KR102150992B1 - Novel Perovskites and its use - Google Patents

Abstract

The present invention relates to a perovskite which is stable and emits excellent white light, and the use thereof. The perovskite comprises: an edge-shared helical chain consisting of a unit structure of chemical formula 1, [PbX_5]^(3-); and a plurality of piperazinium of chemical formula 2.

Description

Novel Perovskites and its use

The present invention relates to a stable, excellent white light perovskite and its use.

Perovskite LED devices were first reported with an EQE of 0.1-0.4% and a maximum brightness of 364 cd/m ^-2 using CH ₃ NH ₃ PbBr ₃ and CH ₃ NH ₃ PbBr ₂ I materials. Perovskite is capable of adjusting the band gap by the halide configuration, enabling EL emission of various colors, and non-radiative recombination due to surface defects compared to currently commercialized III-V group compound semiconductors, OLEDs, and QLED devices. Nonradiative recombination) is small and solution processing is possible, which has the advantage of reducing process cost. However, it is very sensitive to moisture and oxygen in the air, and its thermal stability is low, so it has a structure in which cations are mixed ([HC(NH ₂ ) ₂ ] _0.83 Cs _0.17 Pb(I _0.6 Br _0.4 ) ₃ ) and inorganic-based CsPbBr ₃ Performance is improved by improving turn-on voltage and brightness. However, the problem of being easily decomposed in the air due to the low formation energy of the structure itself of perovskite is still a limitation in applying perovskite to LED devices.

In order to solve the instability of perovskite, low-dimensional perovskite from zero to secondary structure has been reported as an LED material instead of the conventional tertiary structure by introducing bulk organic cations while the structure is hydrophobic. In particular, white light-emitting perovskite, which emits broadband by self-trapped excitons by electron-phonon coupling due to structural distortion in the (110) direction, is applied to solid state light emission and displays. It is considered a material with great potential. To date (NMEDA)[PbBr ₄ ](N-MEDA=N1-methylethane-1,2-diammonium), (EDBE)[PbX ₄ ] (EDBE=2,2′-(ethylenedioxy)bis-(ethylammonium); X = Cl or Br), α-(DMEN)PbBr ₄ (DMEN=2-(dimethylamino)ethylamine), (EDBE)PbI ₄ (EDBE=2,2-(ethylenedioxy)bis(ethylammonium)), (CH ₃ CH ₂ NH ₃ ) ₄ Pb ₃ Br _10-x Cl _x and (C ₆ H ₁₁ NH ₃ ) ₂ PbBr ₄ has been reported. However, the PLQE is only 0.5-9%, and there is a problem of overcoming moisture, air, and thermal stability in the air.

Korean Patent Publication No. 2019-0007812

An object of the present invention is to provide a stable, excellent white light emitting perovskite and use thereof.

1. An edge-covalent helical chain consisting of a unit structure of the following formula 1 and a plurality of piperazinium of the following formula 2

The piperazinium N ⁺ -H is a secondary trigonal perovskite compound represented by the unit structure of the following formula (3), which forms a hydrogen interaction with each other X ^- of the chain:

[Formula 1]

[PbX ₅ ] ^3-

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

[Formula 2]

[Formula 3]

(pip) _0.5n Pb _n X _3n

(Wherein, pip is piperazinium of Formula 2, X is one selected from the group consisting of Cl, Br, and I, and n is an integer of 3 or more).

2. The compound of 1 above, wherein X in Formula 1 is Cl.

3. The compound according to the above 1, wherein the edge-covalent helical chain is at least partially connected to form a ring.

4. The compound of 1 above, wherein the CRI value of the compound is 70 or more.

5. The compound of 1 above, wherein the CRI value of the compound is 90 or higher.

6. A light-emitting device including any one of the compounds 1 to 5 above.

7. A light-emitting device including the light-emitting device of 6 above.

The perovskite of the present invention is stable and can emit excellent white light, and thus can exhibit excellent performance in its use as an LED.

