CN100463231C - Setup method for indium-gallium-nitride p-n node type multi-node solar battery structure - Google Patents

Abstract

The invention is concerned with a setting method of structure to multi-junction solar battery in type of InGaN p-n. It takes current-pressure equation, relation formula between InxGa1-xN energy gap and In composing and correlative parameters of InxGa1-xN of solar battery in type of InGaN p-n to count the largest transition efficiency of InGaN multi-junction (solo-junction) solar battery and the best energy gap of junction material to get the said transition efficiency and corresponding value of In composing. Take InxGa1-xN with those different In composing as junction material and connect them with tunnel kink in series. Set metal conduct pole on the first junction n (or p)-Inx1Ga1-x1N and the last I junction p (or n)-InxiGa1-xiN, and cover film to reduce reflection on incidence surface.

Description

The method to set up of the structure of indium-gallium-nitride p-n node type multi-node solar battery

Technical field

The present invention relates to a kind of semiconductor solar cell.Especially relate to a kind of novel semiconductor material In _xGa _1-xN p-n junction type is tied the method to set up of the structure of (containing unijunction) solar cell more.

Background technology

Since the nineties, the application study of III group nitride material such as semiconductor gallium nitride GaN and alloy aluminum gallium nitride AlGaN thereof, indium gallium nitrogen InGaN and device development is very fast, is mainly used in opto-electronic device and high-frequency high-power microelectronic component.2002, people such as the W.Walukiewicz of the U.S. found that the energy gap of InN is 0.7eV, rather than the 1.89eV that reported in the past.This makes In _xGa _1-xThe energy gap of N alloy is adjustable continuously to the 0.7eV of InN (x=1) from the 3.4eV of GaN (x=0) with the variation of In component x, the wavelength of its corresponding absorption spectrum can extend to near-infrared part (1770nm) from ultraviolet portion (365nm) always, almost intactly covered whole solar spectrum, than existing Si, solar cell materials such as InGaAsP series can only want superior many by the cover part solar spectrum, and this provides new ideal material for designing and preparing the high efficiency solar battery.The InGaN material is compared with the semi-conducting material of existing preparation solar cell also has many advantages: 1. In _xGa _1-xN is the direct band gap material, its absorption coefficient height, and photoelectric conversion efficiency will be higher.2. the electron mobility height of InGaN helps improving photoelectric conversion efficiency.3. the uptake zone thickness of the InGaN solar cell of high absorption coefficient can be thinner, and the weight of device is lighter.4. InGaN has stronger capability of resistance to radiation.5. be particularly suitable for preparation " many knots " (or claiming " series connection ", " laminated ") solar cell.Unijunction (referring to contain 1 p-n junction) solar cell is because of the band gap width E of material _gNecessarily, has only energy in the solar spectrum greater than E _gPhoton could produce photo-generated carrier, and energy is much larger than E _gLight can in transfer process, produce heat, cause energy loss, therefore conversion efficiency is not high enough, many knot (referring to contain 1 with last p-n junction) solar cells calculate and need be together in series the material of different energy gaps by theory, make the light of different-waveband in the solar spectrum by the absorbed of different energy gaps, thereby make conversion efficiency reach maximum.The solar cell selection of the many knots of preparation at present is difficulty, is not easy to search out at all suitable materials of aspects such as energy gap, lattice mismatch and thermal mismatchings, and for example existing three-junction solar battery will be used Ga _0.51In _0.49Three kinds of materials of P/GaAs/Ge, this brings difficulty for the material growth and the preparation of battery.Use In _xGa _1-xThe advantage of N material preparation multijunction solar cell is to change In component x just can regulate In continuously _xCa _1-xThe energy gap of N (it almost covers whole solar spectrum) therefore only needs to use a kind of In _xCa _1-xThe N ternary-alloy material can obtain needed different energy gap, and the conversion efficiency of battery also will improve many, and growth of the material of battery and preparation will be easier also.

