CN114649479A - Composite cathode electrode layer for positive organic solar cell and preparation method thereof - Google Patents

Abstract

The invention relates to a composite cathode electrode layer for a forward organic solar cell and a preparation method thereof. The composite cathode electrode layer is a double-layer metal ytterbium Yb and silver Ag; one side of the Yb layer is an Ag layer, and the other side is an active layer of a forward organic solar cell. Further, the thickness of Yb is 0.5nm-20nm, and the thickness of Ag is 5nm-500nm. The double-layer electrode of Yb and Ag can reduce its work function and match the LUMO energy level of the commonly used organic active layer acceptor material, so that ohmic contact is formed between the organic active layer and the metal cathode, and the device performance of organic solar cells is improved. . The method for preparing the composite cathode electrode layer adopts the vacuum thermal evaporation coating method. Compared with the prior art, the present invention has the significant advantages that the cathode interface layer is not used, the preparation steps are reduced, and the industrialized production cost is reduced.

Description

A composite cathode electrode layer for forward organic solar cells and preparation method thereof

technical field

The invention relates to an organic solar cell device, in particular to a composite cathode electrode layer for a forward organic solar cell and a preparation method thereof.

Background technique

Organic solar cells (Organic Solar Cells, OSC) have been intensively studied for many years and have begun to be applied in the market due to their translucency, flexibility and rollability, light weight and portability, as well as color and shape designability. The working principle of solar cells is to use photovoltaic devices to convert light energy into electrical energy. During the conversion process, sunlight irradiates organic materials, which absorb photons and generate excitons, that is, electron-hole pairs. Electron-hole pairs occur under the action of a built-in electric field. They are separated and move toward the corresponding electrodes respectively, and are finally collected by the electrodes on both sides to generate electromotive force. If the two ends are connected to an external circuit, the photo-generated electromotive force can form a current, completing the conversion from light to electricity. OSC is generally a sandwich structure, including a cathode, an anode and an organic photoactive layer sandwiched in the middle. In traditional OSC devices, the positive OSC anode functions to collect holes, and the cathode functions to collect electrons. The most commonly used cathode materials for positive OSCs are silver (Ag), aluminum (Al), etc., which form ohmic contacts on the metal surface of the active layer to improve electron collection efficiency. However, the work function of such metal cathodes is relatively high, about -4.3 eV. In order to reduce the cathode work function, reduce the series resistance and charge recombination loss, and form a good ohmic contact between the active layer and the electrode, it is necessary to insert a cathode interface layer between the cathode and the active layer, which is helpful for electron transport and cathode collection of electrons. .

Common cathode interface materials mainly include solution-preparable organic polymer PFN (Adv. Mater. 2011, 23, 4636-4643) and its derivative PFN-Br, but these organic polymers have difficult synthetic routes and high production costs. , and in the process of module preparation, the material utilization rate of the solution coating method is low, which is not conducive to the industrialized preparation of organic solar cells.

SUMMARY OF THE INVENTION

The object of the present invention is a composite cathode electrode layer for a forward organic solar cell and a preparation method thereof.

For realizing the purpose of the present invention, concrete technical solutions are as follows:

A composite cathode electrode layer for a forward organic solar cell is a double-layer metal ytterbium Yb and silver Ag; one side of the Yb layer is an Ag layer, and the other side is an active layer of the forward organic solar cell.

Further, the thickness of Yb is 0.5nm-20nm, and the thickness of Ag is 5nm-500nm. In a more preferred solution, the thickness of Yb is 0.5nm-20nm, and the thickness of Ag is 5nm-500nm, and the purity of the Yb layer is ≥99.9%.

A method for preparing a composite cathode electrode layer, wherein the composite cathode electrode layer is prepared by a vacuum thermal evaporation coating method.

