CN85107575A - Be rich in the thin layer heterojunction photovolatic cell of Hg1-x CdxTe of cadmium and the electrodeposition process of Hg1-xCdxTe - Google Patents

Abstract

The thin layer Hg of x may command (x＞0.5) _1-xCd _xThe electro-deposition of Te compound cathode is to the surface of CdS thin layer, and this CdS thin layer is positioned on the surface of the ITO electrically conductive layer that is deposited on the glass substrate.Treated Hg after electro-deposition _1-xCd _xTe surface deposition skim conductive layer can make the solar cell of improvement.Handle Hg _1-xCd _xTe is in order to obtain the surface of being rich in Te of good ohmic contact.

Description

Be rich in the thin layer heterojunction photovolatic cell of Hg1-x CdxTe of cadmium and the electrodeposition process of Hg1-xCdxTe

The present invention relates to utilize the Hg that is rich in Cd _1-XCdxTe is as the thin layer photocell of variable strip zone gap material and have controlled stoichiometry (1-x), the Hg that promptly has controlled performance and optical property _1-The cathode electrodeposition of xCdxTe thin layer.

Authorizing F.A. Kroger, in No. 4400244, the United States Patent (USP) of R.L. Luo De and M.P.R. Pei Nieke the patent owner be (this patent has transferred the Monot Suo La Monosolar of Co., Ltd, Inc), by the agency of general CdTe electrodeposition process.Speak briefly, promptly containing HTeO ⁺ ₂Cation and Cd ²⁺In the cationic electrolyte, by electro-deposition, at cathode surface formation one deck cadmium telluride overcoat of conduction.At negative electrode, the HTeO of discharge ⁺ ₂Ion and Cd ²⁺Ionic reaction forms CdTe simultaneously and is deposited on the negative electrode.

Authorizing B.M.Among the Ba Suoer, No. 4388483, the United States Patent (USP) of the old and R.L. Luo De of E.S. (surrenderee be a Monot Suo La Co., Ltd), introduced the electrodeposition condition of CdTe more particularly, and with the detailed process rules of these thin layers manufacturing heterojunction solar batteries.Say briefly, promptly utilize common deposition technique on a surface of transparent insulation materials such as a sheet glass, preparation-transparent electrically conductive layer is as tin oxide or tin indium oxide (ITO) layer.Then, electro-deposition one semiconductor layer such as cadmium sulfide layer.The n molded breadth gap semiconductor that is different from next surface sediments cadmium-telluride layer has been formed in the combination of conductive oxide and cadmium sulfide.Then, this sandwich construction of heat treatment between 250 °-500 ℃ makes the CdTe thin layer be transformed into low-resistance P type semiconductor compound fully.Again at CdTe surface deposition skim conductive layer, as the gold layer, just obtained photocell.Photocell is by the glass substrate receiver radiation, and the n N-type semiconductor N is as the broad-band gap window.

Heat treatment Cd-Te can make photronic power output improve 60 times.Can believe that without heat treatment, the Cd-Te of electro-deposition is a kind of high-resistance n section bar material, and cadmium sulfide is the injection contact that electronics arrives a surface of Cd-Te thin layer, rather than adjustable contact.When upper strata electric conducting material (for example gold) when depositing to Cd-Te thin layer surface, has just obtained the n-CdTe/Au Schottky barrier.This is a kind of inefficient structure of inherence.If through Overheating Treatment (before deposited gold), obviously owing to produce phone Cd room, nearly all Cd-Te is transformed into the P type.This just makes potential barrier drift about from the n-CdTe/Au interface to the CdS/P-CdTe interface, thereby obtains heterojunction structure efficiently.

Hg ₁-xCdxTe is a kind of crucial infra-red detection modulator material, and its band gap is the function that compound chemistry metering is formed, when X when 0.17 changes to 1.0, its band gap changes to 1.5eV from 0.

Up to now, this material still is limited to the infrared application aspect.HgO2 continues ₇₉The early stage work of Cd0.205Te detector (to λ=8-12 mum wavelength sensitivity) aspect is that 1-3,3-5 and the interior panel detector structure of 15-30 micrometer range are studied to being applicable to wavelength.All these purposes all need to be rich in the material (x＜0.5) of Hg.Existing documents and materials also are not applied to the report of the success of solar cell about the cadmium mercury telluride that is rich in Cd.

