CN111326656A - A solid additive for organic polymer solar cells - Google Patents

Abstract

The invention relates to a solid additive for organic polymer solar cells, characterized in that the solid additive is an aromatic substance containing carbonyl, carboxyl, aldehyde or ester groups, and its molecular weight is 100-500 g/mol. The invention also relates to an organic polymer solar cell device, which is characterized in that: the organic polymer solar cell device sequentially comprises: a transparent electrode, an electron transport/hole blocking layer, an active layer, an electron blocking/hole transport layer, A metal electrode, wherein the active layer comprises a wide band gap conjugated polymer electron donor, a non-fullerene type small molecule electron acceptor, and the solid additive. The solid additive of the invention can prolong the lifetime of the acceptor excitons, which is beneficial to the effective migration of the excitons to the electron-donor-acceptor interface, thereby improving the exciton separation efficiency, thereby improving the short-circuit current density and filling factor of the solar cell device and Photoelectric conversion efficiency.

Description

A solid additive for organic polymer solar cells

technical field

The invention belongs to the field of organic semiconductor devices, and relates to a solid additive which can be used to improve the performance of organic polymer solar cells. The additive is applied to the active layer part of the cell device structure.

Background technique

With the rapid development of the times, the problem of energy shortage and pollution is becoming more and more serious. In order to solve this problem, finding a new type of energy with abundant reserves, clean and pollution-free has become the focus of social attention. Solar energy is radiated into the atmosphere with an ultra-high energy density of 1366W/m2 per ^second . Although it can cause losses through absorption and reflection, it still has an energy density of 1000W/m2 in the 280nm ^- 4000nm band. "Inexhaustible and inexhaustible" energy has become an important way to solve the energy problem. The development of solar cells is the most direct and effective means of applying solar energy. Among them, organic polymer solar cells have received extensive attention due to their simple preparation, low cost and flexibility, and have made great breakthroughs in efficiency in recent years. However, the commercialization of organic solar cells is still a long way off. In this regard, the search for new strategies to improve efficiency has become an essential step in the development of organic solar cell devices.

The core part of polymer solar cells is the active layer of bulk heterojunction. In the mechanism of polymer solar cells, the active layer can generate photogenerated Frenkel excitons after being irradiated by visible light, and the excitons diffuse to the acceptor. Under the action of the built-in electric field, the interface forms a charge transfer state and separates electrons and holes to form carriers, which are transported to the positive and negative electrodes respectively to realize the final photoelectric conversion. Due to the limitation of exciton lifetime, the diffusion distance of excitons is usually 5-20 nm, which requires a small phase separation size for the acceptor. However, too small area size is not conducive to the transport of carriers. Therefore, a suitable active layer morphology plays an important role in the balance of exciton diffusion, separation and carrier transport. It is also the key to realizing high-efficiency battery devices. fundamental requirement. In the preparation process of organic solar cell devices, the use of additives is a very common way to control the morphology of the active layer. For example to PCPDTBT (poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b]-dithiophene)-alt-4, 7-(2,1,3-benzothiadiazole)]): PC ₇₁ BM ([6,6]-phenyl C ₇₁ -butyric acid methyl ester) system with a small amount of additive 1,8-octanedisulfide alcohol, the photoelectric conversion efficiency can be increased from 2.8% to 5.5%. Commonly used additives are usually high-boiling small-molecule liquid additives such as 1,8-diiodooctane (DIO), 1-chloronaphthalene (CN), diphenyl ether (DPE), etc., which can dissolve small molecule receptors better. In the spin coating process, the residence time of small molecules in the solvent system is prolonged, and the donor polymer has sufficient time to form a better fiber network structure to achieve a better bulk heterojunction structure. However, such liquid additives are difficult to remove due to their high boiling point, which brings difficulties to large-area fabrication of devices. At the same time, such additives used to adjust the morphology of the active layer only have a significant improvement effect on the system with poor morphology of the active layer prepared natively (no addition, no post-treatment), but have a significant improvement on the morphology of the active layer itself prepared natively. Better systems often have no adjustment effect or even have a negative effect. Therefore, additives that simply act to adjust the morphology have great limitations on the improvement of device performance.

Therefore, based on the simplicity of the current organic polymer solar cell devices as acceptor materials and the use of additives for device optimization, the development of a new type of active layer additive with regulatory functions is of great significance for improving the performance of battery devices.

SUMMARY OF THE INVENTION

The purpose of the present invention is to find and provide a non-volatile solid additive which is different from morphology control and can prolong exciton lifetime. By improving the short-circuit current density and fill factor of the solar cell device, two device performance parameters, the photoelectric conversion efficiency of the device is improved.

To this end, the present invention provides a solid additive for organic polymer solar cells, characterized in that: the solid additive is an aromatic substance containing carbonyl, carboxyl, aldehyde or ester groups, and its molecular weight is 100-500 g /mol.

