WO2019236011A1

WO2019236011A1 - Perovskites and uses thereof

Info

Publication number: WO2019236011A1
Application number: PCT/SG2019/050292
Authority: WO
Inventors: Kian Ping Loh; In-Hyeok Park
Original assignee: National University Of Singapore
Priority date: 2018-06-08
Filing date: 2019-06-10
Publication date: 2019-12-12

Abstract

The present disclosure relates to perovskites and their uses. In particular, the present disclosure relates to derivatized metal halide perovskites. The metal halide perovskite comprises a metal cation, a stilbene derived ammonium cation and a halide anion. The present disclosure also relates to optoelectronic devices and materials comprising the presently disclosed perovskites.

Description

PEROVSKITES AND USES THEREOF

FIELD

The present disclosure relates to perovskites. In particular, the present disclosure relates to derivatized metal halide perovskites. The present disclosure also relates to optoelectronic devices and materials comprising the presently disclosed perovskites.

BACKGROUND

Recently, hybrid organic-inorganic three-dimensional (3D) perovskites have emerged as highly attractive solar cell materials. In this regard, 3D perovskites are a class of bulk materials that consist of a framework of comer- sharing cation-anion octahedral that extends in all three dimensions, with other small cations fitting into the void spaces between the octahedral. However, one major problem of 3D perovskites is the lack of stability in air often due to its chemical reactivity with moisture, which causes it to degrade. It has been proposed that 2D perovskites may offer stability advantages, but still there is much room to improve in terms of the photostability and performance of 2D perovskites. 2D perovskites in this sense means sheets or layers of perovskites arranged in a specific crystallographic direction (i.e. separated by an organic layer). SUMMARY

The present inventors have found that specifically derivatized 2D perovskites comprising a particular salt have advantageous air stability. The derivatized perovskites comprising a particular salt also have advantageous thermal stability. In particular, derivatized metal halide 2D perovskites according to the present invention comprising a stilbene derived ammonium salt have been found to possess advantageous thermal and air stability, together with good chemical and structural stability. Such perovskites may show particular utility in optoelectronic devices such as solar cell and LED technology.

In a first aspect, the present disclosure provides a metal halide 2D perovskite comprising a metal cation, a stilbene derived ammonium cation and a halide anion. In an embodiment, the stilbene derived ammonium cation is a compound of Formula (I):

wherein R is selected from F, Cl, Br and I; and

n and m are independently an integer selected from 0-5.

In a second aspect, the present disclosure provides a metal halide 2D perovskite compound of Formula (II):

[A]₂[B][C]4 (II)

wherein [A] is a compound of Formula (I);

[B] is a divalent metal cation; and

[C] is a halide anion.

In all embodiments, compound of Formula (I) is in the E (trans) configuration. In some embodiments, R is F.

In some embodiments, n is selected from 1-5.

In another embodiment, m is selected from 1-5.

In some embodiments, compound of Formula (I) is selected from one of the following:

In some embodiments, compound of Formula (I) is selected from:

In another embodiment, the halide is selected from fluoride, chloride, bromide and iodide. In some embodiments, the metal cation is selected from Ca²⁺, Sr²⁺, Cd²⁺, Cu²⁺, Ni²⁺, Mn²⁺, Fe²⁺, Co²⁺, Pd²⁺, Ge²⁺, Sn²⁺ and Pb²⁺.

In some embodiments, the metal cation is selected from Sn²⁺ and Pb²⁺. In a third aspect, the present disclosure provides an optoelectronic device or material, comprising metal halide 2D perovskite of the present invention.

BRIEF DESCRIPTION OF DRAWINGS

Some embodiments of the present invention will now be described by way of non-limiting example only, with reference to the accompanying drawings in which:

Figure 1 illustrates an example of single crystal structure of metal halide perovskite of the present disclosure: (a) Pb(II) core unit. Symmetry codes: (A) -l-x, y, -2-z; (B) -l-x, l+y, - 2-z. (b) 2D [Pbl₄]² layer (c) Packing mode showing alignment of amine molecules along c- axis.

