SOLAR CELL AND METHOD FOR MANUFACTURING SOLAR CELL

Abstract

A first object of the present invention is to provide a solar cell having excellent photoelectric conversion efficiency and produced through a process including favorable scribing (e.g., mechanical patterning), and a method for producing the solar cell. A first aspect of the present invention provides a solar cell including, above a flexible substrate, an electrode, a transparent electrode, and a photoelectric conversion layer disposed between the electrode and the transparent electrode, the solar cell further including a hard film disposed between the flexible substrate and the electrode, the hard film containing a nitride, carbide, or boride, the nitride, carbide, or boride containing at least one element selected from the group consisting of titanium, zirconium, aluminum, silicon, magnesium, vanadium, chromium, molybdenum, tantalum, and tungsten.

Claims

1. A solar cell comprising, above a flexible substrate: an electrode; a transparent electrode; and a photoelectric conversion layer disposed between the electrode and the transparent electrode, the solar cell further comprising a hard film disposed between the flexible substrate and the electrode, the hard film containing a nitride, carbide, or boride, the nitride, carbide, or boride containing at least one element selected from the group consisting of titanium, zirconium, aluminum, silicon, magnesium, vanadium, chromium, molybdenum, tantalum, and tungsten.

2. The solar cell according to claim 1, wherein the hard film has a Vickers hardness of 500 to 3,500 HV.

3. The solar cell according to claim 1, wherein the flexible substrate includes a metal foil and an insulating layer formed on the metal foil.

4. The solar cell according to claim 3, wherein the metal foil is an aluminum foil and the insulating layer is an aluminum oxide film.

5. The solar cell according to claim 4, wherein the aluminum oxide film is an anodic oxide film.

6. The solar cell according to claim 1, wherein the photoelectric conversion layer contains an organic-inorganic perovskite compound represented by the formula: R-M-X.sub.3, wherein R represents an organic molecule; M represents a metal atom; and X represents a halogen atom or a chalcogen atom.

7. A method for producing a solar cell, comprising: forming a hard film on a flexible substrate; forming an electrode on the hard film and scribing the electrode; forming a photoelectric conversion layer on the scribed electrode and scribing the photoelectric conversion layer; and forming a transparent electrode on the scribed photoelectric conversion layer and scribing the transparent electrode, the hard film containing a nitride, carbide, or boride, the nitride, carbide, or boride containing at least one element selected from the group consisting of titanium, zirconium, aluminum, silicon, magnesium, vanadium, chromium, molybdenum, tantalum, and tungsten.

8. A solar cell comprising, in the stated order: a cathode; an electron transport layer; a photoelectric conversion layer; and an anode, the photoelectric conversion layer containing an organic-inorganic perovskite compound represented by the formula: R-M-X3, wherein R represents an organic molecule; M represents a metal atom; and X represents a halogen atom or a chalcogen atom, the cathode containing a metal having a lower ionization tendency than titanium.

9. The solar cell according to claim 8, wherein the metal having a lower ionization tendency than titanium includes one or more metals selected from the group consisting of molybdenum, cobalt, and nickel.

10. The solar cell according to claim 9, wherein the metal having a lower ionization tendency than titanium is molybdenum.

11. The solar cell according to claim 8, further comprising a conductive layer below the cathode.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0128] FIG. 1 includes schematic cross-sectional views illustrating an exemplary production process for the solar cell of the first aspect of the present invention.

[0129] FIG. 2 is a schematic view of an exemplary crystal structure of an organic-inorganic perovskite compound.

[0130] FIG. 3 is a schematic cross-sectional view of an exemplary solar cell of the second aspect of the present invention.

DESCRIPTION OF EMBODIMENTS

[0131] Embodiments of the present invention are more specifically described with reference to, but not limited to, the following examples.

EXAMPLE 1

[0132] An aluminum foil (available from UACJ Corp., multipurpose aluminum material A1N30 grade, thickness: 100 pm) was subjected to sulfuric acid anodizing for a treatment duration of 30 minutes, so that an aluminum oxide film (thickness: 5 m, proportion of thickness: 5%) was formed on a surface of the aluminum foil. Thereby, a flexible substrate was obtained.

