CN102262698A - Method for detecting defect state density of emission layer and buffer layer based on solar cell performance impact estimation - Google Patents

Abstract

The invention relates to a method for detecting defect state density of an emission layer and a buffer layer based on solar cell performance impact estimation, and belongs to the technical field of manufacturing of solar cells. In the method, a defect state distribution model in an amorphous silicon layer is established according to original data distributed by state density in amorphous silicon to calculate charge trapped in a defect state, a modified Poisson equation is obtained, and the changes of a space charge area and a built-in electric field are further solved to realize impact estimation on heterojunction with intrinsic thinlayer (HIT) battery performance based on the defect state density, so the optimal defect state density is solved and used for setting passivation and cleaning operation in technology production. Compared with the prior art, the method is high in reliability and more comprehensive.

Description

Emission layer and buffering layer defects density of states detection method based on the assessment of solar cell performance impact

Technical field

What the present invention relates to is the method in a kind of solar cell manufacturing technology field, specifically is a kind of emission layer and buffering layer defects density of states detection method based on the assessment of solar cell performance impact.

Background technology

At present, the core that the large-scale develops and utilizes solar energy power generating production cost that is to promote the photoelectric transformation efficiency of solar cell and reduces solar cell.The amorphous silicon/monocrystalline silicon heterojunction solar cell that has the intrinsic thin layer, it is the HIT solar cell, can come for the pyroprocess that replaces in traditional crystal silicon battery production technology with the low temperature amorphous silicon deposition technology below 200 ℃, thereby be expected to become the cheap alternative of monocrystalline silicon battery, realizing at a low price having very important application prospect aspect the efficient solar battery.At present, the Sanyo Electric company of Japan has realized 23.0% conversion efficiency at the HIT solar cell of research and development in 2011, and other seminar all can't reach more than 20% in the world.Therefore, surpass 20% efficient HIT battery in order to develop conversion efficiency, battery structure is carried out theoretical modeling assess HIT battery each side factor to obtaining high efficiency influence, the work of the parameter of optimizing structure this respect has crucial meaning.

Through the retrieval of existing HIT solar cell simulation aspect document is found, (the 107th rolls up at " U.S.'s applicating physical magazine (J.Appl.Phys.) " as people such as Rahmouni, 054521-1 is to the 054521-14 page or leaf, 2010) on " heterojunction solar battery that has the intrinsic thin layer of carrier transport and n type single crystal silicon substrate: The study of computer simulation (Carrier transport and sensitivity issues in heterojunction with intrinsic thin layer solar cells on N-type crystalline silicon:A computer simulation study) " delivered, this article has adopted simple defect state distributed model on simulation HIT structure, ignored in amorphous silicon layer as thin as a wafer and can have a large amount of defect states, even produced the possibility of remarkable trap effect.In fact, this just simple, incomplete processing causes in HIT battery emission layer and the cushion defect state density influence is not taken into full account to battery performance.This is accurately assessing HIT battery each side factor to obtaining high efficiency influence, and it is unsafty instructing the actual production aspect.

Summary of the invention

The present invention is directed to the prior art above shortcomings, a kind of emission layer and buffering layer defects density of states detection method based on the assessment of solar cell performance impact is provided, compared with prior art, reliability of the present invention is high and more comprehensive.

The present invention is achieved by the following technical solutions, the defect state distributed model that the present invention sets up in the amorphous silicon layer according to the raw data of density-of-states distribution in the amorphous silicon is used for calculating the electric charge that is absorbed in defect state, obtain revising the variation that Poisson equation is also further obtained space charge region and built in field, realization is based on the impact evaluation of defect state density to the HIT battery performance, thereby try to achieve optimized defect state density, be used for being provided with the passivation and the cleaning operation of explained hereafter.

