Method for forming perovskite films

Abstract

It forms high-quality perovskite films. [Solution] The method of the embodiment involves applying a solution containing a perovskite precursor and a solvent to a substrate, and crystallizing the perovskite precursor on the substrate to form a perovskite film. The method comprises the steps of: heating the solution on the transported substrate to a temperature at which the perovskite precursor does not crystallize and removing part of the solvent by irradiating the solution with infrared rays that are not absorbed by the perovskite precursor but are absorbed by the solvent, and blowing hot air in the same direction as the transport direction of the substrate; and heating the solution on the substrate to remove the solvent remaining in the solvent removal step and crystallize the perovskite precursor to form a perovskite film. The temperature of the hot air is 68°C to 80°C, and the relative velocity of the hot air with respect to the transport speed of the substrate is 0.1 m / sec to 1.0 m / sec.

Description

Technical Field

[0001] The present invention relates to a method for forming a perovskite film.

Background Art

[0002] In recent years, perovskite solar cells have attracted attention as thin, lightweight solar cells with high power generation efficiency. A perovskite solar cell is a battery that generates electricity by absorbing sunlight in a perovskite film and generating free electrons and holes.

[0003] In a conventional general method for forming a perovskite film, first, a solution is applied to a substrate. This coating method is a so-called spin coating method in which a solution containing a perovskite precursor and a solvent is ejected onto the substrate and the substrate is rotated to spread the solution on the substrate. Then, the substrate coated with the solution is heated by a hot plate to remove the solvent and at the same time crystallize the perovskite precursor to form a perovskite film.

[0004] However, in the above method, evaporation of a large amount of solvent and formation of the perovskite film proceed simultaneously. As a result, the crystal state of the perovskite becomes disordered and non-uniform, resulting in a decrease in the power generation efficiency of the perovskite solar cell, or defects (voids) are formed in the perovskite film, causing a short circuit. The current situation that it is difficult to form a high-quality perovskite film is an obstacle to the widespread use of perovskite solar cells.

[0005] Therefore, as described in Patent Document 1, the applicant invented a method of proceeding to a step of crystallizing a perovskite precursor to form a perovskite film after a step of removing the solvent from a solution containing the perovskite precursor and the solvent.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

[0007] The method described in Patent Document 1, which includes the steps of removing the solvent from a solution containing a perovskite precursor and crystallizing the perovskite precursor, has not been thoroughly studied to determine how to optimize various conditions, such as temperature, to form a higher-quality perovskite film.

[0008] This invention has been made in view of these circumstances, and aims to provide a method for forming higher quality perovskite films. [Means for solving the problem]

[0009] The perovskite film formation method of the embodiment comprises a solvent removal step, in which a solution containing a perovskite precursor and a solvent is applied to a substrate, and the perovskite precursor is crystallized on the substrate to form a perovskite film, and the solvent removal step is to remove a portion of the solvent by irradiating the solution on the substrate being conveyed by rollers with infrared rays that are not absorbed by the perovskite precursor but are absorbed by the solvent, and by blowing hot air in the same direction as the conveying direction of the substrate, thereby heating the solution to a temperature at which the perovskite precursor does not crystallize; and a crystallization step, in which the remaining solvent is removed and the perovskite precursor is crystallized to form a perovskite film by heating the solution on the substrate after the solvent removal step, wherein the temperature of the hot air is 68°C or higher and 80°C or lower, and the relative velocity of the hot air to the conveying speed of the substrate is 0.1 m / sec or higher and 1.0 m / sec or lower. Furthermore, the perovskite precursor contains lead iodide, and the solvent contains DMF and a slow-release solvent. It is characterized by the following: [Effects of the Invention]

[0010] According to the perovskite film formation method of this embodiment, a higher quality perovskite film can be formed. [Brief explanation of the drawing]

