Organic photovoltaic device based on gradient donor-acceptor ratio, and preparation method and application thereof

Abstract

The application relates to the technical field of organic photovoltaic devices, in particular to an organic photovoltaic device based on a gradient acceptor proportion and a preparation method and application thereof. A first active layer material is scraped on a hole transport layer along a defined direction to prepare a first active layer with a gradually decreasing thickness along the defined direction; at the end point of scraping the first active layer, a second active layer material is scraped along the opposite direction of the defined direction to prepare a second active layer with a gradually decreasing thickness along the opposite direction of the defined direction; the first active layer and the second active layer have the same thickness gradient. After the donor or acceptor in the second active layer is mixed with the first active layer, the proportion of the donor and the acceptor in the whole active layer gradually changes, thereby forming a gradient acceptor proportion. The active layer based on the gradient acceptor proportion provided by the application realizes a large range and dense acceptor proportion change within a limited length range, and can be applied to the screening of solution processing conditions of organic solar cells as a high-throughput screening model.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of organic photovoltaic devices, in particular to an organic photovoltaic device based on gradient acceptor proportion and a preparation method and application thereof. BACKGROUND

[0002] The information disclosed in this Background section is only for the purpose of increasing an understanding of the general background of the application and does not necessarily constitute an admission or a recognition that the information forms part of the prior art that is already known in any country in the world.

[0003] Organic photovoltaic cells can be prepared by solution method, which is easy to realize large-area and low-cost roll-to-roll printing and is considered as one of the most promising photovoltaic technologies. Organic photovoltaic cells use organic materials as light-sensitive active layers and do not contain toxic heavy metal ions such as lead. The photoelectric conversion efficiency of small-area organic photovoltaic devices based on bulk heterojunction structure in the laboratory has exceeded 20%, becoming the next generation of photovoltaic technology.

[0004] The light-active layer of high-efficiency organic solar cells adopts a blended bulk heterojunction structure, which mixes electron donors and electron acceptors to form an interpenetrating network structure, realizing effective exciton dissociation and charge transport. Since the composition ratio of donors and acceptors in the active layer affects the morphology of the blended bulk heterojunction and the absorption of light, it further affects the physical processes such as exciton generation, exciton separation, and carrier transport, which are closely related to the energy conversion efficiency and stability of organic solar cells. In recent years, a large number of new donor and acceptor organic photovoltaic materials have emerged, which are expensive. Optimizing the solution processing parameters that affect the performance and stability of organic solar cells, including the ratio between different donor and acceptor materials, requires a lot of manpower and resources, so there is an urgent need for a high-throughput manufacturing method to accelerate this process. SUMMARY

[0005] In order to overcome the above problems, the present application provides an organic photovoltaic device based on gradient acceptor proportion and a preparation method and application thereof.

[0006] In a first aspect of the present application, a preparation method of an organic photovoltaic device based on gradient acceptor proportion is provided, comprising:

[0007] (1) under an air atmosphere, a hole transport layer is prepared by blade coating on the surface of conductive glass;

[0008] (2) under an air atmosphere, a first active layer material is blade coated on the hole transport layer along a defined direction to prepare a first active layer with a thickness gradually decreasing along the defined direction; at the end point of blade coating the first active layer, a second active layer material is blade coated on the first active layer along the opposite direction of the defined direction to prepare a second active layer with a thickness gradually decreasing along the opposite direction of the defined direction; under an inert atmosphere, annealing is performed to prepare an active layer;

[0009] (3) under air atmosphere, the electron transport layer is prepared by doctor blading on the surface of the active layer;

[0010] (4) under vacuum condition, the cathode is prepared on the electron transport layer, and the process is completed.

[0011] In a second aspect of the present application, an organic photovoltaic device based on gradient donor-acceptor ratio is provided, which comprises a substrate, an anode, a hole transport layer, an active layer, an electron transport layer and a cathode which are sequentially stacked from bottom to top.

[0012] The active layer has a gradient donor-acceptor ratio.

[0013] In a third aspect of the present application, the application of the organic photovoltaic device based on gradient donor-acceptor ratio prepared by the preparation method of the first aspect in screening solution processing conditions of organic solar cells is provided.

