KR102170685B1 - Stacked Perovskite structure and its use - Google Patents

Abstract

The perovskite structure of the present invention is stable and has excellent conductivity, and can exhibit excellent performance in the use of the photovoltaic device for solar cells.

Description

Stacked Perovskite structure and its use

The present invention relates to a layered perovskite structure that is stable and has excellent conductivity and uses thereof.

Perovskite is an excellent material as a solar cell light absorber, but it is very vulnerable to moisture and air. To solve the problems of the existing perovskite, perovskite that introduces a low-dimensional structure to a three-dimensional structure Is being developed. The low-dimensional structure with bulk cations serves to prevent the three-dimensional structure from being easily degraded.

However, in general, the layered 2D structure introduced with the secondary structure in the tertiary structure can be typically described as Ruddlesden-Popper (RP) and Dion-Jacobson (DJ) structures. It is difficult to form a vertical stacked structure with a structure in which the unit cells of perovskite are shifted. Therefore, because the crystal is generated in the lateral direction, there is a side in which the collection of carriers is insufficient in the photoelectric device.

Korean Patent Publication No. 2019-0007812

An object of the present invention is to provide a laminated perovskite structure having a stable and excellent conductivity and a use thereof.

1. Two secondary or tertiary perovskite layers comprising the unit structure of Formula 1 and spaced apart from each other; And

As a laminated perovskite structure represented by Formula 2, comprising a divalent organic cation compound of an aromatic heterocyclic compound substituted with at least one aminoalkyl group,

Two cationic groups are the nitrogen atom and the hetero atom hydrogenated (hydrogenation), each forming a hydrogen interaction with X ^- of different layers structure:

[Formula 1]

[PbX ₆ ] ^2-

(Wherein, X is one selected from the group consisting of Cl, Br and I)

[Formula 2]

(C) ₂ (A) _n-1 Pb _n X _3n+1

(Wherein, C is the divalent organic cation compound, A is methylammonium or formammonium (HC(NH ₂ ) ₂ ⁺ ), X is one selected from the group consisting of Cl, Br and I, and n is 6 An integer greater than or equal to).

2. The structure of 1 above, wherein the aminoalkyl group includes C _1-3 alkyl.

3. The structure of the above 1, wherein the aromatic heterocyclic compound is a 4 to 7 membered ring compound.

4. The structure of the above 1, wherein the aromatic heterocyclic compound is at least one selected from the group consisting of compounds represented by the following Formulas 3 to 10:

[Formula 3]

[Formula 4]

[Formula 5]

[Formula 6]

[Formula 7]

[Formula 8]

[Formula 9]

[Formula 10]

.

.

5. The structure of the above 1, wherein the aromatic heterocyclic compound is represented by the following formula (10):

[Formula 10]

.

.

6. The structure of the above 5, wherein the divalent organic cation compound of the aromatic heterocyclic compound is represented by the following formula (11):

[Formula 11]

.

.

7. The structure of the above 1, wherein the divalent organic cation compound of the aromatic heterocyclic compound is located at a distance between the two perovskite layers.

8. The structure according to the above 1, wherein X in Formulas 1 and 2 is I.

9. In the above 1, A in Formula 2 is formammonium (HC(NH ₂ ) ₂ ) ⁺ phosphorus structure.

10. A perovskite structure stacked vertically with respect to the perovskite layer in a unit of any one of the structures 1 to 9 above.

11. A photovoltaic device for a solar cell comprising any one of the above structures 1 to 9.

The perovskite structure of the present invention is stable and has excellent conductivity, and can exhibit excellent performance in the use of the photovoltaic device for solar cells.

Figure 1: (a) Crystal structure of HAPbI ₄ , (b) Inorganic [PbI ₆ ] 4 hydrogen bonds per histamine unit formed between the two ^- layer protonated amine and adjacent 4 iodine ions, (c) d-FAPbI ₃ 1D crystal structure and (d) 2D layered (HA) ₂ (FA)Pb ₂ I ₇ perovskite crystal structure.
Figure 2: (a) Crystal structure of HAPbI ₄ , (b) 2D layered (HA) ₂ (FA)Pb ₂ I ₇ perovskite crystal structure, (c) HR- of perovskite crystal of 2D HAPbI ₄ TEM image, (d) HR-TEM image of 2D layered (HA) ₂ (FA)Pb ₂ I ₇ perovskite crystal.
Figure 3: (a) HAPbI ₄ plate-shaped SEM image, (b) vertically stacked 2D (HA) ₂ (MA) _n-1 Pb _n I _3n+1 perovskite SEM image, (c) (b) Magnified SEM image of the yellow square portion of, (d) 2D (HA) ₂ (FA) _n-1 Pb _n I _3n+1 high magnification SEM image of perovskite, (e) elemental map of (d).
Figure 4: Used to determine the band gap of 2D (HA) ₂ (A) _n-1 Pb _n I _3n+1 (A = MA or FA), HAPbI ₄ , MAPbI ₃ and a-FAPbI ₃ perovskites UV visible diffuse reflection spectrum.
Figure 5: Powder X-ray diffraction of 2D (HA) ₂ (A) _n-1 Pb _n I _3n+1 (A = MA or FA), HAPbI ₄ , MAPbI ₃ and a-FAPbI ₃ perovskite.
Figure 6: Instantaneous photoluminescence of 2D (HA) ₂ (A) _n-1 Pb _n I _3n+1 (A = MA or FA), HAPbI ₄ , MAPbI ₃ and a-FAPbI ₃ perovskites.
Figure 7: (a) 2D (HA) ₂ (A) _n-1 Pb _n I _3n+1 (A = MA or FA) series, (HA)PbI ₄ , MAPbI ₃ , and a-FAPbI ₃ pages on FTO substrate UPS spectrum of Lobskyite, (b) cut-off edge area of photoluminescence spectrum, (c) UPS spectrum above occupied state, (d) FTO / TiO ₂ / perovskite / spiro-MeOTAD / Au Energy level of 2D perovskite for heterojunction solar cell construction.
Figure 8: (a) (HA)PbI ₄ , (b) (HA) ₂ (MA) _n-1 Pb _n I _3n+1 and (c) (HA) on the FTO/TiO ₂ blocking layer/TiO ₂ mesoporous layer ) ₂ (FA) _n-1 Pb _n I _3n+1 SEM image of the perovskite film, measured on the surface of the SEM image (d) (HA)PbI ₄ , (e) (HA) ₂ (MA) _n AFM images of _-1 Pb _n I _3n+1 and (f) (HA) ₂ (FA) _n-1 Pb _n I _3n+1 perovskite films.
Figure 9: Photovoltaic performance of perovskite solar cells made of (a) pure 2D and (b) mixed perovskite under simulated AM (air mass) 1.5G (global) illumination (100 mW/cm ^-2 ) (JV curve obtained from forward scan).
Figure 10: Steady-state photoluminescence spectrum of 2D (HA) ₂ (A) _n-1 Pb _n I _3n+1 (A = MA or FA), HAPbI ₄ , MAPbI ₃ and a-FAPbI ₃ perovskite.

