CN116367562A - Modification method of n/i interface of perovskite solar cell - Google Patents

Abstract

The invention provides a method for modifying the n/i interface of a perovskite solar cell. The perovskite solar cell includes a transparent conductive substrate, an electron transport layer, an n/i interface modification layer, a perovskite active layer, and a hole transport layer. and a metal electrode, the n/i interface modification layer is a formamidine formate material, and the formamidine formate material is a modification layer including both carboxyl and amino compounds. The invention can effectively improve the electrical properties of the electron transport material and passivate the defects on the surface of the electron transport layer through the interface modification layer. In addition, formamidine formate can also improve interfacial contact performance by constructing chemical bridges at the n/i interface, and obtain high-quality perovskite films by regulating the perovskite growth process. At the same time, the modification layer can significantly improve the open-circuit voltage, short-circuit current density, fill factor, and photoelectric conversion efficiency of the device; the modification method proposed by the present invention provides a broad prospect for the preparation of high-efficiency conventional perovskite solar cells.

Description

A method for modifying the n/i interface of perovskite solar cells

technical field

The invention relates to the technical field of photoelectric functional materials and devices. The invention relates to a method for modifying the n/i interface of a perovskite solar cell. The introduction of the n/i interface modification layer can greatly improve the performance of the perovskite solar cell device. More importantly, it involves the perovskite bottom Interface optimization issues.

Background technique

Among emerging solar cells, perovskite solar cells have experienced a rapid development in the past ten years. The efficiency of single-junction perovskite solar cells has rapidly increased from 3.8% in 2009 to 25.7% today, which is almost close to the efficiency of single-crystal silicon cells whose preparation technology is very mature. Due to the excellent optoelectronic semiconductor properties, such as high light absorption coefficient, tunable bandgap, low exciton binding energy, long carrier lifetime and diffusion length, and low cost that can be prepared by low-temperature solution, perovskite solar cells have been widely used in The field of optoelectronics has very broad application prospects.

The two most commonly used inorganic electron transport layer (ETL) materials in nip-type perovskite solar cells are: titanium dioxide (TiO ₂ ) and tin dioxide (SnO ₂ ). Compared with TiO ₂ , ^which requires high ^- temperature annealing and has obvious hysteresis effect, SnO ₂ is considered to be more suitable ^for Potential electron transport layer materials.

Although the conversion efficiency of perovskite solar cells has achieved significant progress, there is still a lot of room for improvement from the Shockley-Queisser theoretical limit of more than 30%, and the long-term operational stability of the device has not been completely resolved, which also hinders large-scale commercialization of perovskite solar cells. Among the important characterization parameters of perovskite solar cells, the current short-circuit current density is close to the theoretical value, so in order to further improve the conversion efficiency, it is necessary to increase the open-circuit voltage and fill factor by reducing non-radiative recombination. Previous studies have shown that a large number of defects at the surface interface is an important factor for non-radiative recombination and open-circuit voltage loss. At present, there are very mature methods and various materials for the passivation of the upper surface of perovskite, such as ammonium salts, Lewis acids and bases, polymers, etc., but there are few related studies on the passivation of the bottom interface of perovskite.

However, it has been reported that the defect density at the bottom interface of perovskite is even higher than that at the upper surface of perovskite, which will seriously hinder the transport of carriers and cause serious energy loss. In addition, many defects will inevitably be introduced during the preparation of _SnO2 , such as surface dangling bonds, hydroxyl groups, and two typical O vacancies and Sn interstitial impurities, which not only lead to non-radiative recombination, but also hinder electron transfer. Efficient extraction and transfer. At the same time, the morphology and wettability of the SnO ₂ surface will affect the quality of the perovskite film deposited on it, and the physical properties that do not match with the perovskite will also cause significant interface residual stress, thus affecting the perovskite solar energy. Battery efficiency and stability. In short, effective regulation of the perovskite bottom interface is critical to further improve device performance.

