WO2002082864A1

WO2002082864A1 - Electroluminescent element having lead bromide based layered perovskite compound as luminescent layer

Info

Publication number: WO2002082864A1
Application number: PCT/JP2001/011016
Authority: WO
Inventors: Masanao Era
Original assignee: Japan Science And Technology Corporation
Priority date: 2001-04-03
Filing date: 2001-12-17
Publication date: 2002-10-17
Also published as: JP2002299063A

Abstract

An electroluminescent element having a lead bromide based layered perovskite compound as a luminescent layer, characterized in that it has a three-layered laminate structure wherein the luminescent layer is sandwiched between an organic molecule layer having a positive hole transporting function and an organic molecule layer having an electron transporting function.

Description

Specification

Electroluminescent device using lead bromide-based layered perovskite compound as light emitting layer

The present invention belongs to the technical field of light-emitting devices, and particularly relates to a novel electroluminescent device using a lead bromide-based layered perovskite compound as a light-emitting layer.

Background technology ■

An electroluminescent element is an element utilizing a phenomenon in which a substance emits light when an electric field is applied. As materials for electroluminescent devices, those using inorganic semiconductors such as gallium arsenide and those using luminescent organic molecules have been known. Recently, a halide-based layered perovskite is expected to be applied to a light-emitting device because of its small exciton emission with a small emission wavelength width in the visible region. The present inventors have previously reported a lead iodide-based layered perovskite as an electroluminescent device using a halide-based layered perovskite, but the emission color is limited to green (M. Era, S. Morimoto, T. Tsutsui, and S. Saito, Appl. Phys. Lett., 65, 676-678 (1994)) ₀

The present inventors have proposed an electroluminescent device including a lead bromide-based layered perovskite compound as an electroluminescent device using a halide-based layered perovskite. Lead bromide-based layered base Robusukai DOO compound is represented by the general formula A ₂ P b B r ₄ when the A and organic Anmoniumu molecules, organic Anmoniumu molecules A layer and lead bromide P b B r ₄ layers and are alternately It is known to form a superlattice structure stacked on the surface (David B. itzi, "Synthesis, Structure, and Properties of Organic-Inorganic Perovskites and Related Materials," Progress in Organic Chemistry, Vol. 48, Edited by Kenneth D. Karlin, John Wiley & Sons, Inc. (1999)), the present inventors have found that this compound shows strong exciton emission in the violet to blue region (M. Era, N. Kakiyama, T. Ano, and Μ. Nagano, Trans. Mater. Res. Soc. Jpn., 24, 509-511 (1999)). Figure 6 shows a lead bromide layered perovsk with an alkyl ammonium molecule as the organic layer. FIG. 2 shows a diagram of an absorption spectrum and a light emission spectrum of a kite. It can be seen that the peak wavelength of the exciton emission changes from 400 nm to 450 nm depending on the alkyl chain length of the alkyl ammonium molecule, showing a violet to blue emission color.

As described above, the lead bromide-based layered perovskite provides a new type of electroluminescent device having a wide range of light emission from purple to blue, but requires a relatively large driving voltage to obtain a predetermined current. In addition, the efficiency is not good in that the emission intensity obtained by a predetermined current value is low.

An object of the present invention is to provide an electroluminescent device which emits a violet to blue light and can be driven at a low voltage with high efficiency, using a lead bromide-based layered perovskite as a light emitting layer.

As a result of repeated studies, the present inventors succeeded in producing a multilayer structure in which a light-emitting layer composed of a lead bromide-based layered perovskite compound was combined with an organic molecule having a carrier-transporting property. Good electroluminescence was enabled.

Thus, according to the present invention, represented by the general formula A ₂ P b B r ₄ A as organic Anmoniumu molecules, organic Anmoniumu molecules Α layer and lead bromide P b B r ₄ layers are alternately stacked ultra The lead bromide-based layered buskite compound having a lattice structure is used as the light-emitting layer, and a two-layer carrier transport layer composed of an organic molecule layer having a hole transport property and an organic molecule layer having an electron transport property is provided. There is provided an electroluminescent device having a three-layered laminated structure sandwiching a light emitting layer of the lead bromide-based layered perovskite compound.

In the electroluminescent device of the present invention, the organic ammonium molecule of A is generally represented by the formula R_ (CH ₂ ) _n —NH ₃ , wherein n represents 0 or an integer of 1 to 6. R represents an alkyl group having 1 to 6 carbon atoms, a phenyl group, or a 5- to 7-membered cycloalkyl group or a cycloalkenyl group. In a preferred embodiment of the electroluminescent device of the present invention, a phthalocyanine, a diamine derivative, a fluorene derivative, or a polythiophene derivative is used as the hole-transporting organic molecule, and the oxadiazole derivative is used as the electron-transporting organic molecule. Triazole derivatives, A perylene derivative or a quinolinol metal complex is used.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a three-layer laminated light emitting device of the present invention in which a lead bromide layered perovskite light emitting layer is sandwiched between an organic molecular layer having a hole transporting property and an organic molecular layer having an electron transporting property. It is a schematic diagram.

