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 including lithium thin film manufactured by the method

Abstract

The present invention provides a lithium alloy for vacuum deposition, which contains more than 23 wt% and less than 91 wt% bismuth (Bi), and the remainder lithium (Li) and other unavoidable impurities, and which contains at least a LiBi phase and a lithium phase; a method for producing the lithium alloy for vacuum deposition; a method for producing a lithium thin film for a photoelectric element; and a photoelectric element including the lithium thin film produced thereby.

Description

[Technical Field]

[0001] The present invention relates to a lithium alloy for vacuum deposition, 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 including the lithium thin film manufactured thereby. [Background technology]

[0002] A photoelectric device is, in a broad sense, a device that converts light energy into electrical energy or electrical energy into light energy. Examples of photoelectric devices include organic light-emitting diodes (OLEDs), solar cells, and transistors. It is known that when lithium (Li) is added to the charge generation layer (CGL) or electron injection layer (EIL) of a photoelectric device such as an OLED having a tandem structure, high light-emitting characteristics can be realized even at low current densities, and the device life can be improved.

[0003] The lithium thin film used in the photovoltaic device can be formed by thermal vacuum deposition. Figure 2 shows an example of a thermal vacuum deposition apparatus for forming the lithium thin film for the photovoltaic device.

[0004] 2, the thermal vacuum deposition apparatus includes a vacuum deposition chamber 10 where thermal vacuum deposition is performed. The interior of the vacuum deposition chamber 10 is maintained in a vacuum state using a vacuum pump (not shown). The interior of the vacuum deposition chamber 10 is configured to include an evaporation source container 12 and a substrate holder 11. The evaporation source container 12 accommodates an evaporation source 20, and the substrate holder 11 is fitted with a substrate S on which a lithium thin film 30 is to be formed.

[0005] The evaporation source 20 is heated by various heat sources in the evaporation source container 12 to melt, and then evaporated to be injected in a gaseous state onto one surface of the substrate S, thereby forming a lithium thin film 30 on one surface of the substrate S.

[0006] When pure lithium metal is used as the evaporation source for thermal vacuum deposition, the high activity of pure lithium poses a high risk of explosion or fire during the waiting or preheating process for deposition, making it a hazardous material. In addition, the thermal vacuum deposition equipment must be manufactured to be explosion-proof, which significantly increases the cost of manufacturing the equipment.

[0007] When pure lithium is exposed to the atmosphere during the deposition preparation process, its surface undergoes rapid oxidation or nitridation, forming a thick surface film composed of compounds (Li2O, LiOH, Li3N, etc.). When exposed to moisture, Li3N (lithium nitride) formed on the lithium surface can convert to LiOH (lithium hydroxide), generating ammonia gas. LiOH and Li2O (lithium oxide) formed on the surface have high melting points of 462°C and 1438°C, respectively, making them unusable as lithium evaporation sources. Therefore, if the surface is mostly oxidized or nitrided, it becomes very difficult to vaporize and deposit the pure lithium present below the surface. While lithium deposition can be achieved by heating the lithium to melt and evaporate it at temperatures above 500°C, this method is difficult to apply because the increased heating temperature of lithium leads to degradation of the performance of the resulting electronic device.

[0008] To solve this problem, the surface of lithium (Li) metal can be coated with mineral oil or hydrocarbon compounds to prevent the formation of an oxide layer / nitride layer on the surface. However, when this is used for thermal vacuum deposition of photoelectric devices, it is difficult to completely remove organic substances such as mineral oil before use, and if the remaining organic components volatilize, they can contaminate the device on which the lithium is deposited, causing various problems. Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention has been made to solve these problems, and aims to provide a lithium alloy for vacuum deposition that can reduce surface oxidation and nitridation without using organic substances such as mineral oil, and that can selectively evaporate only lithium upon heating to form a lithium thin film on a substrate, and a method for manufacturing the same. Another aim is to provide a method for forming a lithium thin film for a photoelectric device using the lithium alloy for vacuum deposition, and a photoelectric device including the lithium thin film. However, these problems are merely examples, and the scope of the present invention is not limited thereto. [Means for solving the problem]

[0010] According to one aspect of the present invention, a lithium alloy for vacuum deposition is provided.

