CN115528180A - A biofriendly carbon quantum dot modified electron transport layer to induce crystallization on the lower surface of perovskite - Google Patents

Abstract

The invention belongs to the technical field of perovskite solar cells, and provides a biofriendly method for modifying an electron transport layer with carbon quantum dots to induce crystallization on the lower surface of perovskite. The present invention adopts a simple and effective method of operation. Under low temperature conditions, a carbon material is introduced into SnO ₂ . This composite ETL is more conducive to charge transport, and can passivate the surface and internal defects of SnO ₂ to obtain better transport performance. , ETL with smaller interface recombination loss. This has a certain impetus to the optimization of the electron transport layer and the lower surface of the perovskite, improving the PCE and stability of PSCs.

Description

A biofriendly carbon quantum dot-modified electron transport layer induces the lower surface of perovskite method of crystallization

technical field

The invention belongs to the technical field of perovskite solar cells, and relates to a biofriendly method for modifying an electron transport layer with carbon quantum dots to induce crystallization on the lower surface of perovskite.

Background technique

The new type of perovskite solar cells (Perovskite Solar Cells, referred to as PSCs) has developed rapidly in recent years and is expected to break through the limitations of existing technologies and provide transformative technical support for the development and efficient utilization of clean solar energy. great concern. As a class of direct bandgap semiconductor materials, metal halide perovskite materials have a series of excellent optoelectronic properties, and can be grown by a simple and low-cost solution method, making them shine in the field of photovoltaics. The photoelectric conversion efficiency (PCE) of small-area single-junction PSCs has been recorded as high as 25.7% [Science 2022, 375, 302-306], which has become the leader of low-cost high-efficiency solar cells and one of the most anticipated new photovoltaic technologies. In PSCs, the electron transport layer (ETL) plays a crucial role in the efficient transport and extraction of photogenerated carriers, and thus has great significance for the PCE and operational stability of the device. At present, although SnO ₂ is commonly used as the ETL in PSCs, there are also unsatisfactory energy level alignments with the perovskite layer, and it is inevitable to form defect states at the ETL/perovskite interface, resulting in non-radiative recombination of carriers. , which in turn affects the PCE and long-term stability of the device [Angew.Chem.Int.Ed.2019,58,11497].

Contents of the invention

The present invention provides a kind of method that carbon quantum dots (CQDs) are embedded in _SnO Form composite ETL, prepare high-efficiency and high-stability perovskite solar cell, because CQDs surface has some organic functional groups, such as: carboxyl, hydroxyl , amino groups, etc.; these organic functional groups interact with SnO ₂ to improve the electrical properties of SnO ₂ , reduce defects and match the perovskite energy level arrangement more closely, reducing the energy loss during carrier transport. This composite ETL can also directly increase the grain size of the lower surface of the perovskite to obtain a smoother perovskite film, and a perovskite film with fewer defects and higher quality will help improve efficiency and stability.

Technical scheme of the present invention:

A bio-friendly method for modifying the electron transport layer with carbon quantum dots to induce crystallization on the lower surface of perovskite, the steps are as follows:

Step (1), preparing carbon quantum dots;

Uniformly dissolve neutral red and citric acid in deionized water at a molar ratio of 1:1000, transfer to a hydrothermal kettle after ultrasonic dispersion for 5 to 15 minutes, and react at a temperature of 150 to 200°C for 3 to 6 hours, using 15,000 ~18000rpm centrifuged three times to obtain CQDs aqueous solution, and then freeze-dried to obtain CQDs powder;

Step (2), cleaning the conductive substrate;

First, clean the surface of the conductive substrate with FTO cleaning agent, then use deionized water, absolute ethanol, acetone, and isopropanol to ultrasonically clean it for 15-25 minutes, and dry it with nitrogen gas for use;

Step (3), preparing CQD-SnO ₂ ETL;

Treat the conductive substrate obtained in step (2) with ultraviolet ozone for 15-30min for use; add CQDs in 5wt% _SnO2 aqueous solution, the concentration of CQDs is 0.5-3wt%, after shaking, use a 0.22 μm organic needle filter to filter After obtaining CQD- _SnO Dispersion liquid;

