CN104916743A - Thermal evaporation method for preparing stoichiometric CdS thin film by using quantum dots as precursors - Google Patents

Abstract

The invention discloses a thermal evaporation method for preparing near-stoichiometric CdS thin films with quantum dots as precursors. The cleaned substrate was placed on the sample holder of the vacuum chamber of the thermal evaporator (Emitech, K950X). Put the appropriate size precursor, 0.1-0.3 g, in the W basket and close the chamber. The chamber was evacuated to a vacuum of 1.0 x 10 ^{-3 -} 1.0 x 10 ^-5 mbar at room temperature and the evaporation rate was controlled by adjusting the current through the W basket. First, slowly increase the current from 0A to 6-10A, then wait until the W basket turns red. Then, the current is further increased to 13-20A and maintained for 5-10s, and finally, the current is reduced to 0A to complete the entire evaporation process. The advantage of the present invention is that single-source thermal evaporation technology is used, which avoids the complex control problem of each evaporation source in multiple thermal evaporation technology; the present invention uses CdS QDS rich in element Cd as the precursor, and the preparation method of the quantum dots is room temperature The co-precipitation method is simple, low consumption, easy to operate and high in yield.

Description

A Thermal Evaporation Method for Preparing Near-Stoichiometric CdS Thin Films with Quantum Dots as Precursors

technical field

The invention belongs to the technical field of material chemistry, and in particular relates to a thermal evaporation method for preparing near-stoichiometric CdS thin films with quantum dots as precursors.

Background technique

With the increasing shortage of energy, the development and utilization of new energy has become a hot research issue. Solar energy is a clean and inexhaustible new energy source. A solar cell is a device that directly applies solar energy. CdS is a common semiconductor material with a direct bandgap about 2.4 eV wide. The wide band gap allows most of the visible light to pass through, the photoconductive effect and high electron affinity make CdS a better window layer and transition layer material in optoelectronic devices.

Currently, different techniques are usually used to prepare CdS thin films with good crystallinity and balanced stoichiometry. These preparation techniques mainly include chemical bath deposition (CBD), spray thermal decomposition, chemical vapor deposition (CVD), electrochemical deposition, magnetron sputtering, physical vapor deposition, and thermal evaporation. Among these preparation techniques, thermal evaporation and solution-based methods are suitable for large-scale and reproducible preparation of uniform CdS thin films due to their advantages of convenient operation and low cost. Among the above two preparation methods, the solution-based preparation technique usually inevitably introduces some specific impurities into the film. For example, a compound from a reaction solution or a compound containing hydrogen or oxygen from a precursor, etc. Although thermal evaporation technology can fundamentally avoid the above-mentioned impurities, it is still difficult to obtain near-stoichiometric semiconductor films through traditional thermal evaporation technology due to the different saturation vapor pressures among the constituent elements of the precursor. For example, in the CdS compound, the saturated vapor pressure of the element Cd is smaller than that of the element S. Therefore, commercial CdS powder is used as a precursor to thermally evaporate CdS thin films at room temperature substrates, which usually results in the lack of Cd element in the prepared CdS thin films. However, the performance of semiconductor devices is often closely related to the stoichiometry of the film, and CdS films with balanced stoichiometry are more suitable for photovoltaic applications. In addition, there are many applications for preparing thin films on room temperature substrates. For example, when using organic thin films as substrates to make corresponding devices, organic substances cannot withstand high temperatures. In addition, it is not suitable to heat the existing devices when evaporating top electrodes for various optoelectronic devices.

In order to thermally evaporate CdS thin films with equilibrium stoichiometry on room temperature substrates, we can adopt several schemes. First, the application of flash evaporation technology. It does this by transporting powdered precursors to hot porcelain boats for rapid evaporation, which requires some additional mechanical equipment to disperse the precursors. Another option is to apply multi-source co-evaporation technology. It controls the stoichiometry of the CdS film by adjusting the temperature of each evaporation source and replacing the CdS compound with elemental Cd and elemental S as precursors, so this evaporation technique requires more equipment to precisely control the temperature of each evaporation source. In fact, it is the most convenient strategy to construct Cd-rich element CdS compounds on low-temperature substrates as single-source precursors to evaporate CdS thin films. However, in order to obtain precursors rich in Cd elements, the existing methods need to use powdered CdS, and the CdS powder needs to be heated in a hydrogen flow at 800°C, which increases the complexity of the preparation process.