[0011] [Figure 1] Side view of a perovskite film formation apparatus. [Figure 2] Side view of a substrate to which a solution has been applied. [Figure 3] Cross-sectional view of a perovskite solar cell. [Figure 4] Side view of the solvent removal chamber. [Figure 5] Side view of the crystallization chamber. [Figure 6] Block diagram of a perovskite film deposition apparatus. [Figure 7] A diagram showing the relationship between hot air temperature and PCE (Pressure Control Energy). [Figure 8] A diagram showing the relationship between the relative velocity of the hot air to the transport speed of the substrate and the PCE (Pressure Control Energy). [Modes for carrying out the invention]

[0012] This embodiment will be described with reference to the drawings. This embodiment is presented as an example, and the scope of the invention is not limited thereto. Various modifications, including substitutions and omissions, can be made to this embodiment without departing from the spirit of the invention. This embodiment and its modifications are included in the scope of the invention and its equivalents as described in the claims.

[0013] In the following explanation, the side of the elongated base material 1 that is in the direction of travel will be referred to as the front, and the opposite side as the rear. Also, left and right refer to the left and right when viewed from the front to the rear.

[0014] (1) Overall configuration of the perovskite film forming apparatus 10 As shown in FIG. 1, the perovskite film forming apparatus 10 is configured such that a coating chamber 13, a solvent removal chamber 14, a crystallization chamber 15, and an annealing chamber 16 are arranged in sequence from the rear to the front. Further, pressure adjustment chambers 17, 18, and 19 are provided between the coating chamber 13 and the solvent removal chamber 14, between the solvent removal chamber 14 and the crystallization chamber 15, and between the crystallization chamber 15 and the annealing chamber 16, respectively. Each of the pressure adjustment chambers 17, 18, and 19 and the areas on both sides adjacent to them in the front and rear are partitioned by partition walls 29 (see FIGS. 4 and 5) in which openings through which the substrate 1 can pass are formed. The perovskite film forming apparatus 10 also includes a pay-out section 11 and a surface treatment section 12.

[0015] (2) Configuration of the pay-out section 11, the surface treatment section 12, and the coating chamber 13 A take-up shaft 20 is provided in the pay-out section 11. The substrate 1 before the solution is applied is wound around the take-up shaft 20. The structure of the substrate 1 will be described later. The take-up shaft 20 rotates by the drive of a motor to pay out the substrate 1. The width of the substrate 1 is, for example, 200 mm or more and 1000 mm or less.

[0016] The surface treatment section 12 is a part that performs surface treatment on the substrate 1 conveyed from the pay-out section 11. The surface treatment is a treatment for improving the wettability of the surface of the substrate 1, and a treatment of irradiating excimer light is preferable, but corona treatment, plasma treatment, UV treatment using ultraviolet rays other than excimer light, etc. may also be used.

[0017] In the coating chamber 13, a die 21 and a backup roller 22 in front of the die 21 are provided. The backup roller 22 is one of the rollers that conveys the substrate 1 and rotates by the drive of a motor. The substrate 1 conveyed from the surface treatment section 12 below the backup roller 22 changes its conveyance direction at the backup roller 22 and is conveyed forward. In the vicinity of the die 21, the backup roller 22 conveys the substrate 1 from the bottom to the top.

[0018] The die 21 discharges a solution toward the base material 1 in contact with the backup roller 22, and applies the solution over the entire width direction (left - right direction) of the base material 1. The composition of the solution will be described later. The surface of the base material 1 where the solution is applied is the upper surface in the solvent removal chamber 14 and the crystallization chamber 15. For reference, the state where the solution is applied on the base material 1 and the solution layer 2 is formed is shown in FIG. 2. FIG. 2 is a view showing the base material 1 in the solvent removal chamber 14. In this specification, the base material 1 coated with the solution may also be simply expressed as "base material 1".

[0019] (3) The base material 1 and the solution used The structure of the base material 1 varies depending on the structure of the perovskite solar cell to be manufactured.