Ag层的镀膜速率为

优选的，真空度是5×10^-6～1×10^-7Torr，Yb层的镀膜速率为

Ag层的镀膜速率为

Further, the vacuum degree of the vacuum thermal evaporation coating method is 1×10 ^-5 to 1×10 ^-8 Torr, and the coating rate of the Yb layer is

The deposition rate of the Ag layer is

Preferably, the degree of vacuum is 5×10 ^-6 to 1×10 ^-7 Torr, and the coating rate of the Yb layer is

The deposition rate of the Ag layer is

The principle of the invention is as follows: Yb and Ag double-layer metal is used as the cathode layer of the forward OSC device, because the work function of Yb is -2.4～-2.6eV, the work function of Ag is -4.26～-4.4eV, and the difference between Yb and Ag is The double-layer electrode can reduce its work function and better match the LUMO energy level (generally -4.0 to -4.3 eV) of the commonly used organic active layer acceptor material. The ohmic contact is formed between the organic active layer and the metal cathode, which improves the device performance of the organic solar cell.

Compared with the prior art, the present invention has the following significant advantages:

1. The composite cathode layer provided by the present invention is preferably a vacuum thermal evaporation coating method, and the metal Yb is directly evaporated on the substrate without using a cathode interface layer, and the metal Yb does not need to be synthesized. device preparation;

2. The composite cathode layer provided by the present invention is preferably prepared by vacuum thermal evaporation coating method, which is to heat and evaporate Yb and Ag to make them vaporize and deposit on the surface of the active layer, which requires less raw materials and can reduce the use of materials. Waste, reduce production costs, and facilitate the industrialized preparation of organic solar cells;

3. The composite cathode layer provided by the present invention is applied to the forward organic solar cell device, and the performance is slightly better than that of the device with the cathode interface layer (PFN-Br) added, the energy conversion rate is increased by 2.8%, and the filling factor is increased. 2.5%.

Description of drawings

Fig. 1 is the structure schematic diagram of the forward organic solar cell device of the present invention;

In the figure: 101 substrate; 102 anode; 103 hole transport layer (HTL); 104 active layer; 105 cathode.

Detailed ways

The present invention will be further described in detail below with reference to specific embodiments, but the present invention is not limited thereto. The assay methods not described in detail in the present invention are all conventional techniques in the art.

The following four parameters are the most direct standards to measure the battery performance, as follows:

1. Short-circuit current density (Jsc):

The operating current of the OSC under short-circuit conditions, that is, the current (A) output by both ends of the photovoltaic device when the external circuit voltage → 0;

2. Open-circuit voltage (Voc)

The output voltage of OSC under open-circuit condition, that is, the output voltage (V) at both ends of the photovoltaic device when the external circuit voltage→∞;

3. Fill Factor (FF)

The ratio of the maximum output power Pm of the photovoltaic device to the product of Jsc and Voc:

4. Photoelectric conversion efficiency PCE

It refers to the ratio of the output electric energy to the input light energy, which is the most direct response to the quality of the battery.

In the formula, Pin is the incident light power per unit area (W), and L is the effective area of the photovoltaic device (m ² ).

Forward organic solar cells may include double-layer solar cells, bulk heterojunction solar cells, PMHJ (planer-mixed hertero junction) solar cells, and tandem solar cells. Preferably, the forward organic solar cell structure as shown in FIG. 1 includes: a substrate (101), an anode (102), a hole transport layer (103), an active layer (104), and a cathode (105). Wherein, the cathode is the composite cathode electrode layer provided by the present invention. in:

The substrate (101) is transparent. Organic solar cells require a transparent bottom to absorb incident light. The substrate can be rigid or elastic. The substrate can be plastic or glass. Preferably the substrate has a smooth surface. Substrates free of surface defects are particularly desirable. In a preferred embodiment, the substrate is flexible, optionally a polymer film or plastic, with a glass transition temperature Tg above 150°C, preferably above 200°C, more preferably above 250°C, most preferably over 300°C. Examples of suitable flexible substrates are poly(ethylene terephthalate) (PET) and polyethylene glycol (2,6-naphthalene) (PEN).