[0011] The lithium alloy for vacuum deposition contains bismuth (Bi): more than 23 wt% and less than 91 wt%, and the remainder is lithium (Li) and other unavoidable impurities, and can contain at least a Li3Bi phase and a lithium phase.

[0012] According to one embodiment, the bismuth (Bi) may have a range of 50 wt% to 70 wt%.

[0013] According to one embodiment, the Li3Bi phase may be in the range of 10 wt% to 84 wt% based on the total weight of the lithium alloy for vacuum deposition.

[0014] According to one embodiment, the Li3Bi phase may have a content in the range of 39 wt% to 70 wt% based on the total weight of the lithium alloy for deposition.

[0015] According to one embodiment, when the lithium alloy is melted in a vacuum atmosphere in a range above the melting point of lithium and below the melting point of the Li3Bi phase, only lithium can be selectively vaporized.

[0016] According to another aspect of the present invention, a method for producing a lithium alloy for vacuum deposition is provided.

[0017] The method for producing the lithium alloy for vacuum deposition may include: (a) forming a molten metal containing more than 23 wt% and less than 91 wt% bismuth (Bi), with the remainder being lithium (Li) and other unavoidable impurities; and (b) maintaining the molten metal at a temperature at which the molten metal is completely in a liquid phase, followed by quenching the molten metal to cast the lithium alloy.

[0018] According to one embodiment, the quenching may include a step of pouring the molten metal into a mold maintained at a temperature of 25° C. or less and cooling the molten metal.

[0019] According to one embodiment, the bismuth (Bi) may have a range of 50 to 70 wt %.

[0020] According to one embodiment, after the step (b), a pretreatment step (c) of maintaining the lithium alloy prepared in the step (b) in an argon (Ar) gas atmosphere for a predetermined time may be further performed.

[0021] According to one embodiment, the step (c) may be performed in a gas atmosphere chamber including a glove box.

[0022] According to another aspect of the present invention, there is provided a method for producing a lithium thin film for a photoelectric device.

[0023] The method for manufacturing a lithium thin film for a photoelectric element includes a step of heating a lithium alloy for vacuum deposition in a chamber under a vacuum atmosphere to selectively deposit lithium and form a lithium thin film on at least one surface of a substrate, and the lithium alloy for vacuum deposition may be composed of bismuth (Bi): more than 23 wt% and less than 91 wt%, and the remainder being lithium (Li) and other unavoidable impurities, and may include at least a LiBi phase and a lithium phase.

[0024] According to one embodiment, in the step of forming the lithium thin film, the temperature to which the lithium alloy for vacuum deposition is heated may be in a temperature range higher than the melting point of lithium and lower than the melting point of the Li3Bi phase.

[0025] According to one embodiment, the temperature may be in the range of 200°C to 500°C.

[0026] According to one embodiment, the temperature may be in a range equal to or lower than the sublimation temperature of lithium.

[0027] According to an embodiment, before the step of forming a lithium thin film in the vacuum chamber, a pre-treatment step of maintaining the lithium alloy for vacuum deposition in an argon (Ar) gas atmosphere for a predetermined time may be performed.

[0028] According to one embodiment, the vacuum atmosphere has a vacuum degree of 10 -8 ~10 -7 Torr.

[0029] According to another aspect of the present invention, a photoelectric device is provided.

[0030] The photoelectric device may include a positive electrode and a negative electrode facing each other on a substrate; and a charge generation layer, an electron injection layer, and an electron transport layer formed between the positive electrode and the negative electrode, and at least one layer of the negative electrode, the charge generation layer, and the electron injection layer may include a lithium thin film formed by the method for manufacturing a lithium thin film for a photoelectric device.

[0031] According to an embodiment, the photoelectric element may be selected from the group consisting of an organic light emitting element, a solar cell, and a transistor. [Effects of the Invention]

[0032] When using a lithium alloy for vacuum deposition according to the technical concept of the present invention, the formation of a coating such as an oxide film or a nitride film on the surface can be suppressed compared to pure lithium, and since a coating for suppressing the formation of a coating like pure lithium is not required, the problem of device contamination by a coating during deposition can be prevented and the performance of a photoelectric device including a lithium thin film can be improved. Of course, the scope of the present invention is not limited by these effects. [Brief explanation of the drawings]

[0033] [Figure 1] This is a binary phase equilibrium diagram of lithium (Li) and bismuth (Bi).