Figure 2 illustrates plots of comparisons of current density and voltage for device stability based on methylammonium lead iodide (MALI) and metal halide perovskites of the present disclosure. DETAILED DESCRIPTION

The term“perovskite”, as generally used herein, refers to a material with a three-dimensional crystal structure related to that of CaTi0₃, or a 2D layer of perovskite, wherein the layer has a structure related to that of CaTi0₃. In this regard, 2D perovskites can be viewed as derivatives of 3D perovskites formed by“slicing” the 3D frameworks into well-defined 2D slabs. It will be appreciated however that the present invention provides for derivatized 2D perovskites. 2D perovskites have the generic chemical formula of A_p+iBX_3p+i (p is an integer), where A is a cation acting as a spacer between the perovskite layers, and the B cation and X anions form the perovskite framework. In this regard, A and B are cations of different sizes. The 2D network consists of inorganic perovskite layers of corner-sharing [BX₆]^4_ octahedra confined between interdigitating layer of A. This layer can be a bilayer. The unit layers are held together by a combination of Coulombic and hydrophobic forces, which maintain the structural integrity. The skilled person will appreciate that when A, B and X are varied, the different ion sizes may cause the structure of the perovskite material to distort away from the structure adopted by CaTi0₃ to a lower- symmetry distorted structure. For example, methylammonium lead iodide (MALI) when a solid, is a compound with perovskite structure and a chemical formula of CH₃NH₃PbI₃. The symmetry will also be lower if the perovskite comprises a 2D layer that has a structure related to that of CaTi0₃.

The term“halide” refers to an anion of a group 7 element, i.e., of a halogen. Typically, halide refers to a fluoride anion, a chloride anion, a bromide anion or an iodide anion.

In an embodiment, the metal cation is a divalent metal cation. In another embodiment, the metal cation may be selected from Ca²⁺, Sr²⁺, Cd²⁺, Cu²⁺, Ni²⁺, Mn²⁺, Fe²⁺, Co²⁺, Pd²⁺, Ge²⁺, Pb²⁺ and Sn²⁺. In another embodiment, the metal cation is selected from Sn²⁺ and Pb²⁺. In some embodiments, the metal cation is Pb²⁺.

The inventors have found that perovskites comprising stilbene derived ammonium salts have advantageous properties. For instance, advantageously, the disclosed perovskites display thermal and air stability. Further, the disclosed perovskites comprise long chain conjugated ligands which contribute to their chemical and structural stability. It was found that these perovskites impart extra photo- stability on the perovskites in ambient conditions. Also, without wanting to be bound by theory, in other embodiments, it is believed that (when present) the fluorine substituent on the phenyl of stilbene may additionally provides the stilbene, and hence the new perovskite (as a whole) a hydrophobic character (i.e. water repelling), thus making it is less likely to be degraded by moisture. It is also believed that the stilbene moiety may also result in a unique packing structure which may be responsible for the enhanced tolerance towards moisture. The different fluorine functionalities (when present) may also advantageously alter the optoelectronic properties of the perovskite compared to, for instance, commercially known methylammonium lead iodide (MALI). Additionally, stilbene in the E (trans) configuration is advantageous to the Z (cis) configuration as it results in a unique packing structure which may further be responsible for the enhanced tolerance towards moisture. In this regard, it is believed that steric hindrance between the stilbene (when in Z configuration) will result in a less than optimal packing structure in the perovskite. The Z configuration is also believed to be less stable, and accordingly may not be applicable for use in optoelectronic devices or material.