Figure 1: (a) As an organic molecule of diamonium cationic piperazinium, pip = piperazine, 1mpz = 1-methylpiperazine and 2,5-dmpz = trans-2,5-dimehtylpiperazine, (b) (pip) ₂ PbBr ₆ , SEM images of (pip) ₃ Pb ₆ Cl ₁₈ , (1mpz) ₄ Pb ₂ Br ₁₂ , and (2,5-dmpz) _0.5 PbBr ₃ perovskite crystals.
Figure 2: (a) (pip) ₂ PbBr ₆ Pb-Br binding length of perovskite is 2.89Å and 3.23Å in the trans direction, 2.93Å and 3.07Å in the axial direction, piperazine organic molecule and NH-Br Forming a supramolecular chain with an inorganic chain through a hydrogen bond, (b) two metal halide dimers (Pb ₂ Br ₁₂ ^8- ) are completely separated from each other, and an organic cation and an inorganic chain are connected through NH-Br bonds, Structure of alternating (pip) ₂ PbBr ₆ single crystals.
Figure 3: (a) c-axis direction of 1D chain edge-covalent (pip) ₃ Pb ₆ Cl ₁₈ crystal structure, (b) hydrogen bonds between inorganic chains, PbCl ₅ and organic cations (red dashed line), (c) Concentric arrangement of inorganic layers due to helical accumulation in the c-axis direction.
Figure 4: (a) 0D (1mpz) ₄ Pb ₂ Br ₁₂ showing a hydrogen bond (yellow broken line) between a monoclinic space group P2/n along the a-axis, and [PbBr ₆ ] ^4- octahedron and 1mpz divalent cations The crystal structure of (b, c) [PbBr ₆ ] ^4- is separated by a large 1-methylpiperazine divalent cation along the c axis.
Figure 5: Crystal structure of (a) (2,5-dmpz) _0.5 PbBr ₃ ·2 ((CH ₃ ) ₂ SO) (monoclinic space group P2 ₁ /C), (b) (2,5-dmpz) Crystal structure of PbBr ₃ · (CH ₃ ) ₂ SO (orthorhombic space group Pbca), (c) (2,5-dmpz) PbBr ₃ · (CH ₃ ) ₂ SO 1D chain and (2,5-dmpz) under UV rays ((λ _ex = 365 nm) White light emission of PbBr ₃ · (CH ₃ ) ₂ SO, (d, e) (2,5-dmpz) along the b axis with 2,5-dmpz linked to DMSO by hydrogen bonds (2,5-dmpz) _0.5 PbBr ₃ ·2((CH ₃₎ 1D [PbBr _3] of ₂ SO) ^- the inorganic chain.
Figure 6: (pip) ₂ PbBr ₆ , (pip) ₃ Pb ₆ Cl ₁₈ , (1mpz) ₄ Pb ₂ Br ₁₂ and (2,5-dmpz) _0.5 PbBr ₃ Experimental and theoretical XRD patterns of perovskite crystal structures .
Figure 7: (a, b, c) (pip) ₂ PbBr ₆ , (pip) ₃ Pb ₆ Cl ₁₈ , (1mpz) ₄ Pb ₂ Br ₁₂ and (2,5- dmpz) _0.5 PbBr ₃ ·2((CH ₃ ) ₂ SO) Raman spectrum of perovskite, (d) (pip) ₂ PbBr ₆ , (pip) ₃ Pb ₆ Cl ₁₈ , (1mpz) ₄ Pb ₂ Br ₁₂ and (2,5- dmpz) _0.5 PbBr ₃ ·2((CH ₃ ) ₂ SO) UV visible diffuse reflection spectrum for the bandgap determination of perovskite.
Figure 8: (pip) ₂ PbBr ₆ , (pip) ₃ Pb ₆ Cl ₁₈ , (1mpz) ₄ Pb ₂ Br ₁₂ and (2,5- dmpz) _0.5 PbBr ₃ · 2 ((CH ₃ ) ₂ SO) perovskite Photoluminescence data of skyt fluorescence.
Figure 9: (pip) ₂ PbBr ₆ , (pip) ₃ Pb ₆ Cl ₁₈ , (1mpz) ₄ Pb ₂ Br ₁₂ and (2,5- dmpz) _0.5 PbBr ₃ ·2((CH ₃ ) ₂ SO) Symmetric pipe Time-resolved photoluminescence decay curves of a radiinium-based perovskite
Figure 10: (pip) ₂ PbBr ₆ , (pip) ₃ Pb ₆ Cl ₁₈ , (1mpz) ₄ Pb ₂ Br ₁₂ and (2,5-dmpz) _0.5 PbBr ₃ · 2 ((CH ₃ ) ₂ SO) perovskite Skyt's (a, b) steady state PL, (c) CIE color adjustment, (d) (1mpz) ₄ Pb ₂ Br ₁₂ and (2,5-dmpz) _0.5 PbBr ₃ ·2((CH ₃ ) ₂ SO ) Perovskite crystals were photographed under ambient light and 4W 310nm ultraviolet light, respectively.
Figure 11: (2,5-dmpz) PbBr 3 · (CH 3) 2 SO page as shown hydrogen structure of perovskite, yellow and red dotted lines respectively [PbBr _3] ^- and 2,5-octahedral dmpz It represents a hydrogen bond between a divalent cation, 2,5-dmpz divalent cation and a DMSO solvent molecule.