Drop the CQD-SnO ₂ dispersion on the conductive substrate after UV ozone treatment, spread evenly and use 3000-5000rpm/min spin-coating procedure to cover the CQD-SnO ₂ dispersion evenly on the conductive substrate, then at 120-180℃ Anneal on a hot plate for 20-60 minutes to obtain CQD-SnO ₂ composite ETL;

Step (4), preparation of perovskite active layer, hole transport layer Spiro-OMeTAD, evaporated metal electrode; perovskite layer adopts two-step spin coating process, first spin coating PbI2 layer, and then spin coating organic ammonium salt; The hole transport layer adopts the method of dynamic spin coating, and the metal electrode adopts the method of vacuum evaporation to complete.

Beneficial effect of the present invention: the present invention has designed the perovskite solar cell of CQD-SnO ₂ composite ETL, and this method is simple and easy to operate, and cost is low, and effect is remarkable, and can reduce a large amount of internal defects in ETL, electron mobility from 8.19 ×10 ^-3 cm ² V ^-1 s ^-1 increased to 2.49×10 ^-2 cm ² V ^-1 s ^-1 ; while improving the perovskite lower surface and inducing perovskite crystallization, the efficiency of perovskite devices has been improved A substantial increase from 21.62 to 23.42%; the long-term stability of PSCs is also improved due to the stability of CDQs making the electron transport layer and perovskite layer more stable.

Description of drawings

Figure 1 is the infrared spectrum of CQDs, SnO ₂ , and CQD-SnO ₂ materials;

Figure 2 is a schematic diagram of a complete device structure;

Figure 3 is a distribution diagram of the photoelectric conversion efficiency of PSCs based on SnO ₂ ETL with different concentrations of CQDs;

Fig. 4 is the electron mobility curve of two kinds of _SnO electron transport layers;

Fig. 5 is two kinds of _SnO Electron-transport layer defect state density analysis curves;

Fig. 6 is a current-voltage curve diagram of the photoelectric conversion efficiency of the test device based on two kinds of ETL.

detailed description

The specific implementation manners of the present invention will be further described below in conjunction with the accompanying drawings and technical solutions.

Example 1

A bio-friendly method for modifying the electron transport layer with carbon quantum dots to induce crystallization on the lower surface of perovskite, the steps are as follows:

Step (1), preparing carbon quantum dots;

Dissolve 2.1mg of neutral red and 1.2g of citric acid in 10mL of deionized water evenly, after 10min ultrasonically dissolve 2.1mg of neutral red and 1.5g of citric acid in 5mL of deionized water, transfer to 25mL of water after 10min of ultrasonic dispersion In a hot kettle, react in an oven at 180°C for 4 hours, use 17000rpm centrifugal washing three times to obtain the CQDs aqueous solution, and then freeze-dry to obtain the A-CQDs powder;

Step (2), cleaning the conductive substrate;

First, clean the surface of the conductive substrate with FTO cleaning agent, then use deionized water, absolute ethanol, acetone, and isopropanol to ultrasonically clean it for 15 minutes, and then dry it with nitrogen gas for use;

Step (3), preparing CQD-SnO ₂ ETL;

The conductive base ultraviolet ozone treatment that step (2) obtains is stand-by for 15min;

Add 1.5wt% A-CQDs in 5wt% SnO ₂ aqueous solution, after dissolving and shaking, use 0.22 μm organic needle filter to obtain A-CQD-SnO ₂ dispersion solution, drop it on the conductive surface after UV ozone treatment On the substrate, after uniform spreading, the A-CQD-SnO ₂ solution was uniformly covered with a conductive substrate using a 3000rpm/min spin-coating procedure, and then annealed on a hot plate at 150°C for 35min to form an A-CQD-SnO ₂ composite ETL;

Step (4), preparing the perovskite active layer;

A two-step method was used to prepare the perovskite layer. First, the three ETL substrates prepared in step (3) were spin-coated with _PbI2 solution, annealed at 70 °C for 20 s, then spin-coated with organic salt solution, and heated at 90 °C for 30 s. Heat on a hot plate at 150°C for 12 minutes to obtain a perovskite film.

