandgap emission region of the prior art (Ec: conduction band bottom energy, Ef: Fermi level, Ev: valence band top energy).

Fig. 2 is an energy band diagram of a heterojunction solar cell with a field-assisted structure containing an undoped layer in the narrow bandgap region of the prior art.

Fig. 3 is an energy band diagram of a heterojunction solar cell with bilateral field-assisted effect according to the present invention.

Fig. 4 is a schematic structural diagram of a preferred embodiment of a heterojunction solar cell with a double-sided field-assisted effect provided by the present invention.

Fig. 5 is a schematic structural diagram of a preferred embodiment of a heterojunction solar cell with a double-sided field-assisted effect provided by the present invention.

detailed description

The technical solutions of the present invention will be further described below in conjunction with the drawings and embodiments.

As shown in Figure 4, the present invention is used to provide a heterojunction solar cell containing a double-sided field-assisted effect. The present invention provides a heterojunction solar cell containing a double-sided field-assisted effect. Gap material region 10 , narrow bandgap material region 20 and window layer region 30 .

The wide bandgap material region 10 includes a wide bandgap base region 11 and an undoped region 12 arranged in sequence.

The wide bandgap base region 11 and the undoped region 12 form a first homojunction having a field-assisted structure.

The narrow bandgap material region 20 and the window layer region 30 form a first heterojunction having a field-assisted structure.

The region of wide bandgap material 10 and the region of narrow bandgap material 20 form a second heterojunction.

The wide bandgap base region 11 is made of i/p-/p+ type Al _y Ga _1-y As, 0.24 ≤ y ≤ 0.3, the thickness is 10-3000 nm, and the p-type doping concentration is from 10 ¹⁶ to 10 ¹⁸ cm ^-3 . As shown in FIG. 3 , the energy difference between the bottom of the conduction band and the top of the valence band of the wide bandgap base region 11 is relatively large.

The narrow bandgap material region 20 is made of n+/n- type Al _x Ga _1-x As, x ≤ 0.2, a thickness of 10-100 nm, and an n-type doping concentration of 10 ¹⁶ cm ^-3 to 10 ¹⁸ cm ^-3 . As shown in FIG. 3 , the energy difference between the bottom of the conduction band and the top of the valence band of the narrow bandgap material region 20 is small.

The window layer region 30 is made of n-type Al(Ga)InP or AlzGa1 _- zAs, _z≥0.4 , the thickness is 10-50nm, and the n-type doping concentration is 10 ¹⁷ -10 ¹⁸ cm ^-3 .

The narrow bandgap material region 20 includes a weakly n-type doped region 21 and a heavily n-type doped region 22 arranged in sequence, and the n-type doping concentrations of the weakly n-type doped region 21 and the heavily n-type doped region 22 are different.

The thicknesses of the weakly n-type doped region 21 and the heavily n-type doped region 22 are both 10-50 nm.

The weakly n-type doped region 21 and the heavily n-type doped region 22 form a second homojunction, and the second homojunction has a field-assisted structure.

The field aid structures of the second homojunction and the first heterojunction are both n+/n-type field aids. The n+/n-type field assistance enhances the hole collection efficiency of low-mobility aluminum-containing compounds.

The field aid structure of the first homojunction is i/p-type field aid. The i/p-type field-assisted effect enhances the probability of carriers crossing the heterojunction barrier, thereby increasing the short-circuit current density.

The doping concentration distribution function of the wide bandgap base region 11 and the narrow bandgap material region 20 is any one of gradient, linear, polynomial or exponential form.

The undoped region 12 is made of _{AlyGa1 -} yAs, 0.24≤y≤0.3, with a thickness of 10-100nm, and is undoped.

The solar cell also includes a back field 40 disposed on the side of the wide bandgap base region 11 .

The back field 40 is made of n-type Al _z Ga _1-z As, z≥0.4, the thickness is 10-50mm, and the p-type doping concentration is 10 ¹⁷ -10 ¹⁸ cm ^-3 .