[0133] A hard film (thickness: 100 nm, Vickers hardness: 2,100 HV) made of titanium nitride (TiN) was formed on the aluminum oxide film using a batch-type sputtering device (available from Ulvac, Inc.) at a RF output of 300 W against a 6-inch Ti target. In this procedure, 20 sccm of Ar and 5 sccm of N.sub.2 were introduced as process gases to control the pressure in film formation to 0.1 Pa.

[0134] An Al film having a thickness of 100 nm was formed on the hard film using a vapor deposition device, and then a Ti film having a thickness of 100 nm was formed on the Al film by a sputtering method. Thereby, a cathode (Ti/Al film) was prepared. The Ti/Al film was then patterned (scribing width: 40 m) by mechanical patterning using a mechanical scribing device (KMPD100, available from Mitsuboshi Diamond Industrial Co., Ltd.).

[0135] A titanium oxide paste containing polyisobutyl methacrylate as an organic binder and titanium oxide (mixture of those with an average particle size of 10 nm and those with an average particle size of 30 nm) was applied to the Ti/Al film by a spin coating method, followed by firing at 200 C. for 30 minutes. Thereby, a porous electron transport layer with a thickness of 500 nm was formed.

[0136] Subsequently, lead iodide as a metal halide compound was dissolved in N,N-dimethylformamide (DMF) to prepare a 1 M solution, and the resulting solution was applied to the porous electron transport layer by a spin coating method to form a film, thereby preparing a sample. Separately, methylammonium iodide as an amine compound was dissolved in 2-propanol to prepare a 1 M solution. The sample with the above lead iodide film was immersed into this solution to form a layer containing CH.sub.3NH.sub.3PbI.sub.3 which is an organic-inorganic perovskite compound. Thereafter, the obtained sample was subjected to annealing treatment at 120 C. for 30 minutes.

[0137] Next, 68 mM of Spiro-OMeTAD (having a spirobifluorene skeleton), 55 mM of t-butylpyridine, and 9 mM of a bis(trifluoromethylsulfonyl)imide silver salt were dissolved in 25 L of chlorobenzene to prepare a solution. This solution was applied to the photoelectric conversion layer by a spin coating method. Thereby, a hole transport layer having a thickness of 150 nm was formed.

[0138] Subsequently, the layer that is a combination of the electron transport layer, the photoelectric conversion layer, and the hole transport layer was patterned by mechanical patterning.

[0139] An ITO film having a thickness of 100 nm was formed as an anode (transparent electrode) on the resulting hole transport layer by a sputtering method. The ITO film was then patterned by mechanical patterning.

[0140] A barrier layer having a thickness of 100 nm was formed from ZnSnO by a sputtering method on the resulting anode. Thereby, a solar cell was obtained.

EXAMPLES 2 TO 12

[0141] A solar cell was obtained in the same manner as in Example 1, except that the hard film was changed as shown in Table 1.

COMPARATIVE EXAMPLE 1

[0142] A solar cell was obtained in the same manner as in Example 1, except that no hard film was formed.

COMPARATIVE EXAMPLE 2

[0143] A solar cell was obtained in the same manner as in Example 1, except that no hard film was formed and the thickness of the aluminum oxide film was changed to 10 m.

COMPARATIVE EXAMPLE 3

[0144] A solar cell was obtained in the same manner as in Example 1, except that the hard film was changed as shown in Table 1.

<Evaluation 1>

[0145] The solar cells obtained in Examples 1 to 12 and Comparative Examples 1 to 3 were evaluated as follows.

(1) Measurement of Photoelectric Conversion Efficiency

[0146] A power source (model 236, available from Keithley Instruments Inc.) was connected between the electrodes of the solar cell, and the photoelectric conversion efficiency was measured with an exposed area of 1 cm.sup.2 using a solar simulator (available from Yamashita Denso Corp.) at an intensity of 100 mW/cm.sup.2.

