Patent Publication Number: US-2022230813-A1

Title: Method for preparing perovskite solar cell absorbing layer by means of chemical vapor deposition

Description:
TECHNICAL FIELD 
     The present invention relates to a solar cell, and more particularly to a method for preparing a light absorption layer for perovskite solar cells using chemical vapor deposition. 
     BACKGROUND ART 
     A solar cell is a device that converts solar energy into electrical energy. The currently commercialized solar cells are mostly silicon solar cells that use a crystalline silicon substrate and occupy more than 80% of the total market. 
     But, the silicon solar cell has a limit in reducing the production cost because the price of the substrate accounting for too much of the product price and the necessity of using a complicated production process. 
     In order to overcome this problem, there have been developed various types of thin film solar cells, such as CdTe, CIGS, and DSSC. As one of the new thin film solar cells, the perovskite solar cell is being actively developed. 
     When it comes to the studies on the perovskite solar cells, it is known that energy conversion efficiency of 20% or higher has been achieved at the laboratory level thanks to the development of many research groups. 
     The solution method such as spin coating is most commonly used as a method for preparing a light absorption layer of the perovskite solar cell. The preparation method for perovskite solar cells using the solution method is a non-vacuum method, so it has advantages of low production cost and easy implementation. Yet, it also has a disadvantage in that large-area solar cells are difficult to implement due to poor uniformity of the deposited thin film. 
     Besides, the conventional solution method is disadvantageous in that there are a number of pinholes in the perovskite thin film to be deposited, thereby deteriorating the quality of the solar cell. 
     SUMMARY OF THE DISCLOSURE 
     It is therefore an object of the present invention to provide a method for preparing a perovskite light absorption layer using chemical vapor deposition (CVD). 
     It is another object of the present invention to provide a method for preparing a solar cell that can improve the uniformity of the thin film to enable the production of a large-area solar cell and enhance the quality of the thin film to increase the efficiency of the solar cell. 
     In accordance with one aspect of the present invention for achieving the objects, there is provided a method for preparing a perovskite solar cell absorbing layer that is a method for preparing a perovskite solar cell light absorbing layer using chemical vapor deposition (CVD), where the method includes: forming a PbI x  (1≤x≤2) thin film on a substrate by means of chemical vapor deposition; supplying CH 3 NH 2  (methylamine) gas and an iodine (I) precursor on the PbI x  (1≤x≤2) thin film; and forming a CH 3 NH 3 PbI 3  thin film having a perovskite structure through heat treatment after the supplying of the CH 3 NH 2  (methylamine) gas and the iodine precursor on the PbI x  (1≤x≤2) thin film. 
     In an embodiment, the forming of the PbI x  thin film may include using, as a lead (Pb) precursor, tetraethyl-lead, tetramethyl-lead, acetylacetonate-lead(II), and bis(2,2,6,6-tetramethyl-3,5-heptanedionate) lead(II). 
     In an embodiment, the forming of the PbI x  thin film may include using, as an iodine (I) precursor, iodine (I 2 ), 6-iodo-1-hexyne, tertiary-butyl iodide, isopropyl iodide, and ethyl iodide. 
     In an embodiment, the forming of the PbI x  thin film may include supplying the lead (Pb) precursor and the iodide (I) precursor into a reaction chamber in simultaneous or sequential manner. 
     In an embodiment, the forming of the PbI x  thin film may include maintaining a canister temperature for the lead (Pb) precursor or iodide (I) precursor in the range of −20 to 100° C. 
     In an embodiment, the forming of the PbI x  thin film may include maintaining the temperature of a precursor supply line for supplying the lead (Pb) precursor or iodide (I) precursor in the range from a room temperature to 200° C. 
     In an embodiment, forming of the PbI x  thin film may include maintaining a temperature of a substrate for the lead (Pb) precursor or iodide (I) precursor deposited thereon in the range of 50 to 300° C. 
     In an embodiment, the forming of the PbI x  thin film may include using a carrier gas in supplying the lead (Pb) precursor or iodide (I) precursor into the reaction chamber, where the carrier gas may be any one of argon (Ar), helium (He) or nitrogen (N 2 ), or a mixture thereof. 
     In an embodiment, the forming of the PbI x  thin film may include maintaining an internal pressure of the reaction chamber in the range of 1 mTorr to 100 Torr. 
     In an embodiment, the forming of the PbI x  thin film may include using plasma in order to increase the deposition rate and quality of a thin film. 
