CN111540835A

CN111540835A - Method for improving thermal stability of perovskite solar cell

Info

Publication number: CN111540835A
Application number: CN202010389771.XA
Authority: CN
Inventors: 隋曼龄; 刘宏朋; 卢岳
Original assignee: Beijing University of Technology
Current assignee: Beijing University of Technology
Priority date: 2020-05-11
Filing date: 2020-05-11
Publication date: 2020-08-14
Anticipated expiration: 2040-05-11
Also published as: CN111540835B

Abstract

The invention discloses a method for improving the thermal stability of a perovskite solar cell, in particular to the treatment of an electron transport layer in a perovskite solar cell device, and the method adds a step of carrying out oxygen atmosphere Plasma cleaning (Plasma) on an SnO2 electron transport layer on the basis of the basic steps of conventional preparation, realizes the conversion of SnO2 from an anoxic state to an oxygen-rich state, improves the formation energy and diffusion barrier of oxygen vacancies in SnO2, and prevents SnO₂And the O in the perovskite layer enters the perovskite layer to damage the perovskite layer, so that the thermal stability of the whole device is improved.

Description

Method for improving thermal stability of perovskite solar cell

Technical Field

The invention belongs to the field of photoelectric devices, and particularly relates to a method for changing the thermal stability of an organic-inorganic hybrid perovskite solar cell.

Background

Due to the continuous consumption of fossil energy and the increasingly prominent problem of environmental pollution, the development and utilization of non-renewable energy sources such as fossil energy and the like are difficult to meet the sustainable economic and energy development concept required by the modern society. The solar energy is an inexhaustible renewable energy source, and has great amount, cleanness and environmental protection, so that the solar energy is greatly concerned by people. Up to now, there are two main ways of utilizing solar energy, one is to convert solar energy into heat energy through photothermal effect, and the second is to convert light energy into electric energy through photoelectric effect. Among the two energy conversion methods for effectively utilizing solar energy, the conversion of solar energy into electric energy is one of the most developed, widely applied and potential technical directions. It is expected that in the future, although fossil fuels are still the main body of the world energy structure, the development of new energy sources such as solar energy and the like will inevitably become an irreversible trend and become one of the main members for constructing the world energy stage of the sustainable economic society development, which leads the 21 st century.

Solar cells have been developed to date, and have undergone substantially three generations of innovations and changes in technology. The first generation mainly comprises crystalline silicon-based solar cells, but because the cost is high and raw material extraction is difficult, people pay attention to the development and utilization of the second generation thin film silicon solar cells. However, the second generation solar cell contains a large amount of toxic and rare elements, and the performance of the second generation solar cell has not yet achieved a very satisfactory effect, so people are continuously exploring and developing a novel solar cell technology, and the third generation solar cell is produced at the same time. The third generation solar cell generally refers to some new concept cells with high conversion efficiency, such as dye-sensitized cells, quantum dot cells, organic solar cells, and the like. The organic solar cell is a solar cell with a core light absorption layer material having organic components, and has the following advantages: the material source is wider than that of the inorganic solar cell and is cheaper; the environmental stability is higher; the weight is light, and the photoelectric performance is good; the preparation process is simple, and the structure can be designed and processed. The battery can meet the requirements of general electronic devices due to simple preparation and low cost, has specific flexibility and larger deformability, and can be worn and applied to the surface of a human body. The improved solar cell belongs to an all-solid-state organic halide perovskite solar cell developed and evolved on the basis of a dye-sensitized cell. Compared with the traditional dye-sensitized solar cell, the perovskite type solar cell has certain breakthrough in performance and structure, and the largest change is that the all-solid perovskite material is used as the core light absorption layer.