Hg ₁The preparation of-xCdxTe crystal can be adopted the technology that everybody is familiar with (as Bridgman method, zone melting and look into the Clusky method).Can realize epitaxial growth by liquid phase oriented growth and vapor phase oriented growth, but Hg ₁The work of-xCdxTe polycrystalline thin layer aspect is also carried out seldom so far.Based on this view, obviously, be difficult to evaluate the polycrystalline Hg that is rich in cadmium to prior art ₁-xCdxTe is applied to the potentiality of solar cell, and this perhaps partly is to exist difficulty owing to prepare this thin layer at an easy rate with this two aspect of its stoichiometry of control.Restudying of existing technology shown also do not have a kind of cheap Hg of manufacturing ₁The method of-xCdxTe thin layer.Hg ₁The character of-xCdxTe band gap control is vital for the high efficiency laminated cell, and in laminated cell, two or more batteries are in response to the difference spectrum district of solar spectrum.Aspect the noncrystal battery of thin layer, variable band gap alloy (as noncrystal Si-Ge alloy) has been carried out extensive studies, this class alloy is suitable for the upper strata amorphous silicon battery.But up to the present invention, just successfully having found can cheapness and the variable band gap polycrystalline thin layer that controllably produces and use.

The objective of the invention is to prove the Hg that is rich in Cd ₁-xCdxTe thin layer can be applicable to solar cell.By the present invention, can make sensitive battery, thereby might produce efficiently laminated cell (tandem battery) and evenly or the single junction cell of gradient band gap the difference of solar spectrum spectrum district.

The electro-deposition techniques that another purpose provides a kind of cheapness is used for making the Hg with controllable electrical property and optical property ₁-xCdxTe thin layer.

A further object of the invention provides a kind of specific composition of plating, can produce high efficiency Hg with it ₁-xCdTe and Cd-Te solar cell.

According to the present invention, from containing the Cd of 0.2M to 1.5M ²⁺Ion, 10 ^-5M to 10 ^-3MHTeO ⁺ ₂Ion and Hg ²⁺In the aqueous solution of ion, can obtain Hg polycrystalline, that Hg content can be controlled on the conductive substrate surface with the cathode electrodeposition method ₁-xCdxTe thin layer.Hg ²⁺The concentration of ion is 1 to 20ppm, depends on to want the sedimental stoichiometry that obtains.The pH value of electrolyte is controlled at certain value between 1 and 3.The voltage that regulate to use makes the current potential of deposit surface, with respect to the current potential of (being QRP, accurate rest potential) Ag-Agcl reference electrode under the open-circuit condition ,-300mv and-600mv between, the temperature of electrolyte is maintained at about 85 ℃ to 90 ℃.This electrodeposition process is initial, and that be concerned about is cation (Cd ²⁺And HTeO ⁺ ₂), but anionic kind also can have influence on the character of thin layer.In solution, add Cl ^-Ion can improve photronic short circuit current, as follows the example 3 of face.

With Hg ₁-xCdxTe deposits on the CdS thin layer of glass/ITO/CdS substrate can make thin-layer solar cell.With containing the electrolyte of 0.1M to the cadmium sulfate of 0.5M or caddy and about 0.01M to the sodium thiosulfate of 0.05M, the control pH value can be with the CdS Thin Layer Electrodeposition to being coated with the on glass of ITO about 4 when electroplating beginning.Deposition voltage remains between-0.6 volt and-0.7 volt (for calomel reference electrode), and the temperature of electrolyte is about 90 ℃.

The processing of battery was included in 400 ℃ of following calcination 8-10 minutes, with at Cds/Hg ₁-xCdxTe interface forms can adjust knot; Etching Hg ₁The surface of-xCdxTe thin layer; Handle etched surface with strong base solution again; At last metallic ohmic contact is deposited on etching and the surface treated, just obtained spendable battery.Change Hg ₁The stoichiometry of-xCdxTe thin layer just makes (1-x) to change, and can produce the battery with various wavelength responses.

Fig. 1 is a chemical electro-deposition schematic representation of apparatus among the present invention.