At present to In _xGa _1-xN is the In of high In ingredient, thick film particularly _xGa _1-xThe research of N ternary alloy three-partalloy starting soon, material growing technology such as material growth, the doping of p type and rerum natura are still among continuous research and development.The structure of solar cell mainly contains types such as p-n junction, surface potential barrier, the internal electric field that relies on these knots with light induced electron-hole to separately and scan out the electric current that forms external circuit.Before preparation InGaN solar cell, must carry out the Theoretical Calculation of maximum conversion efficiency to InGaN unijunction and multijunction solar cell, obtain the best energy gap and the corresponding In component value of material then, carry out the structural design of solar cell on this basis.

Referring to: [1] William Shockley and Hans.J.Queisser, J.Appl.Phys.1961,32 (3): 510.

[2]K.P.O′Donnell，I.Fernandez-Torrente，P.R.Edwards，R.W.Martin，Journal?of?Crystal?Growth，2004，296：100

[3]Hasna?Hamzaoui，Ahmed?S.Bouazzi，Bahri?Rezig，Sol.Energy?Mat.Sol.Cells.2005，87：595

[4] Michael E.Levinshtein, Sergey L.Rumyantsev, Michael S.Shur.Properties of AdvancedSemiconductor Materials (semi-conducting material that preparation is advanced): GaN, AlN, InN, BN, SiC, SiGe.New Jersey:John Wiley﹠amp; Sons, 2001

[5]Landolt?Bornstein，Berlin：Springer-Verlag，1982，PIII/17

Summary of the invention

The objective of the invention is: propose indium gallium nitrogen (In _xCa _1-xN) the p-n junction type is tied the calculating of (containing unijunction) solar cell conversion efficiency, best energy gap and corresponding indium component value and the structure setting method of solar cell more.

The object of the present invention is achieved like this: the method to set up of the structure of indium-gallium-nitride p-n node type multi-node solar battery, and with current-voltage equation, the In of p-n junction type solar cell _xGa _1-xN energy gap and In component relational expression and In _xGa _1-xThe computational methods of the relevant parameter of N material, the best energy gap of wherein respectively tying material and corresponding In component value when calculating the maximum conversion efficiency of many knot InGaN solar cells and obtaining this conversion efficiency are with the In of these different I n component _xGa _1-xN is each junction battery material wherein, vertically is together in series with tunnel junction between each junction battery, becomes the structure that the p-n junction type is tied the InGaN solar cell more.

The structural design of described solar cell has just shines and shines two kinds of the back ofs the body.Select semi-conducting material In for use _xGa _1-xN (0.01≤x≤0.99) is the light absorption district, and sapphire (sapphire) or other materials are substrate.In with different I n component x _xGa _1-xN is each junction battery material wherein, and each ties putting in order of material is to arrange by In component ascending (its energy gap is descending) along the sunlight incident direction.Between each junction battery, vertically be together in series with tunnel junction.N (or p)-In at the 1st knot _X1Ga _1-x1P (or n)-In of N and last i knot _XiGa _1-XiN is provided with the metallic conduction electrode, and incidence surface covers the structure that antireflective coating becomes multijunction solar cell.

Characteristics of the present invention are: indium gallium nitrogen (In _xGa _1-xN) the p-n junction type is tied (containing unijunction) solar cell conversion efficiency more and is improved, and can reach 41.3% as three more satisfactory junction structures, and the multijunction cell material only need be used a kind of In _xGa _1-xThe N ternary-alloy material is once finished the growth of many knot materials, preparation technology and existing microelectronic technique compatibility in growth apparatus.Clear variation relation of having expressed solar cell conversion efficiency and energy gap, as the variation relation curve between the two that provides.

Description of drawings

Fig. 1 calculates the In of gained for the present invention _xGa _1-xThe variation relation figure of N unijunction solar cell conversion efficiency and energy gap.

Fig. 2 calculates the In of gained for the present invention _xGa _1-xN two connection solar cell conversion efficiencies and two single junction cell material energy gap Eg wherein ₁, Eg ₂Variation relation figure.

