Method for carrying out solvent steam annealing on active layer of organic solar cell

Abstract

The invention provides a method for carrying out solvent vapor annealing on an active layer of an organic solar cell, which comprises the following steps of: coating a hole transport layer or an electron transport layer on a substrate, carrying out thermal annealing treatment, coating an active layer on the hole transport layer, then placing a base with a cavity in the center between the substrate and a heating table, and carrying out solvent vapor annealing treatment on the active layer. A solvent is added into the cavity, then heating is carried out for solvent steam annealing, and finally other subsequent steps are carried out. According to the method, the rearrangement among active layer molecules caused by heating in the conventional solvent steam annealing process is greatly slowed down, so that the erosion of the solvent to the active layer is dominated in the stage, the steam annealing can be simply realized, the preparation process of the organic solar cell is optimized, and the organic solar cell with better performance can be obtained.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of organic photovoltaic device or organic semiconductor thin film solar cell preparation, and particularly relates to a method for solvent vapor annealing of an active layer of an organic solar cell. BACKGROUND

[0002] Solution-processed organic solar cells have been widely concerned due to their low cost, light weight, flexibility, semi-transparency, roll-to-roll printing and other advantages, and can convert green and sustainable solar energy into electrical energy, which is an important way for solar energy utilization and has important significance for alleviating energy shortage, improving the environment and promoting green and ecological development.

[0003] The basic structure of an organic solar cell includes an ITO anode (indium tin oxide), a hole transport layer (poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid), also known as "PEDOT:PSS"), an active layer (a donor material and an acceptor material), an electron transport layer (PDINO, PDINN, PFN-Br, PNDIT-F3N, PNDIT-F3N-Br, etc.), and a metal cathode (aluminum, silver, gold, etc.). Among them, the forward device structure is the most commonly used structure, in addition to which there are inverted and stacked organic solar cells, and the inverted device is a reversed hole and electron transport layer of the forward device.

[0004] The morphology of the active layer of an organic solar cell plays a crucial role in the performance of the device. The methods for improving the morphology mainly include thermal annealing, solvent vapor annealing and adding additives. For organic photovoltaic devices, solvent vapor annealing (SVA) is a very good method for adjusting the morphology of the active layer, which can adjust the morphology of the active layer in a non-equilibrium state to a more favorable morphology state for photovoltaic performance. The role of annealing is to accelerate the movement of certain units in the polymer chain, and the source of annealing energy in the traditional sense is heat. Therefore, solvent annealing is to use solvent to erode macromolecules and then provide sufficient free volume for macromolecular chains to make some changes, but the energy source here is not heat but the erosion of solvent molecules to macromolecules.

[0005] At present, the efficiency of high-performance organic solar cells has exceeded 19%, and how to use existing high-performance materials to improve the performance of organic solar cells through process means is a problem we need to solve. SUMMARY

[0006] To solve the above problems, the application provides a method for solvent vapor annealing of an active layer of an organic solar cell, which greatly slows down the intermolecular rearrangement of the active layer caused by heating in a conventional solvent vapor annealing process, so that the erosion of the solvent to the active layer is dominant in this stage, and the vapor annealing can be simply realized, the preparation process of the organic solar cell is optimized, and an organic solar cell with better performance can be obtained.

[0007] To achieve the above object, the technical scheme of the application is as follows:

[0008] A method for solvent vapor annealing of an active layer of an organic solar cell, comprising: coating a hole transport layer or an electron transport layer on a substrate and performing a thermal annealing treatment, coating an active layer on the hole transport layer, then placing a substrate with a cavity in the center between the substrate and a heating table, adding a solvent into the cavity, then heating to perform solvent vapor annealing, and finally performing other subsequent steps.

[0009] The application can slow down the heat conduction between the layers, prolong the solvent evaporation time, and place the solvent in the cavity to slow down the evaporation of the solvent, which is beneficial to the morphology control of the active layer. On the other hand, the presence of the substrate greatly slows down the intermolecular rearrangement of the active layer caused by heating, so that the erosion of the solvent to the active layer is dominant in this stage, and an active layer with better morphology can be obtained.