Fig. 2 is a Hg solution ²⁺The Hg of concentration and electro-deposition ₁The Hg that is recorded in-xCdxTe the thin layer ₁The stoichiometric graph of a relation of-xCdxTe.Show that it is possible reaching stoichiometry control with the present invention.

Fig. 3 is that energy gap Eg is as Hg ₁The functional arrangement of Hg content in the-xCdxTe thin layer.The content of Hg can be obtained by transmitted light and reverberation determination data in the thin layer.

Fig. 4 is the photronic sectional view of drawing according to the present invention.

Fig. 5 is one group of thin layer Hg ₁The spectral response figure of-xCdxTe solar cell.These solar cells can be controlled X and make in electrodeposition process.

Fig. 6 is Voc and the Isc functional arrangement as (1-X) in the thin layer photocell, and that these thin layer photocells use is thin layer Hg ₁-xCdxTe.

To illustrate with various examples now: how (1) can realize Hg ₁The electro-deposition of-xCdxTe thin layer; (2) how how to improve their characteristic with these thin layers manufacturing thin-layer solar cells and (3).

The explanation of most preferred embodiment

Please referring to accompanying drawing 1, this is the chemical electro-deposition schematic representation of apparatus that the present invention uses.In fact, it is the same with any electrodeposition process, and container 10 holds electrolyte among the figure, electro-deposition Hg ₁The electrolyte of-xCdxTe is to contain Cd ²⁺, HTeO ⁺ ₂And Hg ²⁺The aqueous solution of ion.Anode is a Te anode 12, negative electrode is the electrically conductive layer 14 that is positioned at glass substrate 16 surfaces, reference electrode 18 links to each other with potentiostat/galvanostat 20, thermometer 22 is used to observe the temperature of electrolyte, in using usually, also add an inertia graphite anode 24 and a switch 26, this switch can make graphite electrode and Te electrode alternately join with potentiostat/galvanostat 20, with the electrical power of control use.In the drawings, switch is represented with manual switch, is actually electronic, and it is controlled with timing circuit 30.

Example 1(Hg ₁The electro-deposition of-xCdxTe)

Prepare electrolyte as follows: in one 3 liters beaker, with American Chemical Society's level (ACSgrade) CdSO ₄Be dissolved in the redistilled water, the volume of electrolyte is 1.6 liters, Cd ²⁺Concentration is 0.5M, and PH is 4.3.Beaker is placed on the electric hot plate, and heated solution to 90 ℃ constantly stirs with electromagnetic stirrer simultaneously.Then, with inertia graphite anode 24 and platinum guaze negative electrode with electrolyte purification two hours, during this " vacation " is electroplated, cathode potential, current potential with respect to the Ag-Agcl reference electrode remains on-620mv, and it is to make the impurity concentration in the electrolyte be reduced to the permission level that this step electroplates.Behind the purifying, in solution, add hydrochloric acid, make Cl ^-Ion concentration increases 0.015M, and this is a crucial step for obtaining high-efficiency battery, and the back will be used an example and speak.

Add Cl ^-After, in solution, add dense H ₂SO ₄, make pH value be transferred to 1.6(at room temperature).Then introduce HTeO ⁺ ₂, it is introduced by pure Te anode 12 and a Pt net negative electrode.The current potential of Te anode, the current potential with respect to Ag-Agcl reference electrode 18 is controlled at+500mv, reaches 38ppm(up to the concentration of Te and controls Te concentration with Atomic Absorption Spectrometer, does not draw among the figure).At glass (after the ITO/CdS substrate surface electroplates 9 CdTe thin layers, from the Hgcl of 1000ppm ₂Draw the Hg of 3.5ppm in the storing solution ²⁺Be added in the electrolyte.Be respectively Te rod and a graphite rod with anode 12 and anode 24() be glass/ITO/CdS substrate surface electro-deposition Hg of 5Cm * 6Cm at area ₁-xCdxTe thin layer.Make that Te concentration is maintained at about 3 * 10 in the solution switching time (timer can alternately be connected two anodes) by control timer 30 ^-4M, in the whole deposition process of this experiment, alternately the time of connection was respectively the Te anode 12,1 minutes to two anodes; 24,15 seconds of graphite anode, except initial a few minutes current potential was low, QRP value (accurate rest potential) all maintained-600mV extremely-700mV.Electroplating parameter sees Table 1 in the whole deposition process.