Hereinafter, the present invention will be described in detail.

The present invention introduces piperazinium, which is a divalent organic cation, to an inorganic layer composed of lead halide, thereby distorting the connection of the lead halide octahedral unit structure, thereby emitting white light. It relates to skyt compounds. This is because the excited electrons are collected for a long time, and the electron lifetime, which will be specifically mentioned in the examples to be described later, is high, so that the ability to emit white light is very excellent.

Thus, specifically, the present invention includes an edge-covalent helical chain consisting of a unit structure of the following formula (1) and a plurality of piperazinium of the following formula (2), wherein the piperazinium N ⁺ -H is each different X of the chain ^- and to which, to form a hydrogen interaction provides a second trigonal crystal system perovskite compounds represented by the structural unit of formula (3):

[Formula 1]

[PbX ₅ ] ^3-

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

[Formula 2]

[Formula 3]

(pip) _0.5n Pb _n X _3n

(Wherein, pip is piperazinium of Formula 2, X is one selected from the group consisting of Cl, Br, and I, and n is an integer of 3 or more).

In the general formula 1, 3, X is specifically can be a Cl, l titanium in large N ⁺ -H and ^X-excessive warping of the perovskite dielectric base layer caused by the excessive bulky ^in-between the excess hydrogen interactions or X It may be preferable compared to Br and I in terms of preventing and maintaining excellent electrical conductivity.

The formula edge-covalent helical chain may be specifically arranged in a concentric circle and formed by regularly accumulating in a unit structure, and more specifically, at least a part of the chain may be connected to form a ring. With reference to the drawings, the shape may be specified.

The compound has the specificity of emitting white light, and the color rendering index (CRI) value is only around 60 in the case of a commercially available fluorescent lamp, whereas the compound of the present invention has a value of 70 or more, 75 or more, 80 or more, It may be 85 or more or 90 or more, and preferably it may represent a very high value of 90 or more.

The compound of the present invention can be prepared by separately dissolving the above constituent compounds (lead halide, piperazinium), and then mixing and stirring all of them by a method known in the art. More specifically, after heating and stirring the constituent compounds with a solvent well known in the art corresponding to each, a solution of one compound is mixed by drop by drop into a solution of another compound, and then the precipitated compound of the present invention is Can be obtained. In addition, a method known in the art for overcoming the structural defects of lead halide, which is a constituent compound of the present compound, may be used, and specifically, an antisolvent method may be used.

The present invention also provides a light emitting device comprising the compound.

As described above, the light emitting device of the present invention is excellently used as an optical device in various fields of the industry requiring white color as the white light emission level of the compound of the present invention included in the device is very high. Can be.

The present invention also provides a light-emitting device including the light-emitting element.