[0010] According to an embodiment of the application, the thickness of the substrate is 0.5 cm or more, for example 0.6-3 cm, such as 0.6-1 cm.

[0011] According to an embodiment of the application, the diameter of the cavity of the substrate is 0.5-4 cm, for example 0.8-2 cm.

[0012] According to an embodiment of the application, the substrate is made of plastic.

[0013] According to an embodiment of the application, the amount of solvent in the cavity is 100-300 μl, for example 120-180 μl, such as 150 μl.

[0014] According to an embodiment of the application, the solvent added into the cavity is at least one of the following compounds: DCM, CF, CS2 or THF.

[0015] According to an embodiment of the application, the substrate is composed of transparent glass and transparent conductive electrode ITO.

[0016] According to an embodiment of the present application, the hole transport layer material is PEDOT:PSS, and the thickness of the hole transport layer material is 10-40 nm, for example, 30 nm.

[0017] According to an embodiment of the present application, the electron transport layer is PDINO, and the thickness of the electron transport layer is 2-10 nm, for example, 5 nm.

[0018] According to an embodiment of the present application, the organic solar cell further comprises a metal electrode, which is a metal Ag electrode, and the thickness of the metal electrode is 70-100 nm, for example, 80 nm.

[0019] According to an embodiment of the present application, the active layer comprises an electron donor and an electron acceptor.

[0020] According to an embodiment of the present application, the electron donor has a structure as shown in Formula I below, or a structure as shown in Formula II below:

[0021]

[0022] In Formula I, X is F, Cl or Br, R and R2 are the same or different, and are independently selected from H, C 1-20 alkyl; n is an integer of 50-200; for example, R and R2 are the same or different, and are independently selected from H or C 2-15 alkyl; n is an integer of 50-200; for example, R and R2 are the same or different, and are independently selected from H or C

[0023]

[0024]

[0025] In Formula II, X is F, Cl or Br, R and R3 are the same or different, and are independently selected from H, C 1-20 alkyl; n is an integer of 50-200; for example, R and R3 are the same or different, and are independently selected from H or C 2-15 alkyl; n is an integer of 50-200; for example, R and R3 are the same or different, and are independently selected from H or C

[0026] Preferably, the electron donor is selected from one or both of PM6 and D18-Cl, wherein the structural formulae of PM6 and D18-Cl are shown as follows, respectively:

[0027]

[0028] In PM6, R is 2-ethylhexyl.

[0029] According to an embodiment of the present application, the electron acceptor is selected from IT-4F or IDIC, or has a structure as shown in Formula III below:

[0030]

[0031] In formula III, X is F, Cl, Br or CF3, R1and R4are the same or different, and are independently selected from H, C 1-20 one of alkyl, for example, R1and R4are the same or different, and are independently selected from H or C 2-15 alkyl.

[0032] Preferably, the electron acceptor is selected from at least one of Y6, L8-BO, BTP-BO-4F, BTP-eC9, IT-4F, IDIC, ITIC, wherein the structures of Y6, L8-BO, BTP-BO-4F and BTP-eC9, IT-4F and IDIC are shown as follows, respectively:

[0033]

[0034] According to an embodiment of the present application, the mass ratio of electron donor to electron acceptor in the active layer is 5:1-1:5, for example, 4:1-1:4, 3:1-1:4 or 2:1-1:2.

[0035] According to an embodiment of the present application, the total concentration of electron donor and electron acceptor in the active layer configured before coating is 10-22 mg / mL, for example, 13-20 mg / mL.

[0036] According to an embodiment of the present application, the organic solar cell comprises, from bottom to top, a substrate, a hole transport layer, an active layer, an electron transport layer and a metal electrode arranged in sequence; or, comprises, from bottom to top, a substrate, an electron transport layer, an active layer, a hole transport layer and a metal electrode arranged in sequence.