The organic salt is one or more of methyl iodide, methyl chloride, methyl bromide and methyl iodide mixed and dissolved in isopropanol solution.

Step (5), preparing the hole transport layer Spiro-OMeTAD;

Prepare a 72 mg/mL Spiro-OMeTAD chlorobenzene solution, filter it with a needle filter with a pore size of 0.22 μm, and cover it evenly on the surface of the perovskite active layer at a speed of 3000 rpm/min;

Step (6), preparing metal electrodes

的速率将银电极蒸至厚度为80nm完成器件制备。Put the film prepared through the above steps into a vacuum evaporation chamber, and evaporate metal electrodes. After the vacuum degree is lower than 9*10 ^-4 Pa, the

The silver electrode was evaporated to a thickness of 80nm at a high speed to complete the device preparation.

Comparative example 1

A bio-friendly method for modifying the electron transport layer with carbon quantum dots to induce crystallization on the lower surface of perovskite, the steps are as follows:

Step (1), preparing carbon quantum dots;

Dissolve 3 g of citric acid and 3 g of urea in 10 mL of deionized water, heat in a microwave oven on high heat for 8 min, and disperse the resulting lumpy substance in 200 mL of deionized water. After ultrasonication for 30 min, use 18,000 rpm to wash three times, and take the supernatant to freeze-dry. Obtain B-CQDs powder;

Step (2), cleaning the conductive substrate;

First, clean the surface of the conductive substrate with FTO cleaning agent, then use deionized water, absolute ethanol, acetone, and isopropanol to ultrasonically clean it for 15 minutes, and then dry it with nitrogen gas for use;

Step (3), preparing CQD-SnO ₂ ETL;

The conductive base ultraviolet ozone treatment that step (2) obtains is stand-by for 15min;

Add 1.5wt% B-CQDs to 5wt% SnO ₂ aqueous solution, after dissolving and shaking, use 0.22 μm organic needle filter to obtain B-CQD-SnO ₂ dispersion solution, drop it on the conductive surface after UV ozone treatment On the substrate, after uniform spreading, the B-CQD-SnO ₂ solution was uniformly covered with a conductive substrate using a 3000rpm/min spin-coating procedure, and then annealed on a hot plate at 150°C for 35min to form a B-CQD-SnO ₂ composite ETL;

Step (4), preparing the perovskite active layer;

A two-step method was used to prepare the perovskite layer. First, the three ETL substrates prepared in step (3) were spin-coated with _PbI2 solution, annealed at 70 °C for 20 s, then spin-coated with organic salt solution, and heated at 90 °C for 30 s. Heat on a hot plate at 150°C for 12 minutes to obtain a perovskite film.

The organic salt is one or more of methyl iodide, methyl chloride, methyl bromide and methyl iodide mixed and dissolved in isopropanol solution.

Step (5), preparing the hole transport layer Spiro-OMeTAD;

Prepare a 72 mg/mL Spiro-OMeTAD chlorobenzene solution, filter it with a needle filter with a pore size of 0.22 μm, and cover it evenly on the surface of the perovskite active layer at a speed of 3000 rpm/min;

Step (6), preparing metal electrodes

的速率将银电极蒸至厚度为80nm完成器件制备。Put the film prepared through the above steps into a vacuum evaporation chamber, and evaporate metal electrodes. After the vacuum degree is lower than 9*10 ^-4 Pa, the

The silver electrode was evaporated to a thickness of 80nm at a high speed to complete the device preparation.

Comparative example 2

A bio-friendly method for modifying the electron transport layer with carbon quantum dots to induce crystallization on the lower surface of perovskite, the steps are as follows:

Step (1), preparing carbon quantum dots;

Use 5 g of 3,4-diaminobenzenesulfonic acid to directly heat in a water heater at 180°C for anhydrous reaction for 12 hours. The obtained powder is dispersed in 200 mL of deionized water, ultrasonicated for 15 minutes, washed three times by centrifugation at 18,000 rpm, and the supernatant is lyophilized to obtain C-CQDs powder;

Step (2), cleaning the conductive substrate;

First, clean the surface of the conductive substrate with FTO cleaning agent, then use deionized water, absolute ethanol, acetone, and isopropanol to ultrasonically clean it for 15 minutes, and then dry it with nitrogen gas for use;

