CN101979704A - Method for preparing ZnS/SnS double-layer membrane by vacuum evaporation - Google Patents

Abstract

The invention relates to a method for preparing a ZnS/SnS double-layer membrane of a solar cell by a vacuum evaporation method, which belongs to the technical field of preparation technology for inorganic membrane elements of solar cells. SnS of a P semiconductor is taken as an absorbing layer, a vacuum evaporation system is used and the double-layer membrane is obtained by continuously evaporating a ZnS membrane and a SnS membrane on different boats. A sample holder is adjusted; the temperature of an indium tin oxide (ITO) glass substrate is controlled to be between 150 and 160 DEG C; the vacuum pressure is between 2*10<-3> and 3*10<-3>Pa; the distance between the substrate and an evaporation source molybdenum boat is about 20 centimeters; the evaporation temperatures of the SnS and the ZnS are controlled to be between 1,000 and 1,200 DEG C; after an evaporation process is finished, annealing is performed in a vacuum tubular annealing furnace; and the annealing temperatures are 300 DEG C, 400 DEG C and 500 DEG C. The method of the invention has simple process and high membrane preparation efficiency; and the prepared membrane has high electrical performance and optical performance and is applied to the solar cells.

Description

Vacuum-evaporation prepares the method for ZnS/SnS bilayer film

Technical field

The present invention relates to prepare the method for ZnS/SnS bilayer film, belong to solar cell inorganic thin film component fabrication Technology field with vacuum vapor deposition method.

Background technology

Improving efficiency of conversion and reducing cost is the subject matter that photovoltaic industry faces, and thin-film solar cells is compared with the monocrystalline polysilicon solar cell, it is advantageous that manufacturing cost is lower, preparation process more simple itself and diversified.II-VI compound semiconductor SnS, crystalline network is a=4.329, b=11.193, c=3.980, Sn and S atom link together by Van der Waals force.Because its Nantural non-toxic and at the good band gap width (indirect band gap 1.0-1.1, direct band gap 1.3-1.5) of visible-range causes people's attention.

The SnS film is fit to do absorption layer in solar cell, be the P type of nature again, can form the P-N knot with N-type semiconductor, and the transformation efficiency of SnS thin-film solar cells can reach 25% in theory.The maximum structure of research is a SnS/CdS heterojunction type battery in the external at present report, and K.T.R. Reddy research group uses spray heating decomposition with SnCl and thiocarbamide mixing solutions, is 350 ℃ plating SnO in temperature ₂Glass substrate on make the SnS film, use vacuum vapor deposition method to make the CdS film, the In that has mixed 2 at% reduces CdS resistivity, last on CdS the In electrode of evaporation.The CdS/SnS solar cell transformation efficiency of making is 1.3%, and quantum yield is 70%.This is the highest SnS hull cell of reporting at present of transformation efficiency.But the efficient of SnS/CdS battery can't rise to more than 2% mostly, and Masaya Ichimura proves that theoretically what caused the SnS/CdS heterojunction can be with skew owing to the structure problem of SnS and CdS.The skew of SnS conduction band has stoped the flowing between PN junction of photo-generated carrier, this with regard to partial interpretation the low problem of SnS/CdS efficiency of conversion.

Based on above-mentioned problem, people have attempted the whole bag of tricks and have sought another N-type semiconductor and make the SnS thin-film solar cells.SnS/ZnO, SnS/ZnS and SnS/SnS ₂Preparation Deng heterojunction has entered people's the visual field with research.It is Window layer as the SnS hull cell that Masaya Ichimura group and Biswajit Ghosh group select electro-deposition techniques to make ZnO film.Used a kind of new method at Tetsuya Miyawaki, promptly photochemical precipitation method (PCD) is made the Window layer of ZnS film as solar cell.Same M. Gunasekaran group uses photochemical precipitation to send out and obtains the CdZnS film.Though these attempt not haveing breakthrough on the efficient of the solar cell that improves the SnS film so far, these researchs provide a lot of references for successors' research.

Summary of the invention

The purpose of this invention is to provide the method that a kind of vacuum-evaporation prepares solar cell ZnS/SnS bilayer film.

A kind of vacuum-evaporation of the present invention prepares the method for solar cell ZnS/SnS bilayer film, it is characterized in that having following process and step.