[0014] The present application has the following advantages:

[0015] (1) The active layer based on gradient donor-acceptor ratio provided by the present application realizes a wide range and dense donor-acceptor ratio change within a limited length range (7.5 cm), and can be applied to the screening of solution processing conditions of organic solar cells as a high-throughput screening model.

[0016] (2) Compared with traditional organic solar cells, the organic photovoltaic device prepared by the method provided by the present application shows the sensitivity of energy conversion efficiency and stability to the donor-acceptor ratio, which facilitates the exploration of the relationship between performance and stability and the donor-acceptor ratio.

[0017] (3) The organic photovoltaic device based on gradient donor-acceptor ratio provided by the present application has a simpler preparation process, which greatly reduces the time and resource consumption of preparing and screening solution processing conditions of organic solar cells. BRIEF DESCRIPTION OF DRAWINGS

[0018] The drawings accompanying the specification of the present application serve to provide a further understanding of the present application, and the schematic embodiments of the present application and the description thereof serve to explain the present application, and do not constitute an improper limitation on the present application.

[0019] Figure 1 FIG. 1 is a structural schematic diagram of the organic photovoltaic device based on gradient donor-acceptor ratio;

[0020] Figure 2 FIG. 2 is a sampling point of the organic photovoltaic device based on gradient donor-acceptor ratio;

[0021] Figure 3Sampling points of the active layer thin film with gradient donor-acceptor PM6:L8-BO ratio prepared in Examples 2-4, wherein a is the sampling point position of the ultraviolet-visible absorption spectrum, and b is the sampling point position of the steady-state fluorescence spectrum; the sampling point position of the ultraviolet-visible absorption spectrum is measured at three rows and nine columns of points uniformly in the entire film, and the different positions and the acceptor absorption peak value ratio are indicated by the 27 points, and the steady-state fluorescence spectrum sampling point position is uniformly measured at 15 points on the central line of the film;

[0022] Figure 4 The ultraviolet-visible absorption spectrum (b-d) of the active layer thin film with gradient donor-acceptor PM6:L8-BO ratio (a) prepared in Example 2 at different points, the acceptor absorption peak value ratio (e) at different positions, and the steady-state fluorescence spectrum (f); wherein 1-1 in the b figure indicates the first point-first column according to the sampling point shown in the figure, 2-1 indicates the second point-first column, and 3-1 indicates the third point-first column; Figure 3

[0023] Figure 5 The ultraviolet-visible absorption spectrum (b-d) of the active layer thin film with gradient donor-acceptor PM6:L8-BO ratio (a) prepared in Example 3 at different points, the acceptor absorption peak value ratio (e) at different positions, and the steady-state fluorescence spectrum (f); wherein 1-2 in the b figure indicates the first point-second column according to the sampling point shown in the figure, 2-2 indicates the second point-second column, and 3-2 indicates the third point-second column; Figure 3

[0024] Figure 6 The ultraviolet-visible absorption spectrum (b-d) of the active layer thin film with gradient donor-acceptor PM6:L8-BO ratio (a) prepared in Example 4 at different points, the acceptor absorption peak value ratio (e) at different positions, and the steady-state fluorescence spectrum (f); wherein 1-3 in the b figure indicates the first point-third column according to the sampling point shown in the figure, 2-3 indicates the second point-third column, and 3-3 indicates the third point-third column; Figure 3

[0025] Figure 7 Summary diagram of device performance parameters of the active layer organic photovoltaic device based on gradient donor-acceptor ratio in Example 2, including open circuit voltage (a), short circuit current density (b), fill factor (c), and power conversion efficiency (d);

[0026] Figure 8 a and b are both device performance decay diagrams of the active layer organic photovoltaic device based on gradient donor-acceptor ratio in Example 2 under one sunlight and 60°C heating conditions;

[0027] Figure 9 ​​​Figure 2 shows the power conversion efficiency of the organic photovoltaic device with different donor-acceptor ratios under one sun illumination and 60°C heating condition. DETAILED DESCRIPTION

[0028] It should be noted that the following detailed description is exemplary in nature and is intended to provide further description of the application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0029] It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting, as the scope of the application will be limited only by the appended claims. As used herein, unless the context clearly dictates otherwise, the use of the singular herein is not intended to exclude the plural. Furthermore, to the extent that any term is used in the singular herein, we also intend that the plural of said term, and vice versa, also be covered.