Step (3), preparing CQD-SnO ₂ ETL;

The conductive base ultraviolet ozone treatment that step (2) obtains is stand-by for 15min;

Add 1.5wt% C-CQDs to 5wt% SnO ₂ aqueous solution, after dissolving and shaking, use a 0.22 μm organic needle filter to obtain a C-CQD-SnO ₂ dispersion solution, drop it on the conductive surface after UV ozone treatment On the substrate, after uniform spreading, the C-CQD-SnO ₂ solution was uniformly covered with a conductive substrate using a 3000rpm/min spin-coating procedure, and then annealed on a hot plate at 150°C for 35min to form a C-CQD-SnO ₂ composite ETL;

Step (4), preparing the perovskite active layer;

A two-step method was used to prepare the perovskite layer. First, the three ETL substrates prepared in step (3) were spin-coated with _PbI2 solution, annealed at 70 °C for 20 s, then spin-coated with organic salt solution, and heated at 90 °C for 30 s. Heat on a hot plate at 150°C for 12 minutes to obtain a perovskite film.

Step (5), preparing the hole transport layer Spiro-OMeTAD;

Prepare a 72 mg/mL Spiro-OMeTAD chlorobenzene solution, filter it with a needle filter with a pore size of 0.22 μm, and cover it evenly on the surface of the perovskite active layer at a speed of 3000 rpm/min;

Step (6), preparing metal electrodes

的速率将银电极蒸至厚度为80nm完成器件制备。Put the film prepared through the above steps into a vacuum evaporation chamber, and evaporate metal electrodes. After the vacuum degree is lower than 9*10 ^-4 Pa, the

The silver electrode was evaporated to a thickness of 80nm at a high speed to complete the device preparation.

The schematic diagram of the device structure is shown in Figure 1. The fabricated device was exposed to AM1.5G (100mW/cm ² ) under standard simulated sunlight, the light intensity was calibrated with a standard silicon cell (B5-520), and tested with a Keithley2450 instrument. - The voltage test results are shown in Table 1. Since the three CQDs have different contents of oxygen-containing functional groups, the addition of yellow-green B-CQDs to SnO ₂ affects the light absorption of _{SnO 2} itself, resulting in a decrease in efficiency, and the size of C-CQDs is too large. In the middle, the interface roughness is too large, which will affect the crystallization of the perovskite surface after mixing with SnO ₂ , and affect the efficiency of the device. According to the efficiency test results, only A-CQD-SnO ₂ was used as ETL, and the PCE of PSCs was the highest.

Table 1

Example 2

A bio-friendly method for modifying the electron transport layer with carbon quantum dots to induce crystallization on the lower surface of perovskite, the steps are as follows:

Step (1), preparing carbon quantum dots;

Dissolve 2.1mg of neutral red and 1.5g of citric acid in 5mL of deionized water evenly, transfer to a 25mL hydrothermal kettle after ultrasonic dispersion for 10min, react in an oven at 180°C for 4h, and use 17000rpm centrifugal washing three times to obtain the CQDs aqueous solution. Then obtain CQDs powder through freeze-drying;

Step (2), cleaning the conductive substrate;

First, clean the surface of the conductive substrate with FTO cleaning agent, then use deionized water, absolute ethanol, acetone, and isopropanol to ultrasonically clean it for 15 minutes, and then dry it with nitrogen gas for use;

Step (3), preparing CQD-SnO ₂ ETL;

The FTO ultraviolet ozone treatment 15min that step (2) obtains is stand-by;

Add 0.5wt% CQDs to 5wt% _SnO2 aqueous solution, after dissolving and shaking, use 0.22μm organic needle filter to obtain CQD- _SnO2 dispersion solution, drop it on the conductive substrate after UV ozone treatment, evenly After spreading, the CQD-SnO ₂ solution was uniformly covered on the conductive substrate using a 3000rpm/min spin-coating procedure, followed by annealing on a hot plate at 150°C for 35min to form a CQD-SnO ₂ composite ETL;

Step (4), preparing the perovskite active layer;

A two-step method was used to prepare the perovskite layer. First, the four ETL substrates prepared in step (3) were spin-coated with _PbI2 solution, annealed at 70 °C for 20 s, then spin-coated with organic salt solution, and heated at 90 °C for 30 s. Heat on a hot plate at 150°C for 12 minutes to obtain a perovskite film.