[0037] In some embodiments of the present application, the method for solvent vapor annealing the active layer of the organic solar cell comprises:

[0038] (1) coating a hole transport layer on a substrate, and performing a thermal annealing treatment;

[0039] (2) coating an active layer on the hole transport layer, and performing a solvent vapor annealing treatment;

[0040] (3) coating an electron transport layer on the active layer;

[0041] (4) evaporating a metal electrode on the electron transport layer to obtain the organic solar cell;

[0042] Alternatively,

[0043] a. coating an electron transport layer on a substrate;

[0044] b. coating an active layer on the electron transport layer, and performing a solvent vapor annealing treatment;

[0045] c. evaporating a hole transport layer on the active layer, and performing a thermal annealing treatment;

[0046] d. evaporating a metal electrode on the hole transport layer to obtain the organic solar cell.

[0047] According to an embodiment of the present application, in step (1) or c, the thermal annealing treatment has a temperature of 120-180℃, and a time of 10-30min.

[0048] According to an embodiment of the present application, in step (2) or step b, the solvent vapor annealing treatment comprises two steps of heating after injecting solvent and heating after removing the substrate, and the two steps of heating have a temperature of 20-90℃, and a time of 0.5-10min. For example, the heating after injecting solvent and the heating after removing the substrate have a temperature of 20℃, 40℃, 60℃, 80℃ or 90℃, and a time of 30s, 1min, 2min, 4min, 5min or 10min.

[0049] In the present application, the coating method is spin coating.

[0050] According to an embodiment of the present application, in step (2) or b, the active layer is spin coated at a speed of 2000-5000rpm, for example, 2000rpm, 3000rpm, 3500rpm, 4000rpm, 4500rpm or 5000rpm, and a time of 30-60s.

[0051] The present application also provides an organic solar cell prepared by the above method.

[0052] In some embodiments of the present application, the organic solar cell comprises, from bottom to top, a substrate (consisting of transparent glass and transparent conductive electrode ITO), a hole transport layer PEDOT:PSS (30nm), an active layer (150nm), an electron transport layer PDINO (5nm) and a metal electrode Ag (80nm); wherein the active layer comprises an electron donor D18-Cl and an electron acceptor Y6; the mass ratio of the electron donor to the electron acceptor is 1:1.6.

[0053] Alternatively, the electron acceptor is Y6 and BTP-eC9; the electron donor is D18-Cl; the mass ratio of D18-Cl, Y6 and BTP-eC9 is 1:1.4:0.2.

[0054] Advantages of the present application

[0055] 1. Solvent vapor annealing (SVA) is a solution-aided method, which is cost-effective and can improve the crystallinity of the organic molecule thin film in the active layer.

[0056] 2. By exposing the active layer of the organic solar cell to an environment full of solvent vapor, the molecules constituting the active layer will reorganize with a higher degree of order.

[0057] 3. The availability of materials facilitates commercialization and has a good application prospect.

[0058] 4. The vapor annealing is simpler to achieve, the preparation process of the organic solar cell is optimized, and a higher performance organic solar cell is obtained.

[0059] In summary, the method of the present application adds a substrate with a cavity in the center between the substrate and the heating table to slow down heat conduction and prolong the solvent evaporation time. The solvent is injected into the cavity for annealing; the small surface area of the cavity will reduce the evaporation of the solvent, which is beneficial to the morphology control of the active layer; on the other hand, the presence of the substrate makes the ITO not in direct contact with the heating table, which greatly slows down the intermolecular rearrangement caused by heating, so that the solvent erosion of the active layer is dominant at this stage. Therefore, the morphology of the non-equilibrium active layer can be adjusted to a more favorable morphology state for photovoltaic performance. Compared with the conventional solvent vapor annealing method, the photovoltaic performance of the organic solar cell is significantly improved. BRIEF DESCRIPTION OF DRAWINGS

[0060] Figure 1 A structural schematic diagram of an organic solar cell provided by the present application.

[0061] Figure 2 The current density (current density) and voltage (voltage) characteristic curve of the organic solar cell prepared for Comparative Example 1 under standard test conditions (AM1.5, 100 mW / cm 2 ).