In terms of raw material performance, the organic-inorganic halide perovskite has excellent electron-hole transmission capacity, and can simultaneously carry out processes such as absorption of incident light, excitation, transportation, separation, conversion and the like of photon-generated carriers, so that the perovskite solar cell can show excellent light absorption performance and high-efficiency photoelectric conversion capacity. The perovskite has such excellent photoelectric properties due to its peculiar crystal structure. The perovskite structure is a compound having an ABX₃Crystalline materials of crystalline structure, compounds of such structure were first discovered earlier than calcium titanate (CaTiO)₃) Among the minerals, the perovskite structure is also known. Wherein X represents an anion, A and B are cations of different sizes (A is greater than B), the crystal structure of the perovskite. The perovskite material used in the present invention is the most commonly used CH₃NH₃PbI₃Organic-inorganic hybrid perovskites, i.e. with the A-position being CH₃NH₃ ⁺(MA⁺) The B-position is Pb and the X-position is I.

The microstructure of the material often determines its macroscopic properties, and the excellent optoelectronic properties of perovskites are also mainly related to this peculiar crystal structure. Compared with the prior solar cell technology, the perovskite solar cell has excellent photovoltaic performance comparable to that of a silicon-based cell, and has the following outstanding advantages in physicochemical properties: 1) can simultaneously complete a plurality of processes of absorption of incident light, excitation, transportation, separation and the like of photon-generated carriers. 2) The efficiency of transporting electrons and holes is high, and the transport length of the electron-hole is more than 1 μm. 3) The carrier lifetime is much higher than other solar cells. 4) The energy band width is suitably about 1.5 eV. 5) The extinction coefficient is extremely high, the light absorption capacity of perovskite is more than 10 times of that of the traditional organic dye, and a film with the thickness of 400nm can absorb all photons in the ultraviolet-near infrared spectrum range. 6) High open-circuit voltage, 1.3V. Structurally, compared with other solar cells, the perovskite solar cell has a simple structure and has great advantages in the similar technologies. The perovskite solar cell exhibits a sandwich layered structure as shown in fig. 1 (a). The battery has five basic structures, namely a metal electrode, a hole transport layer, a perovskite light absorption layer, an electron transport layer and a transparent electrode.

To date, perovskite solar cell technology is not commercialized in a large scale, cannot meet the stability problem of 'double 85' (85 ℃, 85 Rh%) test standard of solar cell outdoor application, and is the largest limiting factor for commercial perovskite solar cell technology at present. The instability of the perovskite solar cell is mainly reflected in two aspects: one is the instability of the phase structure of the perovskite material itself, and the other is the instability of the overall device structure. In terms of actual application at present, the key problem affecting the stability of the perovskite solar cell is that the efficiency of the device can be attenuated due to the conditions of water, oxygen, temperature, illumination and the like in the environment. Wherein the stability of the cell at high temperature is also crucial for the preparation of perovskite solar cells, since such photovoltaic devices are frequently exposed to high temperature environments, such as desert climates or hot summer roof environments, etc., whether during the preparation process (multiple annealing), the post-encapsulation process, or even during actual operation. If the perovskite material and the device can not keep the stability of the phase structure and the performance under the high-temperature environment (above 85 ℃), the repeatability preparation and the long-period use of the high-efficiency perovskite solar cell device can not be realized, and the industrialization of the low-cost high-efficiency perovskite solar cell can not be realized fundamentally. Therefore, the study on the thermal stability of the perovskite solar cell is very important for the commercialization of the perovskite solar cell.