[0020] As the structure of the perovskite solar cell, the mesoporous structure shown in FIG. 3(a), the normal structure shown in FIG. 3(b), and the inverted structure shown in FIG. 3(c) are known. The mesoporous structure is a structure in which a transparent electrode 4, an electron transport layer 5, a mesoporous titanium oxide layer 6, a perovskite layer 7, a hole transport layer 8, and a back electrode 9 are laminated in this order. The normal structure is a structure in which a transparent electrode 4, an electron transport layer 5, a perovskite layer 7, a hole transport layer 8, and a back electrode 9 are laminated in this order. The inverted structure is a structure in which a transparent electrode 4, a hole transport layer 8, a perovskite layer 7, an electron transport layer 5, and a back electrode 9 are laminated in this order. In any of the structures, the perovskite layer 7 is a perovskite film formed from the solution applied to the base material 1 by the method of the present embodiment.

[0021] The base material 1 is one in which a layer above or below the perovskite layer 7 in the structures of FIGS. 3(a) to (c) is laminated on a transparent film such as a polyethylene terephthalate film. The solution is applied on the uppermost layer of the laminate (the layer that will contact the perovskite layer 7), and a perovskite film is formed from the solution, and that perovskite film directly becomes the perovskite layer 7. Another layer is further laminated on the perovskite layer 7 to complete the structures of FIGS. 3(a) to (c).

[0022] Furthermore, the solution applied to the substrate 1 consists of a perovskite precursor and a solvent.

[0023] Perovskite precursors are materials in the stage before they crystallize and become perovskite films. For example, when trying to produce methylammonium lead iodide (CH3NH3PbI3) as a perovskite, lead iodide (PbI2) and methylammonium iodide (CH3NH3I) are used as perovskite precursors.

[0024] The solvent consists of DMF (NN-dimethylformamide), a slow-release solvent, and a surfactant. As the slow-release solvent, an organic solvent that evaporates less easily than DMF is used. More specifically, an organic solvent that evaporates less easily in the relatively low-temperature solvent removal chamber 14 and evaporates in the relatively high-temperature crystallization chamber 15 is used. DMSO (dimethyl sulfoxide) is preferred as such a slow-release solvent, but NMP (N-methyl-2-pyrrolidone) and DCM (dichloromethane) can also be used. The type of surfactant is not limited. These substances constituting the solvent absorb infrared wavelengths different from those of the perovskite precursor. Different infrared wavelengths mean different infrared absorption spectra.

[0025] The ratio of the slow-acting solvent to the total amount of DMF and slow-acting solvent is preferably more than 20% by mass and 50% by mass or less. The ratio of the surfactant to the total solution is preferably 0.1% by mass or more and 1.0% by mass or less. The concentration of the perovskite precursor in the solution is preferably 20% by mass or more and 38% by mass or less. These ratios are those in the solution before it is introduced into the die 21, but it can be assumed that these ratios are maintained even when the solution is applied to the substrate 1.

[0026] (4) Configuration of the solvent removal chamber 14 The solvent removal chamber 14 has an inlet for the substrate 1 at its rear and an outlet for the substrate 1 at its front. As shown in Figure 4, multiple transport rollers 30 are arranged front to back in the solvent removal chamber 14. Each transport roller 30 rotates by the drive of a motor. The substrate 1 is transported on these transport rollers 30.

[0027] A roller cooling device 33 (see Figure 6) is provided to cool these multiple transport rollers 30. The roller cooling device 33 cools the transport rollers 30, thereby cooling the substrate 1 placed on the transport rollers 30 from below. In the solvent removal chamber 14, a portion of the solvent evaporates from the solution layer 2 on the substrate 1, and latent heat of vaporization is removed from the surface (upper surface) of the solution layer 2. The cooling capacity of the roller cooling device 33 is set so that the cooled transport rollers 30 remove an amount of heat from the substrate 1 equal to the latent heat removed at this time.

