CN106128954A - A kind of method promoting perovskite crystalline - Google Patents

Abstract

The invention discloses a kind of method promoting perovskite thin film crystal property, it is in perovskite preparation process, anneals under dimethyl sulfoxide solvent atmosphere, improves a kind of method of perovskite crystalline.During annealing, perovskite sample is placed under dimethyl sulfoxide atmosphere and can promote grain growth, generate crystalline property excellence, the perovskite thin film of defect concentration reduction.This thin film can reduce the Carrier recombination of perovskite solaode and promote the performance of perovskite solaode.Annealing relative to conventional steam and dimethylformamide equal solvent, dimethyl sulfoxide has lower vapour pressure and higher boiling point, has bigger advantage in terms of strengthening perovskite crystalline.

Description

A method to improve the crystallinity of perovskite

technical field

The invention relates to a solar cell based on an organic-inorganic hybrid perovskite material, in particular to an annealing method for improving the crystallinity of the perovskite.

Background technique

Solar photovoltaic technology is an important part of green energy. Among the current types of solar cells, perovskite solar cells have attracted many scientific researches due to their high absorbency, high carrier mobility, low cost, and simple process. The concern of personnel, and is considered to be a new type of photovoltaic cell with great development prospects. At present, the conversion efficiency of perovskite photovoltaic cells has reached more than 20%, which has reached the same level as commercial silicon cells.

At present, perovskite materials are mainly prepared by one-step spin coating method, two-step method, and co-evaporation method. However, these preparation methods are difficult to prepare highly crystalline perovskite thin films. In order to produce high-efficiency perovskite solar cell devices, the perovskite light absorbing layer should have good coverage, excellent flatness and sufficient crystallinity. The good crystallinity of the perovskite film helps to reduce its defect state density and reduce the recombination of carriers. Annealing treatment is often used to obtain better crystallinity.

The conventional annealing method of perovskite is to crystallize by heating at 100 degrees Celsius under a nitrogen atmosphere (thermal annealing). During this crystallization process, methylammonium iodide (MAI) interacts with lead iodide (PbI ₂ ) to form perovskite crystals. Nitrogen plays the role of a protective gas here to prevent the perovskite from decomposing when it encounters water and oxygen. The solvent annealing method can significantly improve the crystallization properties of perovskite thin films, and the solvent atmospheres often used include water vapor, dimethylformamide, etc. Although the perovskite component will decompose under the water atmosphere to form excess lead iodide and methylammonium iodide, it can dissolve the grains and promote the crystallization properties of the perovskite film to a certain extent. As a solvent for perovskite precursors, dimethylformamide can enhance the crystallization performance, but its high volatility and low boiling point hinder its application in solvent annealing. The annealing under the dimethyl sulfoxide atmosphere proposed by the present invention can significantly enhance the crystallization properties of the perovskite film. Applying this method to perovskite photovoltaic cells can significantly improve the energy conversion efficiency of the device.

Contents of the invention

In order to solve the problem of unsatisfactory crystallization properties of perovskite thin films in the background technology, the object of the present invention is to provide an annealing method that can improve the crystallinity of perovskite: solvent annealing under dimethyl sulfoxide atmosphere.

The technical solution adopted in the present invention is a method for improving the crystallinity of perovskite: firstly, a perovskite film is deposited on a substrate, and then the film is annealed and crystallized in a dimethyl sulfoxide atmosphere at a temperature of 100°C 2 minutes to 2 hours.

In the above solution, a perovskite film with a thickness ranging from 50 to 600 nm is prepared by solution spin coating or vapor deposition.

The perovskite crystalline film obtained by the annealing method described in the above scheme is applied in the battery structure: transparent conductive film, hole transport layer, perovskite film, electron transport layer, metal electrode.

The invention adopts a solvent annealing method, and the perovskite film is annealed and crystallized under the atmosphere of dimethyl sulfoxide. The whole reaction process has low energy consumption and simple preparation process. The crystallinity of the prepared perovskite crystalline film is obviously enhanced, the grain size is enlarged and the defect state density of the crystalline film is reduced. The perovskite crystalline thin film prepared by the method can obviously reduce the carrier defect state density when applied in a solar cell, and has broad industrial application prospects.

Advantages of the present invention:

1. Mild reaction conditions and low energy consumption. Perovskite can be annealed and crystallized at 100 °C.

2. It can significantly improve the crystallization performance of the thin film and improve the energy conversion efficiency of the device.

3. Annealing under dimethyl sulfoxide atmosphere has high repeatability and can be stably applied to industrial production.

Description of drawings

Fig. 1 is a process flow diagram of the present invention;

Fig. 2 is a schematic diagram of the present invention;

Fig. 3 is the electron microscope morphology comparison of thermal annealing and dimethyl sulfoxide annealing in the present invention;

Fig. 4 is the perovskite battery performance of DMSO annealing in the present invention.

Fig. 5 is a photo of the surface morphology (upper row) and cross-sectional morphology (lower row) of the perovskite thin film annealed under different atmospheres in the present invention. From left to right, thermal annealing (nitrogen atmosphere N ₂ , water vapor annealing H ₂ O, γ-hydroxybutyrolactone atmosphere annealing GBL, dimethylformamide atmosphere annealing DMF and dimethyl sulfoxide atmosphere annealing DMSO.

detailed description

The present invention will be further described below in conjunction with accompanying drawing and example.