[0034] [Figure 2] 1 is a schematic diagram illustrating a process of forming a lithium thin film according to an embodiment of the present invention;

[0035] [Figure 3] 1 is a cross-sectional view showing a stacked structure of an organic light emitting device according to an embodiment of the present invention.

[0036] [Figure 4] 1 is an XRD analysis result showing the composition of a lithium alloy manufactured according to an example of the present invention. BEST MODE FOR CARRYING OUT THE INVENTION

[0037] Various embodiments of the present invention will be described in detail below with reference to the accompanying drawings. The embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art, and the following embodiments may be modified into various other forms, and the scope of the present invention is not limited to the following embodiments. Rather, these embodiments are provided to make the present disclosure more complete and complete, and to fully convey the concept of the present invention to those skilled in the art. In addition, the thickness and size of each layer in the drawings are exaggerated for convenience and clarity of explanation.

[0038] In the present invention, lithium (Li) is an example of an alkali metal, and sodium (Na), potassium (K), rubidium (Rb), or cesium (Cs) may be used instead of lithium (Li). However, lithium (Li) will be used as a representative example in the following description.

[0039] Bismuth (Bi) is a low-melting metal with a melting point of 500°C or less. Thallium (Tl), lead (Pb), bismuth (Bi) or polonium (Po) metal may be used instead of bismuth (Bi), but the following description will be given taking bismuth (Bi) as a representative example.

[0040] Hereinafter, a method for producing a lithium alloy for vacuum deposition according to one embodiment of the present invention and a lithium alloy for vacuum deposition produced by the method will be described.

[0041] A method for producing a lithium alloy for vacuum deposition according to an embodiment of the present invention includes the steps of: forming a molten metal containing, by weight, more than 23 wt% and less than 91 wt% bismuth (Bi), and the remainder being lithium (Li) and other unavoidable impurities (S100); and maintaining the molten metal at a temperature at which the molten metal is completely in a liquid phase, followed by quenching the molten metal to cast a lithium alloy (S200).

[0042] In step S100, lithium and bismuth are placed in a crucible and heated to melt them to produce a molten metal. In the molten metal, the bismuth content is, for example, in the range of more than 23 wt% and less than 91 wt%, with the remainder being lithium and unavoidable impurities. Preferably, the bismuth content is in the range of 50 to 90 wt%, or 50 to 70 wt%.

[0043] If the amount of lithium is too high, the reactivity of lithium will cause stability problems, which is undesirable from the viewpoint of environmental safety and commercialization.On the other hand, if the amount of lithium is too low, the amount of soluble material due to oxidation will decrease, and the manufacturing time may be shortened due to limitations on the continuous deposition time.

[0044] To prevent lithium from reacting with oxygen during the production of the molten metal, the production of the molten metal may be carried out in an inert atmosphere or a vacuum atmosphere.

[0045] Bismuth (Bi) is an alloying element that can form intermetallic compounds with lithium (Li). Figure 1 shows the phase equilibrium diagram for the lithium-bismuth binary system.

[0046] Referring to Figure 1, when bismuth is added in excess of 23 wt%, an intermetallic compound, Li3Bi phase, is formed. Li3Bi has a melting point of approximately 1,145°C, which is much higher than that of pure lithium or bismuth. To maintain the melt in the crucible in a completely molten state, it is necessary to maintain the temperature higher than the melting point of Li3Bi.

[0047] In step S200, the temperature of the molten metal is maintained at 1,145°C or higher, which is the temperature condition for completely dissolving the LiBi phase, and then the molten metal is poured into a mold and cooled to cast a lithium alloy. The cooling process may include a quenching process. The quenching process may include pouring the molten metal into a mold that is cooled by a cooling medium and maintained at a temperature of 25°C or lower, and then cooling the molten metal. For example, the molten metal may be quenched by pouring it into a metal mold that is cooled by cooling water at 10°C or lower.

