JPH01122938A - Method and apparatus for producing polycrystalline film - Google Patents

Abstract

PURPOSE: To make it possible to produce a thin polycrystalline layer which has crystals of a large diameter and is adequate for formation of photovoltaic cells by compressing the polycrystalline CdS film obtd. by adhering a slurry contg. CdS on a glass substrate and drying this slurry, then heating the film.

CONSTITUTION: The slurry formed by mixing fine powder of CdS and a fluid carrier, such as propylene glycol, is sprayed or adhered onto the glass substrate. This slurry is dried to evaporate the greater part of the fluid carrier, by which the polycrystalline CdS film is formed on the substrate. Next, this panel 24 is mounted on a table 14 and plural rollers 24 movable in, for example, a perpendicular direction are activated by hydrostatic cylinders to compress the CdS film on the panel 24 moved horizontally by the table 14, by which its film thickness of the CdS film is drastically reduced. The film is then heated and the large-crystal CdS polycrystalline film consisting of the crystals of the average diameter of the micocrystal in the polycrystal equal to or larger than the thickness of the film after the heating, is formed.

COPYRIGHT: (C)1989,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application J] The present invention relates to the production of thin semiconductor layers. More particularly, the present invention relates to the production of thin polycrystalline CdS layers having crystals with large diameters and suitable for making photovoltaic cells.

[Prior Art 1] Solar energy has long been attracting attention as an alternative to conventional hydrocarbon energy resources.

Therefore, the field of directly converting solar energy into electrical energy through the photovoltaic phenomenon is being increasingly researched and developed. However, recently commercially available photovoltaic devices are used only in specific industrial fields, such as expensive telecommunications equipment, lighthouse buoys with low power consumption, and applications in outer space.

Due to the high manufacturing cost of single-crystal photovoltaic cells, the past two
Over the past year, efforts have been intense to develop low cost polycrystalline photovoltaic cells. For the commercialization of polycrystalline silicon solar cells and amorphous silicon solar cells, and also polycrystalline cadmium sulfide solar cells,
Tremendous financial investments have been and are being made. Unfortunately, such cells are inherently less efficient than single crystal cells. Due to the large investments involved and the high production costs of producing such cells according to modern manufacturing techniques, there are considerable difficulties in bringing them to market.

One promising way to mass produce polycrystalline solar energy devices at low cost is to use a transparent glass substrate, such as ordinary float glass, on which to sequentially fabricate photovoltaic films. . One "back wall" structure disclosed in U.S. Pat. No. 4,362,896 includes a thin layer of tin oxide, a thin layer of cadmium sulfide, a thin layer of cuprous sulfide, and an electrode material. A cell is constructed by stacking the layers, and the light energy is transmitted through the glass and the tin oxide layer and absorbed at the CdS/CU2S heterojunction.

Another similar multi-day photovoltaic cell uses cadmium telluride instead of cuprous sulfide.

In order to manufacture such cells at low cost, the cadmium sulfide layer must be relatively thin, less than 10 microns in size. It is also possible to produce a cadmium sulfide layer by the spray pyrolysis method disclosed, for example, in U.S. Pat. No. 4,338,078.
I know it's difficult to control. Changing the temperature of the surface of the glass substrate impairs the yield and therefore significantly increases manufacturing costs.

[Summary of the Invention 1 The present invention basically provides a manufacturing method for forming an improved polycrystalline semiconductor film on a solid substrate, and thus provides a manufacturing apparatus for implementing the method. It is possible,
And, a novel polycrystalline photovoltaic cell is provided. According to one preferred embodiment of the invention, a thin monolayer CdS film is formed on a glass substrate. By depositing layers one after the other, a low cost photovoltaic cell with a back wall structure is produced.

