Lithium alloy for vacuum deposition, method for manufacturing lithium alloy for vacuum deposition, method for manufacturing lithium thin film for photoelectric device, and photoelectric device comprising lithium thin film manufactured based on same

Abstract

The present invention provides a lithium alloy for vacuum deposition comprising more than 23 wt% and less than 91 wt% of lithium (Li) and other unavoidable impurities, a method for manufacturing the lithium alloy for vacuum deposition, a method for manufacturing a lithium thin film for a photoelectric device, and a photoelectric device comprising the lithium thin film manufactured on the basis of the method, the lithium alloy for vacuum deposition comprising more than 23 wt% and less than 91 wt% of lithium (Li) and other unavoidable impurities, and at least a Li3Bi phase and a lithium phase.

Description

Technical Field

[0001] The present invention relates to a lithium alloy for vacuum deposition, a method for manufacturing a lithium alloy for vacuum deposition, a method for manufacturing a lithium thin film for optoelectronic devices, and an optoelectronic device including the lithium thin film manufactured based thereon. Background Art

[0002] An optoelectronic device, in a broad sense, refers to a component that converts light energy into electrical energy or converts electrical energy into light energy. Examples of the optoelectronic device include an organic light emitting device (OLED; Organic Light Emitting Diodes), a solar cell, a transistor, etc. Regarding an optoelectronic device such as an OLED having a tandem structure, research shows that when lithium (Li) is added to a charge generation layer (CGL; Charge Generation Layer) or an electron injection layer (EIL, Electron Injection Layer) of the optoelectronic device, high luminous characteristics can be achieved even at a low current density, thereby improving the lifespan of the component.

[0003] The lithium thin film used in an optoelectronic device can be formed based on a thermal vacuum deposition method. Figure 2 An example of a thermal vacuum deposition apparatus for forming a lithium thin film for an optoelectronic device is shown.

[0004] Refer to Figure 2 , the thermal vacuum deposition apparatus includes a vacuum deposition chamber (10) for performing thermal vacuum deposition. The inside of the vacuum deposition chamber (10) is maintained in a vacuum state by a vacuum pump (not shown). An evaporation source container (12) and a substrate holder (11) are arranged inside the vacuum deposition chamber (10). The evaporation source container (12) houses an evaporation source (20), and a substrate (S) is mounted on the substrate holder (11), and a lithium thin film (30) is formed on the substrate (S).

[0005] After the evaporation source (20) is heated and melted by various heat sources in the evaporation source container (12), it is introduced onto one side of the substrate (S) in a gaseous state after evaporation, and a lithium thin film (30) is formed on one side of the substrate (S).

[0006] When the thermal vacuum deposition method uses pure lithium metal as the evaporation source, due to the high activity of pure lithium, there is a high risk of explosion or fire during the deposition preparation or preheating process, and the risk level becomes high. In addition, since the thermal vacuum deposition apparatus needs to be manufactured as an explosion-proof type, there is a problem that the equipment manufacturing cost increases significantly.

[0007] For pure lithium, during the preparation for deposition, its surface is exposed to the atmosphere and rapid oxidation or nitridation occurs, forming a relatively thick surface film composed of compounds (such as Li2O, LiOH, Li3N, etc.). When Li3N (lithium nitride) formed on the surface of lithium encounters moisture, ammonia gas is generated while it is converted to LiOH (lithium hydroxide). The melting points of LiOH and Li2O (lithum oxide) formed on the surface are 462°C and 1438°C respectively, which are relatively high and cannot be used as an evaporation source for lithium. Therefore, if most of the surface is oxidized or nitrided, it will be very difficult to vaporize and deposit the pure lithium existing in the lower part of the surface. In order to melt and evaporate lithium, the heating temperature can be raised to above 500°C to evaporate lithium, but as the heating temperature of lithium increases, the characteristics of the formed electronic components are prone to deterioration problems, making it very difficult to apply.

[0008] To solve the above problems, although mineral oil or hydrocarbons can be used to coat the surface of lithium (Li) metal to inhibit the formation of an oxide layer / nitride layer on the surface, when it is used for the thermal vacuum deposition of optoelectronic devices, it is very difficult to completely remove organic substances such as mineral oil before use. If the remaining organic components volatilize, the lithium deposition device will be contaminated, causing various problems. Summary of the Invention

[0009] Technical Problem

[0010] The present invention is proposed to solve the existing problems as described above, aiming to provide a lithium alloy for vacuum deposition that alleviates oxidation and nitridation on the surface without using organic substances such as mineral oil, selectively evaporates only lithium during heating, and forms a lithium thin film on a substrate, and a manufacturing method thereof. In addition, it aims to provide a method for forming a lithium thin film for optoelectronic devices using such a lithium alloy for vacuum deposition, and an optoelectronic device including such a lithium thin film. However, these technical problems are only exemplary and are not used to limit the scope of the present invention.