Disclosure of Invention

The invention aims to improve the existing preparation technical means, and improve SnO in a titanium ore solar cell by a convenient, simple and low-cost Plasma (Plasma) technology₂An electron transport layer, thereby achieving the purpose of improving efficiency and stability. The principle of the method is as follows: in the preparation of MAPbI₃SnO obtained by spin-coating annealing in conventional method during perovskite solar cell₂The surface and the interior of the electron transport layer have certain oxygen atom deletion to form an oxygen-deficient state with much Sn and little O, and the oxygen-deficient state can cause SnO₂The formation energy of the intermediate oxygen vacancy and the diffusion barrier are greatly reduced, oxygen atoms can continuously move and escape,access to the immediate perovskite layer causes it to decompose (fig. 2), resulting in a substantial reduction in stability (fig. 3). The invention provides that air containing oxygen is used for preparing the prepared SnO₂Performing Plasma treatment on the electron transport layer to remove SnO in an anoxic state under a normal state₂And the oxygen-rich state is formed, so that oxygen vacancies on the surface and inside are eliminated. Thus, SnO can be improved₂The formation energy and diffusion barrier of oxygen vacancy on the crystal surface and inside thereof can be inhibited, thereby inhibiting the O from being SnO₂Mesogenic MAPbI₃The process of immigration and diffusion to prevent MAPbI₃Is decomposed, and the overall thermal stability of the perovskite solar cell device is improved.

The technical scheme provided by the invention is as follows:

the invention discloses a technology for improving the thermal stability of a perovskite solar cell by a Plasma treatment technology. The general perovskite solar cell has a structure from top to bottom, namely, a metal electrode, a hole transport layer, a perovskite light absorption layer, an electron transport layer and a transparent electrode.

The conventional preparation method comprises the following steps:

1) cleaning a substrate: the conductive glass is used as an anode of the battery, and an electron transmission layer and a light absorption layer are required to be attached to the surface of the conductive glass through a spin coating method. Therefore, it is required that the glass surface be kept as clean as possible to reduce the interface defects, so that the conductive glass substrate needs to be carefully cleaned. Generally, ultrasonic cleaning is carried out by adopting a flow of acetone (30min), liquid detergent (30min), deionized water (30min) and absolute ethyl alcohol (30 min). After blow-drying, ultraviolet irradiation is used for hydrophilic treatment.

2) Preparing an electron transport layer: SnO with the configuration of 2.37%₂Uniformly stirring the suspension by using ultrasonic waves, sucking 50 mu l of the suspension by using a liquid-transferring gun after the stirring is finished, uniformly covering the suspension on a cleaned ITO substrate, spin-coating the substrate for 30s at the rotating speed of 3000r/min, and then annealing the substrate at 150 ℃ for 30min to form a layer of uniform, compact and firm SnO on the ITO surface₂An electron transport layer.

3) Preparing a perovskite light absorption layer: lead iodide (PbI)₂) And methylamine iodide (CH)₃NH₃I) Mixing and adding into N, N-dimethylformamide according to the molecular ratio of 1:1(DMF) to obtain a precursor solution, and stirring the precursor solution at 70 ℃ until the precursor solution is fully and uniformly mixed. And (3) sucking 50 mu l of precursor solution by using a liquid-moving gun, uniformly coating the precursor solution on the substrate prepared in the step (2), carrying out spin coating at a rotating speed of 3000r/min for 30s, uniformly and quickly dripping diethyl ether anti-solvent when the last 10s is about after the spin coating is finished, and annealing on a heating plate at 100 ℃ for 10min after the spin coating is finished to obtain a perovskite layer with uniform and compact grains. And placing the annealed product in a nitrogen glove for later use.

4) Preparing a hole transport layer: and (3) in an anhydrous and oxygen-free glove box, sucking 50 mu l of the prepared Spiro-MOeTAD precursor solution by using a liquid transfer gun, uniformly coating the solution on the perovskite prepared in the step (3), and spin-coating the solution at the rotating speed of 3000r/min for 30s to complete the preparation of the hole transport layer.

5) Evaporating an electrode: and (3) evaporating a gold (Au) electrode on the cyclone-OMeTAD hole transport layer by adopting a thermal evaporation method, wherein the interface of the electrode evaporated by the thermal evaporation method and the hole transport layer is well combined, the mass distribution of the electrode is uniform, the thickness of the electrode is consistent, and the thickness of the electrode is about 100 nm.