Hereinafter, the present invention will be described in detail.

The present invention is at the core of developing a multilayered perovskite structure by introducing a divalent organic cation into a secondary or tertiary perovskite. In general, secondary perovskite has only lateral growth and has a disadvantage in that it has a lot of carrier loss when used as a photovoltaic device, but it has the advantage of superior stability to the surrounding environment. Tea perovskite has the disadvantage of rapid decay due to its remarkably low stability to the surrounding environment, but has advantages such as vertical growth, low carrier loss, and high conductivity. Therefore, in order to combine the above and advantages, it was attempted to develop a three-dimensional structure vertically grown by introducing a divalent organic cation between the secondary or tertiary perovskite layers, which has excellent stability to the surrounding environment. In addition, vertical growth is possible, carrier loss is low, and conductivity is high, and it is believed that its utilization as a solar cell optical device will be high.

Thus, specifically, the present invention includes the unit structure of the following formula (1), two secondary or tertiary perovskite layers spaced apart from each other; And it provides a laminated perovskite structure represented by the formula (2) comprising a divalent organic cation (organic dication) compound of an aromatic heterocyclic compound substituted with at least one aminoalkyl group:

[Formula 1]

[PbX ₆ ] ^2-

(Wherein, X is one selected from the group consisting of Cl, Br and I)

[Formula 2]

(C) ₂ (A) _n-1 Pb _n X _3n+1

(Wherein, C is the divalent organic cation compound, A is methylammonium or formammonium (HC(NH ₂ ) ₂ ⁺ ), X is one selected from the group consisting of Cl, Br and I, and n is 6 Or more integers).

In Formulas 1 and 2, X may be specifically I, which may be more preferable than Br and Cl in terms of forming a strong hydrogen interaction between the hydrogen atom of the cationic group of the divalent organic cation and X ⁻ have.

In Formula 2, A may be specifically formammonium (HC(NH ₂ ) ₂ ⁺ ), which maintains stable lateral growth of the perovskite layer, and carrier loss of the structure itself (carrier loss) may be more preferable than methylammonium.

In the aromatic heterocyclic compound substituted with the aminoalkyl group, the alkyl group of the aminoalkyl group is 10, 1 to 9, 1 to 8, 1 to 7, 1 to 6, 1 to 5, 1 to 4, or 1 in carbon 1 It may contain to 3 atoms, but there is no particular limitation on the number of carbon atoms in the alkyl group as long as both perovskite layers can be stably linked by hydrogen interaction, more preferably 1 to 3 carbon atoms, It is possible to ensure the stability of the structure itself and the connectivity between both perovskite layers.

In the aromatic heterocyclic compound substituted with the aminoalkyl group, the aromatic heterocyclic compound may be a 3 to 10 atom, 4 to 9 atom, 4 to 8 atom, or 4 to 7 membered ring compound, but both perovskites If the layers can be stably linked by hydrogen interaction, there is no particular limitation on the size of the ring, and more preferably as a 4 to 7 membered ring compound, the stability of the structure itself and the connectivity between both perovskite layers can be secured. have.

In the aromatic heterocyclic compound substituted with the aminoalkyl group, the two cationic groups are the nitrogen atom and the hetero atom hydrogenated, and may form hydrogen interactions with X ⁻ of different layers, respectively. The action is the main factor that enables the structure of the present invention to be grown vertically with respect to the perovskite layer, and to ensure the stability of the structure itself.

In the aromatic heterocyclic compound substituted with the aminoalkyl group, specifically, it may be at least one selected from the group consisting of compounds represented by the following formulas 3 to 10:

[Formula 3]

[Formula 4]

[Formula 5]

[Formula 6]

[Formula 7]

[Formula 8]

[Formula 9]

[Formula 10]

.

.