A kind of back illumination In that Fig. 3 proposes for the present invention _xGa _1-xThe structural representation of N two connection solar cells (In wherein _X1Ga _1-x1N and In _X2Ga _1-x2In component x among the N ₁＜x ₂).

Embodiment

1. the setting of the structure of indium-gallium-nitride p-n node type multi-node solar battery

Described many knot (containing unijunction) solar cells need be selected the In of different I n component for use _xGa _1-xThe N material, definite process of In component is as follows: at first calculate maximum conversion efficiency, the best energy gap of each material when drawing this conversion efficiency then obtains corresponding In component value at last.The theoretical calculation method of solar cell conversion efficiency is as follows: InGaN p-n junction type solar cell satisfies the current-voltage equation of desirable p-n junction ^[1], do following hypothesis in computational process: 1) solar battery structure is desirable p-n junction; 2) ignore the surface reflection that sunlight incides battery; 3) each knot of solar cell only absorbs the photon of energy greater than (contain equal, as follows) this knot energy gap; 4) energy only excites a pair of electron-hole pair greater than each photon of material energy gap; 5) do not consider the various losses of photo-generated carrier in battery, all scan out external circuit; 6) when many knots series connection solar cells were simulated, the short-circuit current density of solar cell was got the minimum value of each junction battery short-circuit current density, the open circuit voltage of solar cell be each junction battery open circuit voltage with.

The definition of solar cell efficiency eta is:

$\mathrm{\η}\≡\frac{P_m}{P_i}=\frac{J_m\·V_m}{P_i}=\frac{\mathrm{FF}\·V_{\mathrm{oc}}\·J_{\mathrm{sc}}}{P_i}---\left(1\right)$

P in the formula _mBe the peak power output of solar cell unit are, J _mAnd V _mBe maximum current and the maximum voltage of this moment, P _iFor projecting the sunlight power of battery surface unit are, FF, V _OcAnd J _ScBe respectively fill factor, curve factor, open circuit voltage and the short-circuit current density of solar cell.From then on formula will be tried to achieve P as can be known _m, J that will be when p-n junction current-voltage equation is tried to achieve peak power output _mAnd V _mCurrent-voltage equation when illumination is arranged is:

J＝J _sc-J ₀(e ^V/Vc-1) (2)

V wherein _c=kT/q is the thermal voltage under the room temperature (300K), and its value is 0.026V.J ₀Be reverse saturation current density, have

$J_0={\mathrm{qN}}_C{N}_V(\frac{D_n}{N_A{L}_n}+\frac{D_p}{N_D{L}_p})\exp (-\frac{E_g}{\mathrm{kT}})---\left(3\right)$

N in the formula _cAnd N _vBe respectively the density of states of conduction band and valence band, N _AAnd N _DBe respectively the doping content in p district and n district, D _nAnd D _pBe respectively the diffusion coefficient in electronics and hole, L _nAnd L _pBe respectively the diffusion length in electronics and hole, E _gIt is the energy gap of material.

During open circuit, J=0 is arranged, the voltage that can be got this moment by (2) formula is open circuit voltage V _OcExpression formula be

V _oc＝V _cln(J _sc/J ₀+1) (4)

Work as J=0, short-circuit current density J in the time of illumination can being got by (2) formula _ScFor

J _sc＝J ₀exp(V _oc/V _c)-J ₀ (5)

Short-circuit current density J _ScBeing photogenerated current density, when illumination is on solar cell, according to Lambert law, is that the number of photons at x place satisfies apart from the battery surface degree of depth:

Q(λ，x)＝Q _s(λ)exp(-α(λ)x) (6)

Q wherein _xFor energy in this following unit interval of radiation, unit are greater than E _gThe number of photon, α is the absorption coefficient of material, it is the function of wavelength X.And number of photons is exactly the generation rate G of electron-hole pair with the negative value of change in depth rate, promptly

G(λ，x)＝-dQ(λ，x)/dx＝Q _s(λ)α(λ)exp(-α(λ)x) (7)