A. will there be the glass of tin-doped indium oxide (ITO) under ultrasound condition, to clean respectively earlier as the coated that substrate is used with deionized water, acetone, dehydrated alcohol; Be contained in after the oven dry on the specimen holder of vacuum coater; Adopting vacuum vaporation system, is that 96% SnS powder and purity are that 99% ZnS powder is put into two evaporation molybdenum boats respectively with purity, adopts and successively divides the mode of boat evaporation ZnS and SnS to form bilayer film continuously; Two molybdenum boats are connected on the temperature-control device of outside with electric wire respectively; The control underlayer temperature is 150 ℃～160 ℃, and vacuum pressure is (2～3) * 10-3Pa; Distance between specimen holder and the molybdenum boat evaporation source is 20～25cm; The Heating temperature of evaporation source SnS and ZnS is respectively 1000 ℃ 1200 ℃;

B. behind the vacuum-evaporation end of processing, have the substrate of bilayer film to put into the electron tubes type annealing furnace plating and anneal, the annealed temperature is chosen as 300 ℃, 400 ℃ and 500 ℃; The temperature curve of control annealing furnace is ladder rising form; Need in the whole annealing process to feed nitrogen, in case film surface generation oxidation.

The present invention utilizes P-type semiconductor SnS as absorption layer, and ZnS is the direct band gap N-type semiconductor, and its energy gap is 3.5～3.8eV, has excellent photoelectric performance, is suitable as the Window layer of solar cell.

Characteristics of the present invention and advantage are as described below:

1. adopt the vacuum-evaporation thin films.It is simple that this method has technology, and film forming is even, advantages such as fast growth.

2. should invention P type and N type film adopt the same process method, and avoid using different process and the technology that causes does not match, improve the efficient of film preparation simultaneously, reduce the cost of making.

3. the film of this method preparation has good electric property and optical property, and suitable annealing temperature can further improve the performance of film, and very strong practicality is arranged.

4. this membrane structure is simple, can well be applied to the SnS thin-film solar cells.

Description of drawings

Fig. 1 is the annealing temperature curve of ZnS/SnS bilayer film of the present invention.

Fig. 2 is the figure of the ZnS/SnS film X-ray diffraction (XRD) under the different annealing temperature of the present invention.

Fig. 3 is the I-V graphic representation of the present invention's film under 300 ℃ and 400 ℃ of annealing temperatures.

Fig. 4 is the I-V graphic representation of the present invention's film under 500 ℃ of annealing temperatures.

Fig. 5 is the abosrption spectrogram of the ZnS/SnS bilayer film under the different annealing temperature of the present invention.

Embodiment

Now specific embodiments of the invention are described in further detail in the back:

Embodiment: the preparation process and the step of present embodiment are as described below:

(1) before the preparation sample, will in ultrasonic, clean 15 minutes with deionized water, acetone, dehydrated alcohol respectively as the ito glass that substrate is used earlier, on the specimen holder of the vacuum plating unit of packing into after the oven dry.

(2) the present invention uses the DM-450A vacuum vaporation system of Beijing north instrument innovation Vacuum equipment maker, and adopting purity is that 96% SnS powder and purity are 99% ZnS powder, and weight is respectively 50mg and 70mg, is respectively put in two evaporation molybdenum boats.Adjust the distance between specimen holder and evaporation source (molybdenum boat), be about 20cm.Parameter control is as shown in table 1 in the evaporative process.

 

The processing parameter of controlling in table 1 evaporative process

?	Underlayer temperature/℃	Pressure/10 -3 Pa	Evaporation source distance/cm	The evaporation source temperature/℃
					ZnS	150	2.0～3.0	20	1200
SnS	150	2.0～3.0	20	1000

(3) close bell jar, connect mechanical pump, push low valve and earlier system is bled, open simultaneously around the water source of diffusion pump temperature drop pipe.When mechanical pump is evacuated to the 3Pa left and right sides with the system vacuum degree by the time, will hangs down valve and pull out bell jar is begun to bleed, and open diffusion pump simultaneously and begin preheating.When pressure is reduced to the 3Pa left and right sides in the bell jar by the time, and made the diffusion pump preheating about 30 minutes, open high valve, the beginning pumping high vacuum.The baking voltage of regulating coating equipment is with suitable heated substrate glass.When vacuum tightness reaches 10 ^-3During the Pa order of magnitude, regulate vaporization voltage heating molybdenum boat, the start vaporizer plated film, vaporization temperature is 1000 ℃～1200 ℃.It is too fast to it should be noted that evaporation time institute's making alive can not rise, otherwise the SnS powder can spill because being heated inequality.

(4) after using vacuum vapor deposition method to prepare the ZnS/SnS bilayer structure, the bilayer film of gained is put into the GSL 1600X vacuum tube furnace of brilliant Materials Technology Ltd. of Hefei section and annealed.The annealed temperature is chosen as 300 ℃ respectively, and 400 ℃ and 500 ℃, in whole annealed process, the temperature of control annealing furnace is ladder rising form.With 300 ℃ of annealing temperatures is example, in preceding 15min inner control temperature is 200 ℃, rise to the impact of sample for the temperature that reduces in the annealing furnace after the 15min, between 200 ℃ and 300 ℃, select a medium temperature as the buffering temperature, slowly rise to needed 300 ℃ of annealing again, and keep this temperature 1 hour to reach the annealed effect.After annealing was finished, program can be closed automatically, made the temperature in the stove reduce to room temperature.Need pass to nitrogen in the whole annealing process, in order to avoid film surface generation oxidation.After annealing is finished sample is taken out to be measured.Equally, sample is carried out the annealing of 400 ℃ and 500 ℃.Concrete annealing temperature curve is seen Fig. 1.