[0048] Specific gravity is 0.534g / cm 3 and very low specific gravity of lithium (Li) 9.78 g / cm 3 When Li3Bi and bismuth (Bi), which have a relatively high specific gravity, are mixed and melted, phase separation is likely to occur due to the difference in specific gravity. Therefore, it is preferable to use a rapid cooling casting method to minimize this phase separation. Furthermore, this rapid cooling process can induce finer Li3Bi phases formed in the lithium alloy, and this finer Li3Bi phase in the lithium alloy can induce uniform lithium evaporation during the deposition process using the lithium alloy. This will be described in more detail below.

[0049] In the casting step, the upper limit of the temperature of the molten metal to be maintained is preferably 1,200° C. If the temperature exceeds 1,200° C., there are concerns that unnecessary increases in energy costs and an increase in impurities being mixed into the crucible due to excessive temperatures may occur.

[0050] The molten metal poured into the mold in the casting step solidifies from the liquid phase to the solid phase, and is finally cast as a lithium-bismuth binary alloy.

[0051] The lithium alloy contains bismuth (Bi): more than 23 wt% and less than 91 wt%, and the remainder is lithium (Li) and other unavoidable impurities. The lithium alloy also contains at least a LiBi phase and a lithium phase.

[0052] Referring to FIG. 1, when a molten metal is cast at a temperature of 1,145°C or higher, which is the temperature condition under which the LiBi phase completely dissolves, the final lithium alloy upon solidification has a microstructure in which at least the LiBi phase and the lithium phase are mixed.

[0053] Table 1 below was calculated with reference to the phase equilibrium diagram in Figure 1, and shows the fraction (wt%) of Li3Bi phase in the lithium alloy generated during the lithium alloy casting process depending on the blending ratio of lithium (Li) and bismuth (Bi) in the molten metal.

[0054] [Table 1]

[0055] Referring to Figure 1 and Table 1, when the bismuth content exceeds 23 wt%, a Li3Bi phase is formed. As the bismuth content gradually increases, the proportion of the Li3Bi phase formed in the lithium alloy increases, and at 90.9 wt%, the Li3Bi phase in the alloy is 100%. When the bismuth content is greater than 23 wt% but less than 90.9 wt%, the lithium content is greater than 9.1 wt% but less than 77 wt%, and lithium is added in excess of the stoichiometric ratio for forming the Li3Bi phase. Therefore, it can be said that at least a lithium phase and a Li3Bi phase are mixed in the lithium alloy produced using the composition of the present invention.

[0056] Additionally, in the case of the lithium alloy according to an embodiment of the present invention, a pretreatment may be performed by maintaining the lithium alloy in an inert atmosphere glove box for a predetermined period of time before being introduced into a vacuum deposition chamber for manufacturing a lithium thin film. The inert atmosphere may include an argon (Ar) atmosphere. For example, the pretreatment may be performed by maintaining the lithium alloy in an argon atmosphere glove box for 1 to 100 hours. During the argon atmosphere pretreatment step, the lithium alloy may be simultaneously cut into a desired shape or packaged as a product.

[0057] Typically, before loading a lithium alloy into a vacuum deposition chamber, it is left in the atmosphere for a predetermined period of time as a preparation. For example, the lithium alloy to be used for vacuum deposition is removed from its packaging, placed in a loading machine, and then placed in the vacuum deposition chamber. During this process, the lithium alloy must be left in the atmosphere with a humidity of 30% to 40% for a certain period of time. While left in the atmosphere, an oxide or nitride film may form on the surface of the lithium alloy, which may cause deterioration of deposition characteristics.

[0058] In contrast, in the case of a lithium alloy that has undergone the pretreatment, the effects of oxidation or nitridation of the lithium alloy are minimized, compared to a lithium alloy that is directly loaded into a vacuum deposition chamber without such pretreatment, thereby improving lithium deposition characteristics. Specifically, when the pretreatment is performed in an inert atmosphere as described above, even if the lithium alloy is exposed to the air while being transferred to and loaded into a vacuum deposition chamber for the formation of a lithium thin film after the pretreatment is completed, an oxide film or nitride film can be formed on the surface of the lithium alloy at a slow rate, and the formed film can also be thin.