     In an embodiment, the forming of the CH 3 NH 3 PbI 3  thin film may include maintaining a temperature of a supply line of MA (methylamine, CH 3 NH 2 ) and an iodine (I) precursor in the range from a room temperature to 200° C. 
     In an embodiment, the forming of the CH 3 NH 3 PbI 3  thin film may include maintaining a temperature of a substrate for MA (methylamine, CH 3 NH 2 ) and an iodine precursor supplied thereto in the range from a room temperature to 250° C. 
     In an embodiment, the forming of the CH 3 NH 3 PbI 3  thin film may include conducting a heat treatment at a temperature of 100 to 300° C. on the CH 3 NH 3 PbI 3  thin film deposited through the supplying of the CH 3 NH 2  (methylamine) gas and the iodine precursor (I) on the PbI x  (1≤x≤2) thin film. 
     In an embodiment, the forming of the CH 3 NH 3 PbI 3  thin film may include conducting a heat treatment under vacuum or in an atmosphere of one or more gases of argon (Ar), nitrogen (N 2 ), hydrogen (H 2 ), or helium (He). 
     The use of the above-described method for preparing a perovskite solar cell absorbing layer using the chemical vapor deposition (CVD) has beneficial effects to facilitate the implementation of large-area solar cells and use inorganic materials as CVD precursors, which can minimize an issue of deterioration in efficiency over time after the preparation of solar cells. Another beneficial effect lies in that the method can substantially use CVD equipment already verified for use in production of semiconductors or liquid crystal displays (LCDs) in the preparation of the perovskite light absorption layer of solar cells. 
     In addition, the present invention uses a vacuum deposition method, chemical vapor deposition (CVD), to implement a perovskite light absorption layer that has hitherto been manufactured by a non-vacuum solution method, thereby making it possible to produce a large-area perovskite light absorption layer and consequently solar cells with higher efficiency according to the thin film production method that is advantageous over the conventional solution method. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram for illustration of a method for preparing a perovskite solar cell light absorption layer according to an embodiment of the present invention. 
         FIG. 2  is an illustrative diagram of a chemical vapor deposition reaction chamber capable of being used in the method for preparing a perovskite solar cell light absorption layer as shown in  FIG. 1 . 
         FIG. 3 a    shows the surface of the PbI x  thin film deposited on a TiO 2  thin film by means of the CVD method. 
         FIG. 3 b    shows the cross section of the PbI x  thin film deposited on a TiO 2  thin film by means of the CVD method. 
         FIG. 4 a    shows the surface of a metal electrode deposited after forming a CH 3 NH 3 PbI 3  thin film by supplying MA (methylamine) and an iodine precursor on the PbI x  thin film deposited by the CVD method. 
         FIG. 4 b    shows the cross section of a metal electrode deposited after forming a CH 3 NH 3 PbI 3  thin film by supplying MA and an iodine precursor on the PbI x  thin film deposited by the CVD method. 
         FIG. 5  presents a deep analysis of the manufactured CH 3 NH 3 PbI 3  thin film using AES (Auger Electron Spectroscopy). 
         FIG. 6  presents the measurements of the energy conversion efficiency of the CH 3 NH 3 PbI 3  thin film manufactured by the CVD method according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE DISCLOSURE 
     As the present invention allows for various changes and numerous embodiments, particular embodiments will be illustrated in the drawings and described in detail. However, the present invention is not limited to the specific embodiments and should be construed as including all the changes, equivalents, and substitutions included in the spirit and scope of the present invention. In the description of the accompanying drawings, the same reference symbols are assigned to the same components. 
     Although ordinal numbers such as “first”, “second”, “a”, “b”, and so forth will be used to describe various components, those components are not limited by the terms. The terms are used only for distinguishing one component from another component. For example, a first component may be referred to as a second component and likewise, a second component may also be referred to as a first component, without departing from the teaching of the inventive concept. The term “and/or” used herein includes any and all combinations of one or more of the associated listed items. 
     The terminology used herein is for the purpose of describing an embodiment only and is not intended to be limiting of an exemplary embodiment. As used herein, the singular forms are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “has” when used in this specification, specify the presence of stated feature, number, step, operation, component, element, or a combination thereof but do not preclude the presence or addition of one or more other features, numbers, steps, operations, components, elements, or combinations thereof. 
     The terms used herein, including technical and scientific terms, have the same meanings as terms that are generally understood by those skilled in the art, as long as the terms are differently defined. It should be understood that terms defined in a generally-used dictionary have meanings coinciding with those of terms in the related technology. As long as the terms are not defined obviously, they are not ideally or excessively analyzed as formal meanings. 
