An organic-inorganic hybrid perovskite multiferroic material suitable for ferroelectric photovoltaics

Abstract

The application discloses an organic-inorganic hybrid perovskite multiferroic material suitable for ferroelectric photovoltaics, and relates to the field of new functional materials. The chemical formula of the organic-inorganic hybrid perovskite multiferroic material is [NH2NH3][Cr(HCOO)3], the semiconductor material has a band gap width of about 1.67 eV, the crystal structure is orthorhombic perovskite structure, belongs to the orthorhombic system, the space group is Pna21, and the cell parameters are a=0.7 nm, b=0.7 nm and c=0.7 nm. The ferroelectric polarization of the organic-inorganic hybrid perovskite multiferroic material is derived from the BX3 framework distortion, the polar organic cation at the A site and the coupling of the two, the ferroelectric polarization direction is the [001] direction, and the ferroelectric polarization value is about 2.60 muC / cm 2 . Compared with known Cr-based metal ammonium formate framework materials, the ferroelectric polarization value is increased by more than one order of magnitude; the ground state magnetic structure of the organic-inorganic hybrid perovskite multiferroic material is A-type anti-ferromagnetic (A-AFM), the absolute value of the Cr 2+ magnetic moment is 3.85 mu B .

Description

TECHNICAL FIELD

[0001] The present application relates to the field of new functional materials, in particular to a kind of orthorhombic organic-inorganic hybrid perovskite structure multiferroic material. BACKGROUND

[0002] Multiferroic material is a kind of functional material with multiple ferroelectricity coexistence, these ferroelectricity include ferroelectricity, ferromagnetism and ferroelasticity etc..This kind of functional material is widely used in non-volatile memory, sensor, energy collection and actuator etc., demand increases year by year.However, the chemical incompatibility of conventional ferroelectricity and magnetism makes the multiferroic material rare in nature.

[0003] Organic-inorganic hybrid perovskites (OIHP) is a kind of material that is widely used in photovoltaic, light emitting diode, photodetector, piezoelectric and ferroelectric energy collector, multiferroic, catalysis, drug delivery and other fields.Especially in the field of photovoltaic, the certified photoelectric conversion efficiency of OIHP solar cell has reached 25.8%, plus its long carrier lifetime, high light absorption coefficient, simple preparation, low cost and other advantages, making it a potential competitor with traditional commercial photovoltaic products.The general molecular formula of OIHP is ABX3, wherein A is an organic cation, B is a metal cation, and X is an anion coordinated with B, such as halide ion, formate ion, etc.Compared with pure inorganic perovskite, OIHP has more chemical combinations that meet the tolerance factor due to the addition of organic components, and the structure is more complex and variable, and the richness of such chemical diversity and structural flexibility is the fundamental of its wide application.

[0004] We envisage that if a polar organic cation is introduced into the A site to construct OIHP, and through composition and structure regulation to make the polar organic molecules form ordered arrangement, it is possible to break through the contradiction between ferroelectricity and magnetism in traditional multiferroic materials, and become an effective way to design new multiferroic materials. SUMMARY

[0005] The present application designs an organic-inorganic hybrid perovskite with orthorhombic structure by first principle, which is mainly characterized by being a kind of multiferroic material with both magnetism and ferroelectricity, and has not been reported.

[0006] The organic-inorganic hybrid perovskite multiferroic material involved in the present application has a chemical formula of [NH2NH3][Cr(HCOO)3], which is a semiconductor material with a band gap width of about 1.67eV, and the crystal structure is orthorhombic, the space group is Pna21, and the cell parameters are a=0.7nm, b=0.7nm and c=1.2nm. Its ferroelectric polarization is derived from the BX3 framework distortion and the A-site polar organic cation and their coupling, the ferroelectric polarization direction is

[001] direction, and the ferroelectric polarization value is about 2.60 mu C / cm 2 , wherein the contribution of the framework is 2.33 mu C / cm 2 , the contribution of the organic cation is 0.56 mu C / cm 2 , and the coupling of the two is -0.29 mu C / cm 2 , and the ferroelectric flip barrier is 0.54 eV / f.u.; its magnetism is derived from Cr 2+ , the ground state spin collinear magnetic structure of the magnetic ion is A-type antiferromagnetic (A-AFM), and the absolute value of the magnetic moment is 3.85 mu B .

[0007] The organic-inorganic hybrid perovskite multiferroic material can be synthesized by a solvent method, and the specific method is: mixing formic acid, an aqueous solution of hydrazine, Cr(ClO4)2.6H2O and methanol solution, collecting the crystal after standing for two days, washing with ethanol and air drying to obtain.

[0008] Among them, 0.46 g (10 mmol) of formic acid corresponds to 6.0 mmol of 85wt% hydrazine aqueous solution with a concentration of 85wt% and 0.46 g (1.0 mmol) of Cr(ClO4)2.6H2O and 15 mL of methanol.