The skilled person would know that changes to an organic cation in the perovskite will usually have an impact on the structural and/or physical properties of the perovskite. By controlling the organic cation used, the electronic properties and the optical properties of the material may be controlled. For example, it is known that by changing the organic cation, the conductivity of the material may increase or decrease. Further, changing the organic cation may alter the band structure of the material thus, for example, allowing control of the band gap for a semiconducting material. The skilled person would be able to perform the necessary trials to evaluate and tune (without further inventive faculty) the electronic properties and optical properties of the present 2D perovskites for any specific application.

In an embodiment, R is a halide. In another embodiment, R is selected from F, Cl or Br. In certain embodiments, R is F.

In an embodiment, n is an integer selected from 0-5. In another embodiment, n is an integer selected from 1-5. In another embodiment, n is an integer selected from 2-5. In another embodiment, n is an integer selected from 3-5. In another embodiment, n is 0. In another embodiment, n is 1. In another embodiment, n is 2. In another embodiment, n is 3. In another embodiment, n is 4. In another embodiment, n is 5.

In an embodiment, m is an integer selected from 0-5. In another embodiment, m is an integer selected from 1-5. In another embodiment, m is an integer selected from 1-4. In another embodiment, m is an integer selected from 1-3. In another embodiment, m is 0. In another embodiment, m is 1. In another embodiment, m is 2. In another embodiment, m is 3. In another embodiment, m is 4. In another embodiment, m is 5.

Accordingly, a compound of Formula (I) may be selected from the following non-limiting examples/generic embodiments (wherein m is 1):

Accordingly, in certain embodiments and with specific reference to the above structures, each R is F.

In an embodiment, the halide anion is selected from a fluoride anion, a chloride anion, a bromide anion, an iodide anion. In another embodiment, the halide anion is a fluoride anion. In another embodiment, the halide anion is a chloride anion. In another embodiment, the halide anion is a bromide anion. In another embodiment, the halide anion is an iodide anion.

In another aspect, the present disclosure provides a metal halide perovskite compound of Formula (II):

[A]₂[B][C]4 (II)

wherein [A] is a compound of Formula (I);

[B] is a divalent metal cation; and

[C] is a halide anion. In an embodiment, [B] may be selected from Ca²⁺, Sr²⁺, Cd²⁺, Cu²⁺, Ni²⁺, Mn²⁺, Fe²⁺, Co²⁺, Pd²⁺, Ge²⁺, Sn²⁺ and Pb²⁺. In another embodiment, [B] is selected from Sn²⁺ and Pb²⁺. In some embodiments, [B] is Pb²⁺.

The skilled person would be aware that [C] is an anion, which many be derived from the [A] salt (i.e. [A][C]) and the [B] salt (i.e. [B][C]₂). Accordingly, in an embodiment, [C] from the [A] salt and [C] from the [B] salt are similar. In another embodiment, [C] from the [A] salt and [C] from the [B] salt are different. In another embodiment, [C] is selected from a fluoride anion, a chloride anion, a bromide anion, an iodide anion. In another embodiment, [C] is a fluoride anion. In another embodiment, [C] is a chloride anion. In another embodiment, [C] is a bromide anion. In another embodiment, [C] is an iodide anion.

Disclosed herein are metal halide perovskites comprising stilbene derived ammonium salt. As examples, the inventors have designed and synthesized three types of 2D perovskites bearing the stilbene derivative with different fluorine functionalities.

In another aspect, the present disclosure provides an optoelectronic device, comprising metal halide perovskite of the present invention. In particular, the optoelectronic device comprises a metal halide perovskite comprising a first metal cation, a second stilbene derived ammonium cation (compound of Formula (I)) and a halide anion. In another embodiment, the optoelectronic device comprises a metal halide perovskite compound of Formula (II):

[A]₂[B][C]4 (II)

wherein [A] is a compound of Formula (I);

[B] is a divalent metal cation; and

[C] is a halide anion.