Studies have shown that passivation of the perovskite bottom interface can help improve device efficiency. However, these methods have certain limitations. For example, the passivation mechanism is not fully understood due to the lack of techniques to directly characterize the perovskite bottom interface; due to the strong polarity of the perovskite solvent, the passivation molecules at the bottom interface may be involved in the subsequent deposition of perovskite. was destroyed when. Therefore, it is important and challenging to explore a facile passivation method and study its mechanism.

Contents of the invention

(1) Purpose of the invention

The purpose of the present invention is to introduce a modified layer of formamidine formate (FAFa) at the n/i interface, and find that it can not only passivate the interface defects, improve the interface contact performance, but also improve the crystal quality of the perovskite film and improve the conductivity of the electron transport layer. rate, thereby further improving the performance of perovskite solar cells.

(2) Technical solutions

In order to achieve the above object, the present invention adopts the following technical solutions:

。A perovskite solar cell, comprising a transparent conductive substrate, an electron transport layer, an n/i interface modification layer, a perovskite active layer, a hole transport layer and a metal electrode, wherein the n/i interface modification layer is formic acid formamidine material, the molecular structure of the formate formamidine material is

.

The perovskite solar cell is a conventional perovskite solar cell, and the n/i interface modification layer is prepared between the electron transport layer and the perovskite active layer.

The perovskite solar cell, wherein the preparation method of the n/i interface modification layer FAFa comprises the following steps:

S1: Use a precision balance to weigh 1-20 mg of formamidine formate and dissolve it in 1 mL of organic solvent until it is completely dissolved, and prepare FAFa solutions of different concentrations for comparison; the organic solvent includes but is not limited to IPA;

S2: Spin-coat the prepared FAFa solution on the prepared electron transport layer at a speed of 1000-4000 rpm for 20-60 s, and anneal at 80-150° C. for 5-20 min.

In the perovskite solar cell described above, FAFa modification can effectively improve photovoltaic parameters such as short-circuit current, open-circuit voltage, fill factor, and photoelectric conversion efficiency of the device.

The FAFa modification layer can effectively reduce the surface roughness of the _SnO2 film of the electron transport layer, and it is easier to deposit a high-quality perovskite film on it.

The FAFa modification layer can effectively reduce surface defects of the _SnO2 thin film of the electron transport layer and achieve the effect of improving the conductivity of the electron transport layer.

In the FAFa modification layer, a high-quality perovskite film can be obtained by adjusting the growth process, so that the pores on the bottom surface of the perovskite film are reduced, the roughness of the surface interface is reduced, and the crystallization quality of the perovskite is also improved. promote.

In the FAFa modification layer, a chemical bridge can be constructed at the n/i interface to improve interface contact performance.

The FAFa modification layer can effectively reduce the defect density in the perovskite film and suppress non-radiative recombination.

(3) Beneficial effects

The invention provides a method for modifying the n/i interface of a perovskite solar cell. The introduction of a formamidine formate (FAFa) modification layer between the electron transport layer and the perovskite active layer can passivate the surface of the electron transport layer through electrostatic interaction. defects, improve the conductivity of the electron transport layer, and can also adjust the perovskite crystallization process to obtain high-quality perovskite films with high crystallinity and low defect density. In addition, it can also chemically bridge the electron transport layer and perovskite activity. layer to optimize the interface contact performance, thereby greatly improving the performance of solar cell devices. The invention provides a new idea for the modification of the n/i interface of conventional perovskite solar cells, and provides a broad prospect for further improving the performance of conventional perovskite solar cells.

Description of drawings

Fig. 1 is the structural representation of perovskite solar cell of the present invention;

Fig. 2 is the roughness of _SnO surface before and after modification of different concentrations of FAFa in the preferred embodiment of the present invention;

Fig. 3 is the FTIR spectrum and conductivity before and after FAFa modification in the preferred embodiment of the present invention;

Fig. 4 is the SEM picture of the perovskite film before and after different concentrations of FAFa modification in the preferred embodiment of the present invention;

Fig. 5 is the AFM diagram of the perovskite film before and after different concentrations of FAFa modification in the preferred embodiment of the present invention;

Figure 6 is a cross-sectional SEM diagram of the device before and after modification with different concentrations of FAFa in a preferred embodiment of the present invention;

Fig. 7 is the PL and TRPL spectra of the perovskite film before and after modification with different concentrations of FAFa in the preferred embodiment of the present invention;

Fig. 8 is the J-V curves of devices before and after modification with different concentrations of FAFa in a preferred embodiment of the present invention.