In a specific example of hydrogenation of the nitrogen atom and the hetero atom, the hydrogenated form of the compound represented by Formula 10 may be a form represented by the following Formula 11:

[Formula 11]

.

.

In the divalent organic dication compound of the aromatic heterocyclic compound, this increases the stability of the structure itself through hydrogen interaction between the two perovskite layers, thereby remarkably improving the stability of vertical growth and stability from the surrounding environment. From the viewpoint of increasing, it is preferable to be located at a distance between the two perovskite layers.

The present invention provides a perovskite structure in which a plurality of perovskite structures are stacked vertically with respect to a perovskite layer in units of the structures described in detail above.

The plurality of stacked perovskite structures includes a plurality of perovskite layers, and a divalent organic cation compound of the aromatic heterocyclic compound specifically described above is present in a space between each layer, so that a plurality of The perovskite layer may be a vertically grown structure.

In addition, the present invention provides an optical device for a solar cell including the structure described in detail above.

When the optical device of the present invention is used in a solar cell, it has excellent stability to the surrounding environment, has a low carrier loss, and thus has excellent efficiency, and has excellent conductivity in electric conduction using sunlight, and is stably vertical. It can be grown and fabricated to suit a specific use environment, and its industrial value is remarkably high.

Hereinafter, examples will be described in detail to illustrate the present invention in detail.

Experiment method

1. Experimental materials

Lead oxide (PbO, 99%), histamine (CH ₃ (CH ₂ ) ₄ CH ₂ NH ₂ , HA, ≥97%), iodic acid (57% by weight of Hydriodic acid, HI, H ₂ 0), Hypophosphorous acid (50% by weight in H ₃ PO ₂ , H ₂ 0), N,N-dimethylformamide (N,N-dimethylformamide, DMF, anhydride, 99.8%), dimethyl sulfoxide (DMSO, anhydride, ≥99.9%), methylamine hydrochloride (CH ₃ NH ₃ Cl, ≥98%), histamine dihydrochloride (C ₅ H ₉ N ₃ ·2HCl, ≥99%) and chlorobenzene (Chlorobenzene, CB, anhydride, 99.8%) was purchased from Sigma-Aldrich and used without further purification. Spiro-MeOTAD (spiro-MeOTAD) and phenyl-C ₆₁ -butyric acid methyl ester (Phenyl-C61-butyric acid methyl ester, PC ₆₁ BM, >99%) were purchased from Luminescence Technology Corporation. Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate)-poly(styrenesulfonate), PEDOT:PSS, CLEVIOS Al4083) was purchased from Heraeus. CH ₃ NH ₃ I (MAI) was synthesized by neutralization with an equimolar amount of 57% w/w aqueous HI and 40% w/w aqueous methylamine (CH ₃ NH ₂ ). A white precipitate was collected by evaporation of the solvent using rotary evaporation at 60° C. under reduced pressure.

2. Preparation of perovskite

(1) HAPbI ₄

A 100 ml two necked round bottom flask was charged with 5.0 ml of stabilized HI (57% aqueous solution) or a trace amount of hypophosphorous acid (1.5% H ₃ PO ₂ ). The mixture was degassed with nitrogen for 1 minute, and the flask was kept under nitrogen conditions for the duration of the experiment. The flask was heated to 120° C. in an oil bath, PbI ₂ (0.46101 g, 1 mmol) was added and then stirred vigorously until the solid was completely dissolved. Subsequently, histamine dihydrochloride (0.18407 g, 1 mmol) was added to the flask, and an orange precipitate was immediately obtained. The solution was stirred for an additional 15 minutes, then the heat was removed and the flask was air-cooled with gentle stirring. The solution and precipitate were washed with anhydrous ether and centrifuged 3 times. The product was dried in a vacuum oven at 50° C. for 24 hours.

(2) (HA) ₂ (FA) _n-1 Pb _n I _3n+1

A 100 mL two-neck round bottom flask was charged with 5.0 mL of stabilized HI (57% aqueous solution) and 1 mL of hyposulfite (H ₃ PO ₂ 50% by weight aqueous solution). The mixture was degassed with nitrogen for 1 minute, and the flask was kept under nitrogen conditions for the duration of the experiment. The flask was heated to 120° C. in an oil bath, PbO (0.6696 g, 3 mmol) was added and then stirred vigorously, forming a light yellow solution. Then, solid FAI (0.3439 g, ₂ mmol) was added to the hot PbI ₂ solution. When a black precipitate initially started to form, the solution was stirred vigorously to obtain a bright, clear yellow solution that quickly redissolved. In a separate beaker, histaminedihydrochloride (0.1012g, 0.55mmol) was neutralized with an aqueous solution of 57% by weight HI (2 mL, 15 mmol) in an ice bath. The HAI solution was slowly added dropwise (drop by drop) to the PbI ₂ solution while continuously stirring. A black precipitate initially formed, which re-dissolved during boiling the combined solution. Stirring was stopped and the hot solution was slowly cooled to room temperature. During this time, cherry red rectangular-shaped plates began to settle. After allowing the solution to stand for 3 hours, the crystals were separated by suction filtration, washed with diethyl ether, and dried in a vacuum oven at 60°C. A yield of 62% was estimated proportional to the total Pb content.

(3) (HA) ₂ (MA) _n-1 Pb _n I _3n+1

(HA) ₂ (MA) _n-1 Pb _n I _3n+1 was synthesized using a synthetic procedure similar to the above. However, the amount of MACl was increased as MAPbI ₃ is relatively slow compared to precipitate α-FAPbI _3. The experimental ratio of HAI: MAI: PbO was 0.55: 3: 3. The yield based on the total Pb content is 56%.