FIG. 2 is a schematic diagram of a three-layer element and a two-layer element manufactured in the examples. FIG. 3 is an electroluminescence spectrum of the three-layer device manufactured in the example.

FIG. 4 is a diagram comparing current-voltage characteristics of the three-layer element and the two-layer element manufactured in the example.

FIG. 5 is a diagram comparing the current / electroluminescence intensity characteristics of the three-layer element and the two-layer element produced in the example.

FIG. 6 shows a light emission spectrum and an absorption spectrum of a lead bromide-based layered graphite sheet having an alkylammonium molecule as an organic layer. The solid line shows the emission spectrum, and the dotted line shows the absorption spectrum. The formula shown above is the chemical formula of the layered perovskite, and the value of n in the formula indicates the number of carbon atoms in the alkyl chain of the alkylammonium molecule. BEST MODE FOR CARRYING OUT THE INVENTION

In the electroluminescent device of the present invention, the two carrier transporting layers composed of an organic molecular layer having a hole transporting property and an organic molecular layer having an electron transporting property are composed of a lead bromide-based layered perovskite compound. It has a three-layer laminate structure sandwiching layers. FIG. 1 shows a cross section of a typical example of an electroluminescent device according to the present invention, in which the above-described three-layer structure is arranged between electrodes (anode and cathode). Generally, the thickness of the lead bromide-based layered bellows light emitting layer is about 10 to 50 nm, and the thicknesses of the hole transporting organic molecular layer and the electron transporting layer are both: Preferably, it is about 50 to 100 nm.

Each layer constituting the electroluminescent device can be manufactured by a conventionally known thin film forming method. The carrier transport layer and the electrode layer are generally manufactured by a vacuum evaporation method. Further, the lead bromide-based layered perovskite light-emitting layer is preferably produced by a spin coating method. That is, as lead bromide-based layered Bae Robusukai bets crystal sample, or an organic Anmoniumu hydrobromide and lead bromide (P b B r _4), dimethylformamide (DMF) or dimethyl sulfoxide (DMSO) By spin-coating from a solution dissolved in a polar solvent, a lead bromide layered viscous layer having a superlattice structure in which an organic ammonium molecular layer and a lead bromide layer are alternately laminated is formed.

The organic Anmoniumu molecules consist chemical structure or et ammonia is bound to organic molecules, various compounds capable of forming a lamellar base Robusukai preparative coordinated to lead bromide (P b B r ₄₎ are available . Preferred organic ammonium molecules can be represented by the general formula R— (CH ₂ ) _n —NH ₃ , where n is 0 or an integer from 1 to 6, and R is an alkyl group having 1 to 6 carbon atoms. , A phenyl group, or a 5- to 7-membered cycloalkyl or cycloalkenyl group. Thus, a preferred example of the lead bromide-based layered perovskite used in the light emitting layer of the electroluminescent device of the present invention is represented by the following formula (1).

The organic molecules used in the organic molecule layer having a hole transporting property in the carrier transporting layer of the electroluminescent device of the present invention are not particularly limited, and various organic molecules known to exhibit the hole transporting property are used. Molecules (organic compounds) are applicable. Preferred hole transporting organic molecules include phthalocyanines, diamine derivatives, fluorene derivatives and polythiophene derivatives. For example, preferably copper phthalocyanine represented by the following formula as a hole transporting organic molecules (2) mentioned et Re ^ ί ₀

The organic molecules used in the organic molecule layer having an electron transport property of the electroluminescent device of the present invention are not particularly limited, and various organic molecules (organic compounds) known to exhibit the electron transport property are applied. It is possible. Preferred electron transporting organic molecules include oxaziazole derivatives, triazole derivatives, perylene derivatives, and quinolinol metal complexes. For example, a preferable electron transporting organic molecule is an oxaziazol derivative represented by the following formula (3).

As described above, the present invention comprises a three-layer laminated device in which a lead bromide-based layered vesicular luminescent layer is sandwiched between an organic molecular layer having a hole transporting property and an organic molecular layer having an electron transporting property. The electroluminescent device can emit light efficiently at a low voltage, as will be described later in Examples. The reason for the lower drive voltage and lower luminous efficiency is that the lead bromide-based layered perovskite compound has a large band gap and ionization potential, making it difficult to inject carriers. It is inferred that this is the case. That is, 1) the lamination with the organic molecular layer facilitated the injection of holes from the anode and the injection of electrons from the cathode, so that the driving voltage was lowered. 2) Hole transporting molecules have a low ability to transport electrons as well as holes. It serves to confine electrons in the light emitting layer. In addition, the electron-transporting molecule plays a role of confining holes in the light-emitting layer due to its low ability to transport holes as well as electrons. As a result, it is considered that electrons and holes are confined in the light-emitting layer with high density, and the luminous efficiency is increased due to efficient recombination.