Implementation

Below in conjunction with preferred embodiment and complete test result, the present invention is described in further detail, set forth more details in the following description so as to fully understand the present invention, those skilled in the art can be without departing from the connotation of the present invention Similar promotions and deductions are made according to actual application situations, so the content of this specific embodiment should not limit the protection scope of the present invention.

A kind of perovskite solar cell provided by the present invention, as shown in Figure 1, comprises transparent conductive substrate 1, electron transport layer 2, formic acid formamidine modification layer 3, perovskite active layer 4, hole transport layer 5 and metal electrodes6.

The formamidine formic acid modification layer of the present invention is a material that includes both carboxyl and amino groups, wherein both carboxyl and amino groups can passivate charge defects through electrostatic interaction, therefore, different defects can be passivated simultaneously by using bifunctional molecules. According to previous literature reports, there are a large number of holes and deep level traps at the bottom interface of perovskite, and the defect density is even higher than that on the upper surface of perovskite. In addition, the electron transport layer 2 is an inorganic compound SnO ₂ , which will inevitably introduce many defects during the preparation process, such as surface dangling bonds, hydroxyl groups, and two typical O vacancies and Sn interstitial impurities, which will not only lead to non-radiative Recombination also hinders the efficient extraction and transport of electrons. By proposing a unique strategy, the present invention adds a formic acid formamidine modification layer between the electron transport layer and the perovskite active layer, which can effectively optimize the interface performance, thereby obtaining a high-quality perovskite solar cell, and the performance of the solar cell is also improved. raised dramatically. Therefore, it has great research prospects to study the passivation of formamidine formate on the bottom interface of perovskite.

The preparation steps of the formic acid formamidine solution of the present invention are as follows: dissolving the formic acid formamidine using IPA as a solvent. First, weigh 1 mg, 5 mg, and 10 mg of formamidine with a precision balance and put them into vials, then add 1 mL of IPA into the vial, stir until formamidine formate is completely dissolved, and obtain concentrations of 1 mg mL ^{- 1} , 5 mg mL ^-1 , and 10 mg mL ^-1 clear and transparent FAFa solutions, the different concentrations of the FAFa solutions are named 1-FAFa, 5-FAFa, and 10-FAFa in the present invention.

The FAFa modification layer can change the surface of the _SnO2 film. In order to study the influence of FAFa treatment on the surface morphology of the _SnO2 film, the present invention carried out atomic force microscope (AFM) tests on the surface of the _SnO2 film modified with different concentrations of FAFa. As shown in Figure 2, it can be seen that the surface roughness of _SnO2 film treated without FAFa solution is larger, and after spin-coating FAFa solution, the surface roughness of _SnO2 decreases, and the roughness of _SnO2 modified by 5-FAFa decreases most obviously , a smoother and denser film surface is conducive to the subsequent deposition of high-quality perovskite films.