The thin layer (NO.1) that obtains is dissolved in HNO ₃In, with its chemical composition of atomic absorption spectrometry.Discovery contains Cd, Te and Hg, but deposit is with Hg ₁The form existence of-xCdxTe compound still with the form existing problems of mixture, can only rely on optical detecting to solve.When the optical band gap of thin layer is determined, find its optical band gap less than CdTe, proved Hg ₁The existence of-xCdxCe compound.

Example 2(Hg ₁The stoichiometry control of-xCdxTe):

In order to illustrate that present technique might realize stoichiometry control, be utilized as the solution that example 1 is prepared, and in solution, add Hg again, two thin layers of electro-deposition (thin layer NO.2 and NO.3) again, Hg solution ²⁺The concentration of ion and the Hg that obtains ₁The relation of the stoichiometry that records in-xCdxTe the thin layer (1-x) is seen Fig. 2.Table 2 and table 3 have been listed the electroplating parameter of NO.2 and NO.3 thin layer respectively.Also need mention, the QRP value is on the low side when electroplating beginning, rises then, is stabilized in the current potential of ratio-700mV corrigendum.

Fig. 2 shows that the amount of control Hg solution can be controlled stoichiometric variation.By optical detecting, and the electricity of thin layer and the influence of optical property when making solar cell and studied stoichiometric change with these thin layers.Next joint will be introduced the manufacturing of this class battery.Just can obtain the relation curve of Hg content in the energy (Eg) and the thin layer by the transmitted light of optical detecting and reflected light data, see Fig. 3.Also observe band gap magnitude and (1-X) between exist the linear relationship of having estimated in theory.This just illustrated adopt of the present invention simply, deposition technique cheaply, might realize the stoichiometry control of photronic band gap.

The thin layer of use-case 1 and example 2 is made battery

The thin layer that example 1 and example 2 are obtained further processing is made the straticulation photocell, and purpose is in order to prove preparation particular bandgap, the feasibility of sheet cell cheaply.In the schematic diagram of Fig. 4, battery is made up of a slice transparent insulation material (glass) 40, there is layer of transparent electric conducting material (ITO) 41 on this transparent insulation material surface, with electro-deposition skim semiconductor (Cds) 42 is deposited on the transparent conductive material, and skin is Hg again ₁-xCdxTe electro-deposition thin layer 43.Then, skim electric conducting material (Au or Ni) 44 is evaporated on the thin layer 43, as back contact, after the semiconductor layer 42 and 43 with battery-surface etched away, electrically conductive layer 41 had just become front contact.

If the Hg of example 1 and example 2 ₁-xCdxTe thin layer without heat treatment, so, has just obtained the Schottky barrier solar cell to the different wave length response before thin layer 44 depositions.

If according to No. 4388483, the said United States Patent (USP) in front, earlier the thin layer of example 1 and example 2 is heat-treated, just obtained heterojunction so.Heat treated temperature is 400 ℃, continues 8 minutes in air.Can think that this step can form Cd and the Hg room as acceptor in thin layer, and provide and have suitable low-resistance P-type material.After the heat treatment, the thin layer cool to room temperature, carry out following etching and relevant operation:

(a) Hg ₁The surface of-xCdxTe thin layer 43 is at first with the methanol solution etching that contains 0.1% bromine.This etching can be removed very thin one deck (＜100

), material, the operating surface that obtains cleaning.This step is not really crucial, if thin layer 43 has just made, this step etching can save so.

(b) then with 1 second of bichromate solution (name of U.S. science product company is " Dichrol ") etched surfaces, use deionized water rinsing, this step etching can obtain being rich in the surface of Te, and it is necessary for good Ohmic contact.

(c) after the bichromate etching, sample immerses in the beaker fill with hydrazine (expense have a rest scientific company product, be the monohydrate of hydrazine), keeps 10 minutes under the room temperature.Introduce as No. 4456630, United States Patent (USP), this step is very important in the processing procedure of battery with step b, can remove any high resistance relevant with ohmic contact and potential barrier with the surface that this step process is crossed.