Fig. 2 is respectively the XRD figure of film that annealing temperature is the ZnS/SnS film of 300 ℃, 400 ℃ and 500 ℃, in all XRD figure, all can near 2 θ=29.2 °, find a very strong diffraction peak, corresponding is the ZnS crystal of (111) face in β crystal orientation, near 2 θ=32.2 °, find the another one diffraction peak, corresponding iris to crystal (111) crystal orientation of SnS.Should have the minimum surface energy for this two kinds of films (111) face, be the most stable solid matter face, therefore finds stronger diffraction peak on this crystal orientation, and other crystal orientation is then not obvious.So film speed of growth on this crystal orientation is very fast, compare with other crystal face, be evident as preferred orientation.Spend under the annealed situations at 300 degree and 400, ZnS crystalline diffraction peak intensity is basic identical, and weakens along with the diffraction peak that rises to 500 ZnS when spending of annealing temperature has obviously.SnS crystalline diffraction peak rises and then descends along with the elder generation of annealing temperature, and when 400 spent, its diffraction peak reached the strongest.

Fig. 3 and Fig. 4 are the I-V curve of ZnS/SnS film under the different annealing temperature, and control voltage is at-5V ~ 5V.ZnS/SnS film curve is rendered as Schottky contacts when 300 ℃ of degree annealing temperatures, and when voltage was 5V, corresponding electric current was 3 * 10 ^-2A, and the resistivity of this moment is bigger; When annealing temperature was 400 ℃, the I-V curve of film began to present certain ohmic contact, and when voltage was 5V, size of current was 0.3 * 10 ^-2A, but the resistivity of this moment is than the resistivity of 300 ℃ of annealed films about 1 order of magnitude that raise; Fig. 4 is the I-V curve of ZnS/SnS film under 500 ℃ of annealing temperatures, present distant Schottky contacts, and resistivity had greatly than 300 ℃ and 400 ℃ of annealing and reduced, when voltage is 5V, size of current is 40 A, and electric current has increased about four orders of magnitude during than 400 ℃.The electric property of as seen annealing to film has very big influence, and along with the rising of annealing temperature, resistivity constantly reduces.

Fig. 5 is the absorption spectrum of ZnS/SnS film under the different annealing temperature,,, at infrared band specific absorption is preferably arranged, and does not absorb substantially at ultraviolet band along with the increase specific absorption of wavelength constantly reduces at visible light wave range (380-770nm) at all curves.Absorption spectrum absorbs near whole in the 200-300nm specific absorption.Beginning absorption spectrum from 300nm begins to descend with the increase of wavelength, the cutoff wavelength of absorption spectrum is relevant with annealing temperature, unannealed and 300 degree annealed films are about 650nm by absorbing wavelength, and 400 degree annealed cutoff wavelengths are 600nm, and 500 degree annealed cutoff wavelengths are 550nm.

Claims (1)

1. a vacuum-evaporation prepares the method for solar cell ZnS/SnS bilayer film, it is characterized in that having following process and step:

A. will there be the glass of tin-doped indium oxide (ITO) under ultrasound condition, to clean respectively earlier as the coated that substrate is used with deionized water, acetone, dehydrated alcohol; Be contained in after the oven dry on the specimen holder of vacuum coater; Adopting vacuum vaporation system, is that 96% SnS powder and purity are that 99% ZnS powder is put into two evaporation molybdenum boats respectively with purity, adopts and successively divides the mode of boat evaporation ZnS and SnS to form bilayer film continuously; Two molybdenum boats are connected on the temperature-control device of outside with electric wire respectively; The control underlayer temperature is 150 ℃～160 ℃, and vacuum pressure is (2～3) * 10-3Pa; Distance between specimen holder and the molybdenum boat evaporation source is 20～25cm; The Heating temperature of evaporation source SnS and ZnS is respectively 1000 ℃ 1200 ℃;

B. behind the vacuum-evaporation end of processing, have the substrate of bilayer film to put into the electron tubes type annealing furnace plating and anneal, the annealed temperature is chosen as 300 ℃, 400 ℃ and 500 ℃; The temperature curve of control annealing furnace is ladder rising form; Need in the whole annealing process to feed nitrogen, in case film surface generation oxidation.

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