Example

Examples are shown below to further clarify the features of the present invention, but the present invention is not limited to these examples.

As an example, as the hole transporting organic molecule, copper phthalocyanine (CuPc :) of the above formula (2) is used, and as the electron transporting organic molecule, the oxadiazole derivative (OXD 7) of the above formula (3) is used. A three-layer type electroluminescent device sandwiching a light-emitting layer composed of a lead bromide-based layered perovskite compound (CHEPbBrJ) of the above formula (1) was prepared, and its characteristics were evaluated. A single-layer device composed of only a lead-based layered perovskite and a two-layer device composed only of an oxaziazole derivative were also evaluated.

In the three-layer device, a copper phthalocyanine (CuPc) layer is formed on a glass plate coated with indium tin oxide (ITO) as a transparent electrode by vacuum evaporation, and then a lead bromide layered perovskite (CHEPbBr) is formed. ₄ ) The layer was spin-coated from a dimethylformamide solution, and further prepared by vapor-depositing an oxaziazole (OXD7) layer and an aluminum lithium alloy (AlLi) as a cathode. The two-layer element was fabricated by spin-coating a lead bromide-based perovskite on an ITO-coated substrate, and then depositing an OXD7 layer and an AlLi cathode. The single-layer element was fabricated by spin-coating a lead bromide-based layered perovskite on a substrate coated with ITO, and then depositing an AlLi cathode. FIG. 2 shows the element structure of the three-layer element and the two-layer element. Each film thickness was measured by a stylus method using Veeco Dektak.

FIG. 3 shows a light emitting spectrum of the three-layer device according to the present invention. Around 41 Onm Electroluminescence corresponding to exciton emission of a lead bromide layered perovskite is observed. From this spectrum, it was confirmed that light emission from the excitons of the layered perovskite layer was obtained as intended in the three-layer device. Understand. Similar results were obtained for the two-layer type device, and light emission due to excitons in the lead bromide layered perovskite was observed.

In the case of a single-layer device in which only the lead bromide layered perovskite light-emitting layer was coated, the anode and the cathode were electrically connected, and the device could not be driven. This indicates that lamination with an organic molecular layer having good film quality is important for preventing the conduction between the anode and the cathode and for driving the device stably.

Next, we compared the current-voltage characteristics of the three-layer device and the two-layer device that emitted light due to excitons (Fig. 4). Comparing the voltages required to pass a current of 10 O mA, the three-layer type requires 20 V, the two-layer type requires 72 V, and the three-layer type requires less than one third of the voltage. It can be seen that driving was possible.

FIG. 5 shows a comparison of the electroluminescence intensity characteristics between the three-layer type and the two-layer type. Comparing on the high emission intensity side, it can be seen that the three-layer type element has higher emission intensity than the two-layer type element even at the same current value and is more efficient. When compared at a current value of 15 O mA, the electroluminescence intensity of the three-layer type is 30 times that of the two-layer type. This indicates that the electroluminescence efficiency per unit current density of the three-layer device is extremely high, 30 times.

Industrial applicability

According to the present invention, an electroluminescent device having the following effects can be obtained. (1) An electroluminescent device using a lead bromide-based layered perovskite can emit light efficiently at a low voltage.

(2) The excited state of the lead bromide layered perovskite can be efficiently created by current injection, and not only the exciton emission but also the function that the layered perovskite develops via the excited state can be efficiently generated. Can be driven.

(3) Lamination with an organic molecular layer having good film quality can prevent conduction between the anode and the cathode, and a stable device can be constructed.

Claims

The scope of the claims

1. A to be represented by the general formula A ₂ P b B r ₄ as the organic Anmoniumu molecules, to form a superlattice structure in which an organic § Nmoniumu molecule A layer and lead bromide P b B r ₄ layers are alternately stacked The lead bromide-based layered perovskite compound is used as the light-emitting layer, and the two carrier transport layers composed of an organic molecular layer having a hole-transport property and an organic molecular layer having an electron-transport property are formed of the lead bromide-based compound. An electroluminescent device having a three-layer structure in which a light emitting layer of a layered perovskite compound is sandwiched.

2. The organic ammonium molecule of A is represented by R— (CH ₂ ) _n —NH ₃ (n represents 0 or an integer of 1 to 6, and R represents an alkyl group having 1 to 6 carbon atoms, a phenyl group, or 2. The electroluminescent device according to claim 1, wherein the electroluminescent device is represented by a 5- to 7-membered cycloalkyl group or a cycloalkenyl group.

3. The electroluminescent device according to claim 1, wherein a phthalocyanine, a diamine derivative, a fluorene derivative, or a polythiophene derivative is used as the hole transporting organic molecule.

4. The electroluminescent device according to any one of claims 1 to 3, wherein an organic molecule having an electron transporting property is an oxaziazole derivative, a triazole derivative, a perylene derivative, or a quinolinol metal complex.