[0028] An infrared irradiation device 31 is provided above the transport roller 30 in the solvent removal chamber 14. The infrared irradiation device 31 is a device that irradiates infrared light with a wavelength that is absorbed by the solvent but not easily absorbed by the perovskite precursor. Specifically, the wavelength of the infrared light irradiated by the infrared irradiation device 31 is between 1 μm and 10 μm. Such an infrared irradiation device 31 that irradiates infrared light in a specific wavelength range is realized by combining a device that irradiates infrared light in a wider wavelength range with a filter that allows only infrared light in a specific wavelength range to pass through. The infrared irradiation device 31 is sufficiently large in the front-to-back and left-to-right directions, and can irradiate the entire substrate 1 with infrared light over a wide area in the front-to-back direction and in the left-to-right direction (width direction).

[0029] The infrared radiation from this infrared irradiation device 31 is irradiated onto the substrate 1, as shown by the dashed arrow in Figure 4, and a portion of the solvent in the solution layer 2 is evaporated by radiation. Due to the irradiation of infrared radiation, the temperature of the solution layer 2 becomes higher than the ambient temperature of the solvent removal chamber 14 (for example, to around 70°C), but it does not rise to the temperature at which the perovskite precursor crystallizes (for example, to around 100°C). Note that the ambient temperature of the solvent removal chamber 14 is sufficiently lower than the temperature at which the perovskite precursor crystallizes and forms a perovskite film.

[0030] The temperature of the light-emitting part of the infrared irradiation device 31 while irradiating with infrared light will be, for example, between 300°C and 400°C. However, the solution layer 2 will not reach such high temperatures.

[0031] Furthermore, a flow straightening device is provided above the conveyor rollers 30 in the solvent removal chamber 14. The flow straightening device consists of a blower 32a that blows warm air and an intake device 32b that sucks in warm air. The blower 32a is located above and behind the conveyor rollers 30 in the solvent removal chamber 14 and blows warm air forward and horizontally. The intake device 32b is located at the same height as the blower 32a and in front of it in the solvent removal chamber 14 and sucks in the warm air flowing in from the rear.

[0032] With this arrangement of the blower 32a and intake device 32b, warm air is sent from the blower 32a to the intake device 32b, as shown by the solid arrows in Figure 4. As a result, the warm air flows over the substrate 1 on the conveyor roller 30 in the same direction as the conveying direction of the substrate 1. The speed of the warm air is controlled to be slightly faster than the conveying speed of the substrate 1. The relative speed of the warm air to the conveying speed of the substrate 1 (i.e., the value obtained by subtracting the conveying speed of the substrate 1 from the wind speed of the warm air) is between 0.1 m / s and 1.0 m / s, with a more preferable range being between 0.1 m / s and 0.5 m / s. The temperature of the warm air sent from the blower 32a is between 68°C and 80°C, with a more preferable temperature being between 70°C and 75°C. This warm air at this temperature flows in the same direction as the conveying direction of the substrate 1 and comes into contact with the solution layer 2 on the substrate 1.

[0033] (5) Configuration of the crystallization chamber 15 The crystallization chamber 15 has an inlet for the substrate 1 at its rear and an outlet for the substrate 1 at its front. As shown in Figure 5, multiple transport rollers 40 are arranged front to back in the crystallization chamber 15. Each transport roller 40 rotates by the drive of a motor. The substrate 1 is transported on these transport rollers 40.

[0034] In the crystallization chamber 15, multiple nozzles 41 are arranged front to back above the transport roller 40. A front outlet 41a and a rear outlet 41b are formed at the bottom of each nozzle 41. The front outlet 41a is an outlet that blows the hot air from inside the nozzle 41 diagonally forward and downward. The rear outlet 41b is an outlet that blows the hot air from inside the nozzle 41 diagonally backward and downward.

[0035] The temperature of the hot air blown out from the outlets 41a and 41b of the nozzle 41 is preferably between 90°C and 110°C. When this hot air hits the solution layer 2 on the substrate 1 being transported by the transport roller 40, the solvent remaining on the substrate 1 evaporates and is removed, and the perovskite precursor is heated and crystallized.