The light-emitting device of the present invention, as described above, emits white light with excellent efficiency and brightness, and therefore, various light-emitting devices in the industry including the light-emitting device are without particular limitation on the device. It can exhibit an excellent effect on white light emission.

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

Experiment method

1. Experimental materials

Lead bromide (PbBr, 98%), lead chloride (PbCl, 98%), piperazine (99%), 1-methylpiperazine (99%), hydrobromic acid (HBr, 48%), hydrochloric acid (HCl , 37%), hypophosphorous acid (H ₃ PO ₂ , 50 wt% aqueous solution), N,N-dimethylformamide (DMF, anhydride, 99.8%), dimethyl sulfoxide (DMSO, anhydride, 99.9% or more), dichloromethane (Anhydride, 99.8% or more) and chlorobenzene (CB, anhydride, 99.8%) were purchased from Sigma-Aldrich and used without further purification. Trans-2,5-dimethylpiperazine (98%) was purchased from Thermo Fisher Scientific Korea Co., Ltd. Trans-2,5-dimethylpiperazinium bromide was synthesized by neutralizing equimolar amounts of HBr and trans-2,5-dimethylpiperazine. Then, the mixture was stirred at 0° C. for 2 hours, and the resulting solution was evaporated at 50° C. for 1 hour. The precipitate was dried in a vacuum oven at 60° C. for 24 hours and used without further purification. Trans-2,5-dimethylpiperazinium chloride was also prepared in the same manner, but HCl was used.

2. Synthesis of perovskite

0.367 g of PbBr ₂ (1 mmol) was dissolved in 5.0 mL of HBr solution. The flask was heated to 120° C. in an oil bath and then stirred vigorously until the solids were completely dissolved. In a separate beaker, piperazine (0.086 g, 1 mmol) was neutralized with 1 mL HBr solution. While the piperazine solution was continuously stirred, it was slowly added dropwise (drop by drop) to the PbBr ₂ solution. Heat was removed and the flask was air cooled without stirring. During slow cooling, plate-like crystals precipitated. Other perovskites were prepared in the same way. PbBr ₂ was maintained at a constant concentration, and a 1 mL solution of 1-methylpiperazine (1 mmol, 0.100 g) was added dropwise to the stirred 5 mL PbBr ₂ solution. Since the crystal of 2,5-dimethylpiperazinium lead bromide synthesized by the above method has many drawbacks, it was prepared using a conventionally known antisolvent method. A mixture of PbBr ₂ (1 mmol, 0.36701 g) and trans-2,5-dimethylpiperazinium bromide (1 mmol, 0.276 g) was dissolved in 6 mL of DMSO. Dichloromethane was used as antisolvent. Perovskite containing lead chloride as a main component was also prepared as described above, and HCl was used.

3. Physical property analysis

(1) High resolution PXRD and single crystal X-ray diffraction

Powder XRD (PXRD) analysis operates at 40 kV/30 mA, equipped with a position-sensing detector with a flat sample shape, using a calibrated CPS 120 INEL powder X-ray diffractometer (Cu Kα graphite-monochromatic radiation). And carried out at room temperature. Perovskite crystals were coated with paratone-N oil, and in an ADSC Quantum-210 detector (Pohang Accelerator Laboratory in Korea) of BL2D SMC with a silicon (111) double crystal monochromator (DCM), synchrotron radiation (l = 0.61000Å) was used to measure diffraction data at 298K. The PAL BL2D-SMDC program was used for data acquisition (detector distance 63mm, omega scan, Δω = 3°, exposure time 1 second per frame), and HKL3000sm (version 703r) was used for cell segmentation, reduction and absorption correction. The crystal structure of perovskite was solved using the direct method using the SHELXT-2014 program, and refined using full-matrix least-squares calculations with the SHELXL-2014 program package.