[0011] Means for Solving the Problem

[0012] According to one aspect of the present invention, a lithium alloy for vacuum deposition is provided.

[0013] The lithium alloy for vacuum deposition is composed of bismuth (Bi) greater than 23 wt% and less than 91 wt%, and the balance is lithium (Li) and other inevitable impurities, and at least includes a Li3Bi phase and a lithium phase.

[0014] According to an embodiment, the bismuth (Bi) may be in the range of 50 wt% to 70 wt%.

[0015] According to one embodiment, the Li3Bi phase may account for a range of 10 wt% to 84 wt% based on the total weight of the lithium alloy for vacuum deposition.

[0016] According to one embodiment, the Li3Bi phase may account for a range of 39 wt% to 70 wt% based on the total weight of the lithium alloy for deposition.

[0017] According to one embodiment, when the lithium alloy is melted in a vacuum environment in a range greater than or equal to the melting point of lithium and less than the melting point of the Li3Bi phase, lithium can be selectively vaporized only.

[0018] According to another aspect of the present invention, there is provided a method for manufacturing a lithium alloy for vacuum deposition.

[0019] The method for manufacturing the lithium alloy for vacuum deposition may include the following steps: (a) forming a metal solution, the metal solution being formed by melting bismuth (Bi) of more than 23 wt% and less than 91 wt% and the balance being lithium (Li) and other inevitable impurities; and (b) after maintaining the metal solution at a temperature in a completely liquefied state, quenching and performing lithium alloy casting.

[0020] According to one embodiment, the quenching may include the step of pouring the metal solution into a mold maintained at a temperature less than or equal to 25 °C and cooling it.

[0021] According to one embodiment, the bismuth (Bi) may account for a range of 50 to 70 wt%.

[0022] According to one embodiment, after the step (b), the following step may be further performed: (c) pre-treating the lithium alloy manufactured in the step (b) in an argon (Ar) environment for a predetermined time.

[0023] According to one embodiment, the step (c) may be performed in an environmental chamber including a glove box.

[0024] According to another aspect of the present invention, there is provided a method for manufacturing a lithium thin film for optoelectronic devices.

[0025] The method for manufacturing the lithium thin film for optoelectronic devices may include the following steps: heating the lithium alloy for vacuum deposition in a chamber in a vacuum environment, selectively evaporating lithium to form a lithium thin film on at least one surface of a substrate, wherein the lithium alloy for vacuum deposition is composed of bismuth (Bi) of more than 23 wt% and less than 91 wt% and the balance being lithium (Li) and other inevitable impurities, and includes at least a Li3Bi phase and a lithium phase.

[0026] According to one embodiment, in the step of forming the lithium thin film, the heating temperature of the lithium alloy for vacuum deposition may be in a temperature range greater than the melting point of lithium and less than the melting point of the Li3Bi phase.

[0027] According to one embodiment, the temperature may be in the range of 200°C to 500°C.

[0028] According to one embodiment, the temperature may be in a temperature range less than or equal to the sublimation temperature of lithium.

[0029] According to one embodiment, before the step of forming the lithium thin film in the chamber of the vacuum environment, a pretreatment step of maintaining the lithium alloy for vacuum deposition in an argon (Ar) environment for a predetermined time may be first performed.

[0030] According to one embodiment, the vacuum environment may be maintained at a vacuum degree of 10 -8 to 10 -7 Torr.

[0031] According to another aspect of the present invention, an optoelectronic device is provided.

[0032] The optoelectronic device may include: an anode and a cathode, formed to face each other on a substrate; and a charge generation layer, an electron injection layer, and an electron transport layer, formed between the anode and the cathode; at least any one of the cathode, the charge generation layer, and the electron injection layer includes a lithium thin film formed based on the manufacturing method of the lithium thin film for the optoelectronic device.

[0033] According to one embodiment, the optoelectronic device may be selected from the group consisting of an organic light emitting device, a solar cell, and a transistor.

