Electroluminescent device and light-emitting layer and application thereof

Abstract

An electroluminescent device and a light-emitting layer and an application thereof. The light-emitting layer comprises at least one nano-crystalline semiconductor material and at least one exciplex; an emission spectrum of the exciplex is at least partially overlapped with an excitation spectrum of the nano-crystalline semiconductor material; and the attenuation life of an excited state of the exciplex is longer than the attenuation life of an excited state of the nano-crystalline semiconductor material.

Claims

1. A light-emitting layer of an electroluminescent device, the light-emitting layer comprising: at least one nano-crystalline semiconductor material including at least one of CdSe/ZnS quantum dot or CsPbBr.sub.3 quantum dot; and at least one exciplex including at least one of DPTPCz:TAPC or DPTPCz:TCTA; wherein an emission spectrum of the at least one exciplex is at least partially overlapped with an excitation spectrum of the at least one nano-crystalline semiconductor material, and a decay lifetime of an excited state of the exciplex is greater than a decay lifetime of an excited state of the at least one nano-crystalline semiconductor material; and an emission peak value wavelength of the exciplex is less than that of the at least one nano-crystalline semiconductor material.

2. The light-emitting layer of the electroluminescent device according to claim 1, wherein the decay lifetime of the excited state of the exciplex is more than 5 times of the decay lifetime of the excited state of the at least one nano-crystalline semiconductor material.

3. The light-emitting layer of the electroluminescent device according to claim 2, wherein the decay lifetime of the excited state of the at least one nano-crystalline semiconductor material is in a range from 1 ns to 100 ns, and the decay lifetime of the excited state of the exciplex is in a range from 0.5 μs to 100 μs.

4. The light-emitting layer of the electroluminescent device according to claim 1, wherein an energy level difference between a singlet state and a triplet state of the exciplex is less than 0.5 eV.

5. The light-emitting layer of the electroluminescent device according to claim 1, wherein a mole ratio of DPTPCz to TAPC or TCTA consisting of the exciplex is 3:7 to 7:3.

6. The light-emitting layer of the electroluminescent device according to claim 1, wherein a mass percentage of the at least one nano-crystalline semiconductor material in the light-emitting layer is in a range from 1% to 99%.

7. An electroluminescent device, comprising: a light-emitting layer including: at least one nano-crystalline semiconductor material including at least one of CdSe/ZnS quantum dot or CsPbBr.sub.3 quantum dot; and at least one exciplex including at least one of DPTPCz:TAPC or DPTPCz:TCTA; wherein an emission spectrum of the exciplex is at least partially overlapped with an excitation spectrum of the at least one nano-crystalline semiconductor material, and a decay lifetime of an excited state of the exciplex is greater than a decay lifetime of an excited state of the at least one nano-crystalline semiconductor material; and an emission peak value wavelength of the exciplex is less than that of the at least one nano-crystalline semiconductor material.

8. A display or an illumination device, comprising: an electroluminescent device including: a light-emitting layer including: at least one nano-crystalline semiconductor material including at least one of CdSe/ZnS quantum dot or CsPbBr.sub.3 quantum dot; and at least one exciplex including at least one of DPTPCz:TAPC or DPTPCz:TCTA; wherein an emission spectrum of the exciplex is at least partially overlapped with an excitation spectrum of the at least one nano-crystalline semiconductor material, and a decay lifetime of an excited state of the exciplex is greater than a decay lifetime of an excited state of the at least one nano-crystalline semiconductor material; and an emission peak value wavelength of the exciplex is less than that of the at least one nano-crystalline semiconductor material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic diagram of an electroluminescent device according to one embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(2) An electroluminescent device and a light-emitting layer and application thereof are further illustrated in detail with reference to specific embodiments hereafter.

(3) In the present embodiment, a structure of the electroluminescent device is shown in FIG. 1, and includes a first electrode layer 101, a hole injection layer 104, a hole transport layer or an electron blocking layer 105, a light-emitting layer 103, an electron transport layer or a hole blocking layer 106, an electron injection layer 107, and a second electrode layer 102, which are laminated sequentially on a substrate 100.

(4) Information of materials used is shown as follows:

(5) PEDOT:PSS is Poly(3,4-ethylenedioxythiophene)-poly(styrene-sulfonate);

(6) PVK is Poly(9-vinylcarbazole);

(7) CdSe/ZnS quantum dot refers to a dotted nano-crystalline semiconductor material using CdSe as a core and ZnS as a shell; and

(8) CdSe/ZnS quantum rod refers to a rod-shaped nano-crystalline semiconductor material using CdSe as a core and ZnS as a shell.