(2) light absorption spectroscopy

The generated reflectance versus wavelength data was used to estimate the material's band gap by converting the reflectance into absorption data according to the Kubelka-Munk equation:

[Equation 1]

α/S = (1-R) ² (2R) ^-1

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

(3) Steady state and time-resolved photoluminescence

Perovskite emission and exciton photoluminescence (PL) spectra were measured with a FluoroMate FS-2 Fluorescence Spectrometer (Scinco, Republic of Korea). A time resolved PL (TRPL) study was performed using a 60x (air) objective lens using an inverted scanning confocal microscope (MicroTime-200, Picoquant, Germany). Lifespan measurements were performed at the Daegu Center of the Korea Science Foundation (KBSI). Single-mode pulsed diode lasers (375nm and 470nm, pulse width of ~30ps) were used as excitation sources. When the 470 nm laser was irradiated, to collect the emission from the sample, a dichroic mirror (Z375RDC, AHF), a long pass filter (HQ405lp, AHF), a 75 μm pinhole, a band-pass filter and avalanche ) A single photon diode (PDM series, MPD) was used. Time-correlated single-photon counting (TCSPC) technique was used to count fluorescent photons. TRPL images composed of 200 x 200 pixels were recorded using a time-tagged time-resolved (TTTR) data collection method. Using Symphotime-64 software (version 2.2) as an exponential decay model, an exponential fit for the PL decay obtained with a time resolution of 16 ps was performed:

[Equation 2]

(I(t)는 시간-의존 PL 강도, A는 진폭, τ는 PL 수명).

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

Experiment result

Perovskite was synthesized from HI solution concentrated with reducing agent H ₃ PO ₂ , and all crystals showed colorless plate-like crystal structure (FIG. 1). Crystallographic data and structural refinement are presented in Table 1. (pip) ₂ PbBr ₆ was crystallized in the space group Pnnm of a centrally symmetric orthorhombic system. As can be seen in Fig. 2A, the bridging angle between the two octahedrons is almost linear (180°). However, the Pb-I distances at the trans position consisting of the longest 3.2370(8)Å, the shortest 2.8915(13)Å and the intermediate length of the cis- position are 3.0730(11)Å and 2.9339(11)Å, respectively. The piperazine divalent cations were arranged in a chair shape between two dimers [Pb ₂ Br ₁₁ ] moving along the a-axis and toward the b-axis. The inorganic layer contains an edge covalent dimer [PbBr ₆ ] octahedron moving along the a-axis, but adjacent chains are not connected along the b-axis and c-axis. Therefore, the adopted lead bromide motif was 1-D. However, each piperazine divalent cation was linked to four inorganic chains through NH-Br hydrogen bonds forming a three-dimensional supramolecular network. Thus, the two metal halide dimers [Pb ₂ Br ₁₂ ] ^8- were completely separated from each other and were periodically arranged in the organic cation matrix (FIG. 2B).

Because of the highly asymmetric units, (pip) ₃ Pb ₆ Cl ₁₈ crystallized in triangular space group R3 (FIG. 3 ). (pip) ₃ Pb ₆ Cl ₁₈ contains five unique chlorides surrounding the lead atom in the asymmetric unit. The edge covalent chain of PbCl ₅ spirally passed through the unit cell (Fig. 3A). Hydrogen bonds form a 3D supramolecular network with a red dotted line between the inorganic chain and organic cations. Figure 3b shows that each organic cation is connected to four inorganic chains. It is worth noting that the replacement of the halogen causes more significant structural changes than the simple halogen substitution reaction in the perovskite form of the complex. Since the inorganic chains of PbCl ₅ are helically connected in the c-axis direction, the inorganic layers form concentric circles and are accumulated (Fig. 3C).

Due to the large organic cations, an octahedral zero-dimensional (0D) structure was obtained that was separated from the use of 1-methylpiperazine. 0D (1mpz) ₄ Pb ₂ Br ₁₂ was crystallized in the space group P2/n of the centrosymmetric monoclinic system, and the [PbBr ₆ ] ^4- octahedron was separated by 1-methylpiperazine divalent cations. As can be seen in FIG. 4A, the organic cation is an inorganic skeleton adjacently connected through NH-Br as in (pip) ₂ PbBr ₆ . Hydrogen bonding pulled the Br ^- anions out of the perovskite lattice, which created an isolated inorganic framework. 4B and 4C clearly show the truncated [PbBr ₆ ] ^4- octahedron, which is represented by separating the large 1-methylpiperazine along the c-axis. Crystal aggregation is achieved by NH-Br hydrogen bonds with the nearest donor-acceptor distances of 2.4946(9)Å and 2.6321(10)Å.