[0030] In a first exemplary embodiment of the application, a method for preparing a gradient donor-acceptor ratio based organic photovoltaic device is provided, comprising:

[0031] (1) under air atmosphere, spin-coating a hole transport layer on the surface of conductive glass;

[0032] (2) under air atmosphere, spin-coating a first active layer material on the hole transport layer along a defined direction to prepare a first active layer with gradually decreasing thickness along the defined direction; at the end point of the spin-coating of the first active layer, spin-coating a second active layer material on the first active layer along the opposite direction of the defined direction to prepare a second active layer with gradually decreasing thickness along the opposite direction of the defined direction; annealing under inert atmosphere to prepare an active layer;

[0033] (3) under air atmosphere, spin-coating an electron transport layer on the surface of the active layer;

[0034] (4) under vacuum condition, preparing a cathode on the electron transport layer, and the process is completed.

[0035] In one or more embodiments, in step (2), the end point of the spin-coating of the first active layer is the start point of the spin-coating of the second active layer; the end point of the spin-coating of the second active layer is the start point of the spin-coating of the first active layer.

[0036] In one or more embodiments, in step (2), the first active layer is a donor-acceptor blend layer, and the second active layer is a donor layer or an acceptor layer.

[0037] Preferably, the donor material is PM6, and the acceptor material is L8-BO.

[0038] In one or more embodiments, in step (2), the first active layer and the second active layer have a thickness variation of 90-110 nm along the length direction within a length range of 7.5-8 cm.

[0039] The thickness gradient direction of the first active layer is sequentially thinned from the A end to the B end, and the thickness gradient direction of the first active layer is sequentially thinned from the B end to the A end. After the donor or acceptor in the second active layer is mixed with the first active layer, the proportion of the donor and acceptor in the entire active layer gradually changes, thereby forming a gradient of the proportion of the donor and acceptor.

[0040] In one or more embodiments, in step (2), the first active layer and the second active layer have the same scraping speed, which is 10-40 mm / s, preferably 25 mm / s; and the same drop amount, which is 30-70 μL, preferably 45 μL.

[0041] In one or more embodiments, in step (2), the substrate temperature is 60-100°C, preferably 80°C, during scraping; and the substrate is annealed at 40-180°C for 5-10 min, preferably 100°C for 10 min, in an inert atmosphere.

[0042] In one or more embodiments, in step (1), the conductive glass is ITO conductive glass, and before the hole transport layer is prepared, the ITO conductive glass is sequentially ultrasonically cleaned with a cleaning agent, water, acetone, anhydrous ethanol and isopropanol, and is dried by blowing nitrogen, and is then treated with UV for 15-25 min.

[0043] In one or more embodiments, in step (1), the preparation method of the hole transport layer comprises: scraping PEDOT:PSS on the surface of the conductive glass, and annealing at 130-180°C for 10-20 min.

[0044] In one or more embodiments, in step (3), the specific steps for preparing the electron transport layer on the surface of the active layer comprise: scraping a 0.5-1.5 mg / mL F3N-Br solution on the active layer, and the scraping speed is 10-25 mm / s.

[0045] In one or more embodiments, in step (4), the 2.5×10 -4 -5×10 -4 Pa under vacuum conditions, and an Ag electrode of 80-100 nm is prepared by thermal evaporation.

[0046] The second typical embodiment of the present application provides an organic photovoltaic device based on a gradient of the proportion of the donor and acceptor, which comprises, from bottom to top, a substrate, an anode, a hole transport layer, an active layer, an electron transport layer and a cathode.

[0047] wherein the active layer has a gradient donor-acceptor ratio.

[0048] In one or more embodiments, the active layer comprises a first active layer and a second active layer stacked in order from bottom to top, the first active layer being a donor-acceptor blend layer, and the second active layer being a donor layer or an acceptor layer.

[0049] The first active layer and the second active layer have the same thickness gradient along the length direction within a defined length range; the thickness gradient direction of the first active layer is opposite to that of the second active layer.

[0050] Preferably, the first active layer and the second active layer have a thickness variation of 190-210 nm along the length direction within a length range of 7.5-8 cm.

[0051] The thickness gradient direction of the first active layer is opposite to that of the second active layer.

[0052] In one or more embodiments, the substrate is a glass substrate.