The organic salt is one or more of methyl iodide, methyl chloride, methyl bromide and methyl iodide mixed and dissolved in isopropanol solution.

Step (5), preparing the hole transport layer Spiro-OMeTAD;

Prepare a 72 mg/mL Spiro-OMeTAD chlorobenzene solution, filter it with a needle filter with a pore size of 0.22 μm, and cover it evenly on the surface of the perovskite active layer at a speed of 3000 rpm/min;

Step (6), preparing metal electrodes

的速率将银电极蒸至厚度为80nm完成器件制备。Put the film prepared through the above steps into a vacuum evaporation chamber, and evaporate metal electrodes. After the vacuum degree is lower than 9*10 ^-4 Pa, the

The silver electrode was evaporated to a thickness of 80nm at a high speed to complete the device preparation.

Example 3

A bio-friendly method for modifying the electron transport layer with carbon quantum dots to induce crystallization on the lower surface of perovskite, the steps are as follows:

Step (1), preparing carbon quantum dots;

Dissolve 2.1mg of neutral red and 1.5g of citric acid in 5mL of deionized water evenly, transfer to a 25mL hydrothermal kettle after ultrasonic dispersion for 10min, react in an oven at 180°C for 4h, and use 17000rpm centrifugal washing three times to obtain the CQDs aqueous solution. Then obtain CQDs powder through freeze-drying;

Step (2), cleaning the conductive substrate;

First, clean the surface of the conductive substrate with FTO cleaning agent, then use deionized water, absolute ethanol, acetone, and isopropanol to ultrasonically clean it for 15 minutes, and then dry it with nitrogen gas for use;

Step (3), preparing CQD-SnO ₂ ETL;

The FTO ultraviolet ozone treatment 15min that step (2) obtains is stand-by;

Add 1.5wt% CQDs to 5wt% _SnO2 aqueous solution, after dissolving and shaking, use 0.22μm organic needle filter to obtain CQD- _SnO2 dispersion solution, drop it on the conductive substrate after UV ozone treatment, evenly After spreading, the CQD-SnO ₂ solution was uniformly covered on the conductive substrate using a 3000rpm/min spin-coating procedure, followed by annealing on a hot plate at 150°C for 35min to form a CQD-SnO ₂ composite ETL;

Step (4), preparing the perovskite active layer;

A two-step method was used to prepare the perovskite layer. First, the four ETL substrates prepared in step (3) were spin-coated with _PbI2 solution, annealed at 70 °C for 20 s, then spin-coated with organic salt solution, and heated at 90 °C for 30 s. Heat on a hot plate at 150°C for 12 minutes to obtain a perovskite film.

The organic salt is one or more of methyl iodide, methyl chloride, methyl bromide and methyl iodide mixed and dissolved in isopropanol solution.

Step (5), preparing the hole transport layer Spiro-OMeTAD;

Prepare a 72 mg/mL Spiro-OMeTAD chlorobenzene solution, filter it with a needle filter with a pore size of 0.22 μm, and cover it evenly on the surface of the perovskite active layer at a speed of 3000 rpm/min;

Step (6), preparing metal electrodes

的速率将银电极蒸至厚度为80nm完成器件制备。Put the film prepared through the above steps into a vacuum evaporation chamber, and evaporate metal electrodes. After the vacuum degree is lower than 9*10 ^-4 Pa, the

The silver electrode was evaporated to a thickness of 80nm at a high speed to complete the device preparation.