[0036] Furthermore, an intake port 42 for drawing in hot air from inside the crystallization chamber 15 is provided above the transport roller 40. The intake port 42 and the nozzle 41 are arranged alternately in the front-to-back direction. Due to this structure, the hot air blown diagonally downward from the front outlet 41a and rear outlet 41b of the nozzle 41 rises relatively quickly and is drawn into the intake port 42. The flow of this hot air is shown by arrows in Figure 5. This flow of hot air makes it difficult for the hot air to leak out of the crystallization chamber 15.

[0037] Furthermore, the widths (lengths in the left-right direction) of the front outlet 41a, the rear outlet 41b, and the suction port 42 are approximately the same as the left-right length of the conveyor roller 40, and are, for example, between 100% and 120% of the left-right length of the conveyor roller 40. This makes it easier for the entire width (left-right direction) of the substrate 1 to be heated uniformly.

[0038] As shown in Figure 5, an exhaust chamber 43 leading to an intake port 42 is provided above the crystallization chamber 15. An air supply chamber 44 is also provided surrounded by the exhaust chamber 43, and an air supply passage 45 is provided from the air supply chamber 44 to each nozzle 41. Air taken in from outside the perovskite film forming apparatus 10 is heated by a heater (not shown) and blown into the crystallization chamber 15 after passing through the air supply chamber 44, the air supply passage 45 and the nozzles 41. Air drawn in from the intake port 42 is also discharged outside the perovskite film forming apparatus 10 after passing through the exhaust chamber 43.

[0039] (6) Configuration of the annealing chamber 16 and pressure adjustment chambers 17, 18, and 19 As shown in Figure 1, the annealing chamber 16 is provided with an intake port 51 for supplying hot air heated by a heater into the annealing chamber 16, and an exhaust port 52 for discharging the air inside the annealing chamber 16 to the outside. The hot air supplied from the intake port 51 maintains the ambient temperature of the annealing chamber 16 at a temperature lower than the temperature of the crystallization chamber 15 and higher than the ambient temperature of the perovskite film forming apparatus 10.

[0040] The annealing chamber 16 also serves as a winding section for winding up the perovskite film laminate 3, which has a perovskite film formed on the substrate 1. A winding shaft 50 is located in the winding section. The winding shaft 50 rotates when driven by a motor, winding up the perovskite film laminate 3. The perovskite film forming apparatus 10 of this embodiment is a so-called roll-to-roll apparatus comprising an unwinding section 11 for unwinding the substrate 1 and a winding section for winding the substrate 1 into a roll shape.

[0041] Each of the pressure adjustment chambers 17, 18, and 19 is equipped with a pressure adjustment device 17a, 18a, and 19a (see Figure 6). The pressure adjustment devices 17a, 18a, and 19a control the air to eliminate a pressure difference that exceeds a predetermined level when a pressure difference exceeding a predetermined level occurs between the adjacent areas of the pressure adjustment chambers 17, 18, and 19. For example, when a pressure difference exceeding a predetermined level occurs between the solvent removal chamber 14 and the crystallization chamber 15, which are adjacent to the pressure adjustment chamber 18, the pressure adjustment device 18a controls the air to eliminate that pressure difference. This control prevents air from flowing from one area to the other across the pressure adjustment chambers 17, 18, and 19.

[0042] (7) Electrical configuration of the perovskite film forming apparatus 10 The perovskite film forming apparatus 10 is equipped with a control unit 60 consisting of a computer. As shown in Figure 6, the control unit 60 is connected to an infrared irradiation device 31, a roller cooling device 33, a blower 32a, an intake device 32b, and pressure regulating devices 17a, 18a, and 19a. Although not shown, the control unit 60 is also connected to motors for rotating the various rollers and heaters for heating the air. The control unit 60 controls the connected equipment to execute the perovskite film forming method described later.