[0034] Advantageous Effects of the Invention

[0035] When using the lithium alloy for vacuum deposition based on the technical idea of the present invention, compared with pure lithium, it is possible to suppress the formation of films such as an oxide film or a nitride film on the surface, and there is no need to perform coating like pure lithium to suppress the formation of the film, thereby preventing contamination of components caused by coating during the deposition process, and improving the performance of the optoelectronic device including the lithium thin film. Of course, the above effects do not limit the scope of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is the binary phase equilibrium diagram of lithium (Li) and bismuth (Bi).

[0037] Figure 2 is a schematic diagram schematically illustrating the process of forming a lithium thin film according to an embodiment of the present invention.

[0038] Figure 3 is a cross-sectional view of the laminated structure of an organic light emitting device according to an embodiment of the present invention.

[0039] Figure 4 It shows the XRD analysis results of the lithium alloy composition manufactured according to the experimental examples of the present invention. Detailed implementation manners

[0040] Hereinafter, each preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. The embodiments of the present invention are used to more completely illustrate the present invention to those skilled in the art to which the present invention pertains. The following embodiments can be deformed into various other forms, and the scope of the present invention is not limited to the following embodiments. These embodiments can make the present disclosure more fully complete and convey the spirit of the present invention more completely to those skilled in the art to which the present invention pertains. Also, in the following drawings, the thickness or size of each layer is enlarged for easy illustration and clear description.

[0041] In the present invention, as an example of an alkali metal, lithium (Li) may be replaced with sodium (Na), potassium (K), rubidium (Rb), or cesium (Cs), but here mainly lithium (Li) will be taken as an example for description.

[0042] In addition, as a low-melting metal with a melting point of 500 °C or lower, bismuth (Bi) may be replaced with thallium (Tl), lead (Pb), bismuth (Bi), or polonium (Po) metal. Here, mainly bismuth (Bi) will be taken as an example for description.

[0043] Hereinafter, a method for manufacturing a lithium alloy for vacuum deposition according to an embodiment of the present invention and a lithium alloy for vacuum deposition manufactured based thereon will be described.

[0044] The method for manufacturing a lithium alloy for vacuum deposition according to an embodiment of the present invention includes the following steps: a step (S100) of melting bismuth (Bi) in an amount greater than 23 wt% and less than 91 wt% by weight percentage and the balance being lithium (Li) and other inevitable impurities to form a metal solution; and a step (S200) of maintaining the metal solution at a temperature at which it can completely become a liquid state, followed by quenching and casting the lithium alloy.

[0045] In step (S100), lithium and bismuth are placed in a crucible and heated and melted to manufacture a metal solution. In the metal solution, for example, bismuth accounts for a range greater than 23 wt% and less than 91 wt%, and the balance is lithium and inevitable impurities. Preferably, the bismuth may account for a range of 50 to 90 wt%, or may account for a range of 50 to 70 wt%.

[0046] When the amount of lithium is excessive, due to the increased reactivity of lithium, there are problems with stability, which is not very ideal from the aspects of environmental safety and commercialization. On the contrary, when the amount of lithium is too small, problems such as a reduction in the amount of available material due to oxidation and a reduction in manufacturing time due to the limitation of continuous deposition time occur.

[0047] To prevent the reaction between lithium and oxygen during the manufacturing process of the metal solution, the manufacturing of the metal solution can be carried out in an inert environment or a vacuum environment.

[0048] Bismuth (Bi) can form an intermetallic compound with lithium (Li) as an alloying element. Figure 1 The lithium-bismuth binary phase equilibrium diagram is illustrated.

[0049] Refer to Figure 1 , if the added bismuth exceeds 23 wt%, the intermetallic compound, i.e., the Li3Bi phase, is formed. The melting point of Li3Bi is about 1145 °C, which is very high compared to pure lithium or bismuth. To maintain the metal solution in a completely molten state in the crucible, a temperature higher than the melting point of Li3Bi needs to be maintained.

[0050] In step (S200), the temperature of the metal solution is maintained at a temperature above 1145 °C, i.e., the temperature condition at which the Li3Bi phase is completely molten, and then the metal solution is poured into a mold and cooled to perform lithium alloy casting. At this time, the cooling process may include a quenching treatment. Quenching may include the step of pouring the metal solution into a mold for cooling, and the mold can be cooled to a temperature below 25 °C and maintained based on a cooling medium. For example, the metal solution can be poured into a metal mold cooled by cooling water below 10 °C and quenched.