The thickness of supposing absorbed layer is d, and the electron-hole pair sum N that produces in this p-n junction so is:

$N={\∫Q}_s\left(\mathrm{\λ}\right)\mathrm{\α}\left(\mathrm{\λ}\right){\∫}_0^d\exp (-\mathrm{\α}\left(\mathrm{\λ}\right)x)\mathrm{dxd\λ}={\∫Q}_s\left(\mathrm{\λ}\right)[1-\exp (-\mathrm{\α}\left(\mathrm{\λ}\right)d)]\mathrm{d\λ}---\left(8\right)$

Then the photogenerated current density of p-n junction generation is:

J _sc＝q∫Q _s(λ)[1-exp(-α(λ)d)]dλ (9)

Pairing V when finding the solution maximum power _m, to (2) formula differentiate, make dP/dV=d (JV)/dV=0, can get equation:

exp(V _oc/V _c)＝[(V+V _c)/V _c]exp(V/V _c) (10)

(10) formula is a transcendental equation, and its numerical solution is exactly maximum V _m, with V _mSubstitution again (2) formula just can be tried to achieve J at this moment _mThereby, try to achieve efficiency eta and obtain η and the energy gap E of material by (1) formula _gRelation.

In _xGa _1-xThe energy gap E of N material _gWith the relational expression of In component x be ^[2]

E _g(x)＝3.4-2.7x (11)

2.In _xCa _1-xThe material parameter of N and result of calculation

Calculate according to the above-mentioned theory model, as concrete example calculation, made following hypothesis in the calculating: 1) used solar spectrum is the AM1.5 spectrum of standard, data from the breadboard official website of American National regenerative resource, with be American Society for Testingand Materials (ASTM) in 2004 the up-to-date ASTM G173-03:2 that measures) absorption coefficient is by α (λ, Eg)=and (hc/ λ) * A+B relational expression is definite, and coefficient A, B are obtained by following relation: at the band edge absorption coefficient is 9.5 * 10 ³Cm ¹, be 1.3 * 10 at 4eV place absorption coefficient ⁴Cm ^1[3]3) doping content in the P district of InGaN p-n junction solar cell and N district all is made as 10 ¹⁸Cm ^-3The thickness d of battery uptake zone is made as 4 μ m; In _xGa _1-xOther parameters that N is relevant see Table 1 ^[4,5], In wherein _xCa _1-xEach parameter of N is obtained by the linear-in-the-parameter match of GaN and InN.

Used During table 1 calculates _xCa _1-xThe N material parameter

Calculate In _xGa _1-xN is single, two, three-junction solar battery the results are shown in Table 2 and table 3.

The In that table 2 calculates _xCa _1-xThe performance parameter of N list, two, three-joint solar cell

The In that table 3 calculates _xGa _1-xThe energy gap and the In component of N list, two, three-joint solar cell correspondence

Except providing optimal values, the relation for clearer expression solar cell conversion efficiency and energy gap gives change curve between the two.Fig. 1 and Fig. 2 are respectively the In that calculates gained _xGa _1-xThe graph of a relation of N unijunction and two connection solar cell conversion efficiencies and energy gap.As can see from Figure 1, In _xGa _1-xThe high conversion efficiency of N unijunction solar cell is 27.3%, when obtaining this conversion efficiency, and In _xCa _1-xThe energy gap of N is 1.39eV.As can see from Figure 2, the conversion efficiency of two connection solar cell maximums is 36.6%, when obtaining this conversion efficiency, and two junction battery material In _X1Ga _1-x1N and In _X2Ga _1-x2The energy gap of N is respectively 1.73eV and 1.12eV.Result of calculation is consistent with theory expectation, In _xGa _1-xThe conversion efficiency of N solar cell all is higher than the solar cell of current material.

According to above theoretical calculation method, can calculate any i knot (i=1,2,3,4,5.。。Deng integer) many knot In _xGa _1-xThe energy gap and the corresponding In component value thereof of the conversion efficiency of the maximum of N solar cell and each junction battery material.