The present invention also provides an organic polymer solar cell device, which is characterized in that: the organic polymer solar cell device sequentially comprises: a transparent electrode, an electron transport/hole blocking layer, an active layer, and an electron blocking/hole transport layer , a metal electrode, wherein the active layer comprises a wide band gap conjugated polymer electron donor, a non-fullerene type small molecule electron acceptor, and the above-mentioned solid additive.

The active layer material involved in the present invention is a wide band gap donor polymer and a non-fullerene small molecule acceptor. When an appropriate amount of the solid additive is introduced into the donor-acceptor blend system, the lifetime of the acceptor excitons can be extended, which is beneficial to the effective migration of the excitons to the donor-acceptor interface, thereby improving the exciton separation efficiency, thereby improving the solar energy The short-circuit current density and fill factor of battery devices can improve the photoelectric conversion efficiency, and can also reduce the sensitivity of device performance to the thickness of the active layer to a certain extent. It is found in the present invention that it is different from other additives for regulating morphology. When an appropriate amount of the solid additive is added to the system, it has no obvious effect on the original morphology of the blended system. Therefore, the use of this additive is a new strategy for improving device performance. . At the same time, the use of the solid additive in the active layer is also different from the use of a donor:acceptor1:acceptor2 or a donor1:donor2:acceptor ternary system in the active layer.

Description of drawings

Fig. 1 shows the selected donor-acceptor materials (the wide-bandgap conjugated polymer donor material PBDB-T, the non-fullerene-based small molecule electron acceptor material IT-M) and the solid additive FCA selected for the active layer in Example 1. Molecular Structure.

FIG. 2 is a schematic structural diagram of the organic polymer solar cell devices prepared in Example 1 and Comparative Example 1. FIG.

FIG. 3 is a photovoltaic characteristic curve of the organic polymer solar cell devices in Example 1 and Comparative Example 1. FIG.

4 is the external quantum efficiency curves of organic polymer solar cell devices and blank substrates in Example 1 (IT-M/13% FCA thin film) and Comparative Example 1 (IT-M thin film).

Figure 5 shows the fluorescence lifetime curves of pure small molecule acceptors and the addition of solid additive FCA.

Detailed ways

In one embodiment of the present invention, the solid additive is a non-volatile substance. In particular, the solid additive still exists in the active layer after the device is fabricated, even after vacuuming and thermal annealing. Herein, the solid additive is also referred to as a small molecule solid additive.

In one embodiment of the present invention, the solid additive is soluble in an organic solvent. In particular, the solid additive has good solubility in common organic solvents, and when an appropriate amount of the solid additive is added to the system, the original morphology of the electron donor and acceptor blend system is not significantly affected.

In a preferred embodiment of the present invention, the solid additive is 9-fluorenone-1-carboxylic acid (FCA).

In one embodiment of the present invention, the solid additive comprises 1-25% by weight of the active layer, preferably 5-15% by weight, more preferably 8-13% by weight.

In one embodiment of the present invention, the thickness of the active layer is 50-1000 nm.

Preferably, the band gap (E _g ) of the wide-bandgap conjugated polymer electron donor in the active layer is greater than 1.6 eV; the non-fullerene-based small molecule electron acceptor is an electron acceptor that does not contain a fullerene group Conjugated small molecule compounds with band gaps in the range of 1.0-1.6 eV.

In one embodiment of the present invention, the material constituting the transparent electrode is a transparent or semi-transparent conductive material in the visible light region, and its light transmittance is greater than 50%.

Preferably, the conductive material is selected from one or more of tin indium oxide (ITO), aluminum-doped zinc oxide (AZO), graphene, carbon nanotubes, metal nanowire films, and metal films.

In one embodiment of the present invention, the material in the electron transport/hole blocking layer is an organic compound or metal oxide with electron transport ability or hole blocking ability, and the electron transport/hole blocking layer has 1 -200nm thickness.

In one embodiment of the present invention, the material in the electron blocking/hole transport layer is an organic compound or metal oxide with hole transport ability or electron blocking ability, and the electron blocking/hole transport layer has 1 -200nm thickness.

In one embodiment of the present invention, the material constituting the metal electrode is selected from the group consisting of gold, silver, platinum, copper, aluminum or a combination thereof.

The present invention has one or more of the following features and advantages:

1. The present invention uses a small molecular solid as the additive, which is different from the high-boiling liquid additive, and does not need to consider the later removal problem, which provides convenience for the large-area production and industrialization of organic polymer solar cells.