[0051] By mixing lithium (Li) with a very low specific gravity of 0.534 g / cm 3 and bismuth (Bi) with a relatively high specific gravity of 9.78 g / cm 3 , during melting, due to the above-mentioned specific gravity difference, the possibility of phase separation is relatively high. Therefore, to minimize this phase separation, a rapid cooling casting process is preferably adopted. In addition, through this quenching treatment, the Li3Bi phase formed in the lithium alloy can be refined, and the refinement of the Li3Bi phase in this lithium alloy can enable lithium to evaporate uniformly during the deposition process using the lithium alloy. A detailed description related to this will be given later.

[0052] In the casting step, the upper limit of the maintenance temperature of the metal solution is preferably 1200 °C. When it exceeds 1200 °C, it will lead to an increase in unnecessary energy costs, and too high a temperature will increase the possibility of impurities mixing into the crucible, etc.

[0053] In the casting step, the molten metal solution poured into the mold solidifies from the liquid phase to the solid phase, and finally a lithium-bismuth binary alloy is cast.

[0054] The lithium alloy comprises more than 23 wt% and less than 91 wt% of bismuth (Bi), and the balance is lithium (Li) and other inevitable impurities. In addition, the lithium alloy comprises at least Li3Bi phase and lithium phase.

[0055] Referring to Figure 1 , if the molten metal solution maintained at a temperature condition above 1145 °C, which is the temperature condition for completely melting the Li3Bi phase, is cast, then after solidification is completed, the final lithium alloy has a microstructure in which at least the Li3Bi phase and the lithium phase are mixed.

[0056] Table 1 below is calculated with reference to Figure 1 the phase equilibrium diagram, and is the weight percentage of the Li3Bi phase in the lithium alloy formed during the casting process of the lithium alloy according to the mixing ratio of lithium (Li) and bismuth (Bi) in the molten metal solution.

[0057] [Table 1]

[0058]

[0059]

[0060] Referring to Figure 1 and Table 1, when the mixing ratio of the added bismuth exceeds 23 wt%, the Li3Bi phase is formed. As the mixing ratio of bismuth gradually increases, the proportion of the Li3Bi phase formed in the lithium alloy increases. When it reaches 90.9 wt%, the Li3Bi phase in the alloy reaches 100%. When the mixing ratio of bismuth is more than 23 wt% and less than 90.9 wt%, the mixing ratio of lithium is more than 9.1 wt% and less than 77 wt%. At this time, compared with the stoichiometric ratio for forming the Li3Bi phase, the lithium phase is an excessive reactant input. Therefore, according to the mixing ratio of the present invention, it can be determined that at least the lithium phase and the Li3Bi phase are mixed in the manufactured lithium alloy.

[0061] Furthermore, for the lithium alloy according to an embodiment of the present invention, in order to manufacture a lithium thin film, before being introduced into the vacuum deposition chamber, a pretreatment can be carried out in a glove box in an inert environment for a predetermined time. The inert environment includes an argon (Ar) environment. For example, after the glove box is replaced with an argon environment, it is maintained in the glove box for 1 to 100 hours and the pretreatment is carried out. In the pretreatment step in the argon environment, the step of cutting the lithium alloy into products or packaging the products according to the required form can also be carried out simultaneously.

[0062] Generally, before placing the lithium alloy inside the vacuum deposition chamber, for preparatory work, it needs to go through a process of being placed in the atmosphere for a predetermined time. For example, after taking out the lithium alloy used in vacuum deposition from the packaging paper and putting it into a loader, it is then transferred to the vacuum deposition chamber. During this process, the lithium alloy must be placed in the atmosphere with a humidity of 30% to 40% for a certain period of time. During the placement in the atmosphere, an oxide film or a nitride film may form on the surface of the lithium alloy, which will cause deterioration of the deposition characteristics.

[0063] In contrast, compared with the lithium alloy that is directly put into the vacuum deposition chamber without such pretreatment, the lithium alloy pretreated as described above can minimize the influence caused by oxidation or nitridation of the lithium alloy, thereby improving the deposition characteristics of lithium. Specifically, if the pretreatment is carried out in an inert environment as described above, after the pretreatment is completed, when the lithium alloy is transferred to the vacuum deposition chamber and installed for forming a lithium thin film, even if the lithium alloy is exposed to the atmosphere, the oxide film or nitride film will be generated on the surface of the lithium alloy at a slower rate, and the generated film will be formed with a thinner thickness.