Cd51l is made from fine powder of cadmium sulfide and propylene.
It is formed by mixing with a fluid carrier such as glycol to create a slurry of the required concentration. As an example of a slurry, it is composed of approximately 60 grams of sulfur, cadmium oxide, 2 grams of cadmium chloride (which acts as a regrowth flux), and 100 grams of propylene glycol. This slurry is placed on a glass substrate at room temperature.
That is, it is sprayed or deposited at substantially ambient II temperatures. This membrane is dried. This drying is preferably carried out in air at a temperature near the boiling point of the carrier. This membrane was then heated to 350Ky/CIR (5,000
1), S, i, ) not L70ON9/m2 (10,00
It is compressed by mechanically applying a large force of 0D,s,i,). This compacted film is then regrown in a heated mixture of inert gas and oxygen. Chloride is used as a flux to promote this crystal regrowth. By this method, U.S. Patent No. 4.338,
Crystals with a much larger diameter are produced than those produced by the spray pyrolysis method of No. 078.

According to one technique, a dried film is compressed onto a horizontally moving glass substrate by actuating a plurality of vertically movable rollers with a hydrostatic cylinder. The glass substrate moves under the rollers, resulting in a compressed band-like region of CdS film. The cylinder is raised and the glass moves to the next position, then the cylinder is lowered and the glass passes under the cylinder again. In this way, partially overlapping compressed bands are created on the membrane. This process is repeated until almost all of the Cd5III2 is compressed.

CdS films according to the invention typically have a thickness of 10 microns or less. More preferably, the thickness is between 4 and 8 microns. Most of the regrown crystals are pancake-shaped, and their upper and lower surfaces are Cd
They constitute the upper and lower surfaces of the S film, respectively. Therefore, a single-crystalline CdS single-ff is created between the upper and lower surfaces of the CdS film. The length and width of most crystals are
much larger than their height. The air gaps between adjacent crystals are relatively small, so shorts are unlikely to occur through this CdS film if another film is later deposited to produce a photovoltaic cell.

The manufacturing cost of this CdS film is significantly lower. This is because it does not use expensive deposition equipment or difficult quality control parameters such as uniformly heating the glass to a precise fA. Since large crystals are used, the average diameter of most of which is greater than the thickness of the membrane, the efficiency of this photovoltaic cell is greatly improved. By one technique, the membrane of the present invention is a high-quality, low-cost CdS/C
Used to manufacture dTe photovoltaic cells.

EXAMPLE A thin layer of cadmium sulfide formed in accordance with the present invention is deposited on a suitable rigid substrate material. According to the invention, this film layer can be used to produce a photovoltaic cell in a structure with a back plate. Thus, a CdS layer is formed on a transparent glass substrate, and it is coated with a thin layer of a transparent conductive material such as tin oxide.

Since low manufacturing costs are an important feature of the present invention, the glass substrate is preferably an ordinary window glass manufactured by a method in which a glass ribbon is suspended on a hot tin bath. . A conductive tin oxide film with high transmittance is applied to the surface of the floating glass body.

This tin oxide film can also be created when the glass is suspended on a tin bath, as disclosed in U.S. Pat. No. 3,959,565, or as disclosed in U.S. Pat.
It can also be formed by spraying over a glass panel heated with radiant heat, as disclosed in US Pat. No. 224,355. All of these patents are incorporated herein by reference.

The required characteristics of the tin oxide film are that the film resistivity is 10 ohms per square or less, and the absorption rate of the visible light spectrum that produces the photovoltaic effect of solar energy is 10% or less. and (up to a temperature of 350°C) have an emissivity of 0.1 or less for infrared rays with a wavelength of 5 microns or more. Moreover, the presence of small pinholes in such tin oxide films has a great negative effect on forming the conductive tin pattern on the glass panel, but it also reduces the efficiency of polycrystalline photovoltaic cells. However, this is not a serious defect.

In addition to being low in cost, such conductive tin oxide films adhere well to glass substrates and are sufficiently strong that it is safe to partially remove the covering layer.
Chemically stable even at high temperatures, chemically stable against ultraviolet irradiation, Cd5I
] is characterized in that it does not contain any impurities that would give it a bad IF.