3.In _xGa _1-xThe structural design of N multijunction solar cell

On the basis that above-mentioned theory is calculated, provide the structure of following multijunction solar cell: the structure of solar cell can have is just shining and two kinds of back illuminations.Select semi-conducting material In for use _xGa _1-xN (0.01≤x≤0.99) is the light absorption district, and sapphire (sapphire) or other materials are substrate.In with different I n component _xGa _1-xN is each junction battery material wherein, along the 1st, the 2nd, the 3rd of sunlight incident direction.。。Putting in order of knot materials such as i is to arrange by In component ascending (its energy gap is descending), so that the 1st, the 2nd, the 3rd.。。Junction batteries such as i absorb in the solar spectrum light of different-waveband from short to long in proper order.Between each junction battery with on corresponding one the knot material heavy doping p ⁺-n ⁺Tunnel junction vertically is together in series.The n of the 1st knot (or p, on the back of the body, just shining decide)-In _X1Ga _1-x1The p of N and last i knot (or n, on carrying on the back, just shining and deciding)-In _XiCa _1-xiN is provided with the metallic conduction electrode, and incidence surface covers antireflective coating.Fig. 3 is a kind of back illumination In that proposes _xGa _1-xThe structural representation of N two connection solar cells (In wherein _X1Ga _1-x2N and In _X1Ga _1-x2X among the N ₁＜x ₂).

Claims (5)

1.InGaN the method to set up of the structure of p-n junction type multijunction solar cell is characterized in that adopting current-voltage equation, the In of p-n junction type solar cell _xGa _1-xThe energy gap E of N material _gWith In component value relational expression and In _xGa _1-xThe relevant parameter of N material is wherein respectively tied In when calculating the maximum conversion efficiency of InGaN p-n junction type multijunction solar cell and obtaining this conversion efficiency _xGa _1-xThe best energy gap of N material and corresponding In component value x are with the In of these different I n component value x _xGa _1-xThe N material is each junction battery material wherein, vertically is together in series with tunnel junction between each junction battery, becomes the structure of InGaN p-n junction type multijunction solar cell, and the definition of solar cell efficiency eta is:

$\mathrm{\η}\≡\frac{P_m}{P_i}=\frac{J_m\·V_m}{P_i}=\frac{\mathrm{FF}\·V_{\mathrm{oc}}\·J_{\mathrm{sc}}}{P_i}---\left(1\right)$

P in the formula _mBe the peak power output of solar cell unit are, J _mAnd V _mMaximum current and maximum voltage when reaching peak power output, P ₁For projecting the sunlight power of solar cell unit are, FF, V _OcAnd J _ScBe respectively fill factor, curve factor, open circuit voltage and the short-circuit current density of solar cell; From then on formula will be tried to achieve P as can be known _m, J that will be when the current-voltage equation of p-n junction type solar cell is tried to achieve peak power output _mAnd V _mThe current-voltage equation of the p-n junction type solar cell when illumination is arranged is:

$J=J_{\mathrm{sc}}-J_0(e^{V//\mathrm{vc}}-1)---\left(2\right)$

V wherein _c=kT/q is the thermal voltage under the room temperature 300K, and its value is 0.026V; J: the current value of the current-voltage equation of the p-n junction type solar cell when illumination is arranged, V are the magnitude of voltage of the p-n junction type solar cell when illumination is arranged, K: Boltzmann constant, T: above-mentioned room temperature 300K, q are electron charge, J ₀Be reverse saturation current density, have

$J_0=q{N}_C{N}_V(\frac{D_n}{N_A{L}_n}+\frac{D_p}{N_D{L}_p})\exp (-\frac{E_g}{\mathrm{kT}})---\left(3\right)$

N in the formula _cAnd N _vBe respectively the density of states of conduction band and valence band, N _AAnd N _DBe respectively the doping content in p district and n district, D _nAnd D _pBe respectively the diffusion coefficient in electronics and hole, L _nAnd L _pBe respectively the diffusion length in electronics and hole, E _gBe In _xGa _1-xThe energy gap of N material; During open circuit, J=0 is arranged, the voltage that can be got this moment by (2) formula is open circuit voltage V _OcExpression formula be