[0062] Figure 3 The current density (current density) and voltage (voltage) characteristic curve of the organic solar cell prepared for Example 1 under standard test conditions (AM1.5, 100 mW / cm 2 ).

[0063] Figure 4 The current density (current density) and voltage (voltage) characteristic curve of the organic solar cell prepared for Comparative Example 2 under standard test conditions (AM1.5, 100 mW / cm 2 ).

[0064] Figure 5 Current density and voltage characteristics of the organic solar cell prepared for Example 2 under standard test conditions (AM1.5, 100 mW / cm 2 ) are shown in the following graph.

[0065] Figure 6 External quantum efficiency (EQE) of the organic solar cell provided for Example 1 is shown in the following graph; the deviation of the integrated current from the current under standard test is controlled within 3%.

[0066] Figure 7 External quantum efficiency (EQE) of the organic solar cell provided for Example 2 is shown in the following graph; the deviation of the integrated current from the current under standard test is controlled within 3%.

[0067] Figure 8 Schematic diagram of the operation of the conventional solvent vapor annealing and the solvent vapor annealing of the present application. DETAILED DESCRIPTION

[0068] The technical solutions of the present application will be further described in detail below in combination with specific examples. It should be understood that the following examples are only illustratively used to explain and describe the present application, and should not be interpreted as limiting the scope of protection of the present application. Any technology realized based on the above description of the present application is covered within the scope of protection intended by the present application.

[0069] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0070] Comparative Example 1

[0071] As shown in the following graph, the current density and voltage characteristics of the organic solar cell prepared for Example 1 under standard test conditions (AM1.5, 100 mW / cm Figure 1 The organic solar cell includes, from bottom to top, a substrate (consisting of transparent glass and transparent conductive electrode ITO), a hole transport layer PEDOT:PSS, an active layer, an electron transport layer PDINO, and a metal electrode Ag;

[0072] The material for preparing the active layer includes an electron donor, an electron acceptor, and a solvent deuterated chloroform; the electron donor is D18-Cl; the electron acceptor is Y6; the mass ratio of the electron donor to the electron acceptor is 1:1.6;

[0073] The thickness of the active layer is 150 nm;

[0074] The preparation method of the active layer is: dissolving and uniformly mixing D18-Cl and Y6 in deuterated chloroform, and heating and mixing stirring to obtain the active layer of the organic solar cell. The total concentration of the mixture of the electron donor and the electron acceptor in the deuterated chloroform is 13 mg / mL.

[0075] The method for preparing the organic solar cell comprises:

[0076] S1: ultrasonic cleaning the substrate composed of transparent glass and transparent conductive electrode ITO with cleaning solution, deionized water, acetone and isopropanol respectively, and blowing dry with nitrogen after cleaning;

[0077] S2: placing the substrate blown dry with nitrogen into an ozone cleaning machine for treatment for 20 min, spin-coating a hole transport layer material PEDOT:PSS on the substrate in air (spin-coating speed 4500 rpm, spin-coating time 30 s, hole transport layer thickness 30 nm), and then performing thermal annealing treatment (150℃, 20 min) on the hole transport layer in air;

[0078] S3: placing the substrate with the spin-coated hole transport layer into a nitrogen-filled glove box, and spin-coating the active layer on the hole transport layer (spin-coating speed 2500 rpm, spin-coating time 30 s);

[0079] S4: spin-coating an electron transport layer material PDINO on the active layer in the nitrogen-filled glove box (spin-coating speed 3000 rpm, spin-coating time 30 s, electron transport layer thickness 5 nm);

[0080] S5: evaporating an Ag electrode (electrode thickness 80 nm) on the electron transport layer in the nitrogen-filled glove box to obtain the organic solar cell.

[0081] The cell performance of the organic solar cell is: open-circuit voltage: 0.882 V; short-circuit current of the cell: 26.11 mA / cm 2 ; fill factor: 72.96%; energy conversion efficiency: 16.79%.