(d) after above-mentioned surface treatment is finished,, be evaporated to the surface of treated semiconductor lamella as Au or Ni with skim metal 44.This thin metal layer has just become the back contact of finished product battery.

(e) mention as the front, remove thin layer 44 and 43, just obtained front contact, it is an ITO conductive layer 41.

Then, to these battery checks their spectral response and Voc, Isc value.

Fig. 5 has illustrated the response that how can obtain thin-layer solar cell with the present invention.It is 0,0.075,0.105 and 0.125 that curve a, b, c and the d of Fig. 5 corresponds respectively to (1-x) value.Can be clear that by this figure along with the increase of (1-x) value, the battery response is expanded to infrared region.Fig. 6 measured battery (the area 0.02cm that the thin layer of (Fig. 3) makes by before being used for band gap ²) Voc and Isc value.As can from band gap variation infer, along with the increase of Hg content in the thin layer, open circuit voltage descends, short circuit current rises.

Example 3

This example is will illustrate to add Cl in electrolyte ^-The importance of ion, this phenomenon is studied in available following experiment.

Prepare the CdTe electroplate liquid by following procedure:

(a) prepare the CdSO of 700ml0.5MASC level with redistilled water ₄Solution is heated to 90 ℃ with solution, stirs lightly simultaneously;

(b) make negative electrode with the Pt net, the Ag-Agcl electrode is a reference electrode, with electrolyte purifying 2 hours, in the experiment of this step, monitors cathode potential with the PAR173 potentiometer and is-620mV.

(c) add dense H ₂SO ₄, the PH to 1.6 of regulator solution.

(d)+500mV is added on the pure Te bar, uses P ₊Net can be incorporated into Te in the electrolyte as cathode electrode, and when Te concentration arrived 35ppm, introducing stopped.

After preparing this standard electrolytic liquid, change Cl in the solution with dense Hcl ^-Concentration, the method that the thin layer that obtains is introduced by example 3 is made heterojunction solar battery.The mechanical integrity of thin layer and the short-circuit current density and the Cl of battery after the mensuration heat treatment ^-The functional relation of concentration.Table 4 is area 0.02cm ²Battery on experimental result.

Though the battery that the Cl-concentration in the solution can also be satisfied with up to 0.03M,, we can observe, and after 400 ℃ of heat treatment, Cd-Te thin layer and glass substrate have produced disengaging in some zonule.Therefore, the Cl of the best in solution ^-Ion and SO ^-2 ₄The volume mole ratio of ion is 0.01 to 0.06.Ratio is not very effective less than 0.01; And greater than 0.06, the adhesiveness between substrate and Cd-Te thin layer will variation.Cl in the electrolyte ^-Existence how to influence the character of stringer also not fully aware of so far.Perhaps be because Cl ^-There is a kind of compensating effect the grain boundary, and these grain boundaries are to be reduced in recombination rate on these lattice-sites; Also may be because Cl-can influence the growth form of crystal grain, to be formed on the structure that can produce higher short circuit current in the battery (such as, good columnar growth).All above-mentioned discussion all can be applicable to Hg ₁The deposition of-xCdxTe and Cd-Te deposition.Certainly, other halide ion commonly used: Br ^-, F ^-And I ^-Can come replaced C l ^-

From the above mentioned, a kind of new obviously, improved, Hg ₁-xCdxTe Thin Layer Electrodeposition method is set up, and this thin layer can be rich in Cd, and this thin layer has comparatively ideal short circuit current in the photocell of halogen-containing ion.Therefore, also clearly, the invention provides a kind of new, comparatively ideal thin-layer solar cell.In the example of being lifted, the current potential of having mentioned electrodeposition process is with respect to the Ag-AgCl electrode of standard and the current potential of calomel reference electrode in the above.These current potentials also can be expressed as with the current potential of standard hydrogen electrode as reference electrode.The standard hydrogen electrode current potential is than the low 0.22V of Ag-AgCl reference electrode current potential, than the low 0.24V of calomel reference electrode current potential.Because NHE(standard hydrogen electrode) normal potential is zero, and therefore, all current potentials in the claim all are the current potentials with respect to standard hydrogen electrode below.We also can select careless which reference electrode in addition for use.