[0053] In one or more embodiments, the anode is indium tin oxide (ITO).

[0054] In one or more embodiments, the material of the hole transport layer is PEDOT:PSS.

[0055] In one or more embodiments, the material of the electron transport layer is F3N-Br.

[0056] In one or more embodiments, the cathode is a top metal Ag electrode.

[0057] In one or more embodiments, the donor material is PM6 and the acceptor material is L8-BO.

[0058] A third typical embodiment of the present application provides the use of the organic photovoltaic device based on the gradient donor-acceptor ratio prepared by the preparation method of the first aspect in screening solution processing conditions of organic solar cells.

[0059] In order to enable those skilled in the art to more clearly understand the technical solutions of the present application, the technical solutions of the present application will be described in detail below with specific examples.

[0060] Example 1

[0061] Figure 1 A schematic diagram of a gradient donor-acceptor ratio-based organic photovoltaic device, the gradient donor-acceptor ratio-based organic photovoltaic device comprising, from bottom to top, a substrate, an anode, a hole transport layer, an active layer, an electron transport layer, and a cathode;

[0062] The active layer has a gradient donor-acceptor ratio.

[0063] In the preparation process, the active layer comprises, from bottom to top, a first active layer and a second active layer, the first active layer is a donor-acceptor blend layer, and the second active layer is a donor layer or an acceptor layer; the first active layer and the second active layer have the same thickness gradient in the length direction within a defined length range; the thickness gradient direction of the first active layer is opposite to the thickness gradient direction of the second active layer. Specifically, the first active layer and the second active layer have a thickness change of 90-110 nm in the length direction within a length range of 7.5-8 cm. The length direction within the defined length range has two common endpoints, A and B, respectively; the first active layer thickness gradient direction is sequentially thinned from A to B, and the first active layer thickness gradient direction is sequentially thinned from B to A; after the donor or acceptor in the second active layer is blended with the first active layer, the proportion of the donor and the acceptor in the entire active layer gradually changes, thereby forming a gradient donor-acceptor ratio.

[0064] In this embodiment, the substrate is a glass substrate, the anode is ITO, the material of the hole transport layer is PEDOT:PSS, the material of the electron transport layer is F3N-Br, and the cathode is a top metal Ag electrode.

[0065] Example 2

[0066] A preparation of a gradient donor-acceptor ratio-based organic photovoltaic device:

[0067] (1) The conductive glass is ITO conductive glass; before preparing the hole transport layer, the following operations are performed:

[0068] The ITO conductive glass is sequentially ultrasonically cleaned with cleaning agent, deionized water, acetone, anhydrous ethanol, and isopropyl alcohol, and is dried with nitrogen, and is then treated with UV for 15 min.

[0069] (2) The hole transport layer is prepared by scraping on the surface of the conductive glass, comprising:

[0070] PEDOT:PSS aqueous solution is scraped on the surface of the conductive glass in an air atmosphere, wherein PEDOT:PSS is mixed with deionized water at a ratio of 1:1, the scraping speed is 15 mm / s, the drop volume is 100 μL, the substrate temperature is 60°C, and annealing is performed at 150°C for 10 min.

[0071] (3) The active layer is prepared by scraping on the surface of the hole transport layer, comprising:

[0072] A donor solution with a concentration of 10 mg / mL and an acceptor solution with a concentration of 12 mg / mL were used to prepare the active layer by blade coating on the hole transport layer in an air atmosphere, with o-xylene as the solvent, a blade coating speed of 25 mm / s, a drop volume of 45 μL, and a substrate temperature of 80°C. The active layer was annealed at 100°C for 10 min in a nitrogen atmosphere. During the blade coating process, the first active layer material was coated on the hole transport layer in the defined direction (from the A end to the B end as defined in Example 1), to prepare a first active layer with a gradually decreasing thickness in the defined direction. At the end of the blade coating of the first active layer, the second active layer material was coated in the opposite direction of the defined direction (from the B end to the A end as defined in Example 1), to prepare a second active layer with a gradually decreasing thickness in the opposite direction of the defined direction. During the blade coating process, the end of the blade coating of the first active layer was the start of the blade coating of the second active layer, and the end of the blade coating of the second active layer was the start of the blade coating of the first active layer. The thickness of the first active layer gradually decreased from 110 nm to 90 nm in the length direction within a range of 7.5 cm in the defined direction. The thickness of the second active layer gradually decreased from 110 nm to 90 nm in the length direction within a range of 7.5 cm in the opposite direction of the defined direction. After the donor or acceptor in the second active layer was laminated with the first active layer, the proportion of the donor and acceptor in the entire active layer gradually changed, thereby forming a gradient proportion of the donor and acceptor.