The existing preparation method has defects and needs to be improved.

Contents of the invention

The problem to be overcome by the present invention is that in the CdS compound, because the vapor pressure of the S element is larger than that of the Cd element, on the substrate at room temperature, if the commercial CdS powder is used as the precursor, the CdS film prepared by the traditional thermal evaporation method is often The high content of S element leads to the unbalanced stoichiometric ratio of the film. Among them, the commercial CdS powder is often a CdS bulk material with relatively balanced stoichiometry. The present invention provides a simple and easy method to synthesize Cd-rich CdS quantum dots (QDs) to replace CdS powder as a precursor, and prepare CdS thin films by thermal evaporation on room temperature substrates. In addition, the aggregation of CdS QDs does not require additional instruments for dispersion, and the interaction of aggregated CdS QDs is weak, which will essentially accelerate the thermal evaporation process. This is different from the case of flash or conventional thermal evaporation, which require dispersed CdS powder as a precursor, which does not require a dispersion process in our case. In the present invention, using CdS QDs as precursors, the stoichiometry of the as-prepared CdS thin films was effectively restored through a single-source thermal evaporation process.

The problem to be solved by the present invention is to provide a thermal evaporation method for preparing a near-stoichiometric CdS thin film in situ on a room temperature substrate using Cd-rich CdS QDS as a precursor. The technical scheme that the present invention takes to the problem to be solved is:

A thermal evaporation method for preparing near-stoichiometric CdS thin films with quantum dots as precursors. On a substrate at room temperature, CdS quantum dots (QDs) rich in Cd elements are used as precursor materials to prepare near-stoichiometric CdS films in situ by thermal evaporation. CdS film. First, the cleaned substrate was placed on the sample holder in the vacuum chamber of a thermal evaporator (Emitech, K950X). Close the chamber by placing the appropriate size precursor, 0.1-0.3 g, in the W basket. The chamber was evacuated to a vacuum of 1.0 x 10 ^{-3 -} 1.0 x 10 ^-5 mbar at room temperature and the evaporation rate was controlled by adjusting the current through the W basket. First, slowly increase the current from 0 A to 6-10 A, then wait until the W basket turns red. Then, the current was further increased to 13-20 A and maintained for 5-10 s, and finally, the current was reduced to 0 A to complete the entire evaporation process.

On room temperature substrates, CdS quantum dots (QDs) rich in Cd elements were used as precursor materials, and near-stoichiometric CdS thin films were prepared in situ by thermal evaporation. The cleaned substrate was placed on the sample holder of the vacuum chamber of the thermal evaporator (Emitech, K950X). Close the chamber by placing the appropriate size precursor, 0.1-0.3 g, in the W basket. The chamber was evacuated to a vacuum of 1.0 x 10 ^{-3 -} 1.0 x 10 ^-5 mbar at room temperature and the evaporation rate was controlled by adjusting the current through the W basket. First, slowly increase the current from 0 A to 6-10 A, then wait until the W basket turns red. Then, the current was further increased to 13-20 A and maintained for 5-10 s, and finally, the current was reduced to 0 A to complete the entire evaporation process.

The substrate was placed at room temperature without heating or cooling. Among them, the substrate refers to indium tin oxide (ITO) conductive glass, various metal foils or any required substrate material, especially for those substrates that are not resistant to high temperatures in experiments, such as organic substrates.

The CdS-rich CdS QDs used as the precursor of the thermal evaporation process were synthesized by the co-precipitation method. At room temperature and electromagnetic stirring, nitric acid was separated from Cd(NO3)2 4H2O aqueous solution (75 mL, 0.1 -1 M) continuously. into sodium sulfide Na2S aqueous solution (75 mL, 0.1-1 M). Once the reaction started, the orange CdS QDs immediately precipitated out. After the reaction was complete, the precipitated product was centrifuged with the aid of a centrifuge and rinsed thoroughly with deionized (DI) water. Finally, collect the precipitated product into a centrifuge tube and dry at 80-100 ^oC for 4-10 h to form a large piece of light yellow solid, then divide the light yellow solid into many small pieces, ready for subsequent thermal evaporation experiments .

