CN113314691B

CN113314691B - Perovskite nanocrystalline thin film and film forming method and application thereof

Info

Publication number: CN113314691B
Application number: CN202110577125.0A
Authority: CN
Inventors: 陈淑芬; 张文竹; 沈炜; 喻叶
Original assignee: Nanjing University of Posts and Telecommunications
Current assignee: Nanjing University of Posts and Telecommunications
Priority date: 2021-05-26
Filing date: 2021-05-26
Publication date: 2022-07-19
Anticipated expiration: 2041-05-26
Also published as: CN113314691A

Abstract

The invention discloses a perovskite nanocrystalline thin film, a film forming method and application thereof.

Description

Perovskite nanocrystalline thin film and film forming method and application thereof

Technical Field

The invention relates to the technical field of photoelectric device materials, in particular to a perovskite nanocrystalline thin film and a film forming method and application thereof.

Background

Perovskite materials have excellent characteristics such as high fluorescence quantum yield (PLQY), adjustable band gap, and solution processability, and have been rapidly developed in recent years. Thanks to these advantages, perovskite material Light Emitting Diodes (LEDs) have made great progress, with high External Quantum Efficiency (EQE) of green, red and near-infrared perovskite light emitting diodes reaching above 20%. However, perovskite nanocrystal based LEDs are relatively slow to develop. Compared with bulk materials, the PLQY of the perovskite nanocrystal can reach 100%, the band gap regulation range is wider, the color purity is higher, and the promotion of the upgrading of the LED industry is hopeful. The construction of the high-quality perovskite nanocrystalline LED luminescent layer is a key problem for realizing high performance at present.

The blade coating method is suitable for preparing the perovskite nanocrystalline thin film in a large area, but the crystallization process is difficult to control due to the nonuniform nucleation of the perovskite nanocrystalline thin film prepared by the blade coating method, the dependence on annealing equipment is high, and the high-performance perovskite nanocrystalline LED is difficult to prepare. The nanocrystalline thin film prepared by the conventional spin coating method has low surface coverage and thin thickness, and the defects are key factors for restricting the performance and the yield of the nanocrystalline thin film. The perovskite nanocrystalline thin film with low coverage rate and thin thickness often causes short circuit between a hole transport layer and an electron transport layer, so that the LED does not emit light, or the light emission of the hole/electron transport layer occurs uncontrollably, and various performance indexes of the LED are seriously influenced; and the conventional spin coating method is a film forming process through the action of centrifugal force, so that raw materials are seriously wasted in the film forming process, and the actual application requirements are difficult to meet.

Disclosure of Invention

Aiming at the problems, the invention provides a film forming method of a perovskite nanocrystalline film, which improves the coverage rate of the perovskite nanocrystalline film and ensures the thickness of the film layer by adopting a film forming mode of alternatively coating a perovskite nanocrystalline solution by drop coating and spin coating; the yield of the LED device prepared based on the film is greatly improved, the luminous color is purer, the device efficiency is higher, and the film has a universal application prospect in the field of perovskite photoelectric devices.

The invention provides a film forming method of a perovskite nanocrystalline film, which comprises the following steps: the perovskite nanocrystalline solution is coated on the substrate in a multi-step alternating manner, as shown in fig. 5, the multi-step alternating coating means that dripping coating and spin coating are alternately carried out, drying is required after each dripping coating or spin coating, and then the next coating is carried out.

Preferably, the multi-step alternate coating is performed alternately according to the sequence of firstly dripping and then spin coating, the alternating times are 3-10 times, and the alternating times of 1 time is equivalent to the steps of dripping and coating 1 time and then spin coating 1 time;

wherein, the film coverage rate and thickness are optimal when the coating is performed for 3 times alternately, namely, the dripping coating and the spin coating are performed for 3 times respectively;

wherein, the dripping and the spin coating are alternately carried out, and the amount of the perovskite nano-crystal solution used for each dripping and spin coating is 50-200 mu L;

preferably, the dripping drying temperature is 15-60 ℃, and the time is 5-45 minutes;

preferably, the spin-coating rotation speed is 1000-.

Preferably, the solvent of the perovskite nanocrystal solution is any one or a mixture of any several of toluene, octane, n-hexane, cyclohexane, dichlorotoluene, trichlorotoluene, carbon tetrachloride, n-butanol and ethyl acetate; the film prepared by the solvents has better dispersion of the nanocrystalline, and is more beneficial to film formation.

The invention relates to a film forming method of a perovskite nanocrystalline film, wherein the perovskite nanocrystalline material is perovskite halogenationThe structural general formula of the perovskite halide and the derivative thereof comprises ABX₃、AB₂X₅、A₄BX₆、A₂BX₄、A₃BX₅Wherein A ═ Cs⁺、Rb⁺Any one or mixture of any more of methylamine ions and formamidine ions; b ═ Pb²⁺、Sn²⁺、Ge²⁺Any one or a mixture of any several of them; x ═ Cl, Br, and I, or a mixture of any two or more thereof.