As used herein, "optoelectronic devices" are electronic devices and systems that source, detect and control light. In this context, light often includes invisible forms of radiation such as gamma rays, X-rays, ultraviolet and infrared, in addition to visible light. Examples of optoelectronic devices are electrical-to-optical or optical-to-electrical transducers, or instruments that use such devices in their operation. Typically optoelectronic devices are photovoltaic device, a photodiode, a phototransistor, a photomultiplier, a photo resistor, a photo detector, a light-sensitive detector, solid-state triode, a battery electrode, a light- emitting device, a light-emitting diode, a transistor, a solar cell, a laser, and a diode injection laser.

The disclosed perovskites, and in particular 2D perovskites derived from the present invention, can be applied for use in solar cell and LED devices. They may also be extremely useful for fundamental studies such as their non-linear optical properties.

These 2D perovskites can be solution-processed to make processible 2D perovskite optoelectronic devices, eg. flexible photodetector.

The present disclosure also provides a method of forming the metal halide 2D perovskite. As is shown in the examples, the method of forming a metal halide 2D perovskite includes a step (a) of dissolving lead(II) oxide and compound of Formula (I) in a solvent comprising of HI and ethanol and at a predetermined temperature to form a mixture, and a step (b) of cooling the mixture to form the metal halide 2D perovskite. For example, a solvothermal process can be used to form the metal halide 2D perovskite.

As used herein, 'solvothermal' process or synthesis refers to a synthesis method for growing crystals from a non-aqueous solution at high temperature. This can optionally be performed in an autoclave (a thick-walled steel vessel). Additionally, the reaction can also be performed under high pressure.

The inventors have found that the addition of ethanol is advantageous for forming the metal halide 2D perovskite of the present invention. In this regard, the ethanol aids the dissolution of compound of Formula (I), allowing it to mix with the lead(II) oxide.

In some embodiments, step (a) is performed at at least 80 °C, at least 85 °C, at least 90 °C, at least 95 °C or at least 100 °C.

In some embodiments, the mixture in step (b) is allowed to crystallise to form the metal halide 2D perovskite. By allowing the mixture to cool slowly, metal halide 2D perovskites with homogenous crystal size and morphology can be obtained.

Those skilled in the art will appreciate that the invention described herein in susceptible to variations and modifications other than those specifically described. It is to be understood that the invention includes all such variations and modifications which fall within the spirit and scope. The invention also includes all of the steps, features, compositions and compounds referred to or indicated in this specification, individually or collectively, and any and all combinations of any two or more of said steps or features.

Throughout this specification and the claims of invention which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

Certain embodiments of the invention will now be described with reference to the following examples which are intended for the purpose of illustration only and are not intended to limit the scope of the generality hereinbefore described.

Examples

The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

Synthesis of Compound of Formula (I)

Syntheses of the ammonium halides

The stilbene derived amine can be used as additive to improve the stability of perovskites. Three amines were synthesized, namely SAI, FSAI and 5FSAI, with the chemical names of: SAI = 2-(4-stilbenyl)ethanammonium iodide)

FSAI = 2-(4-(3-fluoro)stilbenyl)ethanammonium iodide

5FSAI = 2-(4-(2,3,4,5,6,-pentafluoro)stilbenyl)ethanammonium iodide

2-(4-stilbenyl)ethanamine (SA) was synthesized by a reported procedure; J. E. Francis et ah, J. Med. Chem. 1991, 34, 2570-2579. 3-Fluorostyrene was used instead of styrene to synthesize 2-(4-(3-fluoro)stilbenyl)ethanamine (FSA). The SA and FSA were used directly to prepare ammonium salts (2-(4-stilbenyl)ethanammonium iodide (SAI), 2-(4-(3- fluoro)stilbenyl)ethanammonium iodide (FSAI) by 57% hydroiodic acid (HI). 5FSAI was similarly prepared.

The chemical structures of these compounds are given below:

Other derivatives can be synthesised using a similar approach. For example, to synthesis a stilbene derived amine where R is Cl, chlorostyrene can be used instead of styrene.