[0059] The lithium alloy for vacuum deposition according to one embodiment of the present invention is placed in an evaporation source container of a vacuum chamber during deposition, and then heated and melted, so that only lithium is selectively evaporated or sublimated. At this time, the heating temperature is in the range of the melting point of lithium or higher and lower 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 is 5×10 -8 High vacuum (less than torr) may be used. Lithium melts at about 180°C and begins to rapidly evaporate above that temperature.

[0060] Under these deposition conditions, the lithium in the lithium alloy used as the evaporation source melts, but the LiBi phase, with its high melting point of 1,145°C, does not evaporate under these conditions and remains in a solid phase without participating in the deposition. In other words, the molten lithium alloy in the evaporation source container contains at least liquid lithium and a solid LiBi phase present within the liquid. Therefore, only the liquid lithium evaporates in the vacuum atmosphere, forming a lithium thin film on the substrate. When the lithium in the lithium alloy has completely evaporated and been consumed, the LiBi phase may remain as a residue in the evaporation source container.

[0061] Therefore, although the lithium alloy of the present invention is a binary alloy of lithium and bismuth, it actually functions as a lithium evaporation source that can selectively evaporate only lithium.

[0062] As shown in the phase diagram of Figure 1, if bismuth is added at less than 23 wt%, the Li3Bi phase cannot be formed, and the effects of the present invention cannot be expected. Meanwhile, referring to Table 1, adding bismuth in excess of 23 wt% reduces the amount of lithium soluble in the lithium alloy, and adding 90.9 wt% or more results in the formation of a 100% Li3Bi phase, leaving no lithium available for deposition. Therefore, the amount of bismuth added must be greater than 23 wt% and less than 90.9 wt%.

[0063] The lithium alloy for vacuum deposition according to one embodiment of the present invention contains a LiBi phase that has low reactivity with oxygen or nitrogen, and therefore has superior oxidation resistance or nitridation resistance compared to pure lithium. This slows down the oxidation and nitridation rates, increases deposition efficiency, reduces the risk of explosion or fire, and eliminates the need to construct explosion-proof deposition equipment, resulting in cost savings.

[0064] In the step of casting the lithium alloy, rapid cooling of the molten metal during solidification can reduce the size of the Li3Bi phase in the lithium alloy. When the Li3Bi phase in the lithium alloy is reduced in size in this way, the evaporation of lithium can be made more uniform in the step of depositing the lithium alloy. This can improve the uniformity of the thickness of the lithium thin film deposited on the substrate.

[0065] When a lithium alloy is present in a molten state in an evaporation source container, a non-volatile LiBi phase is present in the liquid lithium. Therefore, if the size of the LiBi phase is coarse and irregular, the evaporation of lithium from the liquid lithium will also be uneven. It is generally known that if rapid cooling is performed during solidification in the casting step, the phases generated during the solidification process become finer. Therefore, the lithium alloy according to an embodiment of the present invention can make the evaporation of lithium more uniform by finely granulating the LiBi phase generated through the rapid cooling treatment during casting.

[0066] A lithium thin film for a photoelectric device can be manufactured using the lithium alloy according to an embodiment of the present invention.

[0067] In the present invention, the lithium thin film means a thin film to which lithium is added, and it means a single metal thin film formed only of lithium, a thin film formed by adding lithium to an organic material, or a thin film formed by mixing lithium with another metal.

[0068] For example, in the case of a charge generation layer (CGL) of a photoelectric element, a lithium thin film is formed by adding lithium to an organic material, and in the case of a cathode layer, a lithium thin film can be formed by simultaneously thermal vacuum depositing silver (Ag) and a lithium alloy.

[0069] Referring again to FIG. 2, a process for forming a lithium thin film for a photoelectric device according to an embodiment of the present invention will be briefly described.

[0070] Referring to FIG. 2, the evaporation source container 12 contains the above-mentioned lithium alloy as the evaporation source 20, and after the substrate is mounted 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). -8 ~10 -3 Torr range, e.g., 10 -8 ~10 -7 The substrate may have a thickness in the range of Torr. To form a photoelectric element, the substrate may have various layers necessary for realizing a photoelectric effect already formed on one side.