The perovskite nanocrystalline thin film prepared by the film forming method of the perovskite nanocrystalline thin film not only can be used as a luminescent layer in an LED device, but also can be applied to various photoelectric devices, including a light absorption layer of a solar cell and a photosensitive layer of a detector.

Compared with the reported technology, the invention has the following effects:

(1) on one hand, the consumption of solution is large in conventional spin coating, although the film thickness can be improved to a certain extent by increasing the spin coating times, due to the effect of centrifugal force in the spin coating process, the nanocrystal solution extends to the periphery and is less remained in the central part of the substrate, and a circular area which does not emit light or emits light weakly at the central part of a film layer is easily formed; according to the film forming method of the perovskite nanocrystalline film, provided by the invention, the waste of the solution is reduced to a certain extent by a mode of alternatively dripping/spin-coating the perovskite nanocrystalline solution in multiple steps;

(2) the perovskite nanocrystalline film prepared by the film forming method of the perovskite nanocrystalline film provided by the invention is more compact, and the coverage rate is obviously improved;

(3) the film forming method of the perovskite nanocrystalline film provided by the invention is simple in process, and the prepared perovskite nanocrystalline film is used as a light emitting layer of an LED device, so that the high efficiency and stability of the LED device can be ensured, and the perovskite nanocrystalline film has higher yield and wider application prospect.

Drawings

FIG. 1 (a) is an optical photograph of a film prepared by the method of comparative example 1 of the present invention under an ultraviolet lamp;

FIG. 1 (b) is an optical photograph of a film produced by the method of example 1 under an ultraviolet lamp;

FIG. 2 (a) is an electroluminescence spectrum of an LED prepared in comparative example 2 of the present invention;

FIG. 2 (b) is an electroluminescence spectrum of an LED prepared in example 2 of the present invention;

FIG. 3 (a) is a normalized electroluminescence spectrum of 10 groups of LEDs prepared in comparative example 2 of the present invention;

FIG. 3 (b) is a normalized electroluminescence spectrum of 10 groups of LEDs prepared in example 2 of the present invention;

FIG. 4 is a statistical plot of the external quantum efficiency of LEDs prepared in comparative example 2 and example 2 of the present invention;

FIG. 5 is a schematic view of an alternate coating process of drop coating and spin coating in accordance with the present invention.

Detailed Description

In order to make the solution and the object of the present invention more clear, the present invention will be described in detail with reference to the accompanying drawings and examples. The specific embodiments described herein are merely illustrative of the invention and do not delimit the invention.

Comparative example 1: making thin films using spin-on methods only

The spin coating process was as follows, 90. mu.L CsPbBr was dropped on an ITO sheet which was left standing in a spin coater₃Soaking the nanocrystalline solution for 10 seconds, spin-coating for 45 seconds at a rotating speed of 3000rpm and an acceleration of 300r/s, repeating the whole process for 6 times, co-spin-coating for 6 layers, and finally standing for 10 minutes at normal temperature.

FIG. 1 (a) shows CsPbBr assembled in comparative example 1₃The optical photo of the nano-sheet film under an ultraviolet lamp has an obvious non-luminous circle area at the center of the sheet, which indicates that the assembly mode is difficult to form a complete nano-crystal film.

Example 1: making thin film by multi-step alternative dripping/spin coating

Step (1) dripping 90 mu L CsPbBr on a sheet which is statically placed on a heating table₃The nanocrystal solution was heated at 30 ℃ for 15 minutes to evaporate the solvent.

Step (2) placing the dried wafer on a spin coater, and dropwise adding 90 mu L CsPbBr₃And soaking the nano-crystalline solution for 10 seconds, and then spin-coating for 45 seconds under the conditions of 3000rpm rotation speed and 300r/s acceleration.

And (3) sequentially and alternately performing the steps (1) and (2) for 3 times, and assembling 6 layers in total.

FIG. 1 (b) shows CsPbBr prepared in example 1₃The optical photo of the nanocrystalline film under an ultraviolet lamp shows uniform luminescence on the whole sheet, the surface of the film is complete, and the coverage rate is obviously improved compared with that of the film prepared in comparative example 1.

The following comparative example 2 and example 2 specifically illustrate the performance of the thin film material prepared by the film forming method of the perovskite nanocrystalline thin film as the light emitting layer of the LED device by taking the light emitting layer in the LED device as an example.