[0043] (8) Method for forming a perovskite film In this embodiment, a single long substrate 1 is unwound from the winding shaft 20 at the unwinding section 11 on one side, and wound onto the winding shaft 50 at the annealing chamber 16 on the other side. As a result, the substrate 1 is continuously transported in the following order: coating chamber 13, pressure adjustment chamber 17, solvent removal chamber 14, pressure adjustment chamber 18, crystallization chamber 15, pressure adjustment chamber 19, and annealing chamber 16. The transport speed of the substrate 1 from the unwinding section 11 to the annealing chamber 16 is adjusted as appropriate, but is, for example, between 5 m / min and 20 m / min.

[0044] In the coating chamber 13, the solution is discharged from the die 21 toward the substrate 1 in contact with the backup roller 22, and the solution is applied to one side of the substrate 1 to form a solution layer 2.

[0045] In the solvent removal chamber 14, the substrate 1 is transported over multiple transport rollers 30. The time required for the substrate 1 to pass through the solvent removal chamber 14 is, for example, several tens of seconds to several minutes. As shown in Figure 2, in the solvent removal chamber 14, the substrate 1 is positioned with the side coated with the solution facing upwards. Thereafter, until just before it is wound onto the winding shaft 50 in the annealing chamber 16, the substrate 1 is transported horizontally with the side coated with the solution facing upwards.

[0046] As the substrate 1 is being transported in the solvent removal chamber 14, infrared radiation is irradiated from the infrared irradiation device 31 above with wavelengths that are absorbed by the solvent but not easily absorbed by the perovskite precursor, specifically wavelengths between 1 μm and 10 μm. As a result, the solvent is heated by radiation.

[0047] Furthermore, over the substrate 1 being transported in the solvent removal chamber 14, a flow straightening device blows hot air in the same direction as the transport direction of the substrate 1. The relative velocity of the hot air to the transport speed of the substrate 1 is 0.1 m / sec to 1.0 m / sec as described above, and the temperature of the hot air is 68°C to 80°C as described above. When this hot air comes into contact with the solution layer 2 on the substrate 1, the solution and the solvent within it are heated.

[0048] In this way, the solvent is heated by infrared radiation and hot air, causing the temperature of solution layer 2 to rise to a temperature at which the solvent can evaporate, and a portion of the solvent actually evaporates and is removed from the substrate 1. The substance removed at this time is mainly DMF. As a result of the removal of a portion of the solvent, the concentration of the perovskite precursor in solution layer 2 increases. However, the heating in the solvent removal chamber 14 does not raise the temperature of solution layer 2 to a temperature at which the perovskite precursor can crystallize. Therefore, a perovskite film is not formed in the solvent removal chamber 14.

[0049] Furthermore, the rectifier also plays a role in reducing air convection on the solution layer 2 on the substrate 1, thereby reducing the formation of wind ripples on the solution layer 2. In addition, the rectifier also plays a role in carrying the solvent evaporated from the solution layer 2 onto the air from the blower 32a, drawing it into the intake device 32b, and discharging it outside the solvent removal chamber 14.

[0050] Incidentally, when the solvent evaporates, latent heat of vaporization is removed from the solution layer 2, and the temperature of the surface (upper side) of the solution layer 2 decreases. In response to this, the conveying roller 30 is cooled by the roller cooling device 33, and the substrate 1 is cooled from the bottom side by the conveying roller 30. As a result, the surface temperature and the temperature of the substrate 1 side in the solution layer 2 become approximately equal, making it difficult for convection to occur in the solution layer 2, and making it difficult for Bénard cells to form in the solution layer 2.

[0051] In the crystallization chamber 15, the substrate 1, from which some of the solvent has been removed, is transported over multiple transport rollers 40. The time required for the substrate 1 to pass through the crystallization chamber 15 is, for example, several tens of seconds to several minutes. During transport, the perovskite precursor on the substrate 1 is heated by hot air from the nozzle 41, causing it to crystallize and form a perovskite film. Also, any solvent (mainly slow-acting solvents) remaining on the substrate 1 is evaporated and removed. Since some of the solvent has been removed from the solution in the solution layer 2 by the time the substrate 1 is transported to the crystallization chamber 15, a large amount of solvent does not evaporate simultaneously with the formation of the perovskite film in the crystallization chamber 15. Therefore, the perovskite film becomes a uniform crystalline state with few defects.