[0064] The lithium alloy for vacuum deposition according to an embodiment of the present invention is accommodated in an evaporation source container in the vacuum chamber during the deposition process and heated and melted to selectively evaporate or vaporize only lithium. At this time, the heating will be carried out in a temperature range greater than or equal to the melting point of lithium and less than the melting point of the Li3Bi phase. For example, the heating temperature of the lithium alloy is in the range of 200°C to 500°C, and the vacuum degree can be a high vacuum less than 5x10 -8 torr. Lithium melts at about 180°C, and starts to rapidly evaporate if the temperature is higher than this.

[0065] In the lithium alloy serving as an evaporation source under the deposition conditions, lithium starts to melt, but the melting point of the Li3Bi phase is relatively high, being 1145°C, and it cannot be evaporated under the said conditions, cannot participate in the deposition and remains in the solid phase. That is, the lithium alloy melted in the evaporation source container is at least in a state where the liquid-phase lithium and the Li3Bi phase existing in the solid phase in the liquid phase are mixed with each other. Therefore, only the liquid-phase lithium is evaporated in the vacuum environment, and a lithium thin film is formed on the substrate. If the lithium in the lithium alloy has evaporated and is all consumed, the Li3Bi phase in the evaporation source container can remain as a residue.

[0066] Therefore, although the lithium alloy in the present invention is a lithium-bismuth binary alloy, it can actually be a lithium evaporation source that selectively evaporates only lithium.

[0067] As Figure 1As shown in the state diagram, when the added bismuth is less than 23 wt%, the Li3Bi phase cannot be formed, and the effects of the present invention cannot be expected. In addition, referring to Table 1, as the added bismuth is greater than 23 wt%, the amount of available lithium in the lithium alloy decreases. If the added amount is greater than or equal to 90.9 wt%, then 100% of the lithium is used to form the Li3Bi phase, and the lithium for deposition will no longer exist. Therefore, the added amount of bismuth should be greater than 23 wt% and less than 90.9 wt%.

[0068] The lithium alloy for vacuum deposition according to an embodiment of the present invention includes a Li3Bi phase that is weakly reactive with oxygen or nitrogen. Therefore, compared with pure lithium, it has excellent oxidation resistance or nitridation resistance, so that the oxidation or nitridation rate becomes slower, and the deposition efficiency is increased. Moreover, by reducing the risk of explosion or ignition, the deposition equipment does not need to be made explosion-proof, thus having the advantage of cost savings.

[0069] In the casting step of the lithium alloy, since the metal solution will be rapidly cooled when solidifying, the size of the Li3Bi phase in the lithium alloy can be refined. If the Li3Bi phase in the lithium alloy is refined as described above, the lithium evaporation can proceed more uniformly in the deposition step using the lithium alloy. Therefore, the thickness of the lithium thin film deposited on the substrate is more uniform.

[0070] When the lithium alloy is in a molten state in the evaporation source container, there is a non-volatile Li3Bi phase in the liquid-phase lithium. Therefore, the size of the Li3Bi phase is thick and irregular, and the lithium in the liquid-phase lithium will also evaporate irregularly to a corresponding extent. Generally, if rapid cooling is used for solidification in the casting step, the phases generated during the solidification process are refined. Therefore, the lithium alloy according to an embodiment of the present invention can refine the generated Li3Bi phase by rapid cooling during casting, so that the lithium evaporation proceeds more uniformly.

[0071] A lithium thin film for optoelectronic devices can be manufactured using the lithium alloy according to an embodiment of the present invention.

[0072] In the present invention, the lithium thin film refers to a thin film added with lithium, which refers to a single metal thin film formed only by lithium, or a thin film formed by adding lithium to an organic substance, or a thin film formed by mixing lithium with other metals.

[0073] For example, for the charge generation layer (CGL) of optoelectronic devices, a lithium thin film is formed by adding lithium to an organic substance. For the cathode layer, a lithium thin film can be formed by simultaneously performing thermal vacuum deposition on a silver (Ag) - lithium alloy.

[0074] Refer again to Figure 2 , according to an embodiment of the present invention, the formation process of the lithium thin film for optoelectronic devices will be briefly described.

[0075] Reference Figure 2 After accommodating the lithium alloy, which serves as the evaporation source 20, in the evaporation source container 12 and mounting the substrate on the substrate holder 11, the inside of the vacuum deposition chamber 10 is maintained in a vacuum state using a vacuum pump (not shown). The degree of vacuum ranges from 10 -8 to 10 -3 Torr, and for example, it can be in the range of 10 -8 to 10 -7 Torr. In order to form an optoelectronic device, various layers required to achieve an optoelectronic effect can be formed on one surface of the substrate.