Comparative example 2: method for preparing LED by spin-coating

Spin-coating PEDOT, including PSS aqueous solution, PVK and PTAA, on the cleaned ITO glass sheet; then, a device light emitting layer was assembled in accordance with comparative example 1; finally, all samples were transferred to an evaporation chamber and TPBi (45nm), LiF (1.2nm), and Al electrode (100nm) were evaporated under high vacuum to prepare LEDs.

FIG. 2 (a) is the electroluminescence spectrum of the device prepared in comparative example 2, the main peak luminescence position is 460nm, and a significant broad peak exists in the region of 380-440nm, which is attributed to PVK luminescence caused by short circuit of partial hole and electron transport layers due to low film coverage.

Fig. 2 (b) is a normalized electroluminescence spectrum of 10 groups of LEDs prepared in comparative example 2 at a voltage of 6V, only 1 sample showed a single peak emission, and the remaining samples all showed PVK luminescence to different degrees, with a yield of 10%.

FIG. 4 is a statistical graph of external quantum efficiency for LEDs prepared according to the scheme of comparative example 2, with only 1 sample having device efficiency, average EQE_maxIs 0.05%.

Example 2: LED (light-emitting diode) prepared by multi-step alternative dripping/spin coating method

Spin-coating PEDOT, namely PSS aqueous solution, PVK and PTAA, on the cleaned ITO glass sheet; then, a light emitting layer of the device was prepared as in example 1; finally, all samples were transferred to an evaporation chamber and TPBi (45nm), LiF (1.2nm), and Al electrode (100nm) were evaporated under high vacuum to prepare LEDs.

Fig. 3 (a) is an electroluminescence spectrum of the LED prepared in example 2, in which the light-emitting peak is a single-peak emission with a light-emitting position of 460nm, which proves that short circuit of the hole and electron transport layers and PVK luminescence are significantly suppressed, and indirectly proves that the film coverage is significantly improved;

fig. 3 (b) shows 10 sets of normalized electroluminescence spectra of the LEDs prepared in example 2 at 6V, the spectra almost coincide, which proves that the light-emitting layer assembled by the scheme of example 2 is more compact, the reproducibility of the device is significantly improved, and the yield is 100%;

FIG. 4 is a statistical chart of external quantum efficiency, average EQE for 10 LEDs prepared according to the scheme of example 2_maxIt was 1.75%.

Therefore, from the test results of comparative example 2 and example 2, the LED index of example 2 is significantly higher than that of comparative example 2, both in terms of yield and device efficiency.

The advantages of the present invention are described above. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.

Claims

1. A film forming method of a perovskite nanocrystalline film is characterized by comprising the following specific steps: the perovskite nanocrystalline solution is coated on a substrate in a multi-step alternating mode, the multi-step alternating coating refers to that dripping coating and spin coating are carried out alternately, drying is carried out after each dripping coating or spin coating, and then the next step of coating is carried out.

2. A film-forming method of a perovskite nanocrystalline thin film according to claim 1, wherein the plurality of steps of alternate coating are performed alternately in the order of drop coating and spin coating, and the number of the alternate coating is 3 to 10.

3. A film-forming method of a perovskite nanocrystalline film according to claim 1, characterized in that the amount of perovskite nanocrystalline solution used at a time of the dropping and spin coating is 50 to 200 μ L.

4. A method for forming a perovskite nanocrystalline thin film according to claim 1, wherein the temperature for dropping coating and drying is 15 to 60 ℃ for 5 to 45 minutes.

5. The method as claimed in claim 1, wherein the spin-coating speed is 1000-.

6. A film-forming method of a perovskite nanocrystalline film according to claim 1, wherein the solvent of the perovskite nanocrystalline solution is any one of toluene, octane, n-hexane, cyclohexane, dichlorotoluene, trichlorotoluene, carbon tetrachloride, n-butanol, ethyl acetate, or a mixture of any several solvents.

7. A film-forming method for a perovskite nanocrystalline film according to claim 1, wherein the perovskite nanocrystalline material in the perovskite nanocrystalline solution is a perovskite halide or a derivative thereof.

8. A film-forming method of a perovskite nanocrystalline film according to claim 7, wherein the general structural formula of the perovskite halide or the derivative thereof includes ABX₃、AB₂X₅、A₄BX₆、A₂BX₄、A₃BX₅Wherein A ═ Cs⁺、Rb⁺Any one or mixture of any more of methylamine ions and formamidine ions; b ═ Pb²⁺、Sn²⁺、Ge²⁺Any one or a mixture of any several of them; x ═ Cl, Br, and I, or a mixture of any two or more thereof.

9. A perovskite nanocrystalline thin film, characterized in that the perovskite nanocrystalline thin film is a thin film produced by the film formation method according to any one of claims 1 to 8.

10. Use of a perovskite nanocrystalline thin film according to claim 9 in the light emitting layer of an LED device.