It is preferable to wash the glass with ion-exchanged water before the step of spraying tin oxide and before applying Cd51i. As will be readily apparent to those skilled in the art, appropriate precautions must be taken to prevent contamination of the film layers that make up the photovoltaic cell to increase the efficiency and manufacturing yield of the photovoltaic cell. Must be.

A CdS slurry is made using commercially available Gatmium Sulfide powder with dimensions of 2 microns or less. A small amount of cadmium chloride is added as a necessary flux to promote crystal growth during the recrystallization step. A suitable carrier such as probylene glycol terpineol is used to obtain the required slurry. The required slurry content will vary in part depending on the technology used, and will also vary slightly depending on the equipment used. When sprayed in air, about 60 grams of cadmium sulfide, about 2 grams of cadmium chloride, and about 10
A mixture of 0 grams of propylene glycol has been found to be preferred.

As is well known to those skilled in the art, adding small amounts of chloride can promote crystal growth, but adding chloride above the G required for reaction with cadmium sulfide can reduce photovoltaic properties and lifetime. to degrade. Therefore, it is necessary to include a step to avoid excess cadmium chloride, that is, cadmium chloride remaining. Finally, if a layer of cadmium telluride is applied on top of the cadmium sulfide film to make a photovoltaic cell, then the low ffi (10P
PM to 101,000 PP of cupric acetate can be added as a dopant into the slurry.

Assuming that a spraying method is used to deposit a CdS slurry onto a glass substrate pre-coated with a tin oxide film, depending on the ambient temperature of the glass substrate being worked on, the slurry being sprayed, and the combination with the carrier material, The cost of this process is significantly reduced and the acceptable uniformity of the uniform layer is greatly increased. This atomization method can be well incorporated into conveyor belt equipment. For example, US patent 4゜2
24.355, the spraying process can be carried out by moving the sprayer across the width of the glass panel placed on the belt. As explained below, the large C of the regrown crystals from about 4 microns to about 7 microns thick is removed by depositing a CdS slurry about 20 microns thick.
It was found that d5I]IJ could be obtained.

The CdS slurry is heated at 60°C or less in a reduced pressure atmosphere,
Or dried in air at about 200°C. Propylene glycol will evaporate from this layer. If desired, the propylene glycol may be removed by conventional distillation methods.

In this way, a polycrystalline CdS layer will be obtained.

However, there will be a fairly large hole where the carrier material has evaporated. In addition, [as-sprayed J
CdS crystals are very small in size, and the photovoltaic cells created with the films so obtained are, in fact,
Efficiency will never be of any reasonable magnitude.

In the present invention, this dried Cd51 is compressed from a thickness of about 20 microns to a thickness of 10 to 14 microns, preferably 12 microns, by mechanically applying a large force. Both the glass substrate and the tin oxide layer weigh 350 kg/m” (5,00
op, s, i, > to 70 OKy/ax2 (10,0
00p, s, i,) required compression crab, preferably 42
0 to 9/lx" (6,0001), s, i,)'iL56ONg/cm" (8,000p, s,
i, ) can easily withstand compressive forces.

The reason why this pre-applying compressive force promotes cell regrowth is not fully understood, but the application of compressive force increases the amount of material that can be seen between the CdS materials when the carrier material evaporates. This greatly reduces the number of holes. Also, the contact area between the particles of the powder is significantly increased by the compression effect.

The increase in powder particle contact area obtained by compaction is directly related to the required increase in crystal size during regrowth.

A suitable apparatus for compressing CdS films is shown in FIG. Compressor 10 has an aerodynamic base 12 and an X-Y table 14. The table pull 14 can be moved manually in the Y direction by a standard worm screw and handle 16, or can be moved by a drive connected to the worm screw shaft 16. 1f! 1lJ118. Movement or direction of the table in the X direction can be manually controlled by the worm screw and handle 20 as well. Alternatively, this driving can also be performed by a driving electric motor.

A panel 24 with said tin oxide and a sprayed cadmium sulphide layer (carrier evaporated) is mounted on table 1.
4 and attached by etch strips 26 and 28. If desired, a standard vacuum table with a plurality of small holes can be used to secure panel 24 in place on the table.