3. Physical property analysis

(1) single crystal X-ray diffraction

Single crystal X-ray diffraction data were obtained from Pohang Accelerator Laboratory, silicon (111) double crystal monochromator (DCM), BL2D SMC to ADSC Quantum-210 detector, and synchrotron radiation (l). = 0.61000Å). The PAL BL2D-SMDC program was used for data acquisition (detector distance 63mm, omega scan; Δω = 3°, exposure time 1 second per frame), HKL3000sm (version 703r) used for cell segmentation, reduction and absorption correction Became. The crystal structure of perovskite was solved by the direct method using the SHELXT-2014 program and refined by full-matrix least-squares calculations with the SHELXL-2014 program package.

(2) Steady state and time-resolved photoluminescence

Steady-state PL spectra were measured by dividing and guiding the PL signal through an optical fiber using a HORIBA LabRAM HR Evolution confocal RAMAN microscope. Using a 532 nm laser (0.01% power), all samples were excitation at 50x magnification. Time-resolved PL (TRPL) studies were performed using an inverted-type scanning confocal microscope (MicroTime-200, Picoquant, Germany) and a 60x (air) objective. Lifetime measurement was performed at the Daegu Center of the Korea Science Foundation (KBSI). A single-mode pulsed diode laser (470nm, pulse width is ~30ps) was used as an excitation source. To collect the emission from the sample, a dichroic mirror (490 DCXR, AHF), a long-pass filter (HQ500lp, AHF), a 75 μm pinhole and a single photon avalanche diode (PDM series), MPD) was used. TRPL images consisting of 200 x 200 pixels were recorded using the time-tag time resolution (TTTR) data collection method. Exponential fittings to the acquired PL decay were performed using Symponotime-64 software (version 2.2) with the exponential decay model:

[Equation 1]

(I(t) is the PL intensity over time, A is the amplitude, and τ is the PL lifetime).

(3) Ultraviolet photoelectron spectroscopy (UPS)

The UPS measurement was performed using an AXD ultra-wideband detector (DLD) (Kratos Inc.) of the Korea Basic Science Research Center in Daejeon, and the He I (21.22 eV) emission line was used as a UV light source.

(4) light absorption spectroscopy

The light diffuse reflection spectrum was measured using an Agilent (Cary-5000) UV-VIS-NIR system. Polytetrafluoroethylene was used as a non-absorption reference material with 100% reflectance. The reflectance versus wavelength was converted into absorption data, and the band gap (Eg) was calculated using the Kubelka-Munk equation:

[Equation 2]

α/S = (1-R) ² (2R) ^-1

(R is reflectance, α and S are absorption and scattering coefficients, respectively).

(5) powder X-ray diffraction

Powder XRD patterns were measured using an Empyrean PANalytical instrument with Cu Kα radiation (40 kV, 30 mA, l = 1.54056 Å) and Ni filter with graphite monochromator.

4. Solar cell manufacturing

The formation of the N-type TiO ₂ layer was used in the following manner. The 50 nm compact layer of TiO ₂ was spin-coated (2000 rpm 30 seconds) of a weak acid solution of titanium isopropoxide (TTIP, 350 mL TTIP in 5 mL EtOH containing 0.013 M HCl) containing ethanol. Was deposited on the FTO substrate by Then, a sintering process was performed at 550° C. for 30 minutes. TiO of a TiO ₂ paste (DYESOL-30NRD) diluted with ethanol at a ratio of 1: 3.5 w/w for 5 seconds at 500 rpm, 10 seconds at 3,000 rpm, and 30 seconds at 6,000 rpm with a mesoporous TiO ₂ layer ₂ Compact layers were spin coated. The substrate was further treated with an aqueous 20 mM TiCl ₄ solution at 70° C. for 30 minutes, rinsed with deionized water and ethanol, and then sintered at 500° C. for 30 minutes. 30% Rb-based perovskite was dissolved in DMSO solvent. This solution was spin-coated on an N-type TiO ₂ layer at 4,000 rpm for 30 seconds and then annealing at 100° C. for 30 minutes. The solution for Spiro-MeOTAD coating was 72.3 mg of Spiro-MeOTAD dissolved in 1 mL of chlorobenzene, 28.8 μL of 4-tert-butylpyridine and 17.5 μL of lithium bis(trifluoromethanesulfonyl)imide It was prepared by adding a solution (520 mg of Li-TSFI, Sigma-Aldrich, 99.8% in 1 mL). Spiro-MeOTAD was deposited on the perovskite layer at 4,000 rpm for 30 seconds. An 800 Å gold layer for the counter electrode was deposited on the perovskite layer with 1.5 Å/s thermal evaporation.