Example 1

Taking a sub-solar cell with a bandgap of 1.7-1.8eV in a five-junction solar cell as an example, as shown in FIG. 4, the cell includes a back field 40, a wide bandgap base region 11, doped region 12 , weakly n-type doped region 21 , heavily n-type doped region 22 and window layer region 30 .

The back field 40 is made of Al _0.4 Ga _0.6 As with a thickness of 10-50 nm and a p-type doping concentration of 10 ¹⁸ cm ^-3 .

The wide bandgap base region 11 is made of Al _0.26 Ga _0.74 As with a thickness of 1000-3000 nm and a p-type doping concentration of 10 ¹⁶ cm ^-3 .

The undoped region 12 is made of Al _0.26 Ga _0.74 As with a thickness of 10-100 nm and is not doped.

The weakly n-type doped region 21 is made of Al _0.2 Ga _0.8 As with a thickness of 10-50 nm and an n-type doping concentration of 10 ¹⁷ cm ^-3 .

The heavily n-type doped region 22 is made of Al _0.2 Ga _0.8 As with a thickness of 10-50 nm and an n-type doping concentration of 10 ¹⁸ cm ^-3 .

The weakly n-type doped region 21 and the heavily n-type doped region 22 form a narrow bandgap material region 20 .

The window layer region 30 is made of Al _0.6 Ga _0.4 As with a thickness of 10-100 nm and an n-type doping concentration of 10 ¹⁸ cm ^-3 .

The sub-solar cell structure was grown using low-pressure metal-organic chemical vapor deposition (MOCVD) equipment. In this solar cell structure, the region 12/region 11 forms a first homojunction, forming an i/p-type field-assisted structure, and the region 22/region 21 forms a second homojunction, forming an n+/n-type field-assisted structure. The narrow bandgap material region 20 and the wide bandgap base region 11 form a second heterojunction, and the above-mentioned i/p-type field-assisted structure and n+/n-type field-assisted structure both form a field-assisted effect on the second heterojunction, through The electric field in the field-assisted structure on both sides accelerates the carrier transport ability.

Experimental results show that the spectral response of the solar cell adopting the structure of the present invention is 5%-10% higher than that of other structural cells under the same experimental conditions in the short and middle wave range of 400-600nm, and the open circuit voltage is increased by 10-30mV.

Example 2

Still taking a sub-solar cell with a band gap of 1.7-1.8eV in the five-junction solar cell, that is, a sub-solar cell with a wavelength of 690nm-730nm as an example, to achieve the same device performance as in Example 1, the structure shown in Figure 5 can also be used, which includes: Field 40 , wide bandgap base region 11 , undoped region 12 , narrow bandgap material region 20 and window layer region 30 .

The back field 40 is made of Al _0.4 Ga _0.6 As with a thickness of 10-50 nm and a p-type doping concentration of 10 ¹⁸ cm ^-3 .

The wide bandgap base region 11 is made of Al _0.26 Ga _0.74 As with a thickness of 1000~3000nm, and the p-type doping concentration changes from 10 ¹⁸ to 10 ¹⁶ cm ^-3 in a linear, polynomial or exponential form.

The undoped region 12 is made of Al _0.26 Ga _0.74 As with a thickness of 10-100 nm and is not doped.

The narrow bandgap material region 20 is made of Al _0.2 Ga _0.8 As with a thickness of 10-100 nm, and the n-type doping concentration changes from 10 ¹⁶ to 10 ¹⁸ cm ^-3 in a linear, polynomial or exponential form.

The window layer region 30 is made of Al _0.6 Ga _0.4 As with a thickness of 10-100 nm and an n-type doping concentration of 10 ¹⁸ cm ^-3 .

The sub-solar cell structure was also grown using low-pressure metal-organic chemical vapor deposition (MOCVD) equipment. In this structure, the region 12/region 11 forms a first homojunction, forming an i/p-type field-assisted structure, and the region 30/region 20 forms a first heterojunction, forming an n+/n-type field-assisted structure. The narrow bandgap material region 20 and the wide bandgap base region 11 form a second heterojunction, and the above-mentioned i/p-type field-assisted structure and n+/n-type field-assisted structure both form a field-assisted effect on the second heterojunction, through The electric field in the field-assisted structure on both sides accelerates the carrier transport ability.