[0147] With the photoelectric conversion efficiency of the solar cell obtained in Example 1 being taken as 1.0, the photoelectric conversion efficiency values of the solar cells in Examples 2 to 12 and Comparative Examples 1 to 3 were standardized. The cases where the standardized value was not lower than 0.9 were evaluated as oo (Excellent), not lower than 0.7 but lower than 0.9 as o (Good), not lower than 0.6 but lower than 0.7 as (Acceptable), and lower than 0.6 as (Poor).

TABLE-US-00001 TABLE 1 Example Example Example Example Example Example Example Example 1 2 3 4 5 6 7 8 Substrate Metal foil Type Aluminum Aluminum Aluminum Aluminum Aluminum Aluminum Aluminum Aluminum foil foil foil foil foil foil foil foil Insulating Type Anodic Anodic Anodic Anodic Anodic Anodic Anodic Anodic layer oxide film oxide film oxide film oxide film oxide film oxide film oxide film oxide film Thickness 5 5 5 5 5 5 5 5 (m) Hard film Type TiN TiN TiN TiC TiB.sub.2 ZrC ZrN VC Vickers hardness (HV) 2100 2100 2100 2800 3000 2500 1600 2900 Thickness (nm) 100 50 10 50 50 50 100 50 Evaluation Photoelectric conversion efficiency Example Example Example Example Comparative Comparative Comparative 9 10 11 12 Example 1 Example 2 Example 3 Substrate Metal foil Type Aluminum Aluminum Aluminum Aluminum Aluminum Aluminum Aluminum foil foil foil foil foil foil foil Insulating Type Anodic Anodic Anodic Anodic Anodic Anodic Anodic layer oxide film oxide film oxide film oxide film oxide film oxide film oxide film Thickness 5 5 5 5 5 10 5 (m) Hard film Type Mo.sub.2B WB Si.sub.3N.sub.4 AlN Absent Absent Cu Vickers hardness (HV) 2300 3100 1700 1200 Thickness (nm) 50 50 100 150 100 Evaluation Photoelectric x x x conversion efficiency

EXAMPLE 13

[0148] An aluminum film having a thickness of 200 nm and serving as a conductive layer and a molybdenum film having a thickness of 50 nm and serving as a cathode were formed on a glass substrate in succession by an electron beam deposition method.

[0149] Next, titanium oxide was sputtered on a surface of the cathode using a sputtering device (available from Ulvac, Inc.). Thereby, a thin-film electron transport layer having a thickness of 30 nm was formed. Further, a dispersion of titanium oxide (mixture of those with an average particle size of 10 nm and those with an average particle size of 30 nm) in ethanol was applied to the thin-film electron transport layer by a spin coating method, followed by firing at 200 C. for 10 minutes. Thereby, a porous electron transport layer having a thickness of 150 nm was formed.

[0150] Next, CH.sub.3NH.sub.3I and PbI.sub.2 at a ratio by mole of 1:1 were dissolved in N,N-dimethylformamide (DMF) serving as a solvent such that the total weight concentration of CH.sub.3NH.sub.3I and PbI.sub.2 was adjusted to 20%. Thereby, a solution for forming an organic-inorganic perovskite compound was prepared. This solution was applied to the electron transport layer by a spin coating method, followed by firing at 100 C. for 10 minutes. Thereby, a photoelectric conversion layer was formed.

[0151] Next, 68 mM of Spiro-OMeTAD (having a spirobifluorene skeleton), 55 mM of t-butylpyridine, and 9 mM of a bis(trifluoromethylsulfonyl)imide silver salt were dissolved in 1 mL of chlorobenzene to prepare a solution. This solution was applied to the photoelectric conversion layer by a spin coating method. Thereby, a hole transport layer having a thickness of 150 nm was formed.

[0152] An ITO film having a thickness of 200 nm was formed as an anode on the resulting hole transport layer by sputtering using a sputtering device (available from Ulvac, Inc.). Thereby, a solar cell with the conductive layer, the cathode, the electron transport layer, the photoelectric conversion layer, the hole transport layer, and the anode being stacked therein was obtained.