[0082] Example 1

[0083] The difference between this example and Example 1 is that vapor annealing is performed after spin-coating the active layer. The vapor annealing comprises two steps of injecting a solvent into the cavity of the substrate and then heating (80℃, 2 min), and then removing the substrate and heating at a temperature and time of (80℃, 5 min) respectively. The solvent used in the vapor annealing is carbon disulfide; the amount used is 150 ul.

[0084] A substrate with a hollow center is used in the vapor annealing process. The substrate has a thickness of 0.6 cm, a diameter of 9 cm, a center hole diameter of 0.8 cm, and a substrate area of 1 cm-2 ITO area is 0.04 cm -2 The substrate is placed under the substrate glass sheet. The detailed operation process is shown in Figure 8

[0085] The cell performance parameters of the obtained organic solar cell are: open circuit voltage: 0.858 V; short circuit current of the cell: 28.03 mA / cm 2 ; fill factor: 76.68%; energy conversion efficiency: 18.44%; cell integral current: 27.04 mA / cm 2 .

[0086] Comparative Example 2

[0087] The difference between this example and Example 1 is only that the electron acceptor is Y6 and BTP-eC9; the mass ratio of D18-Cl, Y6 and BTP-eC9 is 1:1.4:0.2.

[0088] The cell performance of the organic solar cell is: open circuit voltage: 0.894 V; short circuit current of the cell: 26.44 mA / cm 2 ; fill factor: 71.68%; energy conversion efficiency: 16.95%.

[0089] Example 2

[0090] The difference between this example and Comparative Example 2 is only that solvent vapor annealing is performed after spin coating of the active layer, and the heating temperature and time after injection of the solvent are 80°C and 2 min, respectively. The heating temperature and time after removing the substrate are 80°C and 5 min, respectively. The solvent used for the vapor annealing is carbon disulfide; the amount used is 150 μl.

[0091] The cell performance parameters of the prepared organic solar cell are: open circuit voltage: 0.861 V; short circuit current of the cell: 28.54 mA / cm 2 ; fill factor: 76.05%; energy conversion efficiency: 18.69%; cell integral current: 28.21 mA / cm 2 .

[0092] Comparative Example 3

[0093] The same materials as used in Example 1 are used, except that a conventional vapor annealing method is used, and the heating temperature and time are the same as in Example 1.

[0094] The cell performance parameters of the organic solar cell prepared in Comparative Example 3 are: open circuit voltage: 0.861 V; short circuit current of the cell: 26.94 mA / cm 2 ​; fill factor: 75.40%; energy conversion efficiency: 17.49%; battery integrated current: 25.87 mA / cm 2 .

[0095] Comparative Example 4

[0096] The same materials as used in Example 2 were used, except that a conventional solvent annealing method was used, with the same heating temperature and time as in Example 2.

[0097] The battery performance parameters of the organic solar cell prepared in Comparative Example 4 were: open circuit voltage: 0.865 V; short circuit current of the battery: 27.435 mA / cm 2 ; fill factor: 74.88%; energy conversion efficiency: 17.76%; battery integrated current: 26.41 mA / cm 2 .

[0098] From the battery performance parameters of the organic solar cells prepared in Comparative Examples 1 and 3, and Examples 2 and 4, it can be seen that the solvent vapor annealing method of the present application can significantly improve the crystallinity of the organic molecule thin film in the active layer relative to the conventional solvent vapor annealing method, thereby greatly improving the device performance of the organic solar cell.

[0099] The above has exemplarily described the embodiments of the present application. However, the protection scope of the present application is not limited to the above-described embodiments. Any modification, equivalent replacement, improvement, etc. made by those skilled in the art within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method of solvent vapor annealing an active layer of an organic solar cell, characterized in that, The method comprises the following steps: The substrate is heated to perform solvent vapor annealing on the active layer.

2. The method of claim 1, wherein, The thickness of the substrate is greater than 0.5 cm. Preferably, the diameter of the cavity of the substrate is 0.5-4 cm. Preferably, the substrate is made of plastic.

3. The method according to claim 1 or 2, characterized in that, The amount of solvent in the cavity is 100-300 μl. Preferably, the solvent added into the cavity is at least one of DCM, CF, CS2 or THF.