Use deionized water containing detergent to initially remove oil stains and dust on the surface of the substrate. After this process is assisted by ultrasound for 10-50 minutes, clean with deionized water and ultrasonic for 2-20 minutes before replacing it with a new one. Ultrasonic cleaning of deionized water for 2-20 minutes, so that the cycle is 1-5 times, and then the substrate is mixed with ammonia water (NH3·H2O), hydrogen peroxide (H2O2) and deionized water at a volume ratio of 1:2 :5, heat to 80 oC-100 oC and cook until no bubbles are produced, remove all residual organic contamination, after that, clean with deionized water and ultrasonic for 10-30 minutes, then replace with new deionized water for ultrasonic cleaning for 10 minutes Minutes to 30 minutes, so cycle 3-5 times, and finally, dry in an oven at 50-100oC for 3 hours to 8 hours.

The CdS QDS rich in element Cd of the present invention is a precursor and refers to: (1) the stoichiometric imbalance of CdS quantum dots; (2) the content of Cd element is the majority; (3) the preparation method of the quantum dots is co-precipitation at room temperature method, the method is simple, low consumption, easy to operate and high yield.

The thermally evaporated CdS thin film of the present invention refers to: (1) using single-source technology; (2) replacing traditional commercial CdS powder with bulk CdS QDS as the source, (3) not requiring any dispersion equipment, which further simplifies the preparation process, Reduce preparation steps.

The room temperature substrate of the present invention means that the substrate is placed in an environment at room temperature without heating or cooling. Among them, the substrate refers to indium tin oxide (ITO) conductive glass, various metal foils or any required substrate material, especially for those substrates that are not resistant to high temperatures in experiments, such as organic substrates.

The CdS QDs rich in Cd elements used as the precursor of the thermal evaporation process of the present invention are synthesized by the coprecipitation method, which is characterized in that, at room temperature and under electromagnetic stirring, nitric acid is separated from the Cd(NO3)2 4H2O aqueous solution (75 mL, 0.1 -1 M) was continuously dropped into sodium sulfide Na2S aqueous solution (75 mL, 0.1-1 M). Once the reaction started, the orange CdS QDs immediately precipitated out. After the reaction was complete, the precipitated product was centrifuged with the aid of a centrifuge and rinsed thoroughly with deionized (DI) water. Finally, collect the precipitated product into a centrifuge tube and dry at 80-100 ^oC for 4-10 h to form a large piece of light yellow solid, then divide the light yellow solid into many small pieces, ready for subsequent thermal evaporation experiments .

The cleaning method of the substrate of the present invention is characterized in that, use deionized water containing detergent to initially remove oil stains and dust on the surface of the substrate, and this process is carried out after 10-50 minutes under the assistance of ultrasonic waves. Clean with deionized water and ultrasonic for 2-20 minutes, then replace with new deionized water and ultrasonically clean for 2-20 minutes, so cycle 1-5 times. In the mixed solution of ionized water, the volume ratio is 1:2:5, heat to 80 oC-100 oC and cook until no bubbles are generated, remove all residual organic contamination, after that, clean with deionized water and ultrasonic for 10 minutes- After 30 minutes, replace with new deionized water and ultrasonically clean for 10-30 minutes, repeat this cycle 3-5 times, and finally dry in an oven at 50-100oC for 3-8 hours.

Beneficial effects of the present invention:

1. The present invention adopts the single-source thermal evaporation technology, which avoids the complex control problem of each evaporation source in the multiple thermal evaporation technology.

2. The present invention uses CdS QDS rich in element Cd as the precursor, and the preparation method of the quantum dots is room temperature co-precipitation method, which is simple, low consumption, easy to operate and has high yield. Moreover, the CdS QDs aggregated into blocks and the weak interaction between CdS QDs in the block is conducive to rapid thermal evaporation but does not require additional equipment for dispersion, thus further simplifying the preparation process and reducing the preparation steps.

3. The present invention performs thermal evaporation on a room temperature ITO glass substrate, which can be applied to many occasions, such as using organic matter as a substrate or evaporating device terminal electrodes.

The present invention is of great significance to the research of CdS thin film-based optoelectronic devices.

Description of drawings

Fig. 1. Schematic diagram of the instrument structure for preparing CdS thin film by thermal evaporation method in the embodiment and the actual picture of CdS thin film and CdS QDS precursor before and after drying.

Figure 2, the field emission electron micrograph (FE-SEM) illustration of the CdS film prepared in the example is the FE-SEM of the film at a higher magnification.

Figure 3. X-ray electron diffraction spectra (EDX) of the precursor CdS QDs and corresponding CdS thin films in Examples.

Fig. 4. Schematic diagram of the structure of a photoelectrochemical (PEC) cell built on the basis of a CdS thin film in the embodiment and a schematic diagram of the carrier transport induced by transient light.