Described defect state distributed model is meant: according to the experimental measurements of density-of-states distribution in the amorphous silicon body material, set up the interband defect state distributed model that dangling bonds energy level that magnetic tape trailer attitude and double gauss by exponential distribution distribute is formed, specific as follows:

The conduction band magnetic tape trailer attitude N of exponential distribution _CtailWith valence band magnetic tape trailer attitude N _Vtail:

$N_{\mathrm{Ctail}}\left(E\right)=\underset{E_V}{\overset{E_C}{\∫}}{N}_{\mathrm{OC}}\exp \left(\frac{E-E_C}{E_{\mathrm{OC}}}\right)\mathrm{dE}$

$N_{\mathrm{Vtail}}\left(E\right)=\underset{E_V}{\overset{E_C}{\∫}}{N}_{\mathrm{OV}}\exp \left(\frac{E_V-E}{E_{\mathrm{OV}}}\right)\mathrm{dE},$ Wherein: E _CAnd E _VFor lead, valence-band edge, N _OCAnd N _OVThe density of states of representative in leading valence-band edge unit energy scope, E _OCAnd E _OVFor leading the Urbach energy of valence band;

Class alms giver's dangling bonds energy level N that double gauss distributes _TDBe subjected to main dangling bonds energy level N with class _TA:

$N_{\mathrm{tD}}=\underset{E_V}{\overset{E_C}{\&Integral;}}{N}_D\exp [-\frac{{(E-{\mathrm{<figure-callout\; id="0"\; label="E"\; filenames="HDA0000079037260000011.png"\; state="\{\{state\}\}">E</figure-callout>}}^{0/+})}^2}{2{(\mathrm{FWHM}/2)}^2}]\mathrm{dE}$

$N_{\mathrm{tA}}=\underset{E_V}{\overset{E_C}{\&Integral;}}{N}_A\exp [-\frac{{(E-E^{-/0})}^2}{2{(\mathrm{FWHM}/2)}^2}]\mathrm{dE},$ Wherein: N _DAnd N _ABe defect state density peak value, E ^0/+With E ^-/0Be the Gaussian peak energy position, FWHM is a half-peak breadth.

Described correction Poisson equation is meant: from Shockley-Read-HaH (SRH) the composite theory model of classics, consider to derive the integral and calculating formula Q that is absorbed in the electric charge sum in the defect state under the interior class donor level of the material symmetric case equal with class acceptor level density _t, be specially: after considering to be absorbed in the electric charge sum in the defect state, the Poisson equation in the heterojunction space charge region is modified to:

$\frac{{\&PartialD;}^{2}V\left(x\right)}{{\&PartialD;x}^2}=\frac{q}{\mathrm{\&epsiv;}}[-N_A\left(x\right)+N_D\left(x\right)+p\left(x\right)-n\left(x\right)+Q_t\left(x\right)];$

Wherein: V, x, q, ε represent electromotive force respectively, locations of structures coordinate, electron charge and specific inductive capacity; N _A, N _D, p, n be respectively the doping acceptor density, doping donor density, free hole concentration and free electronic concentration; Q _tFor being absorbed in the total electrical charge number of defect level, directly reacted the influence of defect state density to battery performance.

The variation of described space charge region and built in field is meant: according to revising Poisson equation,, calculate the variation of built in field and the wide variety of space charge region by border, the space charge region condition of continuity and electric neutrality equilibrium condition, specific as follows:

$\left\{\begin{array}{c}\frac{{\&PartialD;}^{2}V\left(x\right)}{{\&PartialD;x}^2}=\frac{q}{\mathrm{\&epsiv;}}[-N_A\left(x\right)+N_D\left(x\right)+p\left(x\right)-n\left(x\right)+Q_t\left(x\right)]\\ n=N_C\exp (-\frac{E_C-E_F^n}{\mathrm{KT}})\\ p=N_V\exp (-\frac{E_F^p-E_V}{\mathrm{KT}})\\ Q_t=\underset{E_V}{\overset{E_C}{\&Integral;}}\mathrm{dE}\left(\frac{p-n+N_C\exp (-\frac{E_C-E}{\mathrm{KT}})-N_V\exp (-\frac{E-E_V}{\mathrm{KT}})}{p+n+N_C\exp (-\frac{E_C-E}{\mathrm{KT}})+N_V\exp (-\frac{E-E_V}{\mathrm{KT}})}\right)N_t\left(E\right)\\ -L_p{N}_A+{\mathrm{\&Sigma;Q}}_{\mathrm{tp}}+\mathrm{\&Sigma;}{Q}_{\mathrm{ti}}+L_n{N}_D=0\end{array}\right.,$ Wherein: N _CAnd N _VFor leading valence band available state density, E _F ⁿAnd E _F ^pThe fermi level position that is as the criterion, K and T are respectively Boltzmann constant and temperature, N _t(E) be defect state density, L at energy position E place _pAnd L _nWidth with p type and n type space charge region.