V _oc＝V _cln(J _sc/J ₀+1) (4)

Work as J=0, short-circuit current density J in the time of illumination can being got by (2) formula _ScFor

J _sc＝J _mexp(V _oc/V _c)-J ₀ (5)

Short-circuit current density J _ScBe photogenerated current density, when illumination is on solar cell, according to Lambert law, apart from the solar battery surface degree of depth be the z place number of photons Q (λ, z) satisfy:

Q(λ，z)＝Q _s(λ)exp(-α(λ)z) (6)

Q wherein _sFor energy in this following unit interval of illumination, solar cell unit are greater than E _gNumber of photons, α is In _xGa _1-xThe absorption coefficient of N material, it is the function of the wavelength X of illumination; And number of photons is exactly the generation rate G of electron-hole pair with the negative value of change in depth rate, promptly

G(λ，z)＝-dQ(λ，z)/dz＝Q _s(λ)α(λ)exp(-α(λ)z) (7)

The thickness of supposing absorbed layer is d, and the electron-hole pair sum N that produces in this p-n junction so is:

$N={\∫Q}_s\left(\mathrm{\λ}\right)\mathrm{\α}\left(\mathrm{\λ}\right){\∫}_0^d\exp (-\mathrm{\α}\left(\mathrm{\λ}\right)z)\mathrm{dzd\λ}={\∫Q}_s\left(\mathrm{\λ}\right)[1-\exp (-\mathrm{\α}\left(\mathrm{\λ}\right)d)]\mathrm{d\λ}---\left(8\right)$

Then the photogenerated current density of p-n junction generation is:

J _sc＝q∫Q _s(λ)[1-exp(-α(λ)d)]dλ (9)

Pairing V when finding the solution peak power output _m, to (2) formula differentiate, make dP/dV=d (JV)/dV=0, can get equation:

exp(V _oc/V _c)＝[(V+V _c)/V _c]exp(V/V _c) (10)

(10) formula is a transcendental equation, and its numerical solution is exactly V _m, with V _mSubstitution again (2) formula is just tried to achieve J at this moment _mThereby, try to achieve η and obtain η and In by (1) formula _xGa _1-xThe energy gap E of N material _gRelation;

In _xGa _1-xThe energy gap E of N material _gWith the relational expression of In component value x be

E _g(x)＝3.4-2.7x (11)。

2. the method to set up of the structure of InGaN p-n junction type multijunction solar cell according to claim 1, the structural design that it is characterized in that described solar cell has just shines and two kinds of back illuminations.

3. the method to set up of the structure of InGaN p-n junction type multijunction solar cell according to claim 1 is characterized in that absorbed layer is In _xGa _1-xN material, wherein 0.01≤x≤0.99, the wherein In of each knot _xGa _1-xThe N material only is the different value of getting of In component value x, and the numerical value of In component value x is determined by (11) formula; Tie to the In of last i knot along the 1st of sunlight incident direction _xGa _1-xPutting in order of N material is ascending by In component value x, corresponding In _xGa _1-xThe energy gap E of N material _gDescending arrangement.

4. the method to set up of the structure of InGaN p-n junction type multijunction solar cell according to claim 3 is characterized in that with the sapphire being substrate, with the In of the different I n component value x that calculates _xGa _1-xThe N material is each junction battery wherein, between each junction battery with a knot In on corresponding _xGa _1-xThe tunnel junction of N material vertically is together in series; N type In at the 1st knot _xGa _1-xlN or p type In _xGa _1-xlThe p type In of N and last i knot _XiGa _1-xiN or n type In _XiGa _1-xiN is provided with the metallic conduction electrode, and incidence surface covers antireflective coating.

5. the method to set up of the structure of InGaN p-n junction type multijunction solar cell according to claim 1, the structure that it is characterized in that InGaN p-n junction type multijunction solar cell are the structures of two knots or three knots.

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