EXAMPLES 14 TO 22

[0153] A solar cell with a conductive layer, a cathode, an electron transport layer, a photoelectric conversion layer, a hole transport layer, and an anode being stacked therein was obtained in the same manner as in Example 13, except that the type of the conductive layer, the type of the cathode, the thickness of the cathode, and the type of the electron transport layer were changed as shown in Table 2.

COMPARATIVE EXAMPLE 4

[0154] A solar cell with a cathode, an electron transport layer, a photoelectric conversion layer, a hole transport layer, and an anode being stacked therein was obtained in the same manner as in Example 13, except that no conductive layer was formed and an aluminum film (having a higher ionization tendency than titanium) was formed as the cathode.

COMPARATIVE EXAMPLES 5 AND 6

[0155] A solar cell with a conductive layer, a cathode, an electron transport layer, a photoelectric conversion layer, a hole transport layer, and an anode being stacked therein was obtained in the same manner as in Example 13, except that the type of the cathode was changed as shown in Table 2.

<Evaluation 2>

[0156] The solar cells obtained in Examples 13 to 22 and Comparative Examples 4 to 6 were evaluated as follows. Evaluation results are shown in Table 2.

(1) Measurement of Photoelectric Conversion Efficiency

[0157] A power source (model 236, available from Keithley Instruments Inc.) was connected between the electrodes of the solar cell. A current-voltage curve was drawn using a solar simulator (available from Yamashita Denso Corp.) at an intensity of 100 mW/cm.sup.2, and the photoelectric conversion efficiency was calculated. The cases where the photoelectric conversion efficiency was not lower than 10% were evaluated as oo (Excellent), not lower than 8% but lower than 10% as o (Good), and lower than 8% as (Poor).

(2) Calculation of Series Resistance

[0158] In the current-voltage curve drawn in the Measurement (1), the reciprocal of the slope at the point of intersection of the curve with the X axis was calculated as the series resistance. The cases where the series resistance was lower than 5 were evaluated as oo (Excellent), not lower than 5 but lower than 10 as o (Good), and not lower than 10 as (Poor).

TABLE-US-00002 TABLE 2 Evaluation Thickness of Electron transport Photoelectric Conductive layer Cathode cathode (nm) layer conversion efficiency Series resistance Example 13 Aluminum Molybdenum 50 Titanium oxide Example 14 Aluminum Cobalt 50 Titanium oxide Example 15 Aluminum Nickel 50 Titanium oxide Example 16 Aluminum Molybdenum 20 Titanium oxide Example 17 Aluminum Molybdenum 10 Titanium oxide Example 18 Copper Molybdenum 50 Titanium oxide Example 19 Absent Molybdenum 100 Titanium oxide Example 20 Aluminum Tantalum 50 Titanium oxide Example 21 Aluminum Molybdenum 50 Tin oxide Example 22 Aluminum Molybdenum 50 PCBM Comparative Example 4 Absent Aluminum 100 Titanium oxide x x Comparative Example 5 Aluminum Magnesium 50 Titanium oxide x x Comparative Example 6 Aluminum Titanium 50 Titanium oxide x x

INDUSTRIAL APPLICABILITY

[0159] The present invention can provide a solar cell having excellent photoelectric conversion efficiency and produced through a process including favorable scribing (e.g., mechanical patterning), and a method for producing the solar cell. The present invention can also provide a solar cell having low series resistance and high photoelectric conversion efficiency.

REFERENCE SIGNS LIST

[0160] 1: Metal foil [0161] 2: Insulating layer [0162] 3: Hard film [0163] 4: Electrode [0164] 41: Groove [0165] 5: Scribing tool [0166] 6: Solar cell [0167] 7: Cathode [0168] 8: Electron transport layer [0169] 81: Thin-film electron transport layer [0170] 82: Porous electron transport layer [0171] 9: Photoelectric conversion layer containing organic-inorganic perovskite compound [0172] 10: Hole transport layer [0173] 11: Anode (patterned electrode)