[0076] The evaporation source 20, that is, the lithium alloy, accommodated inside the evaporation source container 12 is heated. Among them, the heating temperature is greater than the melting point of lithium and less than the melting point of the Li3Bi phase, which is 1145°C. For example, it is heated at a temperature of 200°C to 500°C.

[0077] Since the melting point of the Li3Bi phase is greater than the heating temperature, it remains in a solid state. On the contrary, the melting temperature of lithium metal is relatively low, which is 180.54°C. Therefore, the lithium metal is heated and evaporated, and scatters toward the substrate S inside the vacuum deposition chamber 10, and adheres (deposits) on the surface of the substrate S to form a lithium thin film 30. The deposition rate can be appropriately selected within the range of 0.01 to 100 / sec. Figure 3 is a cross-sectional view of a stacked structure of an organic light-emitting device according to an embodiment of the present invention.

[0078] As Figure 3 shown, the light-emitting device according to an embodiment of the present invention includes an anode 101 and a cathode 140 that are formed to face each other on a substrate 100, and a first stack 1101, a charge generation layer (CGL) 120, and a second stack 1301 that are stacked between the anode 101 and the cathode 140.

[0079] Among them, the cathode 140 can use a lithium thin film manufactured according to an embodiment of the present invention. Since lithium has a low work function, it can be used as a material that can reduce the potential barrier formed at the interface of the cathode 140. If a lithium thin film is manufactured using a lithium alloy manufactured according to an embodiment of the present invention, it is more advantageous in terms of processability and stability due to the reduced reactivity.

[0080] In the first stack 210, a hole injection layer 103, a first hole transport layer 105, a first light-emitting layer 110, and a first electron transport layer 111 are sequentially stacked between the anode 101 and the charge generation layer 120. In the second stack 220, a second hole transport layer 125, a second light-emitting layer 130, a second electron transport layer 133, and an electron injection layer (EIL) 135 are sequentially stacked between the charge generation layer 120 and the cathode 140. Among them, an electron injection layer and a hole injection layer can also be respectively provided at the lower and upper portions of the charge generation layer 120.

[0081] The charge generation layer 120 between the first stack 210 and the second stack 220 is formed between the stacks to uniformly adjust the charge between the stacks. Such a charge generation layer 120 can be made of a material with low light loss and electrical loss characteristics, that is, a lithium thin film manufactured according to an embodiment of the present invention.

[0082] The organic layer that the carrier injected from the cathode 140 first encounters is the electron injection layer 135, which serves to smoothly inject the charge from the cathode 140 into the second electron transport layer 133. The electron injection layer 135 plays an important role in reducing the potential barrier formed at the interface. For example, metal halides such as lithium fluoride (LiF) generate an energy level shift and reduce the potential barrier by forming an interface electric double layer with the organic layer. Lithium has a high reactivity with oxygen or moisture and is actually not easily applied in the electron injection layer. However, if the thin film is made of a lithium alloy according to an embodiment of the present invention, it can be used as the material for the electron injection layer 135 due to the reduced reactivity.

[0083] As described above, the organic light-emitting device has been used as an example. According to another embodiment of the present invention, the lithium thin film can also be applied to inorganic light-emitting devices, solar cells, transistors, etc.

[0084] Next, specific experimental examples of the present invention will be disclosed. However, the embodiments described below are for specifically exemplifying or illustrating the present invention and are not for limiting the present invention.

[0085] <Experimental Example>

[0086] 1. Experimental Example 1

[0087] Lithium and bismuth were alloyed at a weight ratio of 3:7 and exposed to the atmosphere. As shown in Table 2 below, compared with the case of using lithium alone, the formation of oxidation and nitride films of the lithium alloy is slower and thinner under the same atmospheric exposure conditions.

[0088] [Table 2]

[0089]

[0090] 2. Experimental Example 2

[0091] Lithium and lithium alloy were heated in a vacuum chamber of 5x10 -8 Torr and the sublimation temperature (or vaporization temperature) was compared. As can be seen from Table 3 below, compared with the single-component lithium alloy (Zr-Al-Li), the lithium-bismuth alloy has the same sublimation temperature as that of lithium alone because of the low melting point of bismuth in the lithium-bismuth alloy.