At this point, the conventional device fabrication process is complete. As an improvement of the above technical solution, the method disclosed by the present invention adds a step after the electron transport layer is prepared in step (2): the annealed electron transport layer was placed in a Plasma meter for 5min with 50w air Plasma treatment, and the subsequent preparation steps were unchanged (fig. 4). The thermal stability of the device thus obtained is greatly improved.

Compared with the prior art, the invention has the improved effects that:

SnO treated by the treatment₂The surface and the inside of the electron transport layer are originally unstable oxygen vacancies and oxygen vacancies, after the oxygen enrichment treatment, the oxygen vacancies are filled, the formation energy and the migration energy of the vacancies are greatly improved, and O becomes extremely stable, so that the infiltration of O element to a perovskite layer is prevented, and the decomposition caused by deprotonation of O on the perovskite layer is further avoided under the high-temperature condition.

Drawings

FIG. 1 is a schematic diagram of a layered structure of a perovskite solar cell, (a) a five-layer structure of a complete device, (b) a Film sample three-layer structure

FIG. 2 perovskite solar cell device SnO₂/MAPbI₃Reaction mechanism diagram at the interface.

FIG. 3 is a transmission electron microscope image comparison of cross-sections of perovskite solar cell devices before and after failure.

FIG. 4 is a flow chart of perovskite solar cell device preparation and a schematic of the improved process of the invention.

FIG. 5 comparison of the results of the experiment with and without the Plasma treatment for thermal stability.

FIG. 6 shows the change of XRD of Film sample with annealing time, phase analysis shows that the black phase is the initial perovskite phase and the yellow phase is annealing-obtained PbI₂And (4) phase(s).

FIG. 7 Film sample from MAPbI₃(granular grain) phase conversion to PbI₂Scanning electron microscope images of the (lamellar crystal grain) phase change process were observed.

Detailed Description

In order to make the technical means, the original characteristics, the achieved purposes and the effects of the invention easy to understand, the invention is further explained by combining the specific embodiments and the drawings.

Example 1 Condition 1 Heat treatment comparative Observation

Two Film samples are prepared simultaneously by the prior art and the improved technology provided by the invention respectively, wherein the Film sample is only ITO/SnO specially prepared for testing thermal stability₂/MAPbI₃Three-layer structure samples (fig. 1b) were prepared in the sense that the effect of the hole transport layer and the metal electrode on the stability of the samples was excluded. Whether or not the samples are to SnO₂The electron transport layer was distinguished by Plasma treatment. The process conditions for preparing the Film sample are exactly the same as for preparing the device, except that the process is terminated when step (3) is performed. After the sample is prepared, the sample is placed in an anhydrous and oxygen-free glove box at the same time, and annealing treatment is carried out at 140 ℃ in a dark place. The course of its change is continuously tracked.

As shown in FIG. 5, the Plasma treatment was not carried out, and the reaction was carried out in SnO₂The sample of the perovskite layer is directly coated by spin coating, and the decomposition is started after 2h and is completely decomposed after 4h, and the sample is represented by black perovskitePhase conversion to yellow PbI₂Phase (1); while allowing the Plasma treated SnO₂The electron transport layer is used as a sample of the substrate, and the electron transport layer starts to decompose after 5 hours and completely decomposes after 10 hours, so that the thermal stability is greatly improved. The phase composition can be found by analyzing the XRD data of fig. 6 and the SEM data of fig. 7.

Example 2 Condition 2 Heat treatment comparative Observation

Respectively using original technique and improved technique proposed by said invention to prepare two Film samples simultaneously, and the samples have or have not only SnO₂The electron transport layer was distinguished by Plasma treatment. The process conditions for preparing the Film sample are exactly the same as for preparing the device, except that the process is terminated when step (3) is performed. After the preparation of the sample, the sample is placed in the air at the same time, and annealing treatment at 85 ℃ in a dark place is carried out. The course of its change is continuously tracked.