[0009] The present application occupies the A site of the perovskite structure with the organic polar cation [NH2NH3]+, and occupies the B site with the Cr 2+ ion to construct an OIHP based on the metal ammonium formate framework (AB(HCOO)3). Compared with the latest reported Cr-based OIHP ferroelectric material (P=0.22 mu C / cm 2 ), the ferroelectric polarization thereof can be increased by more than one order of magnitude (P=2.60 mu C / cm 2 ), and the band gap width thereof is about 1.67 eV, which perfectly matches the visible light spectrum range, and is an excellent organic-inorganic hybrid ferroelectric photovoltaic candidate material. BRIEF DESCRIPTION OF DRAWINGS

[0010] Figure 1 The base state crystal structure (a) and the base state magnetic structure (b) of [NH2NH3][Cr(HCOO)3] are shown.

[0011] The schematic diagram, the middle arrow indicates that the spin is upward, and the two end arrows indicate that the spin is downward.

[0012] Figure 2 The XRD spectrum of [NH2NH3][Cr(HCOO)3] is shown.

[0013] Figure 3The polarization flipping energy diagram and polarization value diagram of [NH2NH3][Cr(HCOO)3] are shown (in the figure, λ represents the degree of deformation of the center-symmetry phase to the polar phase).

[0014] Figure 4 The band and state density diagram of [NH2NH3][Cr(HCOO)3] is shown. DETAILED DESCRIPTION

[0015] In order to make the skilled in the art better understand the present application, the present application is further illustrated below in combination with specific examples, but the present application is not limited to the following examples.

[0016] Example 1

[0017] 0.46 g (10 mmol) of formic acid, 0.35 g (6.0 mmol) of an aqueous solution containing 85% hydrazine and 0.46 g (1.0 mmol) of Cr(ClO4)2·6H2O are mixed with 15 mL of methanol solution, and the crystals are collected after standing for two days, washed with ethanol and air-dried to obtain.

[0018] (1) In order to improve the weak ferroelectricity of [C(NH2)3][Cr(HCOO)3] with a non-polar organic cation at A site, the present application adopts a polar cation [NH2NH3] + , which effectively realizes a large optimization of ferroelectricity. Through symmetry analysis and total energy calculation, the ground state structure of the organic-inorganic hybrid perovskite multiferroic material [NH2NH3][Cr(HCOO)3] is obtained, and the crystal structure thereof is shown in Figure 1 (a), and the XRD spectrum thereof is shown in Figure 2 ; wherein the magnetic moment of the magnetic ion Cr 2+ is 3.85 μ B , the adjacent Cr 2+ is antiferromagnetically coupled, and the ground state magnetic structure of the material is an A-type antiferromagnetic structure, as shown in Figure 1 (b).

[0019] (2) We construct a center-symmetric structure and find various transition states formed by inorganic framework distortion and molecular orientation arrangement, and determine the ferroelectric polarization value thereof to be about 2.60 μC / cm 2 by the Berry phase method, the polarization direction is

[001] direction, and the polarization flipping activation energy is about 540 meV.

[0020] (3) Figure 3 The band structure and state density calculation results of [NH2NH3][M(HCOO)3]. The calculation shows that it is a semiconductor material with a band gap width of about 1.67 eV, which matches well with the visible light spectrum range, and is an excellent candidate material suitable for visible light range ferroelectric photovoltaic devices.

[0021] The details of the application are as follows.

[0022] The above examples are only to illustrate the technical concept and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and to implement it, and cannot limit the protection scope of the present application. Any equivalent changes or modifications made in accordance with the spirit and essence of the present application shall be covered within the protection scope of the present application.

Claims

1. An organic-inorganic hybrid perovskite multiferroic material, characterized in that, The chemical formula is [NH2NH3][Cr(HCOO)3]; The crystal structure is orthorhombic, with space group Pna21 and unit cell parameters a = 9.30 Å, b = 7.63 Å, c = 11.48 Å; It exhibits both magnetic and ferroelectric properties. Its ferroelectric polarization originates from the BX3 framework twist and the polar organic cation at the A site, as well as their coupling. The ferroelectric polarization direction is [001], and the ferroelectric polarization value is 2.60 μC / cm. 2 The framework contributed 2.33 μC / cm³. 2 The contribution of organic cations was 0.56 μC / cm. 2 The coupling between the two is -0.29 μC / cm. 2 The ferroelectric reversal barrier is 0.54 eV / fu; its magnetism originates from Cr. 2+ The ground-state spin collinear magnetic structure of the magnetic ion is A-type antiferromagnetic (A-AFM), with an absolute magnetic moment of 3.85 μm. B ; It is a semiconductor material with a band gap of 1.67 eV.

2. The application of the organic-inorganic hybrid perovskite multiferroic material according to claim 1, characterized in that, The material is compatible with visible light and can be used as a ferroelectric photovoltaic material.

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