     Hereinafter, a detailed description will be given as to the preferred embodiments of the present invention with reference to the accompanying drawings. 
       FIG. 1  is a diagram for illustration of a method for preparing a perovskite solar cell light absorption layer according to an embodiment of the present invention. 
     Referring to  FIG. 1 , the method for preparing a perovskite solar cell light absorption layer according to an embodiment of the present invention is a preparation method for a perovskite solar cell light absorption layer using the chemical vapor deposition (CVD) method. In the preparation method, a PbI x  (1≤x≤2) thin film  14  is formed on a substrate  11  by means of the chemical vapor deposition method. CH 3 NH 2  (methylamine) and an iodine (I) precursor  15  are supplied on the PbI x  (1≤x≤2) thin film  14 . Then, a heat treatment is conducted to form a CH 3 NH 3 PbI 3  thin film  16  having a perovskite structure. 
     More specifically, the step of forming a PbI x  thin film may include using, as a lead (Pb) precursor, any one or more selected from group consisting of tetraethyl-lead, tetramethyl-lead, acetylacetonate-lead(II), and bis(2,2,6,6-tetramethyl-3,5-heptanedionate) lead(II). And, the step of forming a PbI x  thin film may include using, as an iodine (I) precursor, any one or more selected from iodine (I 2 ), 6-iodo-1-hexyne, tertiary-butyl iodide, isopropyl iodide, and ethyl iodide. 
     Further, in the step of forming a PbI x  thin film, the Pb and 
     I precursors may be supplied into a reaction chamber ( 100  of  FIG. 2 ) in simultaneous or sequential manner. 
     Further, in the step of forming a PbI x  thin film, a canister temperature for the Pb or I precursor may be maintained in the range of −20 to 100° C. The canister temperature is set in a temperature range set to form a vapor pressure appropriate for the smooth supply of the precursor into the reaction chamber. If the temperature is out of this temperature range, the efficiency of forming vapor pressure may decrease proportionally to the extent of deviation. 
     Further, in the step of forming a PbI x  thin film, the temperature of a precursor supply line for supplying the Pb or I precursor may be maintained in the range from the room temperature to 200° C. 
     Further, in the step of forming a PbI x  thin film, the temperature of a substrate for the Pb or I precursor deposited thereon may be maintained in the range of 50 to 300° C. 
     Further, the step of forming a PbI x  thin film may include using a carrier gas in supplying the Pb or I precursor into the reaction chamber, where the carrier gas may be any one of argon (Ar), helium (He) and nitrogen (N 2 ), or a mixture thereof. 
     Further, in the step of forming a PbI x  thin film, the internal pressure of the reaction chamber may be maintained in the range of 1 mTorr to 100 Torr. 
     Further, in the step of forming a PbI x  thin film, plasma may be used to increase the deposition rate and quality of the thin film. 
     Subsequently, in the supplying step, the temperature of a supply line of the MA (methylamine, CH 3 NH 2 ) and the iodine precursor may be maintained in the range from the room temperature to 200° C. 
     Further, in the supplying step, the temperature of a substrate for the MA (methylamine, CH 3 NH 2 ) and the iodine (I) precursor supplied thereto in the range from the room temperature to 250° C. 
     Subsequently, in the step of forming a CH 3 NH 3 PbI 3  thin film, a heat treatment may be conducted at a temperature of 100 to 300° C. on the CH 3 NH 3 PbI 3  thin film deposited through the supplying step. 
     Further, in the step of forming a CH 3 NH 3 PbI 3  thin film, a heat treatment may be conducted under vacuum or in an atmosphere of one or more gases of argon (Ar), nitrogen (N 2 ), hydrogen (H z ), and helium (He). 
     On the other hand, a fluorine-doped tin oxide (FTO) thin film  12  and a titanium dioxide (TiO 2 ) thin film  13  may be sequentially deposited between the substrate  11  and the PbI x  thin film  14 . The substrate  11  may be made of glass, plastic, or the like. 
       FIG. 2  is an illustrative diagram of a chemical vapor deposition (CVD) reaction chamber capable of being used in the method for preparing a perovskite solar cell light absorption layer as shown in  FIG. 1 . 