Without Plasma treatment, in SnO₂The sample on which the perovskite layer was directly spin-coated began to decompose after 24 hours, and was completely decomposed after about 50 hours, as reflected by the conversion of the sample from a black perovskite phase to yellow PbI₂Phase (1); while allowing the Plasma treated SnO₂The electron transport layer is used as a substrate sample, decomposition starts after 48 hours, and complete decomposition starts after 120 hours, so that great improvement is shown in thermal stability.

Example 3 Condition 3 Heat treatment comparative Observation

Respectively using original technique and improved technique proposed by said invention to prepare two Film samples simultaneously, and the samples have or have not only SnO₂The electron transport layer was distinguished by Plasma treatment. The process conditions for preparing the Film sample are exactly the same as for preparing the device, except that the process is terminated when step (3) is performed. After the preparation of the sample is finished, the sample is placed in the air at the same time, and the annealing treatment with illumination at 140 ℃ is carried out.

Without Plasma treatment, directly in SnO₂The sample on which the perovskite layer is directly spin-coated is decomposed after 10min and completely decomposed after 20min, and the decomposition is characterized in that the sample is converted from a black perovskite phase to yellow PbI₂Phase (1); while allowing the Plasma treated SnO₂The electron transport layer is used as a sample of the substrate, the decomposition starts to occur after 30min, the complete decomposition is performed after 100min,a great improvement in thermal stability is shown.

Example 4 Condition 4 Heat treatment comparative Observation

Respectively using original technique and improved technique proposed by said invention to prepare two Film samples simultaneously, and the samples have or have not only SnO₂Differentiation of the Plasma treatment was performed. The process conditions for preparing the Film sample are exactly the same as for preparing the device, except that the process is terminated when step (3) is performed. After the preparation of the sample is finished, the sample is placed in the air at the same time, the annealing treatment with illumination at 85 ℃ is carried out, and the change process is continuously tracked.

Without Plasma treatment, in SnO₂The sample on which the perovskite layer is directly spin-coated is decomposed after 3h and completely decomposed after 5h, and the decomposition is specifically shown in the way that the sample is converted from the black perovskite phase to yellow PbI₂Phase (1); while allowing the Plasma treated SnO₂The electron transport layer is used as a substrate sample, decomposition starts after 6 hours, and complete decomposition starts after 14 hours, so that great improvement is shown on thermal stability.

Claims

1. A method for improving the thermal stability of a perovskite solar cell is characterized by comprising the following operation steps:

1) ultrasonically cleaning a conductive glass substrate, drying the conductive glass substrate, and then irradiating the conductive glass substrate by ultraviolet light for hydrophilic treatment;

2) configuration SnO₂Uniformly covering the suspension on the conductive glass substrate subjected to hydrophilic treatment in the step (1), and performing spin-coating annealing to obtain the SnO-containing material₂An electron transport layer;

3) the SnO containing prepared in the step (2)₂Putting the substrate of the electron transport layer into a plasma cleaning instrument, and cleaning for 5min at the power of 50 w;

4) preparing a perovskite precursor solution, uniformly coating the perovskite precursor solution on the substrate cleaned in the step (3), and performing spin-coating annealing to obtain a perovskite layer;

5) uniformly coating the prepared Spiro-MOeTAD precursor solution on the perovskite layer prepared in the step (4) in an anhydrous and oxygen-free glove box, and performing spin coating for 30s to obtain a hole transport layer;

6) and evaporating a gold electrode on the Spiro-OMeTAD hole transport layer by adopting a thermal evaporation method.

2. The method of claim 1, wherein the perovskite material is ABX₃Organic-inorganic hybrid perovskite.

3. The method for improving the thermal stability of the perovskite solar cell as claimed in claim 1, wherein the material of the electron transport layer is SnO₂。

4. The method for improving the thermal stability of a perovskite solar cell as claimed in claim 1, wherein prepared SnO₂And carrying out plasma cleaning treatment on the electron transport layer.

5. A method of improving the thermal stability of perovskite solar cells as claimed in claim 4 wherein the gas used in the plasma cleaning process must contain oxygen.