Fig. 5. The photocurrent density versus time (I-t) curves of the CdS film-based PEC cell device prepared in the example and the empty ITO conductive glass substrate.

Detailed ways

In order to facilitate the understanding of the present invention, the present invention will be described in more detail below in conjunction with the accompanying drawings and specific embodiments. Preferred embodiments of the invention are shown in the accompanying drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described in this specification. On the contrary, these embodiments are provided to make the understanding of the disclosure of the present invention more thorough and comprehensive.

Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the technical field of the invention. The terms used in the description of the present invention in this specification are only for the purpose of describing specific embodiments, and are not used to limit the present invention. The term "and/or" used in this specification includes any and all combinations of one or more of the associated listed items.

The present invention will be further described below in conjunction with accompanying drawings and examples.

A thermal evaporation method for preparing near-stoichiometric CdS thin films with quantum dots as precursors. On a substrate at room temperature, CdS quantum dots (QDs) rich in Cd elements are used as precursor materials to prepare near-stoichiometric CdS films in situ by thermal evaporation. CdS film. First, the cleaned substrate was placed on the sample holder in the vacuum chamber of a thermal evaporator (Emitech, K950X). Close the chamber by placing the appropriate size precursor, 0.1-0.3 g, in the W basket. The chamber was evacuated to a vacuum of 1.0 x 10 ^{-3 -} 1.0 x 10 ^-5 mbar at room temperature and the evaporation rate was controlled by adjusting the current through the W basket. First, slowly increase the current from 0 A to 6-10 A, then wait until the W basket turns red. Then, the current was further increased to 13-20 A and maintained for 5-10 s, and finally, the current was reduced to 0 A to complete the entire evaporation process.

On room temperature substrates, CdS quantum dots (QDs) rich in Cd elements were used as precursor materials, and near-stoichiometric CdS thin films were prepared in situ by thermal evaporation. The cleaned substrate was placed on the sample holder of the vacuum chamber of the thermal evaporator (Emitech, K950X). Close the chamber by placing the appropriate size precursor, 0.1-0.3 g, in the W basket. The chamber was evacuated to a vacuum of 1.0 x 10 ^{-3 -} 1.0 x 10 ^-5 mbar at room temperature and the evaporation rate was controlled by adjusting the current through the W basket. First, slowly increase the current from 0 A to 6-10 A, then wait until the W basket turns red. Then, the current was further increased to 13-20 A and maintained for 5-10 s, and finally, the current was reduced to 0 A to complete the entire evaporation process.

The substrate was placed at room temperature without heating or cooling. Among them, the substrate refers to indium tin oxide (ITO) conductive glass, various metal foils or any required substrate material, especially for those substrates that are not resistant to high temperatures in experiments, such as organic substrates.

The CdS-rich CdS QDs used as the precursor of the thermal evaporation process were synthesized by the co-precipitation method. At room temperature and electromagnetic stirring, nitric acid was separated from Cd(NO3)2 4H2O aqueous solution (75 mL, 0.1 -1 M) continuously. into sodium sulfide Na2S aqueous solution (75 mL, 0.1-1 M). Once the reaction started, the orange CdS QDs immediately precipitated out. After the reaction was complete, the precipitated product was centrifuged with the aid of a centrifuge and rinsed thoroughly with deionized (DI) water. Finally, collect the precipitated product into a centrifuge tube and dry at 80-100 ^oC for 4-10 h to form a large piece of light yellow solid, then divide the light yellow solid into many small pieces, ready for subsequent thermal evaporation experiments .

Use deionized water containing detergent to initially remove oil stains and dust on the surface of the substrate. After this process is assisted by ultrasound for 10-50 minutes, clean with deionized water and ultrasonic for 2-20 minutes before replacing it with a new one. Ultrasonic cleaning of deionized water for 2-20 minutes, so that the cycle is 1-5 times, and then the substrate is mixed with ammonia water (NH3·H2O), hydrogen peroxide (H2O2) and deionized water at a volume ratio of 1:2 :5, heat to 80 oC-100 oC and cook until no bubbles are produced, remove all residual organic contamination, after that, clean with deionized water and ultrasonic for 10-30 minutes, then replace with new deionized water for ultrasonic cleaning for 10 minutes Minutes to 30 minutes, so cycle 3-5 times, and finally, dry in an oven at 50-100oC for 3 hours to 8 hours.