[0073] In this example, the first active layer only contains donor material (the mass ratio of donor to acceptor is 1:0), and the second active layer only contains acceptor material.

[0074] (4) An electron transport layer was prepared on the surface of the active layer by blade coating, including:

[0075] A F3N-Br solution with a concentration of 0.7 mg / mL was blade coated onto the active layer at a blade coating speed of 15 mm / s and a substrate temperature of room temperature.

[0076] (5) A cathode was prepared on the electron transport layer under vacuum conditions, including:

[0077] A 100 nm Ag electrode was prepared by thermal evaporation under vacuum conditions of 4 x 10 -4 Pa.

[0078] Example 3

[0079] This example is different from Example 2 in that the mass ratio of donor to acceptor in the first active layer is 1:2, and the second active layer only contains donor material.

[0080] Example 4

[0081] This example is different from Example 2 in that the mass ratio of donor to acceptor in the first active layer is 1:0.5, and the second active layer only contains donor material.

[0082] Performance parameters of organic solar cells: power conversion efficiency (PCE)

[0083] PCE = J SC × V OC × FF / P in × 100%

[0084] In the formula, J SC is short-circuit current density, V OC is open-circuit voltage, FF is fill factor, P in is incident light intensity (AM1.5G), and PCE can be directly obtained from a solar cell J-V curve test system.

[0085] Figure 4 UV-visible absorption spectra and steady-state fluorescence spectra of the active layer thin film with gradient donor-acceptor PM6:L8-BO ratio prepared in Example 2 at different points can be seen that the absorption peak ratio of the donor-acceptor at different positions is different, representing different donor-acceptor ratios, and the fluorescence peak position of the acceptor has a blue shift trend with the decrease of the donor-acceptor ratio. Figure 5 UV-visible absorption spectra and steady-state fluorescence spectra of the active layer thin film with gradient donor-acceptor PM6:L8-BO ratio prepared in Example 3 at different points can be seen that the ratio of the donor-acceptor is adjusted more greatly, and the fluorescence peak of the acceptor moves to about 840 nanometers, and has a slight blue shift trend with the increase of the donor-acceptor ratio. Figure 6 UV-visible absorption spectra and steady-state fluorescence spectra of the active layer thin film with gradient donor-acceptor PM6:L8-BO ratio prepared in Example 4 at different points can be seen that the ratio of the donor-acceptor is adjusted more greatly, and the fluorescence peak of the acceptor moves to about 880 nanometers, and has no obvious moving trend with the increase of the donor-acceptor ratio.

[0086] Figure 7 The performance summary chart of the device at different points of the active layer thin film with gradient PM6:L8-BO ratio prepared in Example 2 can be seen that with the increase of the donor-acceptor ratio, the open-circuit voltage of the device remains stable, the short-circuit current density increases, and the fill factor decreases. From Figure 8 and Figure 9The device performance decay figures and fitted performance decay rates (fitted using exponential function PCE(t) = PCE(0)exp(-b / t), the fitting parameter 1 / t represents the decay rate) of the devices with different points of the active layer thin film prepared for Example 2 having gradient PM6:L8-BO ratio under one sunlight illumination and 60℃ heating conditions, and the correlation figures of the device performance decay rates with the donor-acceptor ratio can be seen that the device performance decay becomes faster with the increase of the donor-acceptor ratio. Through screening, it can be seen that the donor-acceptor ratio of the device having better performance and light-heat stability is between 1.05 and 1.25. Therefore, by using the method shown in the present application, only a small amount of expensive organic materials is consumed, and the best donor-acceptor ratio photovoltaic device having better performance and better stability can be screened out, which is of great significance for the commercialization and large-scale industrial production of organic photovoltaics.