In summary, the present invention is used to provide a heterojunction solar cell with double-sided field-assisted effect, which not only enhances the overall carrier transport capacity, but also The ability of carriers to cross the heterojunction barrier is enhanced, the efficiency of the battery is improved, and it has certain market development potential and practical value.

Although the content of the present invention has been described in detail through the above preferred embodiments, it should be understood that the above description should not be considered as limiting the present invention. Various modifications and alterations to the present invention will become apparent to those skilled in the art upon reading the above disclosure. Therefore, the protection scope of the present invention should be defined by the appended claims.

Claims (10)

1. a kind of heterojunction solar battery for helping effect containing bilateral field, it is characterised in that the battery bag contains the width for setting gradually Band gap material area（10）, low bandgap material area（20）With Window layer region（30）；

Described wide bandgap material area（10）Comprising the broad-band gap base for setting gradually（11）With undoped p area（12）；

Described broad-band gap base（11）With undoped p area（12）The first homojunction is formd, first homojunction helps knot with field Structure；

Described low bandgap material area（20）With Window layer region（30）The first hetero-junctions is formd, first hetero-junctions has field Help structure；

Described wide bandgap material area（10）With low bandgap material area（20）Form the second hetero-junctions；

Described broad-band gap base（11）Using i/p-/p+ types Al_yGa_1-yAs, 0.24≤y≤0.3, thickness is 10 ~ 3000nm, P-type doping concentration is from 10¹⁶To 10¹⁸cm^-3；

Described low bandgap material area（20）Using n+/n- types Al_xGa_1-xAs, x≤0.2, thickness is 10 ~ 100nm, N-shaped doping Concentration is 10¹⁶cm^-3To 10¹⁸cm^-3；

Described Window layer region（30）Using AlGaInP, AlInP or Al of N-shaped_zGa_1-zAs, z >=0.4, thickness is 10 ~ 50nm, N-shaped doping concentration is 10¹⁷~10¹⁸cm^-3。

2. the heterojunction solar battery for helping effect containing bilateral field according to claim 1, it is characterised in that described is narrow Band gap material area（20）Comprising the weak N-shaped doped region for setting gradually（21）With heavy n-type doped region（22）, the weak N-shaped doped region （21）With heavy n-type doped region（22）N-shaped doping concentration it is different.

3. the heterojunction solar battery for helping effect containing bilateral field according to claim 2, it is characterised in that described is weak N-shaped doped region（21）With heavy n-type doped region（22）Thickness be 10 ~ 50nm.

4. the heterojunction solar battery for helping effect containing bilateral field according to claim 2, it is characterised in that described is weak N-shaped doped region（21）With heavy n-type doped region（22）The second homojunction is formd, second homojunction helps structure with field.

5. the heterojunction solar battery for helping effect containing bilateral field according to claim 4, it is characterised in that described The field of two homojunctions and the first hetero-junctions helps structure to be n+/n- types and helps.

6. the heterojunction solar battery for helping effect containing bilateral field according to claim 1, it is characterised in that described The field of one homojunction helps structure to be helped for i/p- types.

7. the heterojunction solar battery for helping effect containing bilateral field according to claim 1, it is characterised in that described width Band gap base（11）With low bandgap material area（20）Doping concentration distribution function be gradient, linear, multinomial or exponential form In any one.

8. the heterojunction solar battery for helping effect containing bilateral field according to claim 1, it is characterised in that it is described not Doped region（12）Using Al_yGa_1-yAs, 0.24≤y≤0.3, thickness is 10 ~ 100nm, undoped p.

9. the heterojunction solar battery for helping effect containing bilateral field according to claim 1, it is characterised in that it is described too Positive electricity pond also includes and is arranged on broad-band gap base（11）The back surface field of side（40）.

10. the heterojunction solar battery for helping effect containing bilateral field according to claim 9, it is characterised in that described Back surface field（40）Using the Al of p-type_zGa_1-zAs, z >=0.4, thickness is 10 ~ 50mm, and p-type doping concentration is 10¹⁷~10¹⁸cm^-3。