(2,5-dmpz) _0.5 of the asymmetric unit PbBr ₃ is 2,5-dmpz second half of the cation, a [PbBr _3] ^- was composed of DMSO and 2 molecules. The complete divalent cations were created by inversion symmetry leading to a chair shape and occupied the equator with methyl groups (Fig. 5a). This hydrated perchlorate ^- was similar to the three-dimensional structure of ^{_{(C 6 H 16 N 2 2+}} · 2ClO 4 · 2H 2 O). It crystallized in the space group P21/c of the centrosymmetric monoclinic system. The infinite weapon chain [PbBr ₃ ] in the structure extends along the c-axis. In the expanded structure, the divalent cations are linked through NHO _DMSO hydrogen bonds to form a gear-type chain along the (010) direction (Fig. 5D). As shown in Figure 5e, each cation is connected to four DMSO molecules by hydrogen bonds. The donor-acceptor (NHO _DMSO ) distance is 1.95Å and 1.89Å in the diagonal direction, respectively. Hydrogen bonds draw out the isolated lattice and divalent cations from the inorganic lattice in the space of the inorganic chain. This unique hydrogen bonding network helped to maintain the continuity of 1D single facts. Similarly, using a 2,5-dmpz divalent cationic basic compound, (2,5-dmpz) PbBr ₃ ·(CH ₃ ) ₂ SO structure was synthesized (Fig. 5b). This compound was crystallized from the orthorhombic space group Pbca. They showed 1D single-chain inorganic motifs (Fig. 6c), (2,5-dmpz) _0.5 PbBr ₃ ·2((CH ₃ ) ₂ SO) and (2,5-dmpz) PbBr ₃ ·(CH ₃ ) ₂ SO Significant differences in the structure of the liver were observed. As mentioned above, hydrogen bonding at (2,5-dmpz) _0.5 PbBr ₃ ·2((CH ₃ ) ₂ SO) occurs only in the divalent cation and adjacent DMSO molecules, whereas (2,5-dmpz) PbBr ₃ · (CH ₃ ) ₂ SO occurs in a divalent cation and a DMSO molecule (NH-ODMSO) connected thereto, and the inorganic skeleton (NH-Br) is connected by hydrogen bonds (FIG. 11 and Table 4). This compound also produced white light emission (Fig. 5c). Accordingly, the effect of hydrogen bonding between divalent cations, solvent molecules, and inorganic skeletons for performance as a light emitting material was further studied.

High resolution PXRD data of piperazine-based perovskite was extracted using Le Bail refinement (FIG. 6). All perovskites crystallize in high purity without impurities. However, due to the above mentioned supersaturated synthetic preparation, secondary crystals were easily produced at the solution-air interface. They created additional peaks at the XRD peak, leading to differences in theoretical and experimental values.