General Protocol

Crystals of the stilbene perovskite (SP) was obtained under solvothermal conditions by dissolving lead(II) oxide and compound of Formula (I) in a mixture of HI and ethanol (EtOH) at 90 °C, followed by slow cooling to allow for crystallisation of the perovskites. EtOH was used to enhance the solubility of Compound of Formula (I) which was poor in pure HI.

Example 1: Perovskite with 2-(4-stilbcnyl )cthanammonium iodide (SAD

Bright orange plate-shaped crystals of the stilbene perovskite (SP) suitable for single crystal X-ray diffraction (SC-XRD) data collection was obtained under solvothermal conditions by dissolving lead(II) oxide and 2-(4-stilbenyl)ethanammonium iodide (SAI) in a mixture of HI and ethanol (EtOH) at 90 °C, followed by slow cooling.

Example 2: Perovskite with 2-(4-(3-fluoro)stilbenyl)ethanammonium iodide (FSAI)

Bright orange plate-shaped crystals of fluoro stilbene perovskite (FSP) was obtained using the above protocol and replacing SAI with 2-(4-(3-fluoro)stilbenyl)ethanammonium iodide (FSAI). The crystals were suitable for SC-XRD data collection. TGA of the 2D perovskites showed that they were stable up to at least 250 °C.

Example 3: Perovskite with 2-(4-(2.3.4.5.6,-pcn tail uoro)stil hen yl )cthanammonium iodide (5FSAI)

Dark orange plate-shaped crystals of pentafluorostilbene perovskite (5FSP) was obtained using the above protocol and replacing SAI with 2-(4-(2,3,4,5,6,- pentafluoro)stilbenyl)ethanammonium iodide (5FSAI). The crystals were suitable for SC- XRD data collection. TGA of the 2D perovskites showed that they were stable up to at least 250 °C.

Three two-dimensional (2D) lead(II) iodide perovskites with formula [(stilbene-NFF^PbR] were synthesized by incorporating stilbene-derived ammonium salts into the 2D lead(II) iodide perovskite motif. Figure l(a)-(c) illustrates the crystal structure. Based on the general formula [(stilbene-NFF^PbR], the stilbene moiety can be varied to have either SAI = 2-(4- stilbenyl)ethanammonium iodide); FSAI = 2-(4-(3-fluoro)stilbenyl)ethanammonium iodide or 5FSAI = 2-(4-(2,3,4,5,6,-pentafluoro)stilbenyl)ethanammonium iodide. Each of these represents a new 2-D perovskite which has improved air stability and the optical emission from these perovskites can be tuned from 500 - 650 nm. The stilbene derivatives can be added as additive to improve the stability of 3D perovskites for optoelectronic applications.

The synthesized stilbene amine derivatives were investigated as an organic halide salt additive to standard 3D perovskite based on methylammonium lead iodide (MALI) when the latter is evaluated as solar cell material (Fig. 2). By adding the fluorostilbene amine, especially, FSAI into the precursor solution, the stability of MALI is enhanced (Fig. 2) without sacrificing power conversion efficiency.