[0052] In the annealing chamber 16, the perovskite film laminate 3, in which a perovskite film is formed on the substrate 1, is wound onto the winding shaft 50, eventually forming a large roll. The perovskite film is also heated in the annealing chamber 16, relieving internal stresses.

[0053] The perovskite film laminate 3, removed from the annealing chamber 16, is transported to another apparatus. In that apparatus, other layers are laminated on top of the perovskite film to form a perovskite solar cell.

[0054] (9) Effects In this embodiment, a solvent removal step is performed in which a portion of the solvent is removed from the solution applied to the substrate 1 by heating it to a temperature at which the perovskite precursor does not crystallize. Subsequently, a crystallization step is performed in which the remaining solvent is removed and the perovskite precursor is crystallized by heating the solution on the substrate 1 to form a perovskite film.

[0055] In the solvent removal step, infrared light that is not absorbed by the perovskite precursor but is absorbed by the solvent is irradiated onto the solution. This allows the temperature of the solvent to rise and a portion of the solvent to evaporate while preventing the temperature of the perovskite precursor from rising and crystallizing.

[0056] Furthermore, in the solvent removal step, hot air is sent in the same direction as the transport direction of the substrate 1, with the temperature of the hot air being between 68°C and 80°C, and the relative velocity of the hot air to the transport speed of the substrate 1 being between 0.1 m / sec and 1.0 m / sec. This allows for appropriate heat exchange between the hot air and the solution on the substrate 1, preventing the temperature rise and crystallization of the perovskite precursor while raising the temperature of the solvent and evaporating a portion of the solvent.

[0057] Thus, in the solvent removal step, a portion of the solvent evaporates, and in the subsequent crystallization step, the remaining solvent is removed and the perovskite precursor is crystallized. This prevents the simultaneous evaporation of a large amount of solvent and the crystallization of the perovskite precursor. As a result, a higher quality perovskite film with a uniform crystal structure and fewer defects can be formed.

[0058] Furthermore, if the wavelength of the infrared light irradiated onto the solution in the solvent removal step is between 1 μm and 10 μm, the temperature of the perovskite precursor does not rise easily, while the temperature of the solvent rises and evaporation is more likely.

[0059] Furthermore, in the solvent removal step, the direction of the hot air is the same as the transport speed of the substrate 1, and the relative velocity of the hot air to the transport speed of the substrate 1 is between 0.1 m / sec and 1.0 m / sec, so wind-induced irregularities are less likely to occur on the surface of the solution layer 2. As a result of the reduced surface irregularities, the perovskite film is of higher quality.

[0060] Furthermore, in the crystallization step, by sending hot air at 90°C to 110°C toward the substrate 1, the solvent remaining on the substrate 1 is slowly evaporated, allowing the crystallization of the perovskite precursor to proceed over time within that solvent. As a result, the perovskite crystals can be grown sufficiently, and a higher quality perovskite film can be formed.

[0061] Thus, the formation of higher-quality perovskite films results in perovskite solar cells with improved power generation efficiency and reduced short-circuit rates. This is expected to lead to the widespread adoption of perovskite solar cells and a reduction in power generation using fossil fuels and the associated carbon dioxide emissions.

[0062] (10) Example To confirm the effectiveness of this embodiment, a perovskite solar cell containing a perovskite film was fabricated and its power conversion efficiency (PCE) was measured.

[0063] The solution used to form the perovskite film consisted of a perovskite precursor and a solvent. The perovskite precursor was lead iodide (PbI2) and methylammonium iodide (CH3NH3I). The solvent consisted of DMF, DMSO (a slow-acting solvent), and L-α-phosphatidylcholine (a surfactant).

[0064] The perovskite film was formed using the perovskite film formation apparatus 10 described above, according to the perovskite film formation method described above. After the perovskite film was completed, the necessary layers were stacked on top of the perovskite film to manufacture a perovskite solar cell.