Experiment result

2D (HA) ₂ (FA) _n-1 Pb _n I Group _3n+1 compounds were prepared using stoichiometric reactions between PbO, HAI and FAI. HI solution neutralized HAI was added to a concentrated stoichiometric homogenous solution of PbO and FAI without I ₂ . A clear yellow solution was initially formed at boiling temperature under vigorous stirring, which upon cooling to room temperature gave a black precipitate in a 3D rectangular stacking shape. 1 shows the crystal structure of HAPBI ₄ and 2D (HA) ₂ (FA) _n-1 Pb _n I _3n-1 , and crystallographic data are presented in Table 1. HAPBI ₄ is a three-dimensional space group with lattice parameters a = 8.8902(18)Å, b = 20.038(4)Å, c = 9.0050(18)Å, α = 90°, ß = 91.86(3)° and γ = 90° It crystallizes at P21/n. This is a layered perovskite template with a divalent organic cation histammonium (C5N3H11) ²⁺ ) containing both primary ammonium and imidazolim cations. The HA divalent cation layer formed a double layer between the octahedrons that shared the edges of the [PbI ₆ ] ^2- layer, bringing the inorganic layer closer. Since the interlayer iodine-iodine distance is 4.3878(9)Å (Fig. 1A), it is considered to provide a vertical layer structure by deviating from the general trend of plate shape when 2D perovskite is combined with 3D perovskite. Can be. Hereinafter, the formation of a vertical layer structure when HAPbI ₄ is combined with α-FAPbI ₃ or MAPbI ₃ will be described. The MIM bonding angle in hybrid layered perovskite materials is another important feature because the bonding interaction reflected by the bonding angle has the greatest effect on the band gap. The bonding angles of Pb-I-Pb in HAPbI ₄ were 156.17 ^° and 178.05 ^° . The deviation of Pb-I-Pb from the ideal (non-distorted) 180° value is similar to the compounds HAPbBr ₄ (174.84° and 153.66°) and (C ₆ H ₅ C ₂ H ₄ NH ₃ ) ₂ PbCl ₄ (151.45°) , 151.37°, 153.21° and 153.28°). This may be due to differences in hydrogen bond strength due to the special structure of the organic material. The local environment of the organic ammonium group shown in FIG. 1B consists of 4 hydrogen bonds per histamine unit, is formed between protonated amines, and is adjacent to the inorganic [PbI ₆ ] ^2- layered 4 iodine ions. Considering the bonding distance of ³⁹ HI of 2.65Å and 2.78Å between NH of the imidazole group and the iodine group, the hydrogen bonding interaction of 3.01Å and 2.83Å between the amine group and the adjacent iodine ion is weak. Since the imidazole group of the histamine unit has steric hindrance to hydrogen bonding with the inorganic material sheet, an electrostatic interaction occurs more predominantly between the charged organic cations and the inorganic material layer.

To create a vertical layer structure, 2D HAPbI ₄ was introduced inside the α-FAPbI ₃ crystal structure. FAPbI ₃ has two polymorphs: a hexagonal yellow phase (space group P63mc) and a black perovskite phase (α-FAPbI ₃ , space group P3m1), biperovskite (δ-FAPbI ₃ ). α-FAPbI ₃ was slowly transformed into thermodynamically stable δ-FAPbI ₃ . δ-FAPbI ₃ is composed of a face-sharing octahedron that spreads along the c-axis direction (Fig. 1c). The inorganic layer was packed with hcp-lattices to form 1D single chains. The spaces between the 1D inorganic layers were filled with FA+ cations. As discussed in the Stoumpos report, deviations from ideal symmetry can be attributed to severe disorders of the FA+ cations in the crystal structure. The prepared α-FAPbI ₃ is rapidly transformed into δ-FAPbI ₃ through a cooling process from high temperature to room temperature. However, when heated at high temperatures, defective compounds are produced due to partial loss of FA, and the δ-FAPbI ₃ phase reverts to its original form, α-FAPbI ₃ , and very slowly returns to the δ-FAPbI ₃ crystal structure. Goes. Since α-FAPbI ₃ is a more preferable structure as a photoactive material having a band gap (1.48 eV) that is preferable for photoelectric conversion and near-infrared emission, an additional process is required to suppress the formation of a δ-FAPbI ₃ phase. The mixed cationic perovskite prepared by combining HAPbI ₄ and α-FAPbI ₃ stabilizes the α-FAPbI ₃ phase and further reduces the band gap compared to HAPbI ₄ (FIG. 1D ).

The HAPbI ₄ perovskite consists of an inclined layered corner-sharing [PbI ₆ ] ^4- octahedral sheet, propagating along the ac plane with the b axis to form a three-dimensional structure. Each of the imidazolium group and the alkyl ammonium group has two NH bonds, and the inorganic layers are stacked in a distorted form with respect to each other in order to connect the inorganic layers closer to each other (FIG. 2A). Similarly, the inorganic layer of (HA) ₂ (FA) _n-1 Pb _n I _3n+1 was stacked on the other layer along the c-axis, whereas the inorganic layer propagated in the ab plane direction unlike HAPbI ₄ (FIG. 2B ). The HR-TEM image of HAPbI ₄ of FIG. 2C shows a complete octahedral structure of [PbI ₆ ] ⁴ , representing Br atoms with higher contrast than Pb atoms. The [002] plane image of HAPbI ₄ is superimposed on FIG. 2C to coincide with the experimental atomic position. The quantitative agreement between the experimental data and the simulation data indicates that HAPbI ₄ consists only of a single octahedral layer. For comparison, the HR-TEM image of 2D (HA) ₂ (FA)Pb ₂ I ₇ perovskite is shown in FIG. 2D, and the HR-TEM result of (HA) ₂ (FA)Pb ₂ I ₇ 200] A flat image was applied. The two inorganic layers are extracted from the experimental and simulated single crystal images. Therefore, the two-dimensional stacked (HA) ₂ (FA)Pb ₂ I ₇ perovskite was well prepared with the divalent cations HAPbI ₄ and 3D α-FAPbI ₃ .