(9) Structures of organic materials are shown as below:

(10) ##STR00001## ##STR00002##

EXAMPLE 1

(11) An electroluminescent device according to this embodiment has the following structure:

(12) ITO/PEDOT:PSS/PVK/PO-T2T:mCP:(CdSe/ZnS quantum dot)/PO-T2T/LiF/Al.

(13) A light-emitting layer uses PO-T2T (a triplet state energy level being 2.99 eV) and mCP (a triplet state energy level being 2.94 eV) as organic materials to form a delayed fluorescence exciplex (a triplet state energy level being about 2.67 eV, a singlet state energy level being about 2.60 eV, and an emission spectrum being in a blue light wave band).

(14) The CdSe/ZnS quantum dot is used as a nano-crystalline semiconductor material, an excitation spectrum covers ultraviolet to green light wave bands, and an emission spectrum is in a red light wave band.

(15) A decay lifetime (about 500 ns) of an excited state of the exciplex is 10 times of a decay lifetime (about 50 ns) of an excited state of the nano-crystalline semiconductor material.

(16) The electroluminescent device is prepared by the following steps.

(17) (1) Treatment of substrate: cleaning a surface of a substrate sequentially by a glass cleaning agent and pure water, blow-drying by nitrogen gas, then baking at 150° C. for 1 h, and performing UV treatment for 5 min in an atmospheric environment to obtain the clean substrate and an ITO surface.

(18) (2) Preparation of hole injection layer: performing spin coating of PEDOT:PSS ink at a rotating speed of 3000 rpm/min for 30 s, and then baking for 15 min at 110° C. to obtain a hole injection layer film.

(19) (3) Preparation of hole transport layer: performing spin coating of PVK ink (5 mg/ml) at a rotating speed of 1500 rpm/min for 30 s, and then baking for 30 min at 150° C. to obtain a hole transport layer film.

(20) (4) Preparation of light-emitting layer: dissolving a mixture of PO-T2T (9.1 mg/ml), mCP (4.1 mg/ml) and CdSe/ZnS quantum dots (16 mg/ml) into chlorobenzene to form light-emitting layer ink, performing spin coating of the light-emitting layer ink at a rotating speed of 1000 rpm for 30 s, and then baking for 20 min at 150° C. to obtain a light-emitting layer film.

(21) (5) Preparation of electron transport layer, electron injection layer and cathode: sequentially evaporating PO-T2T (40 nm), LiF (1 nm) and Al (150 nm) in an evaporation mode to sequentially form an electron transport layer, an electron injection layer and a cathode.

COMPARATIVE EXAMPLE 1

(22) An electroluminescent device using exciplex-free pure QD as a light-emitting layer according to this comparative example has the following structure:

(23) ITO/PEDOT:PSS/PVK/(CdSe/ZnS quantum dot)/PO-T2T/LiF/Al.

(24) The preparation of the electroluminescent device is similar to that in Example 1. The difference is that the light-emitting layer is of a (CdSe/ZnS quantum dot) nano-crystalline semiconductor material.

EXAMPLE 2

(25) An electroluminescent device according to this embodiment has the following structure:

(26) ITO/PEDOT:PSS/PVK/PO-T2T:mCP:(CdSe/ZnS quantum rod)/PO-T2T/LiF/Al.

(27) A light-emitting layer uses PO-T2T (a triplet state energy level being 2.99 eV) and mCP (a triplet state energy level being 2.94 eV) as organic materials to form a delayed fluorescence exciplex (a triplet state energy level being about 2.67 eV, a singlet state energy level being about 2.60 eV, and an emission spectrum being in a blue light wave band).

(28) The CdSe/ZnS quantum rod is used as a nano-crystalline semiconductor material, an excitation spectrum covers ultraviolet to green light wave bands, and an emission spectrum is in a red light wave band.

(29) A decay lifetime (about 500 ns) of an excited state of the exciplex is 25 times of a decay lifetime (about 20 ns) of an excited state of the quantum rod of the nano-crystalline semiconductor material.

(30) The preparation of the electroluminescent device is similar to that in Example 1. The difference is that the CdSe/ZnS quantum dot in Example 1 is replaced with the CdSe/ZnS quantum rod.

EXAMPLE 3

(31) An electroluminescent device according to this embodiment has the following structure:

(32) ITO/PEDOT:PSS/PVK/DPTPCz:TAPC:(CdSe/ZnS quantum dot)/PO-T2T/LiF/Al.

(33) A light-emitting layer uses DPTPCz (a triplet state energy level being 2.77 eV) and TAPC (a triplet state energy level being 2.91 eV) as organic materials to form a delayed fluorescence exciplex (a triplet state energy level being 2.47 eV, a singlet state energy level being 2.52 eV, and an emission spectrum being in a green light wave band).