[0065] PCE was measured using a solar simulator compliant with JIS C8912 / 8933.

[0066] (10-1) Experiment on the temperature of the warm air blown from the blower 32a The effect on PCE was investigated by changing the temperature of the warm air blown from the blower 32a. All conditions other than the warm air temperature were kept constant.

[0067] The PCE measurement results are shown in Figure 7. The PCE is expressed as a ratio with the value at a hot air temperature of 68.1°C set to 1. Good PCE results were observed when the hot air temperature was between 68°C and 80°C, but as can be seen in Figure 7, the PCE performance was particularly pronounced when the temperature was between 70°C and 75°C.

[0068] (10-2) Experiment on the relative velocity of hot air with respect to the transport speed of substrate 1 The effect on PCE was investigated by changing the relative velocity of the hot air blown from the blower 32a with respect to the conveying speed of the substrate 1. The relative velocity was changed by keeping the conveying speed of the substrate 1 constant and varying the velocity of the hot air blown from the blower 32a. All conditions other than the hot air velocity were fixed.

[0069] The PCE measurement results are shown in Figure 8. The PCE is expressed as a ratio with the value at a relative velocity of 1.35 m / s set to 1. As can be seen from Figure 8, the PCE performance was particularly good when the relative velocity was between 0.1 m / s and 1.0 m / s. [Explanation of Symbols]

[0070] 1...Substrate, 2...Solution layer, 3...Perovskite film laminate, 4...Transparent electrode, 5...Electron transport layer, 6...Mesoporous titanium oxide layer, 7...Perovskite layer, 8...Hole transport layer, 9...Back electrode, 10...Perovskite film formation apparatus, 11...Unwinding section, 12...Surface treatment section, 13...Coating chamber, 14...Solvent removal chamber, 15...Crystallization chamber, 16...Annealing chamber, 17...Pressure adjustment chamber, 17a...Pressure adjustment device, 18...Pressure adjustment chamber, 18a...Pressure adjustment device, 19...Pressure adjustment chamber, 19 a...Pressure regulator, 20...Winding shaft, 21...Die, 22...Backup roller, 29...Partition wall, 30...Conveyor roller, 31...Infrared irradiation device, 32a...Blower, 32b...Intake device, 33...Roller cooling device, 40...Conveyor roller, 41...Nozzle, 41a...Front outlet, 41b...Rear outlet, 42...Intake port, 43...Exhaust chamber, 44...Intake chamber, 45...Intake passage, 50...Winding shaft, 51...Intake port, 52...Outlet port, 60...Control unit

Claims

1. In a method for forming a perovskite film, a solution containing a perovskite precursor and a solvent is applied to a substrate, and the perovskite precursor is crystallized on the substrate to which the solution has been applied to form a perovskite film, A solvent removal step involves irradiating the solution on the substrate being transported by rollers with infrared radiation that is not absorbed by the perovskite precursor but is absorbed by the solvent, and blowing hot air in the same direction as the transport direction of the substrate, thereby heating the solution to a temperature at which the perovskite precursor does not crystallize and removing a portion of the solvent; The process includes a crystallization step in which, after the solvent removal step, the solution is heated on the substrate to remove the remaining solvent and to crystallize the perovskite precursor to form the perovskite film, In the solvent removal step, the temperature of the hot air is set to 68°C or higher and 80°C or lower, and the relative velocity of the hot air with respect to the transport speed of the substrate is set to 0.1 m / sec or higher and 1.0 m / sec or lower. The perovskite precursor contains lead iodide, and the solvent contains DMF and a slow-acting solvent. Method for forming perovskite films.

2. The method for forming a perovskite film according to claim 1, wherein the wavelength of the infrared radiation is 1 μm or more and 10 μm or less.

3. The method for forming a perovskite film according to claim 1 or 2, wherein in the crystallization step, the perovskite precursor is heated by sending hot air at 90°C to 110°C toward the substrate.

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