The result shows, when defect state density is low in the amorphous silicon layer, influences not obvious; But when defect state density is increased near the emission layer doping content, produce remarkable trap effect, built in field sharply weakens, and significantly shrink the space charge region and by monocrystalline silicon one sidesway to amorphous silicon one side.

Because the variation of built in field and space charge region under the high defect state density, directly cause a large amount of holes in the accumulation of whole monocrystalline silicon region and can't collect, make the various performance parameters of battery decline to a great extent, comprise open-circuit voltage at preceding electrode, short-circuit current, fill factor, curve factor and conversion efficiency.Can assess the influence of defect state density by the present invention, and definite only defect state density is chosen scope, optimization battery structure parameter to the HIT battery performance.

The present invention has successfully introduced defect state density in HIT solar battery structure simulation, can draw accurately that defect state density has solved the difficult problem that this part influence factor is difficult to estimate to the influence of battery performance in HIT battery emission layer and the cushion.Wherein, amorphous silicon defect state distributed model is based on a large amount of experiments and provides, so the result is reliable comprehensively.This invention can provide the defect state density upper limit that causes remarkable trap effect, obtains suitable defect state density and chooses scope, for the preparation of efficient HIT battery provides important references, has great importance in battery production technology and photovoltaic application.

Description of drawings

Fig. 1 is interband attitude distributed model in the amorphous silicon of the present invention.

Fig. 2 is a process flow diagram of the present invention.

Embodiment

Below embodiments of the invention are elaborated, present embodiment is being to implement under the prerequisite with the technical solution of the present invention, provided detailed embodiment and concrete operating process, but protection scope of the present invention is not limited to following embodiment.

Embodiment 1

With n type silicon is that the HIT solar cell of substrate is an example, and its concrete structure is TCO/p-a-Si:H/i-a-Si:H/c-Si/n ⁺-a-Si:H/AlBSF, the HIT battery structure parameter of The data Sanyo Electric company.Because the magnetic tape trailer density of states does not change with the dangling bonds level density, thus in the amorphous silicon increase of defect state mainly from the rising of dangling bonds level density.Concrete implementation step is as follows:

(1) set up emission layer and cushion amorphous silicon defect state distributed model, the dangling bonds energy level concentration that p type amorphous silicon emission layer is set is 1 * 10 ¹⁸Cm ^-3To 7 * 10 ¹⁹Cm ^-3Change in the scope, doping content is 7.5 * 10 ¹⁹Cm ^-3Intrinsic amorphous silicon cushion dangling bonds level density is fixed as 2.5 * 10 ¹⁶Cm ^-3

(2) be absorbed in the interior electric charge sum Q of defect state with above-mentioned defect state distributed model integral and calculating _t, and be introduced into the Poisson equation of correction.

(3), calculate the variation of built in field and space charge region by the correction Poisson equation in the step (2).The result shows: the dangling bonds energy level concentration of p type amorphous silicon emission layer is lower than 1 * 10 ¹⁹Cm ^-3The time, influence not obvious; But along with defect state density is increased to 7 * 10 ¹⁹Cm ^-3The time because near the emission layer doping content, produce significant trap effect, built in field sharply weakens, the space charge region significantly shrink and by monocrystalline silicon one sidesway to amorphous silicon one side.