3A and 3B show SEM images of HAPbI ₄ showing a plate-like structure consistent with the 2D structure. Figure 3c shows the SEM image of the lamination structure of these plates in the (HA) ₂ (FA) _n-1 Pb _n I _3n+1 crystal structure, which shows that the divalent cation HA induces the lamination of the 2D perovskite structure. Suggests. The use of diamonium provided a bridge between the 2D perovskites because they have two positive cations. One was attached to itself, and the other could be combined with another slab. Thus, a 3D structure was created by stacking 2D slabs in one direction. The interaction between the divalent cations and the 2D slab was very robust, resulting in a strong and stable structure. (HA) ₂ (MA) _n-1 Pb _n I _3n+1 (FIG. 3D) The same layered structure was obtained for the compound. In FIG. 3C, EDAX was used to confirm the atomic composition of the upper region of the image ( 3e), which shows the composition of (HA) ₂ (FA) _n-1 Pb _n I _3n+1 .

Subsequently, a UV-visible diffuse reflectance spectra was measured and a Kubelka-Munk conversion was performed to confirm the charge transfer process. In HAPbI ₄ (FIG. 4), the charge transfer process is likely to have occurred due to the interaction between histamine and the isolated PbI ₆ octahedron, because the absorption characteristic of histamine is not high and has an orange color. The optical spectrum of HAPbI ₄ shows a high energy absorption edge and a low energy excitonic peak, which are typical 2D perovskite properties. The exciton behavior arises from the dielectric constraints between the organic and inorganic layers to form a quantum well exciton structure in the perovskite structure. The finite quantum confinement effect was observed as the three-dimensional perovskite decreased to a lower-dimensional pseudostructure. The band gap of HAPbI ₄ was assigned by extrapolating the high energy absorption edge to the energy axis, and the (HA) ₂ (A) _n-1 Pb _n I _{3n+1 of the} 2D perovskite layer (A is MA or FA), the peak disappeared. The absorption of excitons was believed to arise from the long-lived exciton state in a strong electric field generated by localized organic cations around the negatively charged inorganic layer in the perovskite structure. The exciton peak is expected to decrease as n increases in the layered 2D perovskite. However, 2D layered perovskite (HA) ₂ (A) _n-1 Pb _n I _3n+1 (A is MA or FA) has a slight tailing at the absorption edge derived from impurities of higher order homogeneity. Had, but pure MAPbI ₃ and black α-FAPbI ₃ showed sharp absorption edges indicating direct bandgap material.

The 2D layered perovskite was confirmed by powder XRD (Fig. 5). (HA) ₂ (A) _n-1 Pb _n I _3n+1 (A is MA or FA) The compound showed two peaks around 14° and 28°, which is (002)/(110) in the vertical growth direction. ) And (004)/(220) crystal planes are reflected (FIGS. 5B, 5C). In particular, (HA) ₂ (MA) _n-1 Pb _n I _3n+1 was only observed, which clearly indicates the vertical growth of the perovskite compound. Thus, the advantage of a dimensionally controlled perovskite structure is that it provides an important opportunity to enhance charge transport into the electron collection layer by a direct path.

To detect the emission characteristics of the 2D layered perovskite at room temperature, PL spectroscopy was measured (Fig. 10). MAPbI ₃ , FAPbI ₃ and HAPbI ₄ perovskites showed a single emission peak with a maximum PL peak position in good agreement with the exciton peak in the absorption spectrum, whereas 2D layered perovskite, (HA) ₂ (A) _n-1 Pb _n I _3n+1 (A is MA or FA) showed several emission peaks, which is evidence that multiple layers of 2D perovskite exist. TRPL was measured to determine the PL lifetime of the 2D perovskite, and the time decay of the fluorescence spectrum was fitted to the tree exponential of FIG. 6. The fit of the single wavelength PL decay of the exponential decay model produced the carrier lifetime of the 2D layered perovskite summarized in Table 2. The faster decay process (τ ₁ ) indicates the radioactive recombination of excitons, and the slow decay process (τ ₂ and τ ₃ ) is associated with the formation of trap states due to electron-phonon bonding in the layered perovskite. As exciton radioactive recombination in 2D perovskite proceeded rapidly, only longer carrier lifetimes were compared. The emission of (HA) ₂ (MA) _n-1 Pb _n I _3n+1 perovskite crystals decayed with a long lifetime of 282 ns, which is about 35 times that of MAPbI ₃ 8.2 ns. This is much longer than other stacked 2D perovskites showing carrier lifetime values of about 0.1 to 200 ps ((NH ₃ C _m H _2m NH ₃ )(CH ₃ NH ₃ ) ₂ Pb ₃ I ₁₀ (m = 7, 8, 9), (C ₆ H ₅ C ₂ H ₄ NH ₃ ) ₂ PbI ₄ ·(CH ₃ NH ₃ PbI ₃ ) _n-1 (n = 1, 2, 3) and A′(CH ₃ NH ₃ ) _n-1 Pb _n I _3n+1 (A′ = 3-(aminomethyl)piperidinium(3AMP) or 4-(aminomethyl)piperidinium(4AMP)).