To study the local structural dynamics effect of piperazinium-based lead bromide perovskite, Raman measurements for perovskite crystals were performed in three different frequency domains: a) 200 cm ^-1 or less (Fig. 7A ), b) 800 to 1700 cm ^-1 (Fig. 7b), c) 2580 to 3100 cm ^-1 (Fig. 7c). Raman spectra were obtained from 514 nm laser excitation at ambient conditions. 3D perovskite Unlike the prior art with respect to the bit, CH ₃ NH ₃ PbB ₃ and ₃ CsPbBr lead halide perovskite compounds showed a very soluble spectrum. Depending on the dimensionality and connectivity mode of the crystal structure, the vibrational responses of these systems exhibited very different properties consistent with the connectivity and cationic effects of inorganic networks. This provided useful information on the interaction between organic and inorganic materials of perovskite materials in terms of phonon-phonon, electron-phonon, and spin-phonon interactions. X-Pb-X (X = Br and Cl) allocates bands at lower wavenumbers (15-200 cm ^-1 ) corresponding to the bending and elongation of bonds, whereas peaks at higher wavenumbers (> 800 cm ^-1 ) Was derived from the free of organic cations. In good agreement with the previously known spectra, the measured Raman spectra of all perovskites showed two strong modes of less than 50 cm ^-1 associated with the bending of the X-Pb-X bond (Fig. 7A). In addition, 84cm ^-1 at (1mpz) ₄ Pb ₂ Br ₁₂ and 75 cm ^-1 at (pip) ₂ PbBr ₆ due mainly to the Pb-X bending mode were clearly observed, whereas (1mpz) ₄ Pb Bands of 125 cm ^-1 at ₂ Br ₁₂ and 135 m ^-1 at (pip) ₂ PbBr ₆ were assigned to the release of organic cations. In the area of 800 to 1700 cm ^-1 (Fig. 7b), (2,5-dmpz) twist around the CN axis (881 cm ^-1 ) and vibration of the CN axis (962 cm ^-1 ) in _0.5 PbBr ₃ compound were observed. All perovskites showed a bending mode of CH bond at 1400cm ^-1 and 1459cm ^-1 . A frequency region of 2850cm ^-1 or more (FIG. 7C) is related to CH and NH stretching. In addition, the 3000 to 3017 cm ^-1 double Nazareth (doublet) associated with the nearby neighborhood 2963cm ^-1 band and asymmetric CH stretching associated with the CH symmetric stretching observed.

Optical properties according to the structural shape were measured using a diffuse reflectance measurement method (Fig. 7d). The optical bands of these materials are generally characterized by the connectivity of [PbBr ₆ ] ^4- and the side-to-side connectivity from edge to edge results in a significant increase in the band gap. This can be commonly understood as the quantum confinement effect expected from the dimensions of the herd network as well as the number of iodides shared between two adjacent lead ions. Specifically, (pip) ₂ PbBr ₆ formed a 1D structure composed of a dimer [PbBr ₆ ] ^4- building block forming a ribbon along the [010] direction. The connectivity of the inorganic part consisted of only the edges that shared the PbBr ₆ octahedron, and had the largest bandgap (3.27 eV) in the series. (1mpz) ₄ Pb ₂ Br ₁₂ is composed of the only PbBr ₆ octahedron that widens the band gap (3.12 eV). Interestingly, the (2,5-dmpz) ₃ Pb ₂ Br ₁₀ perovskite had the lowest bandgap (2.34 eV) in this series, which, as mentioned above, is considered a more distorted structure with edge sharing. .

Before studying the emission mechanism, we tried to confirm that white light emission is a bulk effect, not a result of surface defects. Therefore, fluorescence photoluminescence measurement was performed on the micrometer-sized perovskite powder (FIG. 8). Most of these compounds exhibited wide band emission properties at room temperature, clarifying that the broadband white light emission of the samples of the present invention is an intrinsic property. In the case of (1mpz) ₄ Pb ₂ Br ₁₂ perovskite, since it overlapped with the ramp peak at 630 nm, the emission peak at a long wavelength was removed. However, comparing this result with the confocal microscope PL emission (Fig. 10), the bandwidth of fluorescence emission is slightly narrowed. This is due to the difference between the excitation energy and the scattering effect in the powder sample.

The time-resolved photoluminescence decay shown in FIG. 9 was investigated to study the kinetics of exciton recombination in the symmetric piperazine perovskite, and excitation was selected at 375 nm. The PL decay curve was analyzed with three exponential decay kinetics, and the results are summarized in Table 2. The fast decay process (τ ₁ ) indicates the radiation recombination of the excitons, and the slow decay processes (τ ₂ and τ ₃ ) correspond to the STE of the perovskite crystal structure. (2,5-dmpz) _0.5 PbBr ₃ was a material representing a latent fluorescent light emitting material and showed a significantly longer average life than conventionally known 2D perovskite. The value of τ ₁ at (2,5-dmpz) _0.5 PbBr ₃ corresponding to the radiation recombination of the carrier was the largest among perovskites. (1mpz) ₄ Pb ₂ Br ₁₂ showed an average lifespan of 28 ns, and the τ ₂ component due to STE was the largest value among perovskites. This is probably due to the distorted structure of the PbBr ₆ octahedron. Compared to other perovskites (pip), the average lifetime of ₃ Pb ₆ Cl ₁₈ is the shortest 4.47 ns.