(34) The CdSe/ZnS quantum dot is used as a nano-crystalline semiconductor material, an excitation spectrum covers ultraviolet to green light wave bands, and an emission spectrum is in a red light wave band.

(35) A decay lifetime (about 2 μs) of an excited state of the exciplex is 40 times of the decay lifetime (about 50 ns) of an excited state of the nano-crystalline semiconductor material.

(36) The electroluminescent device is prepared by the following steps.

(37) (1) Treatment of substrate: cleaning a surface of a substrate sequentially by a glass cleaning agent and pure water, blow-drying by nitrogen gas, then baking at 150° C. for 1 h, and performing UV treatment for 5 min in an atmospheric environment to obtain the clean substrate and an ITO surface.

(38) (2) Preparation of hole injection layer: performing spin coating of PEDOT:PSS ink at a rotating speed of 3000 rpm/min for 30 s, and then baking for 15 min at 110° C. to obtain a hole injection layer film.

(39) (3) Preparation of hole transport layer: performing spin coating of PVK ink (5 mg/ml) at a rotating speed of 1500 rpm/min for 30 s, and then baking for 30 min at 150° C. to obtain a hole transport layer film.

(40) (4) Preparation of light-emitting layer: dissolving a mixture of DPTPCz (4.7 mg/ml), TAPC (6.3 mg/ml) and CdSe/ZnS quantum dots (16 mg/ml) into chlorobenzene to form light-emitting layer ink, performing spin coating of the light-emitting layer ink at a rotating speed of 1000 rpm for 30 s, and then baking for 20 min at 150° C. to obtain a light-emitting layer film.

(41) (5) Preparation of electron transport layer, electron injection layer and cathode: sequentially evaporating PO-T2T (40 nm), LiF (1 nm) and Al (150 nm) in an evaporation mode to sequentially form an electron transport layer, an electron injection layer and a cathode.

EXAMPLE 4

(42) An electroluminescent device according to this embodiment has the following structure:

(43) ITO/PEDOT:PSS/PVK/DPTPCz:TCTA:(CdSe/ZnS quantum dot)/PO-T2T/LiF/Al.

(44) A light-emitting layer uses DPTPCz (a triplet state energy level being 2.77 eV) and TCTA (a triplet state energy level being 2.73 eV) as organic materials to form a delayed fluorescence exciplex (a triplet state energy level being 2.49 eV, a singlet state energy level being about 2.55 eV, and an emission spectrum being in a green light wave band).

(45) The CdSe/ZnS quantum dot is used as a nano-crystalline semiconductor material.

(46) A decay lifetime (about 4.5 μs) of an excited state of the exciplex is 90 times of the decay lifetime (about 50 ns) of an excited state of the nano-crystalline semiconductor material.

(47) The electroluminescent device is prepared by the following steps.

(48) (1) Treatment of substrate: cleaning a surface of a substrate sequentially by a glass cleaning agent and pure water, blow-drying by nitrogen gas, then baking at 150° C. for 1 h, and performing UV treatment for 5 min in an atmospheric environment to obtain the clean substrate and an ITO surface.

(49) (2) Preparation of hole injection layer: performing spin coating of PEDOT:PSS ink at a rotating speed of 3000 rpm/min for 30 s, and then baking for 15 min at 110° C. to obtain a hole injection layer film.

(50) (3) Preparation of hole transport layer: performing spin coating of PVK ink (5 mg/ml) at a rotating speed of 1500 rpm/min for 30 s, and then baking for 30 min at 150° C. to obtain a hole transport layer film.

(51) (4) Preparation of light-emitting layer: dissolving a mixture of DPTPCz (4.7 mg/ml), TCTA (7.4 mg/ml) and CdSe/ZnS quantum dots (16 mg/ml) into chlorobenzene to form light-emitting layer ink, performing spin coating of the light-emitting layer ink at a rotating speed of 1000 rpm for 30 s, and then baking for 20 min at 150° C. to obtain a light-emitting layer film.

(52) (5) Preparation of electron transport layer, electron injection layer and cathode: sequentially evaporating PO-T2T (40 nm), LiF (1 nm) and Al (150 nm) in an evaporation mode to sequentially form an electron transport layer, an electron injection layer and a cathode.