The anode (102) may comprise a conductive metal or metal oxide, or a conductive polymer. The anode can easily receive holes output from the hole transport layer (HTL) or the active layer. In one embodiment, the absolute value of the difference between the work function of the anode and the HOMO level or valence band level of the donor in the active layer or the p-type semiconductor material as the HTL is less than 0.5 eV, preferably less than 0.3 eV , preferably less than 0.2eV. Examples of anode materials include, but are not limited to, Al, Cu, Au, Ag, Mg, Fe, Co, Ni, Mn, Pd, Pt, ITO (fumed tin oxide), aluminum doped zinc oxide (AZO), and the like. Other suitable anode materials are known and can be readily selected for use by those of ordinary skill in the art. The anode material may be deposited using any suitable technique, such as a suitable physical vapor deposition method, including radio frequency magnetron sputtering, vacuum thermal evaporation, electron beam (e-beam), and the like. In certain embodiments, the anode is pattern-structured. Patterned ITO conductive substrates are commercially available and can be used to fabricate devices according to the present invention.

The hole transport layer (103) is a material that receives holes from the active layer and transports the holes to the anode, and as the hole transport material, a material having a high hole mobility is suitable. As specific examples, suitable organic HTM materials may optionally contain compounds containing the following structural units: phthalocyanines, porphyrins, amines, aromatic amines, biphenyl-like triarylamines, thiophenes, thiophenes such as dithienothiophene and thiophene, pyrrole , aniline, carbazole, indanazonium fluorene and their derivatives. In addition, suitable HTMs also include polymers containing fluorocarbons, polymers containing conductive dopants, conductive polymers such as PEDOT:PSS.

The active layer (104) is suitable for a material capable of absorbing sunlight, generating excitons and separating them into electrons and holes, and having a wide spectral absorption range. It can be composed of one or more materials. A typical example is the active layer material composed of thiophene polymer or its derivative and fullerene or its derivative, which is combined with the receptor. Currently, the typical and commonly used material is Materials including donor material PM6 (Adv. Mater. 2015, 27, 4655-4660) and acceptor material Y6 (Joule 3, 1140-1151, April 17, 2019) blended.

The cathode (105) may comprise a conductive metal or metal oxide. The cathode can easily accept electrons output from the active layer or ETL. The cathode material can be deposited using any suitable technique, such as a suitable physical vapor deposition method, including radio frequency magnetron sputtering, vacuum thermal evaporation, electron beam (e-beam), and the like.

The devices of the following examples and comparative examples were prepared using commercialized hole transport layer PEDOT:PSS, donor polymer PM6, acceptor small molecule Y6 and electron transport layer PFN-Br materials:

Example 1

Anode ITO/hole transport layer PEDOT:PSS/active layer PM6:Y6/cathode Yb/Ag

的速率蒸镀Yb，厚度为5nm，再以

的速率蒸镀Ag，厚度为50nm。The conductive glass substrate plated with 170nm ITO was cleaned with a variety of solvents, followed by deionized water, acetone, and isopropanol, and then subjected to ultraviolet ozone plasma treatment; Spin-coat on ITO with a coating thickness of about 40 nm, then anneal at 150 degrees for 15 minutes, and transfer to the glove box; spin-coat about 200 nm of PM6:Y6 blended active layer solution on PEDOT:PSS (mass ratio is 1:1.2, The concentration of Y6 is 1.2g/ml, the solvent is chloroform, the additive is chloronaphthalene, the volume of chloronaphthalene is 0.5%), annealed at 110 degrees for 10 minutes; the prepared wafers are placed in the evaporation chamber, and the vacuum degree is 2 × 10 ^-7 Torr at

Yb was evaporated at a rate of 5 nm with a thickness of 5 nm.

Ag was evaporated at a rate of 50 nm in thickness.

Example 2

Anode ITO/hole transport layer PEDOT:PSS/active layer PM6:Y6/cathode Yb/Ag

的速率蒸镀Yb，厚度为10nm，再以

的速率蒸镀Ag，厚度为100nm。Repeat the same procedure as described in Example 1, but in the evaporation chamber, at a vacuum of 2×10 ^-6 Torr

Yb was evaporated at a rate of 10 nm with a thickness of 10 nm.

Ag was evaporated at a rate of 100 nm in thickness.

Example 3

Anode ITO/hole transport layer PEDOT:PSS/active layer PM6:Y6/cathode Yb/Ag

的速率蒸镀Yb，厚度为15nm，再以

的速率蒸镀Ag，厚度为200nm。Repeat the same procedure as described in Example 1, but in the evaporation chamber, under a vacuum of 5×10 ^-6 Torr

Yb was evaporated at a rate of 15 nm with a thickness of 15 nm.