Example 4: Optoelectronic Device Performance

The fluorine-doped tin oxide (FTO) coated glass was etched with Zn powder (Sigma- Aldrich) and 4 M hydrochloric acid (Sigma-Aldrich) and followed by sequential cleaning with decon soap solution (20 minutes), deionized water (15 minutes), ethanol (15 minutes), and acetone (15 minutes). A thin compact layer of Ti0₂ was deposited on the cleaned FTO by spray pyrolysis using N₂ as the carrying gas at 450°C from a precursor solution consisting of 0.6 mL titanium diisopropoxide and 0.4 mL bis(acetylacetonate) dissolved in 9 mL anhydrous Isopropanol (1:9 v/v ratio). The Ti0₂ compact layer was further treated with 50 mM of TiCU solution at 70 °C for 30 minutes, followed by washing with deionized water and ethanol solution. The substrate was finally calcined at 500°C for 30 min. A mesoporous Ti0₂ film was subsequently deposited by spin-coating Ti0₂ paste (30 NR-D, Dyesol) diluted with absolute ethanol (1 :5.5 w/w), the substrate was immediately dried on a hotplate at l00°C, and again calcined at 500°C for 30 min. The meso-Ti0₂ layer was further treated with 50 mM of TiCU solution at 70 °C for 30 minutes, followed by washing with deionized water and ethanol solution. The substrate was finally calcined at 500°C for 30 min. n= 60 based devices of SAI, FSAI and 5FSAI: 1.35 M of A₂(MAI)s9(PbI₂)60 (where A= SAI, FSAI, 5FSAI) solution in 1 mL DMF was made by dissolving 1.35 M Pbl₂, 1.33 M methylammonium iodide (MAI) and 0.05 M A with stirring. The solution was stirred at 70 °C for 30 minutes. The solution was spin-coated on the substrate with a single step process at 5000 rpm for 15 seconds. 100 pL of diethyl ether antisolvent was dropped on the spinning substrate at 5th second. The substrate was then annealed at 100 °C for 30 minutes.

Table 1 illustrates the device performances for solar cell with fresh perovskites. Table 2 illustrates the device performance for solar cell with perovskites after 6 days. Voc refers to the open circuit voltage, Jsc refers to the short circuit current, FF refers to the fill factor and PCE refers to the power conversion efficiency.

Table 1. Device performances for solar cell with fresh perovskites

Table 2. Device performance for solar cell with perovskites after 6 days

Claims

1. A metal halide 2D perovskite comprising a metal cation, a stilbene derived ammonium cation and a halide anion, wherein the stilbene derived ammonium cation is a compound of Formula (I):

wherein R is selected from F, Cl, Br and I; and

n and m are independently an integer selected from 0-5.

2. A metal halide 2D perovskite compound of Formula (II):

[A]₂[B][C]4 (II)

wherein [A] is a compound of Formula (I);

[B] is a divalent metal cation; and

[C] is a halide anion;

wherein compound of Formula (I) is:

wherein R is selected from F, Cl, Br and I; and

n and m are independently an integer selected from 0-5.

3. The metal halide 2D perovskite according to claims 1 or 2, wherein compound of Formula (I) is in the E (trans) configuration.

4. The metal halide 2D perovskite according to any one of claims 1 to 3, wherein R is F.

5. The metal halide 2D perovskite according to any one of claims 1 to 4, wherein n is selected from 1-5.

6. The metal halide 2D perovskite according to any one of claims 1 to 5, wherein m is selected from 1-5.

7. The metal halide 2D perovskite according to any one of claims 1 to 6, wherein compound of Formula (I) is selected from one of the following:

8. The metal halide 2D perovskite according to any one of claims 1 to 7, wherein compound of Formula (I) is selected from:

9. The metal halide 2D perovskite according to any one of claims 1 to 8, wherein the halide is selected from fluoride, chloride, bromide and iodide.

10. The metal halide 2D perovskite according to any one of claims 1 to 9, wherein the metal cation is selected from Ca²⁺, Sr²⁺, Cd²⁺, Cu²⁺, Ni²⁺, Mn²⁺, Fe²⁺, Co²⁺, Pd²⁺, Ge²⁺, Sn²⁺ and Pb²⁺.

11. The metal halide 2D perovskite according to any one of claims 1 to 10, wherein the metal cation is selected from Sn²⁺ and Pb²⁺.

12. An optoelectronic device, comprising metal halide 2D perovskite, the metal halide 2D perovskite comprising a metal cation, a stilbene derived ammonium cation and a halide anion, wherein the stilbene derived ammonium cation is a compound of Formula (I):

wherein R is selected from F, Cl, Br and I; and

n and m are independently an integer selected from 0-5.