In this case, a vacuum exhaust pipe is provided. However,
It has been found that the force applied perpendicularly to a glass substrate by a roll produces only a small force in the in-plane direction of the substrate. Therefore, a vacuum table would not be necessary.

A vertical plate 54 is fixed to the base 12 by means of a holder 11 . Each of the plurality of pneumatic/hydraulic cylinders 32, 34 and 36 is attached to the vertical plate 54. Each of these cylinders is actuated downwardly by air pressure from input pressure tube 38. Each of these cylinders is equipped with a pressure ff40, and a pressure pipe 38
When the air pressure inside is released, return the cylinder to the upper position. Therefore, each cylinder rod 42 is I
Go back and forth along a straight path. Preferably, all cylinders operate simultaneously.

In FIG. 2, block 44 is attached to cylinder shaft 42 at 56
and vertical plate 54
has a dovetail groove 52. A roller 4 is attached by a bin 50 to two arms 48 extending downwardly from the block 44.
6 is rotatably mounted. Therefore, ant groove 5
2 effectively limits the movement of block 44 to the vertical direction.

However, there is sufficient "play" between block 44 and vertical plate 54 to allow block 44, and therefore roller 46, to rotate slightly about bin 56. This slight rotational movement of the roller thus allows the roller to lie "flat" on the glass substrate during the compaction process.

Again in Figure 1, approximately 8,1 K9/cm2 (11
Air pressure of 5p, s, i, ) is supplied by pressure tube 38 from a suitable pressure source (not shown) and is transmitted to roller 46 to exert a downward force on Cd 51. A typical stainless steel roller is approximately 38III in diameter! R (1.5 inches), width approximately 104Il (
0.4 inch) and therefore the instantaneous compression area of one roller is '1.3 mm (0.05 inch) x 10
#I#I (0.4 inch). The force exerted downward by each roller is approximately 71 g (170 bonds), and therefore the compressive force acting on the CdS film is approximately 560/9/
cm2 (8,000 p.s, i,).

The cylinder is actuated to apply a downward force to the roller, and once the roller contacts the substrate, electric motor 18 rotates Y-direction table screw 16 to move table 14 and remove a plurality of compressed CdS films. A band-like area is formed. Once the stopper 58 fixed to the table 14 contacts the limiter 62 fixed to the base plate 12, the rotation of the screw 16 is stopped and the air pressure to the cylinder is vented and pressure is applied to the pressure tube 40. The cylinder will rise. Once the cylinder is raised, the table commands the electric motor 22 to rotate the screw 20 by a number of revolutions equal to the width of the compressed swath. The table then returns to the position shown in FIG. 1 and the process is repeated when stop 58 contacts 60.

If desired, it is easy to modify compression 110 to compress the membrane when the table moves in either the positive Y direction or the negative Y direction.

FIG. 2 shows a thin tin oxide layer 82 on top of a glass substrate 80, with a CdS film on top, and several compressed bands of these layers are shown.

Preferably, these compressed strips have a slight overlapping compressed area 70. It is important to note that the presence of such overlapping areas does not adversely affect the subsequent regrowth process of this film layer, and the presence of such overlap areas ensures that the entire film is compressed. It is from. In FIG. 2, the roller edge 72 of each swath is shown to be slightly inward from the edge of the glass, e.g. This is to avoid breaking the glass when it first descends.

If there are small particles on the CdS film, it will have a negative effect on the compaction process. Typically, the roller is lifted by this particle so that the membrane a region is not sufficiently compressed. However, it has been found that with sufficient care, the deposition of such particles on Cd S II can be prevented or significantly reduced. Alternatively, such particles can easily be removed from the top of the membrane with compressed air to clean the surface of the membrane prior to the compression step. Accordingly, a compressed air jet nozzle 78 is provided to blow such particles away from the substrate before the table is placed in the designated position. Suitable air/fluid cylinders are manufactured by PI-10 of Fort Wayne, Indiana. This is the device No. Y5528 (No. 603).