(4) assess in the amorphous silicon emission layer defect state density to the influence of battery performance by the variation of built in field and space charge region.The parameter area that can be optimized be 1 * 10 ¹⁹Cm ^-3To 5 * 10 ¹⁹Cm ^-3, with this understanding, the HIT battery can obtain the high-level efficiency more than 20%.

As Fig. 1 (a, b, c) shown in, be the interband attitude distributed model in the intrinsic amorphous silicon cushion among Fig. 1 (a), Fig. 1 (b) and Fig. 1 (c) have showed p type and the interior interband attitude distributed model of n type amorphous silicon membrane respectively.This distributed model changes with doping content, can well meet with experimental results such as deep level transient spectroscopy and field effect methods.

Embodiment 2

With n type silicon is that the HIT solar cell of substrate is an example, and its concrete structure is TCO/p-a-Si:H/i-a-Si:H/c-Si/n ⁺-a-Si:H/AlBSF, the structural parameters of The data Sanyo Electric company.Because the magnetic tape trailer density of states does not change with the dangling bonds level density, thus in the amorphous silicon increase of defect state mainly from the rising of dangling bonds level density.Concrete implementation step is as follows:

(1) set up emission layer and cushion amorphous silicon defect state distributed model, the dangling bonds energy level concentration fixed that p type amorphous silicon emission layer is set is for being 4 * 10 ¹⁹Cm ^-3, doping content is 7.5 * 10 ¹⁹Cm ^-3Intrinsic amorphous silicon cushion dangling bonds level density is 2.5 * 10 ¹⁶Cm ^-3To 2 * 10 ¹⁹Cm ^-3Change in the scope.

(2) be absorbed in the interior electric charge sum Q of defect state with above-mentioned defect state distributed model integral and calculating _t, and be introduced into the Poisson equation of correction.

(3), calculate the variation of built in field and space charge region by the correction Poisson equation in the step (2).The result shows: when intrinsic amorphous silicon cushion defect state density is increased to 5 * 10 ¹⁸Cm ^-3The time, the electric charge that is absorbed in the defect state has been introduced tangible background doped, and built in field sharply weakens, and the space charge region is significantly shunk and is caused the hole can't collect at preceding electrode at the monocrystalline silicon region bulk deposition.

(4) assess in the amorphous silicon cushion defect state density to the influence of battery performance by the variation of built in field and space charge region.The parameter area that can be optimized be lower than 5 * 10 ¹⁸Cm ^-3, with this understanding, the HIT battery can obtain the high-level efficiency more than 20%.

Claims (5)

1. emission layer and buffering layer defects density of states detection method based on a solar cell performance impact assessment, it is characterized in that, the defect state distributed model of setting up in the amorphous silicon layer according to the raw data of density-of-states distribution in the amorphous silicon is used for calculating the electric charge that is absorbed in defect state, obtain revising the variation that Poisson equation is also further obtained space charge region and built in field, realization is based on the impact evaluation of defect state density to the HIT battery performance, thereby try to achieve optimized defect state density, be used for being provided with the passivation and the cleaning operation of explained hereafter.

2. method according to claim 1, it is characterized in that, described defect state distributed model is meant: according to the experimental measurements of density-of-states distribution in the amorphous silicon body material, the interband defect state distributed model that the dangling bonds energy level that foundation is distributed by the magnetic tape trailer attitude of exponential distribution and double gauss is formed is specially: the conduction band magnetic tape trailer attitude N of exponential distribution _CtailWith valence band magnetic tape trailer attitude N _Vtail:

$N_{\mathrm{Ctail}}\left(E\right)=\underset{E_V}{\overset{E_C}{\&Integral;}}{N}_{\mathrm{OC}}\exp \left(\frac{E-E_C}{E_{\mathrm{OC}}}\right)\mathrm{dE}$

$N_{\mathrm{Vtail}}\left(E\right)=\underset{E_V}{\overset{E_C}{\&Integral;}}{N}_{\mathrm{OV}}\exp \left(\frac{E_V-E}{E_{\mathrm{OV}}}\right)\mathrm{dE},$ Wherein: E _CAnd E _VFor lead, valence-band edge, N _OCAnd N _OVThe density of states of representative in leading valence-band edge unit energy scope, E _OCAnd E _OVFor leading the Urbach energy of valence band;