Photoluminescence measurements of piperazine-based perovskites were performed, where at 325 nm excitation, (pip) ₂ PbBr ₆ has a higher energy shoulder peak at ~403 nm, a broad emission peak with a maximum at 580 nm and a wide emission peak at 191.30 nm. It showed a broad light emission covering the entire range of the visible spectrum, with a large FWHM (FIG. 10A ). (pip) ₃ Pb ₆ Cl ₁₈ exhibited the same function as (pip) ₂ PbBr ₆ , exhibiting maximum emission at 535 nm, FWHM at 152.61 nm (8.12 eV), and broad emission such as shoulder peak at 410 nm (Fig. 10a) . (2,5-dmpz) _0.5 PbBr ₃ also showed a broad emission with a maximum value at 524 nm and a FWHM of 170.73 nm. (1mpz) ₄ Pb ₂ Br ₁₂ had a maximum value at 607 nm and showed a broad peak with an FWHM of 187.62 nm. However, these compounds did not show obvious high energy shoulder peaks (FIG. 10B ). Importantly, the CRI of all compounds exhibited more than a typical fluorescent light source (ca. 65) showing high accuracy as a light source compared to daylight. The international CIE (International Standard) color coordinates of this compound are (pip) ₂ PbBr ₆ (0.452, 0.472), (pip) ₃ Pb ₆ Cl ₁₈ (0.340, 0.371) in the 1931 color space chromaticity diagram, In the case of (1mpz) ₄ Pb ₂ Br ₁₂ (0.476, 0.456), in the case of (2,5-dmpz) _0.5 PbBr ₃ (0.315, 0.401) were respectively shown (Fig. 10C). Correlated color temperatures (CCT) of (pip) ₂ PbBr ₆ , (pip) ₃ Pb ₆ Cl ₁₈ , and (2,5-dmpz) _0.5 PbBr ₃ were 3247.6K, 5246.0K and 6076.5K, respectively (Table 3). The CCT of (pip) ₃ Pb ₆ Cl ₁₈ and (2,5-dmpz) _0.5 PbBr ₃ ·2((CH ₃ ) ₂ SO) shows a cold white light source for indoor lighting applications above 5000K, while (1mpz) The CCT of ₄ Pb ₂ Br ₁₂ emitted warm orange light at 2810.4K (FIG. 10D).

Claims (7)

Including an edge-covalent helical chain consisting of a unit structure of the following formula (1) and a plurality of piperazinium of the following formula (2),
The perovskite compound represented by the unit structure of the following formula (3), wherein N ⁺ -H of the piperazinium forms a hydrogen interaction with each other X ^- of the chain:
[Formula 1]
[PbX ₅ ] ^3-
(Wherein, X is one selected from the group consisting of Cl, Br and I)
[Formula 2]

[Formula 3]
(pip) _0.5n Pb _n X _3n
(Wherein, pip is piperazinium of Formula 2, X is one selected from the group consisting of Cl, Br, and I, and n is an integer of 3 or more).
The perovskite compound of claim 1, wherein X in Formula 1 is Cl.
The perovskite compound of claim 1, wherein the edge-covalent helical chain is at least partially connected to form a ring.
The perovskite compound of claim 1, wherein the compound has a CRI value of 70 or more.
The perovskite compound of claim 1, wherein the compound has a CRI value of 90 or higher.
A light-emitting device comprising the perovskite compound of any one of claims 1 to 5.
A light-emitting device comprising the light-emitting device of claim 6.

Images