The FAFa modification layer can reduce SnO ₂ surface defects and improve the conductivity of the electron transport layer. The present invention carried out Fourier transform infrared spectroscopy (FTIR) test on SnO ₂ with or without FAFa modification, as shown in Figure 3a. Compared with SnO ₂ , the stretching vibration peak of C=O belonging to FAFa appeared on the SnO ₂ /FAFa film, and the peak position shifted from the original 1732 cm ^-1 to 1724 cm ^-1 , indicating that FAFa did occur with SnO ₂ interaction. In addition, the peak position at 548 cm ^-1 belonging to the stretching vibration of Sn-O in _SnO2 shifted to a higher wavenumber at 568 cm ^-1 after FAFa modification. This indicates that Fa anion bonds with uncoordinated Sn ⁴⁺ through electrostatic coupling or Lewis acid-base coordination, thereby reducing the surface defects of SnO ₂ . In order to further study the influence of FAFa treatment on the conductivity of SnO ₂ films, the present invention, based on the ITO/Au/SnO ₂ /Au structure, carried out the current density-voltage measurement of SnO ₂ films modified with different concentrations of FAFa under dark light conditions. (JV) measurements, as shown in Fig. 3b. The conductivity of the unmodified SnO ₂ film is 1.04×10 ^-3 mS cm ^-1 , and when modified with FAFa at a concentration of 5 mg mL ^-1 , the conductivity is significantly increased to 1.72× ^{10 -3 mS} cm ^-1 . The electron transport layer with higher conductivity is beneficial to facilitate the extraction and transport of carriers, thus improving the device performance.

The FAFa interface modification can obtain a high-quality perovskite film by adjusting the growth process. The present invention characterizes the surface morphology of the perovskite film deposited on the _SnO2 film under the condition of different concentrations of FAFa modification by scanning electron microscope (SEM) and AFM. Figure 4 shows the surface morphology of perovskite thin films on unmodified, 1 mg mL ^-1 , 5 mg mL ^-1 , 10 mg mL ^-1 FAFa interface modification layers. It can be seen that the surface morphology of the perovskite modified by FAFa is cleaner and more uniform, indicating that the FAFa interface modification is beneficial to the growth of perovskite crystals. Figure 5 also shows that the surface roughness of the perovskite film is reduced from 39.0 nm based on SnO ₂ to 30.9 nm based on SnO ₂ /5-FAFa, and a flatter and denser film is beneficial to reduce non-radiative recombination caused by defects. In addition, Figure 6 is the cross-sectional SEM of the perovskite film prepared above the SnO ₂ film with or without FAFa interface modification. Finally, the perovskite film has larger grains equivalent to the film thickness, shallower grain boundary trenches, and fewer holes at the bottom interface of the perovskite, which is conducive to reducing the recombination loss at the grain boundary and accelerating the photogenerated current carrying. The extraction and transport of electrons and the reduction of the density of defect states further confirm that the FAFa modification is beneficial to improve the film quality of the perovskite film.

The FAFa interface modification can construct a chemical bridge at the n/i interface so as to improve the interface contact performance. Studies have shown that Fa anions are more inclined to bind on the _SnO2 surface, so the FA cations repelled by the _SnO2 surface may preferentially interact with _PbI2 in the perovskite precursor and serve as nucleation sites for perovskite growth. Therefore, FAFa treatment can repair structural defects (such as voids) by building a chemical bridge between _SnO2 and perovskite, improving the contact characteristics at the bottom interface of perovskite.

The FAFa interface modification can effectively reduce the defect density of the perovskite film and inhibit the non-radiative recombination of carriers. The present invention measured the photoluminescence (PL) and time-resolved photoluminescence (TRPL) spectra of perovskite thin films modified with different concentrations of FAFa, as shown in Figure 7a. Compared with the unmodified control perovskite film, the PL intensity of the perovskite film on the 5-FAFa interface modification layer is significantly increased, which fully demonstrates that FAFa can effectively reduce the defects of the perovskite film and inhibit non-radiative recombination. Furthermore, it was observed that the PL peak was blue-shifted from 820 nm to 795 nm after 5-FAFa modification, verifying the efficient annihilation of the band tail defect. TRPL also confirmed similar results, as shown in Figure 7b, the TRPL decay curve can be well fitted by a double-exponential decay function, and at the same time, the present invention also estimates the average carrier lifetime according to the fitting result. In the case of 5-FAFa modification, the average carrier lifetime of perovskite was significantly increased from 219.57 ns to 230.35 ns, which means that manipulating the growth process with FAFa can significantly improve the crystalline quality of perovskite and effectively inhibit the perovskite thin film non-radiative recombination pathway.