4. The method according to any one of claims 1 to 3, characterized in that, The substrate is made of transparent glass and transparent conductive electrode ITO. Preferably, the hole transport layer is made of PEDOT:PSS, and the thickness of the hole transport layer is 10-40 nm. Preferably, the electron transport layer is made of PDINO, and the thickness of the electron transport layer is 2-10 nm. Preferably, the organic solar cell further comprises a metal electrode, which is a metal Ag electrode, and the thickness of the metal electrode is 70-100 nm. Preferably, the active layer comprises an electron donor and an electron acceptor. Preferably, the electron donor has the structure shown in Formula I or Formula II. In formula I, X is F, Cl or Br, R and R2are the same or different and independently of each other selected from H, C 1-20 one of alkyl; n is an integer from 50 to 200; In formula II, X is F, Cl or Br, R and R3are the same or different, independently of each other selected from H, C 1-20 one of alkyl; n is an integer of 50-200. Preferably, the electron donor is selected from PM6 and D18-Cl. The structures of PM6 and D18-Cl are shown in the following formulae. In PM6, R is 2-ethylhexyl. Preferably, the electron acceptor is selected from IT-4F or IDIC, or has the structure shown in Formula III. In formula III, X is F, Cl, Br or CF3, R1and R4are the same or different, independently of one another selected from H, C 1-20 one of the alkyl groups. Preferably, the electron acceptor is selected from at least one of Y6, L8-BO, BTP-BO-4F, BTP-eC9, IT-4F, IDIC, ITIC, wherein the structures of Y6, L8-BO, BTP-BO-4F, BTP-eC9, IT-4F and IDIC are shown in the following formulae. Preferably, the mass ratio of the electron donor to the electron acceptor in the active layer is 5:1-1:5, for example, 4:1-1:4, 3:1-1:4 or 2:1-1:

2.

5. The method according to any one of claims 1 to 4, characterized in that, The total concentration of the electron donor and the electron acceptor in the solvent in the active layer configured before coating is 10-22 mg / mL.

6. The method according to any one of claims 1 to 5, characterized in that, The method for performing solvent vapor annealing on the active layer of the organic solar cell comprises the following steps: (1) coating a hole transport layer on a substrate and performing heat annealing treatment; (2) coating an active layer on the hole transport layer and performing solvent vapor annealing treatment; (3) coating an electron transport layer on the active layer; (4) evaporating a metal electrode on the electron transport layer to obtain the organic solar cell; or c. coating an electron transport layer on a substrate; d. coating an active layer on the electron transport layer and performing solvent vapor annealing treatment; c. evaporating a hole transport layer on the active layer and performing heat annealing treatment; d. evaporating a metal electrode on the hole transport layer to obtain the organic solar cell. ​ 7. The method of claim 6, wherein, In step (1) or c, the temperature of the thermal annealing treatment is the same or different, and independently is 120-180℃, and the time of the thermal annealing treatment is the same or different, and independently is 10-30min.

8. The method according to claim 6 or 7, characterized in that, In step (2) or step b, the solvent vapor annealing treatment comprises two steps of heating after injecting the solvent into the cavity and heating after removing the substrate, the temperature of the two steps of heating is the same or different, and independently is 20-90℃, and the time of the treatment is the same or different, and independently is 0.5-10min.

9. The organic solar cell prepared by the method of any one of claims 1-8.

10. The organic solar cell according to claim 9, characterized in that The organic solar cell comprises, from bottom to top, a substrate (consisting of transparent glass and transparent conductive electrode ITO), a hole transport layer PEDOT:PSS (30nm), an active layer (150nm), an electron transport layer PDINO (5nm) and a metal electrode Ag (80nm); wherein the active layer comprises an electron donor D18-Cl and an electron acceptor Y6; the mass ratio of the electron donor to the electron acceptor is 1:1.6; Alternatively, the electron acceptor is Y6 and BTP-eC9; the electron donor is D18-Cl; the mass ratio of the D18-Cl, Y6 and BTP-eC9 is 1:1.4:0.2.

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