[0071] The lithium alloy serving as the evaporation source 20 housed inside the evaporation source container 12 is heated to a temperature higher than the melting point of lithium and lower than 1,145°C, which is the melting point of the LiBi phase, for example, 200°C to 500°C.

[0072] The LiBi phase has a melting point higher than the heating temperature and remains in a solid state, whereas lithium metal has a low melting temperature of 180.54°C and therefore evaporates when heated, flies inside the vacuum deposition chamber 10 toward the substrate S, and adheres (deposits) onto the surface of the substrate S to form a lithium thin film 30. The deposition rate is preferably selected appropriately within the range of 0.01 to 100 Å / sec. FIG. 3 is a cross-sectional view showing a layered structure of an organic light-emitting device according to one embodiment of the present invention.

[0073] As shown in FIG. 3, the light emitting device according to the embodiment of the present invention includes a positive electrode 101 and a negative electrode 140 facing each other on a substrate 100, a first stack 1101 stacked between the positive electrode 101 and the negative electrode 140, a charge generation layer (CGL) 120, and a second stack 1301.

[0074] Here, the lithium thin film manufactured according to the embodiment of the present invention may be used for the anode 140. Since lithium has a low work function, it can be used as a material to lower the potential barrier formed at the interface of the anode 140. When a lithium thin film is manufactured using the lithium alloy manufactured according to the embodiment of the present invention, the reactivity is reduced, which is advantageous in terms of processability and stability.

[0075] The first stack 210 includes a hole injection layer 103, a first hole transport layer 105, a first light-emitting layer 110, and a first electron transport layer 111 stacked in this order between the top of the positive electrode 101 and the charge generation layer 120, while the second stack 220 includes 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 stacked in this order between the charge generation layer 120 and the negative electrode 140. An electron injection layer and a hole injection layer may be further provided below and above the charge generation layer 120, respectively.

[0076] The charge generation layer 120 is formed between the first stack 210 and the second stack 220 to adjust the charge balance between the stacks. The charge generation layer 120 is made of a material having low optical and electrical loss characteristics, and a lithium thin film manufactured according to an embodiment of the present invention can be used.

[0077] The organic layer that carriers injected from the anode 140 first encounter is the electron injection layer 135, which functions to smoothly inject charges from the anode 140 to the second electron transport layer 133. It is important for the electron injection layer 135 to lower the potential barrier formed at the interface. For example, metal halide compounds such as lithium fluoride (LiF) are known to form an interface electric double layer with the organic layer, causing a shift in energy levels and lowering the potential barrier. Due to its high reactivity with oxygen and moisture, lithium has been difficult to use in electron injection layers. However, when a thin film is fabricated using a lithium alloy according to embodiments of the present invention, its reactivity is reduced, making it suitable for use as a material for the electron injection layer 135.

[0078] Although the organic light emitting device has been described above as an example, according to another embodiment of the present invention, the lithium thin film may also be applied to an inorganic light emitting device, a solar cell, a transistor, and the like.

[0079] Specific experimental examples of the present invention will be presented below, but the examples described below are merely for the purpose of specifically illustrating or explaining the present invention and should not be construed as limiting the present invention.

[0080] <Experimental Example>

[0081] 1. Experimental Example 1

[0082] Lithium and bismuth were alloyed in a weight ratio of 3:7 and exposed to the atmosphere. As shown in Table 2 below, in the case of the lithium alloy, oxide and nitride films formed slower and thinner under the same atmospheric exposure conditions than when lithium was used alone.

[0083] [Table 2]

[0084] 2. Experimental Example 2

[0085] 5×10 -8 The sublimation temperature (or vaporization temperature) of lithium and lithium alloys was compared by heating them in a vacuum chamber at 100 Torr. As shown in Table 3 below, compared to a multi-component lithium alloy (Zr-Al-Li), the lithium-bismuth alloy was confirmed to have the same sublimation temperature as lithium alone due to the low melting point of bismuth.

[0086] [Table 3]

[0087] 3. Experimental Example 3

[0088] The lithium alloys were pretreated in glove boxes with an argon or nitrogen atmosphere, respectively, and then taken out into the air. The appearance of the alloys was observed for 2 hours, and the results are summarized in Table 4.