The glass substrate covered with ITO was ultrasonically washed with detergent, acetone, and ethanol for 30 minutes, and dried with a nitrogen gun. A CH3NH3PbI _3-x Cl _x perovskite light-absorbing layer with a thickness of 300nm was prepared by spin coating. Heat at 100°C for 5 minutes. The pre-annealed samples were transferred to a heating stage at 100°C. Place a crucible with a diameter of 1 cm on the heating stage, use a pipette gun to draw 10 μl of dimethyl sulfoxide into the crucible, and then quickly cover the sample and the crucible with a glass cover. The crucible is heated, and the solvent inside turns into steam and evaporates, forming a dimethyl sulfoxide solvent atmosphere in the lid. The solvent annealing time was 30min. As shown in Figure 1.

The principle of annealing under DMSO solvent atmosphere is shown in Figure 2. The perovskite film is placed in a closed space. Solvent molecules can condense on the surface of the film and dissolve the film components. At the same time, the high-temperature substrate will re-evaporate the condensed solvent. The condensation-evaporation inside the cover is a dynamic heat balance process. . The thin film on the hot plate works with a limited solvent vapor pressure, and the evaporated solvent molecules do not cause extensive dissolution of the thin film, but instead lead to the formation of a liquid or semi-liquid phase on the surface and in the pore region. This liquid phase can act like glue, bonding adjoining areas between two grains. Perovskite atoms enter the liquid-phase binder and recrystallize at the liquid-solid interface. This recrystallization process causes the grains in the film to coalesce, growing larger grains.

Figure 3 shows the perovskite grain size obtained by annealing under different atmospheres. The upper row is the surface morphology of the perovskite film, and the lower row is the corresponding cross-sectional morphology. From left to right are thermal annealing (nitrogen atmosphere), water vapor annealing, γ-hydroxybutyrolactone atmosphere annealing, dimethylformamide atmosphere annealing and dimethyl sulfoxide atmosphere annealing. It can be seen from the figure that the grain size produced by conventional nitrogen thermal annealing is about 300nm, as shown in Figure 4 after enlargement. Annealing in water vapor atmosphere did not significantly improve the crystallization properties of the films, similar to thermal annealing. γ-hydroxybutyrolactone atmosphere annealing and dimethylformamide atmosphere annealing can significantly increase the grain size, which is about 500nm at this time, but compared with dimethyl sulfoxide atmosphere, the improvement of crystallization performance is limited. The grain size of perovskite film can reach 1000nm after annealing in DMSO solvent atmosphere.

In order to verify the performance of perovskite films formed under different solvent atmospheres, we made the above-mentioned perovskite films into solar cells. The battery structure adopted in this embodiment is: indium tin oxide semiconductor transparent conductive film/3,4-ethylenedioxythiophene monomer polymer: polystyrene sulfonate/perovskite/fullerene derivative/ silver electrodes. Among them, 3,4-ethylenedioxythiophene monomer polymer: polystyrene sulfonate is a hole-transporting material, and fullerene derivatives are common electron-transporting materials. Its production is to spin-coat the hole transport layer, perovskite, and electron transport layer sequentially on the transparent conductive film, and finally deposit a layer of silver electrode with a thickness of about 100nm by evaporation method.

Figure 5 shows the photoelectric characteristic curves of perovskite solar cells corresponding to annealing under different solvent atmospheres. The open-circuit voltage of the corresponding device under nitrogen atmosphere annealing is 0.93V, the short-circuit current density is 16.9mA/cm ² , the fill factor is 0.53, and the energy conversion efficiency is 8.34%. The open-circuit voltage of the corresponding device under water atmosphere annealing is 0.95V, the short-circuit current density is 18.7mA/cm ² , the fill factor is 0.51, and the energy conversion efficiency is 8.99%. The corresponding device annealed in γ-hydroxybutyrolactone atmosphere has an open-circuit voltage of 0.92V, a short-circuit current density of 20.9mA/cm ² , a fill factor of 0.64, and an energy conversion efficiency of 12.29%. The corresponding device annealed in dimethylformamide atmosphere has an open-circuit voltage of 0.91V, a short-circuit current density of 20.2mA/cm ² , a fill factor of 0.62, and an energy conversion efficiency of 11.29%. The device corresponding to DMSO annealing has an open circuit voltage of 0.93V, a short circuit current density of 20.9 mA/cm ² , a fill factor of 0.68, and an energy conversion efficiency of 13.21%.

It can be seen that after annealing with DMSO, the performance of the battery is greatly improved, which shows that the performance of the perovskite film formed by annealing with DMSO is superior.

Claims (3)

1. A method for improving the crystallinity of perovskite: the method first deposits a perovskite film on a substrate, and then anneals and crystallizes the film in a dimethyl sulfoxide atmosphere at a temperature of 100°C for 2 minutes to 2 hours . 2. A method for improving the crystallinity of perovskite according to claim 1, characterized in that in the method, a perovskite film with a thickness ranging from 50 to 600 nm is prepared by solution spin coating or vapor deposition. 3. a kind of method for promoting perovskite crystallinity as claimed in claim 1 is characterized in that the perovskite crystalline thin film that the annealing method described in the described method obtains is applied in battery structure: transparent conductive film, Hole transport layer, perovskite film, electron transport layer, metal electrode.