To demonstrate that the film of 2D layered perovskite is an efficient light absorber, the energy level of the perovskite layer with the interfacial layer in the photovoltaic device was determined using a UPS (FIG. 8A ). The valence band and work function (WF) were calculated from the low binding energy level and the secondary cutoff edge region in the photoelectron spectral spectrum, respectively. All energies were based on the gold Fermi level (0 eV). The 2D layered perovskite had a slightly lower energy level than the 2D (HAPbI ₄ ) and 3D (MAPbI ₃ and α-FAPbI ₃ ) perovskites (FIG. 8B ). This increases the ionization energy in the order of 2D layered perovskite, HAPbI ₄ and 3D perovskite. However, the WF of the 2D layered perovskite was the highest among the perovskites, indicating an increase in Pbo-related surface state (Fig. 8c). This tends to shift the Fermi level to the conduction band minimum (CBM). Therefore, the electron affinity, which is the difference between WF and CBM, was 4.59 eV for (HA) ₂ (FA) _n-1 Pb _n I _3n+1 perovskite and 3.93 eV for HAPbI ₄ compounds. As shown in FIG. 8D, the CBM position of the 2D layered perovskite is an energy alignment that is very close to the CBM of the TiO ₂ electron transport layer compared to other perovskites. It is expected that there will be no barrier to electron extraction from the 2D layered perovskite to the TiO ₂ layer. The barrier to hole extraction was predicted from the offset between the perovskite VBM and HTL HOMO. In all perovskites, the HOMO level of HTL is closer to the Fermi level than the perovskite VBM. Thus, no perovskite exhibited a hole extraction barrier.

Film morphology, including grain size, crystal orientation, and coverage are important factors in high-efficiency solar cell manufacturing. 8 shows SEM images of HAPbI ₄ , (HA) ₂ (MA) _n-1 Pb _n I _3n+1 and (HA) ₂ (FA) _n-1 Pb _n I _3n+1 perovskite films, respectively. . The perovskite film made of HAPbI ₄ exhibits a uniform and compact shape (Fig. 8a), and (HA) ₂ (MA) _n-1 Pb _n I _3n+1 film exhibits a film quality similar to HAPbI ₄ ( Fig. 8b). However, in the AFM images of the surfaces shown in FIGS. 8A and 8B (FIGS. 8D and 8E ), it can be seen that a large particle size exists and a pinhole is formed between the particle boundaries. This adversely affected the performance of the photovoltaic effect. In contrast, the (HA) ₂ (FA) _n-1 Pb _n I _3n+1 film exhibits a much uniform and smaller particle size (Figs. 8c, 8f). This indicates that the particle growth of (HA) ₂ (FA) _n-1 Pb _n I _3n+1 perovskite proceeds very slowly, so that the particle size is small and uniform, and ultimately, a compact thin film can be formed.

Subsequently, the photovoltaic performance of α-FAPbI ₃ , HAPbI ₄ and (HA) ₂ (A) _n-1 Pb _n I _3n+1 (A is MA or FA) perovskite was investigated. The corresponding photocurrent density-voltage (JV) curves under AM1.5G illumination are shown in FIG. 9, and the photovoltaic parameters are summarized in Table 3. First, with regard to the production of solar cells in the air, in general, since perovskite is very sensitive to humidity and oxygen in the atmosphere, perovskite solar cells are produced in an inert environment, and are ultimately not suitable for commercialization. As can be seen in FIG. 7, the 2D layered perovskite battery shows significantly higher performance compared to the HAPbI ₄ based device. (HA) ₂ (FA) _n-1 Pb _n I _3n+1 Perovskite-based devices have a short current density (Jsc) of 16.70 mA/cm ² , a Voc of 0.76 V, and a fill factor of 52.20%, FF) and 6.75% PCE. (HA) ₂ (MA) _n-1 Pb _n I _3n+1 devices show values of 15.40 mA/cm ² , 0.77 V, 55.00% and 6.53% for Jsc, Voc, FF and PCE, respectively. α-FAPbI ₃ perovskite cells show 5.15%. However, the black phase of the film gradually changed along with the non-perovskite yellow phase, and the efficiency quickly lost. The best performance is the MAPbI ₃ cell, which shows 8.23% PCE. However, when exposed to air, it decomposes quickly and loses its efficiency, whereas the 2D layered perovskite showed excellent stability (FIG. 8). In addition, even if the efficiency of the 2D perovskite solar cell is low, it is expected that a stable and highly efficient solar cell can be obtained if the film shape can be improved.