[0089] [Table 4]

[0090] When pretreatment was performed in an argon atmosphere as described above, a lithium alloy with a clean silver-colored surface with almost no nitriding could be obtained. Furthermore, it was confirmed that the lithium-bismuth alloy exhibited robustness, with oxidation and nitriding progressing after two hours of exposure to the atmosphere.

[0091] 4. Experimental Example 4

[0092] Lithium and bismuth were mixed according to the ratios shown in Table 5 below to form a molten alloy. After maintaining the temperature at 1,200°C, the temperature condition for complete dissolution of the Li3Bi phase, for 1 hour, the molten alloy was poured into a metal mold with flowing cooling water at 3°C ​​to 5°C and rapidly cooled to prepare test specimens. The manufactured test specimens were pretreated in a glove box with an argon (Ar) gas atmosphere containing less than 1 ppm of moisture and oxygen.

[0093] After the test piece was placed in a vacuum deposition chamber, -8 After maintaining a vacuum of Torr, the specimen was preheated to approximately 500°C to 550°C to remove the coating formed on its surface. At this time, the oxide or nitride coating formed on the specimen surface was removed in the form of gas, lowering the vacuum. Once the coating was completely removed, the vacuum was restored, and the thickness of the lithium thin film deposited on the substrate was measured using a thickness sensor attached to the substrate. Once it was confirmed that the lithium thin film was thickening in angstroms (Å) per second and that lithium was being deposited at the desired deposition rate, full-scale deposition began. The preheat-up time required for lithium deposition to begin is shown in Table 5 below.

[0094] In addition, to check the deviation of the composition due to the compounding ratio of the cast specimens, the ratio of lithium (Li) and bismuth (Bi) components was measured by ICP-OES (PerkinElmer, AVIO550) analysis, and the deviation was confirmed by comparing with the design of the composition, and the results are shown in Table 5 below.

[0095] [Table 5]

[0096] Figure 4 shows the XRD analysis results of the test piece cast according to Example 3. Through this, it was confirmed whether the Li3Bi phase was formed.

[0097] Referring to Figure 4, it can be seen that when the lithium (Li) and bismuth (Bi) content ratio is 50:50, it is composed of Li3Bi and Li phases. Although there are differences in the XRD peak intensity depending on the blending ratio, it was confirmed that all test specimens were similarly composed of Li3Bi and Li phases.

[0098] Referring to Table 5, when the bismuth (Bi) content is low, at about 30 wt% to 40 wt%, as in Examples 1 and 2, the lithium content is relatively high, which has the advantage of allowing the deposition thickness to be thicker than the target thickness. However, the preheating time required to remove the oxide / nitride film is increased. This is believed to be because the Li3Bi intermetallic compound is relatively more stable to oxidation and nitridation than pure lithium (Li), but the fraction of Li3Bi produced is low, at about 10% to 25%, which causes surface oxidation and nitridation.

[0099] On the other hand, when the amount of bismuth (Bi) added was excessive at 80 wt%, as in Example 6, the preheating time was short and the deviation in the composition of the cast specimens was small. However, since the fraction of the Li3Bi intermetallic compound produced was high at 83.9%, the amount of lithium (Li) that could actually be vaporized was small, and therefore, the deposited thickness was observed to be low under the same deposition conditions.

[0100] In Examples 3 to 5, when bismuth (Bi) was added in the range of 50 to 70 wt%, the deviation in the composition of the cast lithium alloy was not high, the preheating time for removing the coating was appropriate, and the deviation in thickness after deposition was uniform, within 10%.

[0101] According to the embodiment of the present invention as described above, when lithium and bismuth (Bi) are used as a thermal vacuum deposition material for a photoelectric device by controlling the composition and evaporation conditions, the bismuth (Bi) component is not deposited and only lithium (Li) can be selectively deposited. This shortens the preheating time for removing oxide and nitride coatings before deposition, and enables efficient deposition of lithium (Li) without contamination by organic matter, etc.

[0102] The present invention has been described with reference to the embodiments shown in the drawings, but these are merely illustrative, and those skilled in the art will recognize that various modifications and equivalent embodiments are possible. Therefore, the true technical scope of protection of the present invention should be determined by the technical spirit of the appended claims.