Example 4

A bio-friendly method for modifying the electron transport layer with carbon quantum dots to induce crystallization on the lower surface of perovskite, the steps are as follows:

Step (1), preparing carbon quantum dots;

Dissolve 2.1mg of neutral red and 1.5g of citric acid in 5mL of deionized water evenly, transfer to a 25mL hydrothermal kettle after ultrasonic dispersion for 10min, react in an oven at 180°C for 4h, and use 17000rpm centrifugal washing three times to obtain the CQDs aqueous solution. Then obtain CQDs powder through freeze-drying;

Step (2), cleaning the conductive substrate;

First, clean the surface of the conductive substrate with FTO cleaning agent, then use deionized water, absolute ethanol, acetone, and isopropanol to ultrasonically clean it for 15 minutes, and then dry it with nitrogen gas for use;

Step (3), preparing CQD-SnO ₂ ETL;

The FTO ultraviolet ozone treatment 15min that step (2) obtains is stand-by;

Comparative example 4: Add 2wt% CQDs in 5wt% _SnO2 aqueous solution, after dissolving and shaking, use 0.22μm organic needle filter to obtain CQD- _SnO2 dispersion solution, drop it on the conductive substrate after UV ozone treatment After uniform spreading, the CQD-SnO ₂ solution was uniformly covered on the conductive substrate using a 3000rpm/min spin-coating procedure, followed by annealing on a hot plate at 150°C for 35min to form a CQD-SnO ₂ composite ETL;

Step (4), preparing the perovskite active layer;

A two-step method was used to prepare the perovskite layer. First, the four ETL substrates prepared in step (3) were spin-coated with _PbI2 solution, annealed at 70 °C for 20 s, then spin-coated with organic salt solution, and heated at 90 °C for 30 s. Heat on a hot plate at 150°C for 12 minutes to obtain a perovskite film.

The organic salt is one or more of methyl iodide, methyl chloride, methyl bromide and methyl iodide mixed and dissolved in isopropanol solution.

Step (5), preparing the hole transport layer Spiro-OMeTAD;

Prepare a 72 mg/mL Spiro-OMeTAD chlorobenzene solution, filter it with a needle filter with a pore size of 0.22 μm, and cover it evenly on the surface of the perovskite active layer at a speed of 3000 rpm/min;

Step (6), preparing metal electrodes

的速率将银电极蒸至厚度为80nm完成器件制备。Put the film prepared through the above steps into a vacuum evaporation chamber, and evaporate metal electrodes. After the vacuum degree is lower than 9*10 ^-4 Pa, the

The silver electrode was evaporated to a thickness of 80nm at a high speed to complete the device preparation.

Comparative example 2

A bio-friendly method for modifying the electron transport layer with carbon quantum dots to induce crystallization on the lower surface of perovskite, the steps are as follows:

Step (1), preparing carbon quantum dots;

Dissolve 2.1mg of neutral red and 1.5g of citric acid in 5mL of deionized water evenly, transfer to a 25mL hydrothermal kettle after ultrasonic dispersion for 10min, react in an oven at 180°C for 4h, and use 17000rpm centrifugal washing three times to obtain the CQDs aqueous solution. Then obtain CQDs powder through freeze-drying;

Step (2), cleaning the conductive substrate;

First, clean the surface of the conductive substrate with FTO cleaning agent, then use deionized water, absolute ethanol, acetone, and isopropanol to ultrasonically clean it for 15 minutes, and then dry it with nitrogen gas for use;

Step (3), preparing CQD-SnO ₂ ETL;

The FTO ultraviolet ozone treatment that step (2) obtains 15min stand-by.

Directly use the 5wt% _SnO2 aqueous solution to obtain pure _SnO2 solution after filtering with a 0.22 μm organic needle filter, spread it evenly on the conductive substrate, use the 3000rpm/min spin-coating program to evenly cover the conductive substrate with the _SnO2 solution, and then in 150 Anneal on a hot plate at ℃ for 35min to form pure SnO ₂ ETL;

Step (4), preparing the perovskite active layer;

A two-step method was used to prepare the perovskite layer. First, the four ETL substrates prepared in step (3) were spin-coated with _PbI2 solution, annealed at 70 °C for 20 s, then spin-coated with organic salt solution, and heated at 90 °C for 30 s. Heat on a hot plate at 150°C for 12 minutes to obtain a perovskite film.

The organic salt is one or more of methyl iodide, methyl chloride, methyl bromide and methyl iodide mixed and dissolved in isopropanol solution.