The FAFa interface modification can optimize the performance of the perovskite solar cell device. The present invention adopts a two-step method to prepare a conventional planar perovskite solar cell. The device structure is ITO/SnO ₂ /formamidine formic acid modification layer/FAPbI ₃ calcium Titanite/Spiro-OMeTAD/Au. Figure 8 shows typical JV curves of devices with no modification and n/i interface modified with different concentrations of FAFa, perovskite with an effective area of 0.089 cm ² under one solar light irradiation (AM1.5G, 100 mW/cm ² ). solar cell. Finally, an efficiency of 21.48%, a current density of 23.34 mA cm ^-2 , an open circuit voltage of 1.112 V, and a fill factor of 82.74% were obtained. The performance of the device can be significantly improved by introducing the FAFa interface modification layer, and the optimal concentration of FAFa solution is 5 mg mL ^-1 . The invention provides ideas for further improving the performance of conventional perovskite solar cells.

The English abbreviations in this application are explained below:

IPA (isopropyl alcohol)

FAFa (formamidine formate)

ITO (Indium tin oxide)

MAI (methylammonium iodide)

FAI (formamidinium iodide)

Spiro-OMeTAD (2,2’,7,7’-tetrakis (N,N-di-p-methoxyphenyl-amine)-9,9’-spirobifluorene)

The above content is a description of the preferred embodiments of the invention, which can help those skilled in the art to more fully understand the technical solutions of the invention, and can also stimulate new ideas and change the original thinking in the field of perovskite solar cells mode, and has made a great contribution to the improvement of the performance of conventional perovskite solar cells. For those of ordinary skill in the technical field of the present invention, without departing from the concept of the present invention, they can also make some simple deduction and transformation, which should be regarded as belonging to the protection scope of the present invention.

Claims (8)

1. a perovskite solar cell, comprising transparent conductive substrate, electron transport layer, n/i interface modification layer, perovskite active layer, hole transport layer and metal electrode, is characterized in that, The n/i interface modification layer is a formamidine formate material (FAFa for short), and the molecular structure of the formamidine formate material is

; The perovskite solar cell is a conventional perovskite solar cell, and the n/i interface modification layer is prepared between the electron transport layer and the perovskite active layer. 2. perovskite solar cell according to claim 1, is characterized in that, the preparation method of described n/i interface modification layer FAFa comprises the following steps: S1: Use a precision balance to weigh 1-20 mg of formamidine formate and dissolve it in 1 mL of organic solvent until it is completely dissolved, and prepare FAFa solutions of different concentrations for comparison; the organic solvent includes but is not limited to IPA; S2: Spin-coat the prepared FAFa solution on the prepared electron transport layer at a speed of 1000-4000 rpm for 20-60s, and anneal at 80-150°C for 5-20 min. 3. The perovskite solar cell according to claim 1, wherein FAFa modification can effectively improve photovoltaic parameters such as short-circuit current, open-circuit voltage, fill factor, and photoelectric conversion efficiency of the device. 4. The perovskite solar cell according to claim 1, characterized in that, FAFa can effectively reduce the surface roughness of the electron transport layer _SnO2 film, and it is easier to deposit a high-quality perovskite film thereon. 5. The perovskite solar cell according to claim 1, characterized in that, FAFa can significantly reduce electron transport layer SnO ₂ surface defects of the thin film, and achieve the effect of improving the conductivity of the electron transport layer. 6. The perovskite solar cell according to claim 1, wherein the FAFa interface modification can obtain a high-quality perovskite film by regulating the growth process, so that the pores on the bottom surface of the perovskite film are reduced and the surface interface The roughness is reduced, and the crystal quality of perovskite is also improved. 7. The perovskite solar cell according to claim 1, characterized in that the FAFa interface modification can construct a chemical bridge at the n/i interface to improve the interface contact performance. 8. The perovskite solar cell according to claim 1, wherein the FAFa interface modification can effectively reduce the defect density in the perovskite film and inhibit non-radiative recombination.

Images