[0092] [Table 3]

[0093] Component Sublimation temperature (°C) Comparative Example 1 Lithium (Li) 420 Example Lithium-bismuth 420 Comparative Example 2 Unary lithium alloy 950

[0094] 3. Experimental Example 3

[0095] The lithium alloy was pretreated in a glove box under argon and nitrogen atmospheres respectively. Then the alloy was taken out and placed in the atmosphere, and the appearance of the alloy was observed for 2 hours and recorded in Table 4.

[0096] [Table 4]

[0097]

[0098]

[0099] As described above, after pretreatment in an argon atmosphere, a lithium alloy with a bright silver surface that hardly undergoes nitridation can be obtained. Furthermore, it can be confirmed that for the lithium-bismuth alloy, it has the robustness to be oxidized and nitrided after being exposed to the atmosphere for 2 hours.

[0100] 4. Experimental Example 4

[0101] According to the mixing ratio in Table 5 below, lithium and bismuth were mixed to form a metal solution. After maintaining for 1 hour at the temperature condition of 1200 °C at which the Li3Bi phase is completely melted, the metal solution was poured into a metal mold with flowing cooling water at 3 °C to 5 °C, and rapidly cooled to make a test piece. The made test piece was pretreated in a glove box under an argon (Ar) atmosphere with a moisture and oxygen content of less than 1 ppm.

[0102] After installing the said test piece in a vacuum deposition chamber, after maintaining a vacuum of 10 -8 Torr, in order to remove the film formed on the surface of the test piece, it was preheated at a temperature of about 500 °C to 550 °C. At this time, the oxide or nitride film formed on the surface of the test piece was removed in a gaseous state while the vacuum degree decreased. After all the films were removed, the vacuum degree returned to the original state, and the thickness of the lithium thin film deposited on the substrate was measured using a thickness sensor installed on the substrate. At this time, it can be confirmed that the thickness of the lithium thin film increases in units of angstroms (Å) / second. If the deposition rate of lithium reaches the required deposition rate, the deposition will officially start. Among them, Table 5 below shows the preheat-up time required until the start of lithium deposition.

[0103] In addition, in order to confirm the compositional deviation based on the mixing ratio of the cast test piece, by measuring the ratio of lithium (Li) and bismuth (Bi) components using ICP-OES (PerkinElmer, AVIO550) analysis method, the deviation from the composition design was obtained and shown in Table 5 below.

[0104] [Table 5]

[0105]

[0106]

[0107] Figure 4 This is the XRD analysis result of the test piece cast according to Example 3. Based on this, it was confirmed whether the Li3Bi phase was generated.

[0108] Refer to Figure 4 , when the content ratio of lithium (Li) and bismuth (Bi) is 50:50, it can be confirmed that it is composed of the Li3Bi phase and the Li phase. It can be confirmed that although there are differences in the XRD peak intensity according to the mixing ratio, all the test pieces are similarly composed of the Li3Bi phase and the Li phase.

[0109] Refer to Table 5. As shown in Example 1 and Example 2, when the content of bismuth (Bi) is reduced to the level of 30wt% to 40wt%, the lithium content increases relatively, and it has the advantage that the deposition thickness is greater than the target thickness. However, the preheating time required to remove the oxide / nitride film will increase. This is because although the Li3Bi intermetallic compound is relatively stable in terms of oxidation and nitridation compared to pure lithium (Li), as the proportion of the generated Li3Bi drops to the level of 10% to 25%, oxidation and nitridation will occur on the surface.

[0110] In addition, as shown in Example 6, when the addition amount of bismuth (Bi) is 80wt% and excessive, the displayed preheating time is shorter, and the composition deviation of the cast test piece is also smaller. However, it is observed that when the proportion of the generated Li3Bi intermetallic compound increases to 83.9%, the amount of lithium (Li) that can actually be vaporized becomes less, so the deposition thickness under the same deposition conditions becomes smaller.

[0111] As shown in Examples 3 to 5, when 50 to 70wt% of bismuth (Bi) is added, the composition deviation of the cast lithium alloy is not large, the preheating time for removing the film is appropriate, and the thickness deviation after deposition is also within 10%, which is relatively uniform.

[0112] According to the embodiments of the present invention realized as described above, when used as a thermal vacuum deposition material for optoelectronic devices by controlling the composition and evaporation conditions of lithium and bismuth (Bi), it is possible not to deposit the bismuth (Bi) component and selectively deposit only lithium (Li), which can shorten the preheating time for removing the oxide and nitride films before deposition, there is no pollution such as organic substances, and lithium (Li) deposition can be effectively carried out.