Step (5), preparing the hole transport layer Spiro-OMeTAD;

Prepare a 72 mg/mL Spiro-OMeTAD chlorobenzene solution, filter it with a needle filter with a pore size of 0.22 μm, and cover it evenly on the surface of the perovskite active layer at a speed of 3000 rpm/min;

Step (6), preparing metal electrodes

的速率将银电极蒸至厚度为80nm完成器件制备。Put the film prepared through the above steps into a vacuum evaporation chamber, and evaporate metal electrodes. After the vacuum degree is lower than 9*10 ^-4 Pa, the

The silver electrode was evaporated to a thickness of 80nm at a high speed to complete the device preparation.

With the increase of CQDs concentration, the photoelectric conversion efficiency of the device decreases, and the best efficiency of 23.42% is reached when adding 1.5wt% CQDs. Therefore, 1.5wt% CQDs is the optimal concentration. The infrared spectrum curves of the two ETLs are shown in Figure 2, which shows that in addition to the iconic Sn-O functional groups of SnO ₂ in CQD-SnO ₂ , C=C functional groups contained in CQDs also appeared, and new NH functional group, indicating a new reaction between _SnO2 and CQDs, which is beneficial to reduce the defect state density in ETL, as shown in Fig. 5; specific photoelectric conversion efficiency results of ETL perovskite solar cells with different concentrations of CQDs added As shown in Figure 3. Put the fabricated device under standard simulated sunlight AM1.5 G (100mW/cm ² ), correct the light intensity with a standard silicon cell (B5-520), and test it with a Keithley2450 instrument. The current-voltage test results are shown in Table 2 The JV curve is shown in Figure 6. The results show that the PCE of PSCs is the highest when only 1.5wt% CQD-SnO ₂ is used as ETL.

Table 2

Claims (3)

1. A method for inducing surface crystallization of perovskite by modifying an electron transport layer through bio-friendly carbon quantum dots is characterized by comprising the following steps:

step (1), preparing carbon quantum dots;

mixing neutral red and citric acid according to the ratio of 1: uniformly dissolving 1000 mol ratio in deionized water, performing ultrasonic dispersion for 5-15 min, transferring to a hydrothermal kettle, reacting for 3-6 h at the temperature of 150-200 ℃, performing centrifugal washing for three times at 15000-18000 rpm to obtain CQDs aqueous solution, and performing freeze drying to obtain CQDs powder;

step (2), cleaning the conductive substrate;

firstly, cleaning the surface of a conductive substrate by using an FTO (fluorine-doped tin oxide) cleaning agent, respectively ultrasonically cleaning for 15-25 min by using deionized water, absolute ethyl alcohol, acetone and isopropanol, and drying by using nitrogen for later use;

step (3) of preparing CQD-SnO ₂ ETL；

Carrying out ultraviolet ozone treatment on the conductive substrate obtained in the step (2) for 15-30min for later use; at 5wt% SnO ₂ CQDs with a concentration of 0.5-3wt% are added into the aqueous solution, and the CQDs are shaken and filtered by an organic needle type filter with a diameter of 0.22 μm to obtain CQD-SnO ₂ A dispersion liquid;

CQD-SnO ₂ Dispersing and dripping the dispersion liquid on a conductive substrate treated by ultraviolet ozone, uniformly spreading the dispersion liquid, and then spin-coating CQD-SnO on the conductive substrate at 3000-5000 rpm/min ₂ Uniformly covering the conductive substrate with the dispersion solution, and then annealing on a hot plate at 120-180 ℃ for 20-60 min to obtain CQD-SnO ₂ Compounding the ETL;

preparing a perovskite active layer, a hole transport layer Spiro-OMeTAD and evaporating a metal electrode; the perovskite layer adopts a two-step spin coating process, and PbI is spin-coated firstly ₂ Coating organic ammonium salt; the hole transport layer adopts a dynamic spin coating mode, and the metal electrode adopts a vacuum evaporation mode.

2. The method of claim 1, wherein the conductive substrate is a fluorine-doped tin oxide transparent conductive glass, an indium tin oxide transparent conductive glass, or a transparent indium tin oxide conductive film.

3. The method according to claim 1 or 2, wherein the organic ammonium salt is one or more of iodomethylamine, chloromethylamine, bromomethylamine and iodomethyl ether, and is mixed and dissolved in the isopropanol solution.

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