[0087] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for the preparation of organic photovoltaic devices based on the gradient donor-acceptor ratio, characterized by, The method comprises the following steps: (1) preparing a hole transport layer by blade coating on the surface of conductive glass in air atmosphere; (2) preparing a first active layer with gradually decreasing thickness along a defined direction by blade coating a first active layer material on the hole transport layer in air atmosphere along the defined direction; at the end point of blade coating the first active layer, preparing a second active layer with gradually decreasing thickness along the opposite direction of the defined direction by blade coating a second active layer material on the first active layer along the opposite direction of the defined direction; and annealing in inert atmosphere to prepare an active layer; (3) preparing an electron transport layer by blade coating on the surface of the active layer in air atmosphere; (4) preparing a cathode on the electron transport layer under vacuum condition, thereby obtaining the organic light-emitting diode; In step (2), the end point of blade coating the first active layer is the starting point of blade coating the second active layer, and the end point of blade coating the second active layer is the starting point of blade coating the first active layer. In step (2), the first active layer is a donor-acceptor blend layer, and the second active layer is a donor layer or an acceptor layer.

2. The production method according to claim 1, wherein The donor material is PM6, and the acceptor material is L8-BO.

3. The production method according to claim 1, wherein In step (2), the first active layer and the second active layer have a thickness variation of 190-210 nm along the length direction within a length range of 7.5-8 cm.

4. The production method according to claim 1, wherein In step (2), the blade coating speed of the first active layer and the second active layer is the same, and the drop amount of each time is the same, both of which are 30-70 μL.

5. The production method according to claim 1, wherein In step (2), the substrate temperature is 60-100 ℃ during blade coating, and the annealing is performed at 40-180 ℃ for 5-10 min in inert atmosphere.

6. The production method according to claim 1, wherein In step (1), the conductive glass is ITO conductive glass, and the ITO conductive glass is sequentially ultrasonically cleaned with cleaning agent, water, acetone, anhydrous ethanol and isopropanol, and then dried with nitrogen, and then treated with UV for 15-25 min before preparing the hole transport layer.

7. The production method according to claim 1, wherein In step (1), the method for preparing the hole transport layer comprises blade coating PEDOT:PSS on the surface of the conductive glass, and annealing at 130-180 ℃ for 10-20 min.

8. The production method according to claim 1, wherein In step (3), the specific steps for preparing the electron transport layer on the surface of the active layer comprise blade coating a 0.5-1.5 mg / mL F3N-Br solution on the active layer at a blade coating speed of 10-25 mm / s.

9. The production method according to claim 1, wherein In step (4), 80~100 nm of Ag electrode was prepared by thermal evaporation under a vacuum condition of 2.5x10 -4 ~5x10 -4 Pa.

10. An organic photovoltaic device based on a gradient in the donor-acceptor ratio, characterized in that, The organic light-emitting diode comprises, from bottom to top, a substrate, an anode, a hole transport layer, an active layer, an electron transport layer and a cathode. The active layer has a gradient donor-acceptor ratio. The active layer comprises, from bottom to top, a first active layer and a second active layer, the first active layer is a donor-acceptor blend layer, and the second active layer is a donor layer or an acceptor layer. The first active layer and the second active layer have the same thickness gradient along the length direction within a defined length range; the thickness gradient direction of the first active layer is opposite to the thickness gradient direction of the second active layer.

11. The organic photovoltaic device based on gradient donor-acceptor ratio according to claim 10, wherein, The first active layer and the second active layer have a thickness variation of 90-110 nm along the length direction within a length range of 7.5-8 cm.

12. The organic photovoltaic device based on gradient donor-acceptor ratio according to claim 10, wherein, The substrate is a glass substrate.

13. The organic photovoltaic device based on gradient donor-acceptor ratio according to claim 10, wherein, The anode is indium tin oxide.

14. The organic photovoltaic device based on gradient donor-acceptor ratio according to claim 10, wherein, The material of the hole transport layer is PEDOT:PSS.

15. The organic photovoltaic device based on gradient donor-acceptor ratio according to claim 10, wherein, The material of the electron transport layer is F3N-Br.

16. The organic photovoltaic device based on gradient donor-acceptor ratio according to claim 10, wherein, The cathode is a top metal Ag electrode.

17. The organic photovoltaic device based on gradient donor-acceptor ratio according to claim 10, wherein, The donor material is PM6 and the acceptor material is L8-BO. The donor material is PM6 and the acceptor material is L8-BO.

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