Empirical formula (C ₅ N ₃ H ₁₁ )PbI ₄ δ-HC(NH ₂ ) ₂ PbI ₃ (HA) ₂ (FA)Pb ₂ I ₇ Formula weight 827.96 627.92 1460.92 Temperature (K) 298(2) 296(2) 293(2) Wavelength (Å) 0.700 0.71073 0.700 Crystal system Monoclinic Hexagonal Triclinic Space group P2 _One /n P6 ₃ mc P-1 Unit cell dimensions
a, Å
b, Å
c, Å
a, deg
b, deg
g, deg
8.9020(18)
20.038(4)
9.0050(18)
90°
91.86(3)°
90°
8.6724(12)
8.6724(12)
7.9410(12)
90°
90°
120°
8.9100(18)
9.0510(18)
16.539(3)
86.20(3)
82.61
89.08(3) Volume (Å ³ ) 1605.4(6) 517.23(16) 1319.8(5) Z 4 2 2 Density (calculated) (g/cm ³ ) 3.425 4.032 3.676 Absorption coefficient
(mm ^-1 ) 17.304 24.961 19.929 F(000) 1424 522 1244 Crystal size (mm ³ ) 0.120 x 0.098 x 0.075 0.150 x 0.180 x 0.240 0.40 x 0.61 x 0.92 θ range for data
collection 2.002 to 33.645° 2.712 to 28.367° 2.221 to 33.337° Index ranges -12 = h ≤= 12,
-28 ≤= k ≤= 28,
-12 ≤= l ≤= 12 -11 = h ≤= 11,
-11 ≤= k ≤= 11,
-10 ≤= l ≤= 10 -12 = h ≤= 12,
-13 ≤= k ≤= 13,
-23 ≤= l ≤= 23 Reflections collected 19299 11026 12864 Independent reflections 5106 [R(int) = 0.0391] 519 [R(int) = 0.0457] 6815 [R(int) = 0.0467] Completeness to theta
= 24.835° 95.1% 100.0% 71.5% Refinement method Full-matrix least-
squares on F ² Full-matrix least-
squares on F ² Full-matrix least-
squares on F ² Data / restraints /
parameters 5106/0/120 519/15/27 6815/10/181 Goodness-of-fit 1.060 1.182 1.331 Final R indices
[I> 2σ(I)] R1 = 0.0405,
wR2 = 0.1078 R1 = 0.0208,
wR2 = 0.0557 R1 = 0.1253,
wR2 = 0.3391 R indices [all data] R1 = 0.0411,
wR2 = 0.1086 R1 = 0.0272,
wR2 = 0.0603 R1 = 0.1493,
wR2 = 0.3631 Extinction coefficient 0.0061(3) 0.0040(8) - Largest diff. peak
and hole (eÅ ^-3 ) 2.862 and -2.709 0.696 and -0.611 4.811 and -2.262

Perovskites A _One τ _One /ns A ₂ τ ₂ /ns A ₃ τ ₃ /ns τ _avg /ns τ _amp /ns MAPbI ₃ 3.40 2.83 0.28 8.20 6.50 0.96 2.86 1.77 α-FAPbI ₃ 7.90 0.30 0.09 13.00 0.76 1.91 4.00 0.58 HAPbI ₄ 1.30 4.70 0.13 164.00 5.10 1.10 105.00 5.00 (HA) ₂ (MA) _n-1 Pb _n I _3n+1 4.80 1.10 0.09 282.00 1.10 4.90 197.00 5.80 (HA) ₂ (FA) _n-1 Pb _n I _3n+1 0.09 595.00 6.70 1.60 0.22 82.00 335.00 12.00

The emission decay was analyzed by the following equation ( τ _amp is the average lifetime amplitude):

[Equation 3]

[Equation 4]

[Equation 5]

는 τ _avg임).(In the formula,

Is τ _avg ).

Perovskites Jsc
[mA/cm ² ] Voc
[V] FF
[%] h
[%] MAPbI ₃ 17.70 0.75 61.90 8.23 α-FAPbI ₃ 16.04 0.77 42.00 5.15 (HA)PbI ₄ 2.16 0.77 32.17 0.53 (HA) ₂ (MA) _n-1 Pb _n I _3n+1 15.40 0.77 55.00 6.53 (HA) ₂ (FA) _n-1 Pb _n I _3n+1 16.70 0.76 52.20 6.75

Claims (11)

Two secondary or tertiary perovskite layers comprising the unit structure of Formula 1 and spaced apart from each other; And
As a laminated perovskite structure represented by Formula 2, comprising a divalent organic cation compound of an aromatic heterocyclic compound substituted with at least one aminoalkyl group,
The two cationic groups are the nitrogen atom and the hetero atom hydrogenated (hydrogenation), each of which forms a hydrogen interaction with X ^- of different layers perovskite structure:
[Formula 1]
[PbX ₆ ] ^2-
(Wherein, X is one selected from the group consisting of Cl, Br and I)
[Formula 2]
(C) ₂ (A) _n-1 Pb _n X _3n+1
(Wherein, C is the divalent organic cation compound, A is methylammonium or formammonium (HC(NH ₂ ) ₂ ⁺ ), X is one selected from the group consisting of Cl, Br and I, and n is 6 An integer greater than or equal to).
The perovskite structure of claim 1, wherein the aminoalkyl group includes a C _1-3 alkyl group.
The perovskite structure of claim 1, wherein the aromatic heterocyclic compound is a 4 to 7 membered ring compound.
The method according to claim 1, wherein the aromatic heterocyclic compound is at least one perovskite structure selected from the group consisting of compounds represented by the following formulas 3 to 10:
[Formula 3]

[Formula 4]

[Formula 5]

[Formula 6]

[Formula 7]

[Formula 8]

[Formula 9]

[Formula 10]

.
The perovskite structure of claim 1, wherein the aromatic heterocyclic compound is represented by the following formula (10):
[Formula 10]

.
The perovskite structure according to claim 5, wherein the divalent organic cation compound of the aromatic heterocyclic compound is represented by the following formula (11):
[Formula 11]

.
The perovskite structure according to claim 1, wherein the divalent organic cation compound of the aromatic heterocyclic compound is located at spaces between two perovskite layers.
The perovskite structure of claim 1, wherein X in Formulas 1 and 2 is I.
The method according to claim 1, wherein A in Formula 2 is formammonium (HC(NH ₂ ) ₂ ) ⁺ phosphorus perovskite structure.
A perovskite structure in which a plurality of perovskite structures are stacked vertically with respect to the perovskite layer as a unit of any one of the structures 1 to 9.
An optical device for a solar cell comprising the structure of any one of claims 1 to 9.

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