In conjunction with Fig. 1, Fig. 2, Fig. 3, Fig. 4, Fig. 5, the present invention is further explained,

Fig. 1. Schematic diagram of the instrument structure for preparing CdS thin film by thermal evaporation method in the embodiment and the actual picture of CdS thin film and CdS QDS precursor before and after drying.

It can be seen from the actual figure 1 of the sample that the CdS film we prepared is yellow and transparent. Moreover, tape sticking experiments show that the CdS thin film exhibits excellent adsorption properties to ITO substrates.

Figure 2, the field emission electron micrograph (FE-SEM) illustration of the CdS film prepared in the example is the FE-SEM of the film at a higher magnification.

In Figure 2, a large number of CdS nanorods are uniformly distributed on the surface of the dense CdS film. It can be further seen from the inset that the CdS nanorods have a diameter of about 50 nm and a length of more than 200 nm, and they overlap, intersect and pack closely.

Figure 3. X-ray electron diffraction spectra (EDX) of the precursor CdS QDs and corresponding CdS thin films in Examples.

According to the EDX results, in CdS QDs, the atomic ratio of Cd to S is about 1.13:1, while the atomic ratio of Cd and S in the CdS thin film is about 1.03:1. It can be seen that in the CdS film, the content of the element Cd is reduced and is very close to the stoichiometric ratio of the CdS compound, which has reached our expected result.

Fig. 4. Schematic diagram of the structure of a photoelectrochemical (PEC) cell built on the basis of a CdS thin film in the embodiment and a schematic diagram of the carrier transport induced by transient light.

Fig. 5. The photocurrent density versus time (I-t) curves of the CdS film-based PEC cell device prepared in the example and the empty ITO conductive glass substrate.

The photogenerated current density of the PEC cell (Fig. 5a) and the empty ITO glass substrate (Fig. 5b) increases instantaneously under illumination, and decreases immediately when the illumination stops, which indicates that both the CdS film and the ITO glass substrate have N-type conductivity. characteristic. The difference is that the photoelectric response of the ITO glass substrate is greatly enhanced under the sensitization of the CdS film, which shows that the CdS film has a good sensitization effect on the ITO conductive glass substrate and is an effective photoanode material.

Example

1. Preparation:

(1) Configuration solution: 75 mL, 0.125 M nitric acid, Cd(NO3)2 4H2O aqueous solution and sodium sulfide Na2S aqueous solution.

(2) Cleaning the substrate: Select indium tin oxide (ITO) conductive glass as the substrate. First, the conductive ITO/glass substrate was cleaned with deionized water containing detergent to preliminarily remove oil stains and dust on the substrate surface. After this process was carried out with the assistance of ultrasound for 30 minutes, it was cleaned with deionized water and ultrasonically cleaned for 10 minutes, and then replaced with new deionized water for 10 minutes, and the cycle was repeated 3 times. Then, the substrate was boiled in a mixed solution of ammonia (NH3·H2O), hydrogen peroxide (H2O2) and deionized water at a volume ratio of 1:2:5 at 80 oC until no bubbles were generated to remove all residual organic contamination. Sewage. Afterwards, wash with deionized water and ultrasonically clean for 10 minutes, and then replace with new deionized water for ultrasonic cleaning for 10 minutes, and so cycle 3 times. Finally, it was dried in an oven at 80 oC for 3 hours.

2. Reaction steps:

(1) Synthesis of CdS QDs

CdS QDs were synthesized by co-precipitation as a precursor for thermal evaporation process. The specific process is as follows: under room temperature and electromagnetic stirring, nitric acid aqueous solution (75 mL, 0.125 M) separated by Cd(NO3)2·4H2O was continuously dropped into sodium sulfide Na2S aqueous solution (75 mL, 0.125 M). Once the reaction started, the orange CdS QDs immediately precipitated out. After the reaction was complete, the precipitated product was centrifuged with the aid of a centrifuge and rinsed thoroughly with deionized (DI) water. Finally, the precipitated product was collected into a centrifuge tube and dried at 80 ^o C for 4 h to form a large piece of light yellow solid, which was then divided into many small pieces and placed in a tungsten (W) basket for subsequent Thermal evaporation experiments.