Errata CPCH856671

Claims (16)

1, a kind of the conduction basically, with control Hg stoichiometric method, uses contain reference electrode, with the electrolyte of described conductive substrate as negative electrode and one or several anode, the plating Hg _1-XCd _XThe method of Te thin layer, it comprises following a few step: with containing Cd ²⁺Ion, HTeO ₂ ⁺Ion and Hg ²⁺The acidic aqueous solution of ion is made electrolytic solution; Regulate current potential used between above-mentioned reference electrode and the negative electrode, the Hg of control solution ²⁺Ion concentration makes above-mentioned cathode surface form the stoichiometric Hg of a kind of may command _1-XCd _XThe Te compound.

2, as the method for claim 1 defined, wherein, the temperature of electrolyte remains on 80 ℃ to 95 ℃, and using two anodes is in order to control the composition of electrolyte, and one of them anode is a tellurium.

3, as the method for claim 1 defined, wherein, this electrolyte contains 0.1 gram molecule to 1.5 gram molecule Cd ²⁺Ion, 10 ^-5Gram molecule to 10 ^-3Gram molecule HTeO ⁺ ₂Ion and Hg ²⁺Ion, Hg ²⁺Ion concentration is selected between about 1 to 20ppm, so that the stringer that obtains has the stoichiometry that needs.

4, as the method for claim 1 defined, wherein, the pH value of said electrolyte remains between 1 to 3.

5, as the method for claim 1 defined, wherein, the voltage of use at-300mv between-the 785mv.

6, in the method for claim 1 defined, be included in this Hg _-1Add halide ion in the xCdxTe thin layer.

7, as the method for claim 6 defined, wherein, this halide ion is a chloride ion.

8, in the method for claim 1 defined, this substrate forms through chemical treatment in advance, and its processing procedure is: earlier at glass sheet surface deposition one deck conductive oxide, again with containing Cd ²⁺And S ₂O ^2- ₃Electrolyte solution electro-deposition skim CdS on this sedimentary deposit, electro-deposition voltage, with respect to general hydrogen standard reference electrode, maintain-360mv and-460mv between.

9, in the method for claim 1 defined, also comprise the photronic various processing steps of further preparation: 400 ℃ of left and right sides calcination Hg _1-The xCdxTe thin layer is at above-mentioned Hg _1-Form rectifying junction on xCdxTe thin layer and the CdS thin layer interface,

With this Hg of acid solution etching _1-XCdxTe thin layer surface, the surface of being rich in tellurium with formation,

With the above-mentioned surface that strong base solution is handled acid etching, last, at above-mentioned one deck conductive metal layer that on etching and surface treated, deposits.

10, a kind of solar cell, it is rich in the Hg of Cd at least with one deck _1-XCdTe(x＞0.5) as active solar absorbing layer.

11, the solar cell corresponding with claim 10, wherein, above-mentioned one deck at least is rich in the Hg of Cd _1-The one side of xCdxTe and one deck conductive metal layer ohmic contact; Above-mentioned one deck at least is rich in the Hg of Cd ₁The another side of-xCdxTe contacts with semi-conductor layer, forms heterojunction therebetween.

12, the solar cell corresponding with claim 10, wherein, above-mentioned one deck at least is rich in the Hg of Cd _1-The one side of xCdxTe and one deck conducting metal ohmic contact; Its another side contacts with semi-conductor layer.Form Schottky barrier therebetween.

13, in the solar cell of claim 10 defined, this is rich in the Hg of Cd _1-Also contain halide ion in the xCdxTe layer.

14, a kind of solar cell: scribble the glass of one deck conductive oxide, at the lip-deep CdS thin layer of described conductive oxide, the Hg that is rich in Cd that on described CdS layer, deposits with following composition _1-XCdxTe(x0.5) semiconductor layer and be deposited on described Hg with ohmic contact _1-Conductive metal layer on the xCdxTe layer.

15, as the solar cell of claim 14 defined, wherein, on the interface of ohmic contact, this is rich in the Hg of Cd _1-Tellurium is rich on the surface of xCdxTe thin layer.

16, as the solar cell of claim 14 defined, wherein, at the above-mentioned Hg that is rich in Cd _1-Also comprise halide ion in the xCdxTe layer.

Images