[0113] The present invention has been described with reference to the embodiments shown in the accompanying drawings, but this is only exemplary. For those with ordinary knowledge in the technical field, it should be understood that various modifications can be made based on this and implemented as another equivalent embodiment. Therefore, the true technical protection scope of the present invention should be determined based on the technical idea of the appended claims.

Claims

1. A lithium alloy for vacuum deposition, characterized in that, It is composed of bismuth (Bi) greater than 23 wt% and less than 91 wt% and the balance being lithium (Li) and other inevitable impurities, and at least includes the Li3Bi phase and the lithium phase.

2. The lithium alloy for vacuum deposition according to claim 1, wherein, The bismuth (Bi) ranges from 50 wt% to 70 wt%.

3. The lithium alloy for vacuum deposition according to claim 1, characterized in that, The Li3Bi phase ranges from 10 wt% to 84 wt% relative to the total weight of the lithium alloy for vacuum deposition.

4. The lithium alloy for vacuum deposition according to claim 3, characterized in that, The Li3Bi phase ranges from 39 wt% to 70 wt% relative to the total weight of the deposition lithium alloy.

5. The lithium alloy for vacuum deposition according to claim 1, wherein When the lithium alloy is melted in a vacuum environment in the range greater than or equal to the melting point of lithium and less than the melting point of the Li3Bi phase, lithium is selectively vaporized only.

6. A method for manufacturing a lithium alloy for vacuum deposition, comprising the following steps: (a) Forming a metal solution, which is formed by melting bismuth (Bi) greater than 23 wt% and less than 91 wt% and the balance being lithium (Li) and other inevitable impurities; And (b) After maintaining the metal solution at a temperature at which it can be completely liquefied, quenching and casting the lithium alloy.

7. The manufacturing method of the lithium alloy for vacuum deposition according to claim 6, characterized in that, The quenching includes the step of putting the metal solution into a mold maintained at a temperature less than or equal to 25 °C and cooling it.

8. The manufacturing method of the lithium alloy for vacuum deposition according to claim 6, characterized in that, The bismuth (Bi) ranges from 50 to 70 wt%.

9. The manufacturing method of the lithium alloy for vacuum deposition according to claim 6, characterized in that, After the step (b), the following step is further performed: (c) Pre-treating the lithium alloy manufactured in the step (b) in an argon (Ar) environment for a predetermined time.

10. The method for manufacturing a lithium alloy for vacuum deposition according to claim 9, characterized in that, The step (c) is carried out in an environmental chamber including a glove box.

11. A method for manufacturing a lithium thin film for optoelectronic devices, comprising the following steps: Heating a lithium alloy for vacuum deposition in a chamber in a vacuum environment, selectively depositing lithium to form a lithium thin film on at least one surface of a substrate, The lithium alloy for vacuum deposition is composed of bismuth (Bi) greater than 23 wt% and less than 91 wt% and the balance being lithium (Li) and other inevitable impurities, and at least includes the Li3Bi phase and the lithium phase.

12. The manufacturing method of the lithium thin film for optoelectronic devices according to claim 11, characterized in that, In the lithium thin film forming step, the heating temperature of the lithium alloy for vacuum deposition is in the temperature range greater than the melting point of lithium and less than the melting point of the Li3Bi phase.

13. The manufacturing method of the lithium thin film for optoelectronic devices according to claim 12, characterized in that, The temperature ranges from 200 °C to 500 °C.

14. The manufacturing method of the lithium thin film for optoelectronic devices according to claim 12, characterized in that, The temperature is in the temperature range less than or equal to the sublimation temperature of lithium.

15. The manufacturing method of the lithium thin film for optoelectronic devices according to claim 11, characterized in that, Before the step of forming the lithium thin film in the chamber in the vacuum environment, a pre-treatment step of maintaining the lithium alloy for vacuum deposition in an argon (Ar) environment for a predetermined time is first carried out.

16. The manufacturing method of the lithium thin film for optoelectronic devices according to claim 11, characterized in that, The vacuum environment is maintained at a vacuum degree of 10 -8 to 10 -7 Torr.

17. An optoelectronic device, comprising: An anode and a cathode, formed facing each other on a substrate; And A charge generation layer, an electron injection layer and an electron transport layer, formed between the anode and the cathode, At least any one of the cathode, the charge generation layer and the electron injection layer includes a lithium thin film formed as described in any one of claims 11 to 16.

18. The optoelectronic device according to claim 17, characterized in that, The optoelectronic device is selected from the group consisting of an organic light emitting device, a solar cell and a transistor.

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