(2) Thermally evaporated CdS film

Put the cleaned ITO glass substrate on the sample holder (Emitech, K950X) in the vacuum chamber. Put the appropriate size precursor, about 0.13 g, in the W basket to close the chamber. To prepare CdS thin films by thermal evaporation, the chamber was evacuated to a vacuum of 1.0×10 ⁻³ mbar at room temperature, and the evaporation rate was controlled by adjusting the current through the W basket. First, slowly increase the current from 0 A to 6 A, then wait until the W basket turns red. Then, the current was further increased to 13 A and kept for 5 s, followed by reducing the current to 0 A to complete the entire evaporation process.

3. Characterization and performance research: The yellow transparent CdS film prepared in situ on ITO conductive glass was taken out, and its crystal structure (XRD, Figure 1), surface morphology (FE-SEM, Figure 2), stoichiometry ( EDX, Figure 3) and photoelectrochemical performance (PEC cell, Figure 4 and transient photocurrent response, Figure 5).

The invention is of great significance to the development and research of CdS film-based optoelectronic devices.

It should be noted that the above-mentioned technical features continue to be combined with each other to form various embodiments not listed above, which are all regarded as the scope of the description of the present invention; and, for those of ordinary skill in the art, improvements can be made according to the above description Or transformation, and all these improvements and transformations should belong to the protection scope of the appended claims of the present invention.

Claims (4)

1. a quantum dot is the thermal evaporation that forerunner prepares near-stoichiometric CdS film, it is characterized in that, on room temperature substrate, the CdS quantum dot (QDs) applying rich Cd element is precursor material, the CdS film of near-stoichiometric is prepared by thermal evaporation original position, (Emitech on the specimen holder that the substrate after cleaning is placed on thermal evaporation instrument vacuum chamber, K950X), the presoma of suitable dimension, 0.1-0.3 g, be placed in W basket and close this room, at room temperature, this room is pumped into 1.0 × 10 ^-3-1.0 × 10 ^-5the vacuum of mbar, evaporation rate is controlled by the electric current adjusted through W basket, first, electric current is slowly increased to 6-10 A from 0 A, then wait for that then, electric current increases to 13-20 A further and keeps 5-10 s until W basket becomes red, finally, reducing electric current is that 0 A is to complete whole evaporation process.

2. a kind of quantum dot according to claim 1 is the thermal evaporation that forerunner prepares near-stoichiometric CdS film, it is characterized in that, process of heating or lower the temperature is not carried out in the environment that substrate is put in room temperature, wherein, it is especially particularly applicable to the substrate of those non-refractories in an experiment that substrate refers to tin indium oxide (ITO) electro-conductive glass, various metal pool sheet or any required backing material, such as organic substrate.

3. a kind of quantum dot according to claim 1 is the thermal evaporation that forerunner prepares near-stoichiometric CdS film, it is characterized in that, CdS QDs as the rich Cd element of thermal evaporation process presoma is application Co deposited synthesis, under room temperature and electromagnetic agitation, by nitric acid every Cd (NO3) the 24H2O aqueous solution (75 mL, 0.1-1 M) constantly instill the vulcanized sodium Na2S aqueous solution (75 mL, 0.1-1 M) in, react once, orange CdS QDs has just been precipitated out immediately, after question response completes, the product centrifuge of precipitation is assisted centrifugal down and rinses up hill and dale with deionization (DI) water, finally, the product-collecting of precipitation to a centrifuge tube, at 80-100 ^oCtemperature under dry 4-10 H-shaped become a bulk of faint yellow solid, subsequently faint yellow solid is divided into many fritters, prepare carry out subsequently thermal evaporation experiment.

4. a kind of quantum dot as requested described in 1 is the thermal evaporation that forerunner prepares near-stoichiometric CdS film, it is characterized in that, oil stain on substrate surface and dust is tentatively removed with the deionized water containing liquid detergent, this process ultrasonic auxiliary under carry out 10-50 minute after, by washed with de-ionized water and the deionized water ultrasonic cleaning 2-20 minute renewed again after ultrasonic 2-20 minute, circulation like this 1-5 time, then, this substrate is at ammoniacal liquor (NH3H2O), in the mixed solution of hydrogen peroxide (H2O2) and deionized water, volume ratio is 1:2:5, being heated to 80 oC-100 oC boils to not having bubble to produce, remove the organic contaminations that all are residual, afterwards, by washed with de-ionized water and the deionized water ultrasonic cleaning that renews again after ultrasonic 10 minutes-30 minutes 10 minutes-30 minutes, circulation like this 3-5 time, finally, dry 3 hours-8 hours of 50-100oC in an oven.