After the CdS layer of panel 24 is compressed, a regrowth process is performed on the film. This process is described in U.S. Patent No. 4.362
1 by a technique similar to that disclosed in , No. 896.
It is preferable that the process be carried out in an atmosphere rich in nitrogen. This US patent is incorporated herein by reference.

In particular, it is preferable that the CdS film be heated in an atmosphere containing cadmium chloride vapor before performing this regrowth step.

In order to form the required crystals, this step is carried out in a heated atmosphere with the CdS films of adjacent panels facing each other vertically with a fixed spacing between them. However, unlike the CdS crystals formed by the method disclosed in U.S. Pat. There is.

Most, if not all, crystals have dimensions significantly greater than 1 to 2 microns. In general, the manufacturing cost of the CdS layer is significantly lower than that of spray pyrolysis.

This is because it is not necessary to uniformly heat the glass to a high temperature when spraying the CdS material onto the glass surface. Also, in some photovoltaic devices, zinc can be added to form a (Zn Cd1.)S film with improved voltage characteristics.

The CdS film is typically heated at a temperature of 480° C. to 580° C., preferably about 530° C., in a nitrogen atmosphere containing about 1% to about 3% oxygen. The glass panel is heated for approximately one hour and then cooled over a period of approximately 45 minutes. The required cadmium chloride M gas is released from the membrane and contributes to the required product growth. After the regrowth step, the CdS film is cleaned with methanol and then water to remove excess cadmium chloride on the surface of the CdS film.

Figure 3 shows regrown C created on tin oxide F182.
This is an SEM (scanning electron microscope) image observed from a direction inclined 70' from the perpendicular to the dS layer 84. As mentioned above,
Small pinholes in the tin oxide layer, such as pinhole 86, do not significantly affect the efficiency of this photovoltaic cell. It is clear that the uniform conductive layer is nevertheless cd
This is because it is under sm.

It can be seen that the thickness of the layer shown in FIG. 3 is approximately 7 microns, and that the upper surface of this layer and the lower surface of this layer are effectively the upper and lower surfaces of the crystal. Thus, a single layer of crystals with virtually uniform height is obtained by the method of the invention. Thus, each of the observed crystals 84A-84G has a substantially flat lower surface in contact with the tin oxide apricot and a substantially flat upper surface. These surfaces, together with similarly arranged surfaces of other crystals, constitute the lower and upper surfaces of Cd5II, respectively.

Each of crystals 84A, 84C, 84D and 84H are greater than 7 microns in both their length and width. Therefore, the average diameter is greater than 7 microns. Crystals 84B and 84E are each approximately equal in length and width and their 7 micron height. Their average diameter is therefore approximately equal to the thickness of the CdS layer. Finally, crystals 84F and 84G appear to be slightly smaller in length and width than their height. Therefore, their average diameter is slightly smaller than the membrane thickness. However, as shown in Figure 3, the average diameter of the majority of crystals is greater than, or at least approximately equal to, the thickness of the film.

FIG. 4 is a SEM image showing the crystal 84A shown in FIG. 3 at a larger magnification. Thus, each crystal in the CdS layer has a substantially planar lower surface 9o in contact with the tin oxide layer 82 and a substantially planar upper surface 92.
It has The sides of the crystal are comprised of a plurality of substantially vertical walls 94, which are irregular in shape. It is also shown in FIG. 4 that although the top and bottom surfaces of the crystals are slightly rounded where these surfaces meet the walls, there are very small air gaps 98 between adjacent crystals. Since the voids between adjacent crystals are small or absent, CdS is used to construct the photovoltaic cell with the tin oxide layer.
Eliminates, or at least greatly reduces, the possibility of short circuits with layers disposed above the layer.

A film compressed to a thickness of about 12 microns, when regrown, has a thickness of 4 to 8 microns, preferably 5 microns.
It becomes a CdS film of micron to 7 micron. Therefore, the CdS layer formed according to the present invention is much thinner.