     Referring to  FIG. 2 , a chemical vapor deposition reaction chamber  100  according to this embodiment may be operated to manufacture a solar cell light absorption layer in an internal vacuum atmosphere  110 , that is, forming a PbI x  thin film by means of the chemical vapor deposition method on a substrate placed on a support  30 , supplying methylamine and an iodine precursor for deposition on the PbI x  thin film and then forming a CH 3 NH 3 PbI 3  thin film through a heat treatment under defined temperature and pressure conditions or in a gas atmosphere. 
     According to the above-described embodiment, the FTO thin film  12  and the TiO 2  thin film  13  are sequentially deposited on the substrate  11 , and the Pb and I precursors are then simultaneously or sequentially supplied into the reaction chamber  100  by the chemical vapor deposition (CVD) method to form the PbI x  thin film on the TiO 2  thin film  13 . Then, methylamine and the iodine precursor  15  are supplied on the PbI x  thin film  14 , and a heat treatment is conducted to form the CH 3 NH 3 PbI 3  thin film  16  having a perovskite structure. 
     Further, a light absorption layer formed by the above-described preparation process is used to provide a thin film solar cell with large area and high efficiency relative to the conventional solar cells. 
       FIG. 3 a    shows the surface of the PbI x  thin film deposited on the TiO 2  thin film by means of the CVD method according to this embodiment. 
     As can be seen from  FIG. 3 a   , according to the present invention, the PbI x  thin film was obtained to have a very dense surface. 
       FIG. 3 b    shows the cross section of the PbI x  thin film deposited on the TiO 2  thin film by the CVD method according to this embodiment. 
     As can be seen from  FIG. 3 b   , according to this embodiment, the crystal structure of the PbI x  thin film deposited by the CVD method was relatively uniform with respect to that of the conventional thin film. 
       FIG. 4 a    shows the surface of a metal electrode deposited after forming the CH 3 NH 3 PbI 3  thin film by supplying MA (methylamine) and an iodine (I) precursor on the PbI x  thin film deposited by the CVD method. 
     As can be seen from  FIG. 4 a   , according to this embodiment, the underlying thin film, i.e., the CH 3 NH 3 PbI 3  thin film was very uniform, so the overlying thin film, i.e., the metal electrode also had a uniform surface. The metal electrode thin film used gold (Au). 
       FIG. 4 b    shows the cross section of a metal electrode deposited after forming a CH 3 NH 3 PbI 3  thin film by supplying MA (methylamine) and an iodine (I) precursor on the PbI x  thin film deposited by the CVD method. 
     As can be seen from  FIG. 4 b   , according to this embodiment, the 
     CH 3 NH 3 PbI 3  thin film formed by supplying MA (methylamine) and the iodine (I) precursor on the PbI x  thin film was also a highly dense and uniform thin film. 
       FIG. 5  presents a deep analysis of the CH 3 NH 3 PbI 3  thin film manufactured by the method of this embodiment using AES (Auger Electron Spectroscopy). 
     As can be seen from  FIG. 5 , peaks for Pb and I on the TiO 2 thin film appeared almost at the same positions according to the measurements of the atomic concentration in function of the sputter time, claiming that the CH 3 NH 3 PbI 3  thin film was normally manufactured by the CVD method according to this embodiment. 
       FIG. 6  presents the measurements of the energy conversion efficiency of the CH 3 NH 3 PbI 3  thin film manufactured by the CVD method according to the present invention. 
     As can be seen from  FIG. 6 , the perovskite thin film solar cell manufactured by the CVD method according to this embodiment had an energy conversion efficiency of 15.2%. 
     In other words, the fill factor, corresponding to a value obtained by dividing the power at the maximum power point by the product of the open-circuit voltage (V oc ) and the short-circuit current (I sc ), was calculated as 62.1%. The heat value (J sc ) at the maximum power point was 25.9 mA/cm 2 . And, the size of the specimen used in this embodiment was 2 mm×4 mm. 
     As described above, the aforementioned embodiment of the present invention facilitates the implementation of large-area solar cells, minimizes an issue of deterioration in efficiency over time after the preparation of solar cells, enables the substantial use of the CVD equipment generally available for the preparation of semiconductors, liquid crystal displays (LCDs), or the like, and provides a preparation method for perovskite solar cells with high efficiency relative to the related art. 
     Although the foregoing description of the present invention has been presented with reference to the examples of the present invention, it may be apparent to those skilled in the art that many modifications and variations can be made to the present invention without departing from the spirits and scope of the present invention disclosed in the following claims and that the scope of the claims of the present invention includes such modifications and variations belonging to the principles of the present invention.