Class alms giver's dangling bonds energy level N that double gauss distributes _TDBe subjected to main dangling bonds energy level N with class _TA:

$N_{\mathrm{tD}}=\underset{E_V}{\overset{E_C}{\&Integral;}}{N}_D\exp [-\frac{{(E-E^{0/+})}^2}{2{(\mathrm{FWHM}/2)}^2}]\mathrm{dE}$

$N_{\mathrm{tA}}=\underset{E_V}{\overset{E_C}{\&Integral;}}{N}_A\exp [-\frac{{(E-E^{-/0})}^2}{2{(\mathrm{FWHM}/2)}^2}]\mathrm{dE},$ Wherein: N _DAnd N _ABe defect state density peak value, E ^0/+With E ^-/0Be the Gaussian peak energy position, FWHM is a half-peak breadth.

3. method according to claim 1, it is characterized in that, described correction Poisson equation is meant: from the Shockley-Read-Hall composite theory model of classics, consider to derive the integral and calculating formula Q that is absorbed in the electric charge sum in the defect state under the interior class donor level of the material symmetric case equal with class acceptor level density _t,

4. according to claim 1 or 3 described methods, it is characterized in that described correction Poisson equation is meant: after considering to be absorbed in the electric charge sum in the defect state, the Poisson equation in the heterojunction space charge region is modified to:

$\frac{{\&PartialD;}^{2}V\left(x\right)}{{\&PartialD;x}^2}=\frac{q}{\mathrm{\&epsiv;}}[-N_A\left(x\right)+N_D\left(x\right)+p\left(x\right)-n\left(x\right)+Q_t\left(x\right)];$

Wherein: V, x, q, ε represent electromotive force respectively, locations of structures coordinate, electron charge and specific inductive capacity; N _A, N _D, p, n be respectively the doping acceptor density, doping donor density, free hole concentration and free electronic concentration; Q _tFor being absorbed in the total electrical charge number of defect level, directly reacted the influence of defect state density to battery performance.

5. method according to claim 1, it is characterized in that, the variation of described space charge region and built in field is meant: according to revising Poisson equation, by border, the space charge region condition of continuity and electric neutrality equilibrium condition, calculate the variation of built in field and the wide variety of space charge region, specific as follows:

$\left\{\begin{array}{c}\frac{{\&PartialD;}^{2}V\left(x\right)}{{\&PartialD;x}^2}=\frac{q}{\mathrm{\&epsiv;}}[-N_A\left(x\right)+N_D\left(x\right)+p\left(x\right)-n\left(x\right)+Q_t\left(x\right)]\\ n=N_C\exp (-\frac{E_C-E_F^n}{\mathrm{KT}})\\ p=N_V\exp (-\frac{E_F^p-E_V}{\mathrm{KT}})\\ Q_t=\underset{E_V}{\overset{E_C}{\&Integral;}}\mathrm{dE}\left(\frac{p-n+N_C\exp (-\frac{E_C-E}{\mathrm{KT}})-N_V\exp (-\frac{E-E_V}{\mathrm{KT}})}{p+n+N_C\exp (-\frac{E_C-E}{\mathrm{KT}})+N_V\exp (-\frac{E-E_V}{\mathrm{KT}})}\right)N_t\left(E\right)\\ -L_p{N}_A+{\mathrm{\&Sigma;Q}}_{\mathrm{tp}}+\mathrm{\&Sigma;}{Q}_{\mathrm{ti}}+L_n{N}_D=0\end{array}\right.,$ Wherein: N _CAnd N _VFor leading valence band available state density, E _F ⁿAnd E _F ^pThe fermi level position that is as the criterion, K and T are respectively Boltzmann constant and temperature, N _t(E) be defect state density, L at energy position E place _pAnd L _nWidth with p type and n type space charge region.

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