Therefore, the thickness created by the silk screening method is 20
Cost is lower than micron to 30 micron membranes.

The polycrystalline semiconductor films produced according to the invention are particularly suitable for producing CdS layers for photovoltaic cells with backplates. Accordingly, said layer is
, 362,896.
dS/Cu2S can be used to fabricate photovoltaic cells. Another feature of the present invention is that the CdS film can be used to fabricate a cadmium sulfide/cadmium telluride photovoltaic cell with high efficiency and low manufacturing cost.

FIG. 5 is a cross-sectional schematic diagram of a photovoltaic cell made in accordance with the present invention having an improved cadmium sulfide film. The backplate cell is suitable for economically manufacturing large photovoltaic cells and is made of flat glass of any suitable required thickness, e.g. 3.18# (0.125 inch) thick. fabricated on a substrate 102; The cell includes a conductive layer 104 of tin oxide about 0.7 microns or less thick and a 068 layer 104 about 4 microns to 8 microns thick.
layer 106 and a second layer 106 having a thickness of 1 micron to 4 microns.
It has a polycrystalline layer 108 and an electrode layer in contact with the second polycrystalline layer and having a thickness of 0.5 microns to 2 microns. Second polycrystalline J! i2108 is a suitable material for making photovoltaic heterojunctions with CdS layers.

In accordance with the present invention, the second polycrystalline layer is formed using U.S. Patent No. 4.362.
It can be cuprous sulfide made according to the method disclosed in No. 896. In one preferred embodiment of the invention, this second layer is cadmium telluride. Cadmium sulfide/cadmium telluride panels having dimensions of approximately 12 inches by 12 inches can be manufactured using glass substrate panels of the same or slightly larger dimensions. US Patent No. 4
, 262,411, a photovoltaic cover can be separated into III long strips of interconnected photovoltaic cells. These panels can be electrically combined in parallel or series to create modules by the method disclosed in US Pat. No. 4,223.085.

Although the present invention has been described based on the above embodiment, this is merely an illustration and the present invention is not limited to this embodiment. It will be apparent to those skilled in the art, based on the above description, that other embodiments and alternative methods of operation are possible. Accordingly, these modified embodiments are included within the scope of this invention.

[Brief explanation of the drawing]

Figure 1 is a three-dimensional view of an apparatus for compressing a CdS film according to the present invention, and Figure 2 is a CdS film showing a glass substrate and its cross section.
3. Three-dimensional view of a part of the device of FIG. 1 equipped with an S film;
The figure is a schematic diagram of regrown cadmium sulfide crystals on a glass substrate manufactured by the method of the present invention, and FIG.
FIG. 5 is a schematic cross-sectional view of a portion of a photovoltaic cell made in accordance with the present invention; FIG. [Explanation of symbols] 106 First polycrystalline film, C (Is film 108 2nd g8, second polycrystalline film 110.104 Electrode

Claims (20)