(53) The devices in the above-mentioned examples and comparative example are subjected to device current efficiency test at a current density of 10 mA/cm.sup.2. The current efficiency of Comparative example 1 is normalized into 1, corresponding current efficiency values are obtained, and the results are shown as follows:

(54) TABLE-US-00001 Current Composition of light-emitting layer efficiency Comparative CdSe/ZnS quantum dot 1 example 1 Example 1 PO-T2T:mCP:CdSe/ZnS quantum dot 4 Example 2 PO-T2T:mCP:CdSe/ZnS quantum rod 4.5 Example 3 DPTPCz:TAPC:CdSe/ZnS quantum dot 3 Example 4 DPTPCz:TCTA:CdSe/ZnS quantum dot 3

EXAMPLE 5

(55) An electroluminescent device according to this embodiment has the following structure:

(56) ITO/PEDOT:PSS/PVK/PO-T2T:mCP:(CsPbBr.sub.3 quantum dot)/PO-T2T/LiF/Al.

(57) A light-emitting layer uses PO-T2T (a triplet state energy level being 2.99 eV) and mCP (a triplet state energy level being 2.94 eV) as organic materials to form a delayed fluorescence exciplex (a triplet state energy level being about 2.67 eV, a singlet state energy level being about 2.60 eV, and an emission spectrum being in a blue light wave band).

(58) The CsPbBr.sub.3 quantum dot is used as a nano-crystalline semiconductor material, an excitation spectrum covers ultraviolet to blue light wave bands, and an emission spectrum is in a green light wave band.

(59) A decay lifetime (about 500 ns) of an excited state of the exciplex is about 20 times of a decay lifetime (about 25 ns) of an excited state of the nano-crystalline semiconductor material.

(60) The electroluminescent device is prepared by the following steps.

(61) (1) Treatment of substrate: cleaning a surface of a substrate sequentially by a glass cleaning agent and pure water, blow-drying by nitrogen gas, then baking at 150° C. for 1 h, and performing UV treatment for 5 min in an atmospheric environment to obtain the clean substrate and an ITO surface.

(62) (2) Preparation of hole injection layer: performing spin coating of PEDOT:PSS ink at a rotating speed of 3000 rpm/min for 30 s, and then baking for 15 min at 110° C. to obtain a hole injection layer film.

(63) (3) Preparation of hole transport layer: performing spin coating of PVK ink (5 mg/ml) at a rotating speed of 1500 rpm/min for 30 s, and then baking for 30 min at 150° C. to obtain a hole transport layer film.

(64) (4) Preparation of light-emitting layer: dissolving a mixture of PO-T2T (9.1 mg/ml), mCP (4.1 mg/ml) and CsPbBr.sub.3 quantum dots (16 mg/ml) into chlorobenzene to form light-emitting layer ink, performing spin coating of the light-emitting layer ink at a rotating speed of 1000 rpm for 30 s, and then baking for 20 min at 150° C. to obtain a light-emitting layer film.

(65) (5) Preparation of electron transport layer, electron injection layer and cathode: sequentially evaporating PO-T2T (40 nm), LiF (1 nm) and Al (150 nm) in and evaporation mode to sequentially form an electron transport layer, an electron injection layer and a cathode.

COMPARATIVE EXAMPLE 2

(66) An electroluminescent device using exciplex-free pure QD as a light-emitting layer according to this comparative example has the following structure: ITO/PEDOT:PSS/PVK/(CsPbBr.sub.3 quantum dot)/PO-T2T/LiF/Al.

(67) The preparation of the electroluminescent device is similar to that in Example 5. The difference is that the light-emitting layer is of a (CsPbBr.sub.3 quantum dot) nano-crystalline semiconductor material.

(68) The devices in the above-mentioned example and comparative example are subjected to device current efficiency test at a current density of 10 mA/cm.sup.2. The current efficiency of Comparative example 2 is normalized into 1, corresponding current efficiency values are obtained and the results are shown as follows:

(69) TABLE-US-00002 Current Composition of light-emitting layer efficiency Comparative CsPbBr.sub.3 quantum dot 1 example 2 Example 5 PO-T2T:mCP:CsPbBr.sub.3 quantum dot 3

(70) Various technical features in the foregoing embodiments may be combined randomly. For ease of description, possible combinations of various technical features in the foregoing embodiments are not all described. However, the combinations of the technical features should be considered as falling within the scope recorded in this specification provided that the combinations of the technical features are compatible with each other.

(71) The foregoing embodiments only describe several implementations of the present disclosure, and their description is specific and detailed, but cannot therefore be understood as a limitation to the patent scope of the present disclosure. It should be noted that, a person of ordinary skill in the art may make various changes and improvements without departing from the ideas of the present disclosure, which shall fall within the protection scope of the present disclosure. Therefore, the protection scope of the patent of the present disclosure shall be topic to the claims.