Claims

1. Bismuth (Bi): more than 23 wt% but less than 91 wt%, and the remainder consisting of lithium (Li) and other unavoidable impurities; At least Li ３ A lithium alloy for vacuum deposition, comprising a Bi phase and a lithium phase.

2. 2. The lithium alloy for vacuum deposition according to claim 1, wherein the bismuth (Bi) has a range of 50 wt % to 70 wt %.

3. The Li ３ 2. The lithium alloy for vacuum deposition according to claim 1, wherein the Bi phase has a range of 10 wt % to 84 wt % based on the total weight of the lithium alloy for vacuum deposition.

4. The Li ３ 4. The lithium alloy for vacuum deposition according to claim 3, wherein the Bi phase has a range of 39 wt % to 70 wt % based on the total weight of the lithium alloy for vacuum deposition.

5. The lithium alloy is heated to a temperature above the melting point of lithium in a vacuum atmosphere and ３ 2. The lithium alloy for vacuum deposition according to claim 1, wherein only lithium is selectively vaporized when melted in a range below the melting point of the Bi phase.

6. (a) forming a molten metal containing bismuth (Bi): more than 23 wt % but less than 91 wt %, with the balance being lithium (Li) and other inevitable impurities; (b) maintaining the molten metal at a temperature at which the molten metal is completely liquid, and then quenching the molten metal to cast the lithium alloy.

7. 7. The method for producing a lithium alloy for vacuum deposition according to claim 6, wherein the rapid cooling comprises a step of pouring the molten metal into a mold maintained at a temperature of 25°C or less and cooling the molten metal.

8. 7. The method for producing a lithium alloy for vacuum deposition according to claim 6, wherein the bismuth (Bi) has a range of 50 to 70 wt %.

9. After step (b), 7. The method for producing a lithium alloy for vacuum deposition according to claim 6, further comprising: (c) performing a pretreatment step of maintaining the lithium alloy produced in step (b) in an argon (Ar) gas atmosphere for a predetermined time.

10. The step (c) 10. The method for producing a lithium alloy for vacuum deposition according to claim 9, which is carried out in a gas atmosphere chamber including a glove box.

11. a step of selectively depositing lithium by heating a lithium alloy for vacuum deposition in a vacuum chamber to form a lithium thin film on at least one surface of a substrate; The lithium alloy for vacuum deposition is Bismuth (Bi): more than 23 wt% but less than 91 wt%, and the remainder consisting of lithium (Li) and other unavoidable impurities; At least Li ３ A method for producing a lithium thin film for a photoelectric element, which contains a Bi phase and a lithium phase.

12. In the step of forming the lithium thin film, The temperature to which the lithium alloy for vacuum deposition is heated is higher than the melting point of lithium, ３ The method for producing a lithium thin film for a photoelectric element according to claim 11, wherein the temperature range is lower than the melting point of the Bi phase.

13. The method for producing a lithium thin film for a photoelectric element according to claim 12, wherein the temperature is in the range of 200°C to 500°C.

14. The method for producing a lithium thin film for a photoelectric device according to claim 12, wherein the temperature is in a range equal to or lower than the sublimation temperature of lithium.

15. Before the step of forming a lithium thin film in the vacuum atmosphere chamber, 12. The method for manufacturing a lithium thin film for a photoelectric device according to claim 11, further comprising a pretreatment step of maintaining the lithium alloy for vacuum deposition in an argon (Ar) gas atmosphere for a predetermined time.

16. The vacuum atmosphere has a vacuum degree of 10 －８ ~10 －７ The method for producing a lithium thin film for a photoelectric element according to claim 11, wherein the pressure is maintained at Torr.

17. a positive electrode and a negative electrode facing each other on a substrate; a charge generation layer, an electron injection layer, and an electron transport layer formed between the positive electrode and the negative electrode; A photoelectric element, wherein at least one layer of the negative electrode, the charge generation layer, and the electron injection layer comprises a lithium thin film formed according to any one of claims 11 to 16.

18. 18. The photoelectric device of claim 17, wherein the photoelectric device is selected from the group consisting of an organic light emitting device, a solar cell, and a transistor.

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