[Claims] (1) mixing cadmium sulfide powder and a liquid carrier to create a slurry containing cadmium sulfide at a desired concentration; depositing the slurry onto the glass substrate at ambient temperature; and drying the slurry to evaporate at least a majority of the fluid carrier from the layer containing cadmium sulfide onto the glass substrate. The steps include forming a polycrystalline cadmium sulfide film, applying compressive force to the polycrystalline film to significantly reduce the thickness of the film, and heating the compressed polycrystalline film and the substrate. the heating step of forming a large crystalline cadmium sulfide polycrystalline film comprising crystals in which the average diameter of microcrystals in the polycrystals is equal to or larger than the thickness of the film after the heating; A method for manufacturing a cadmium sulfide polycrystalline film with desired properties on a glass substrate, comprising: (2) The method of manufacturing the cadmium sulfide polycrystalline film according to claim 1, comprising the step of spraying the slurry onto the substrate while the substrate is substantially horizontal. (3) The method of claim 2, comprising the steps of: disposing a series of substrate panels above a horizontally moving conveyor belt; and one or more substrate panels disposed above the conveyor belt. The method for producing the cadmium sulfide polycrystalline film further comprises the steps of: spraying the slurry from a plurality of spray nozzles; and moving the spray nozzle in a lateral direction with respect to the moving substrate panel. (4) The method of manufacturing a cadmium sulfide polycrystalline film according to claim 1, wherein the drying step is performed at a temperature of the attached slurry between room temperature and the boiling point of the liquid carrier. (5) In the method according to claim 1, the step of applying a compressive force to the polycrystalline film applies a compressive force to the polycrystalline film.
The method for producing the cadmium sulfide polycrystalline film includes applying a compressive force of kg/cm^2 (5,000 psi) or more. (6) The method of claim 5, wherein the compressive force is applied to the film by one or more rollers that apply a force perpendicular to the surface of the substrate. manufacturing method. (7) The method of claim 5, wherein the application of the compression force reduces the thickness of the cadmium sulfide film to about 50% to about 70% of the thickness before compression. Method for manufacturing polycrystalline film. (8) In the method of claim 1, the heating of the compressed film comprises: positioning one or more glass substrates in a substantially vertical plane; and then heating the substrate at a temperature of 480° C. or higher in an atmosphere containing an inert gas. 9. The method of claim 8, wherein the step of mixing the slurry includes mixing a fluid carrier with a flux having cadmium sulfide powder, and the step of: positioning the glass substrate in a vertical plane; The stages are
The method of manufacturing comprises positioning the polycrystalline cadmium sulfide films in opposing relationship to maintain the required concentration of flux vapor. (10) The method according to claim 4, wherein the fluxing agent is cadmium chloride. (11) mixing a suitably selected powder with a fluid carrier to form a slurry of a desired concentration to form a polycrystalline film; and substantially mixing said slurry to form a polycrystalline layer. drying the deposited slurry to evaporate at least a majority of the fluid carrier; and depositing a polycrystalline film having relatively small diameter crystals on the substrate at ambient temperature. applying a compressive force to the polycrystalline film to significantly reduce the thickness of the film; and heating the compressed film and substrate to reduce the thickness of the film after this heating. forming a semiconductor film composed of crystals having an average diameter equal to or greater than . Method. (12) In the method according to claim 11,
The method of manufacturing, wherein applying the compressive force reduces the thickness of the membrane to about 50% to about 70% of the thickness before the compressive force is applied. (13) In the method according to claim 11,
The step of depositing the slurry includes placing a series of substrate panels on a horizontally moving conveyor belt, and depositing the slurry onto the substrate panels while the panels are in a substantially horizontal position. The manufacturing method comprises the step of spraying. (14) A photovoltaic cell formed on a transparent glass substrate having a conductive surface on at least one surface: containing cadmium and sulfur and made to a thickness of 4 to 8 microns; a first polycrystalline film layer having crystals with at least one dimension equal to or larger than the thickness; The photovoltaic cell comprising: a second film layer constituting a junction; and an electrode attached to the second film layer. (15) The photovoltaic cell according to claim 14, wherein the conductive surface is comprised of a transparent tin oxide layer. (16) In the photovoltaic cell according to claim 14, the average diameter of most of the crystals constituting the first film layer is equal to or larger than the thickness of the film layer. The photovoltaic cell characterized in that. (17) The photovoltaic cell according to claim 14, wherein the second film layer is a cadmium telluride layer. (18) In the photovoltaic cell according to claim 17, the first film layer has 100p. p. m. or 1,
000p. p. m. The photovoltaic cell characterized in that it contains cupric acetate of (19) In the photovoltaic cell according to claim 14, substantially the entire crystal constituting the first film layer has a flat lower surface and is in contact with the conductive surface. The photovoltaic cell is characterized in that it has a flat and planar upper surface in contact with the second membrane layer. (20) The photovoltaic cell according to claim 19, wherein the plurality of crystals have an average diameter significantly larger than the thickness of the film layer.