Ag was evaporated at a rate of 200 nm in thickness.

Example 4

Anode ITO/hole transport layer PEDOT:PSS/active layer PM6:Y6/cathode Yb/Ag

的速率蒸镀Yb，厚度为20nm，再以

的速率蒸镀Ag，厚度为200nm。Repeat the same procedure as described in Example 1, but with a vacuum of 3×10 ^-7 Torr in the evaporation chamber

Yb was evaporated at a rate of 20 nm with a thickness of 20 nm.

Ag was evaporated at a rate of 200 nm in thickness.

Example 5

Anode ITO/hole transport layer PEDOT:PSS/active layer PM6:Y6/cathode Yb/Ag

的速率蒸镀Yb，厚度为20nm，再以

的速率蒸镀Ag，厚度为300nm。Repeat the same procedure as described in Example 1, but with a vacuum of 1×10 ^-6 Torr in the deposition chamber

Yb was evaporated at a rate of 20 nm with a thickness of 20 nm.

Ag was evaporated at a rate of 300 nm in thickness.

Example 6

Anode ITO/hole transport layer PEDOT:PSS/active layer PM6:Y6/cathode Yb/Ag

的速率蒸镀Yb，厚度为20nm，再以

的速率蒸镀Ag，厚度为500nm。Repeat the same procedure as described in Example 1, but with a vacuum of 1×10 ^-7 Torr in the evaporation chamber

Yb was evaporated at a rate of 20 nm with a thickness of 20 nm.

Ag was evaporated at a rate of 500 nm in thickness.

Comparative ratio

Anode ITO/hole transport layer PEDOT:PSS/active layer PM6:Y6/cathode buffer layer PFN-Br/cathode Ag

的速率蒸镀Ag，厚度为100nm。The conductive glass substrate coated with 170nm ITO was cleaned with a variety of solvents, followed by deionized water, acetone, and isopropanol, and then subjected to ultraviolet ozone plasma treatment; Speed spin-coated on ITO with a coating thickness of about 40 nm, then annealed at 150 degrees for 15 minutes, and transferred to the glove box; spin-coat about 200 nm of PM6:Y6 blended active layer solution on PEDOT:PSS (mass ratio is 1:1.2 , Y6 concentration is 1.2g/ml, the solvent is chloroform, the additive is chloronaphthalene, the volume of chloronaphthalene is 0.5%), annealed at 110 degrees for 10 minutes; PFN-Br (solvent: methanol, concentration: 0.5mg/ml) was Spin coating at 3000rmp; place the prepared film in the evaporation chamber, and then use

Ag was evaporated at a rate of 100 nm in thickness.

The performance of the prepared organic solar cell device was tested, and the cell current-voltage curve was tested under the illumination of a solar simulator (SS-F5-3A) AM1.5G standard light, and the photoelectric conversion efficiency was calculated.

The battery performance of Examples 1-5 is comparable to that of the comparative example, and the photoelectric conversion efficiency is increased by 2.8% and the fill factor is increased by 2.5%.

Claims (5)

1. a composite cathode electrode layer for a forward organic solar cell, is characterized in that: the composite cathode electrode layer is a double-layer metal ytterbium Yb and silver Ag; one side of the Yb layer is an Ag layer, and the other side is a forward organic Active layer of solar cells. 2 . The composite cathode electrode layer for a forward organic solar cell according to claim 1 , wherein the thickness of Yb is 0.5 nm-20 nm, and the thickness of Ag is 5 nm-500 nm. 3 . 3 . The composite cathode electrode layer for a forward organic solar cell according to claim 2 , wherein the thickness of Yb is 10 nm, and the thickness of Ag is 100 nm. 4 . 4. A method for preparing the composite cathode electrode layer according to any one of claims 1-3, wherein the composite cathode electrode layer is prepared by a vacuum thermal evaporation coating method. 5 . The preparation method according to claim 4 , wherein the vacuum degree of the vacuum thermal evaporation coating method is 1×10 ⁻⁵ to 1×10 ⁻⁸ Torr, and the coating rate of the Yb layer is 5 .

The deposition rate of the Ag layer is

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