2. The action mechanism of the small-molecule solid additive used in the present invention is to prolong the lifespan of photogenerated excitons of the small-molecule acceptor, improve the transmission efficiency of excitons to the acceptor interface, and can effectively adjust the short-circuit current density and filling factor in the device. It is a new strategy and new idea to optimize the performance of the device, and the photoelectric conversion performance of the device is improved.

3. The small molecule solid additive used in the present invention will not destroy the original morphology of the blended film, and at the same time, adding an appropriate amount can improve the tolerance of device performance to film thickness, which is also the industrialization of organic polymer solar cells. to offer comfort.

4. The solid additive involved in the present invention has good solubility in the solvent used in the blending system. During the preparation process of the solar cell device, the active layer of the device can still be prepared by the solution method, and the preparation process is simple. This approach can improve material utilization, reduce costs, and increase productivity.

Example

Example 1: The two materials PBDB-T and IT-M shown in Figure 1 were used as the active layer material of the blended organic polymer solar cell device, and the additive 9-fluorenone-1-carboxylic acid (hereinafter referred to as FCA) The structure is shown in Figure 1. Among them, the band gap (E _g ) of the wide band gap polymer donor material PBDB-T is 1.80 eV; the band gap (E _g ) of the non-fullerene small molecule acceptor material is 1.6 eV.

The ITO/ZnO(30nm)/PBDB-T:IT-M:FCA(100nm)/MoO ₃ (8.5nm)/Ag(100nm) device structure is shown in Fig. 2 . The content of the solid additive FCA in the active layer of the device accounts for (mass percent) 13%, based on the sum of the weights of PBDB-T and IT-M. The device fabrication process is as follows:

1. The ITO (transparent electrode) glass substrate is first cleaned with detergent, then rinsed with tap water, deionized water, and ethanol in sequence to remove surface grease and dust. After that, deionized water, acetone, and isopropanol were sonicated for 20 minutes each, and then placed in a vacuum drying oven at 80° C. for vacuum heating for 40 minutes to dry the substrate. Next, the dried ITO substrate was treated with an ultraviolet ozone cleaner (UVO) for 30 min.

2. Spin-coat a layer of ZnO (electron transport layer) with a thickness of about 30 nm on the ITO substrate at a rotational speed of 3500 rpm, and then anneal at 200° C. in air for 20 min.

3. Prepare a mixed solution containing PBDB-T:IT-M:FCA (1:1:0.26 mass ratio) dissolved in 0.5% (v/v) DIO o-dichlorobenzene, the total concentration is 12mg/ml, and FCA accounts for The mass percent of the total solids was 13% based on the sum of the weights of PBDB-T and IT-M. The mixed solution was spin-coated on the ZnO layer with the parameters of 1300 rpm and 60 s as the active layer, and its thickness was about 100 nm.

4. MoO ₃ (8.5nm) and Ag (100nm) were deposited on the active layer by thermal evaporation in sequence under the condition of vacuum degree of 3×10 ^-7 Torr, as electron blocking layer and metal electrode.

Test of device performance: use Keithley 2400 digital multimeter in a glove box to measure the current-voltage curve of the device under AM1.5G illumination, and calculate the open-circuit voltage, short-circuit current density, filling factor and photoelectric conversion efficiency of the device. and other parameters, the effective area of the device is 0.04cm ² . The optimal performance of the obtained blended organic polymer solar cell device containing solid additive FCA is as follows: the open circuit voltage is 0.92V, the short circuit current density is 18.40mA/cm ^-2 , the fill factor is 0.73, and the photoelectric conversion efficiency is 12.31%.

Comparative Example 1 (control group): a reference device was prepared according to the method of Example 1, except that no solid additive FCA was added to the active layer of the device, and the obtained organic polymer solar cell device was measured according to the above-mentioned device performance testing method. The optimal performance is as follows:

PBDB-T:IT-M system: the open-circuit voltage is 0.91V, the short-circuit current density is 17.72mA/cm ^-2 , the fill factor is 0.70, and the photoelectric conversion efficiency is 11.45%. Obviously, the performance of the device in Example 1 is better than that of the device in Comparative Example 1, as shown in FIG. 3 .

In order to verify the improvement of the short-circuit current density of the system, we conducted external quantum efficiency (IPCE) tests on the device of Example 1 and the device of Comparative Example 1.

The test is carried out in an atmospheric environment under a tungsten light source simulator with a spot size of 1mm ² . From FIG. 4 , we can find that the device of Example 1 has a great improvement in absorption in the wavelength band of 550 nm to 700 nm compared with the device of Comparative Example 1, and the external quantum efficiency is increased by nearly 10%.

To verify the effect of the additives, we performed fluorescence lifetime tests on pure small molecule acceptor films and films containing the solid additive FCA.

The test was performed in an atmospheric environment, and the excitation wavelength of the laser used was 656.0 nm. From Figure 5, we can find that the fluorescence lifetime of the small molecule receptor is significantly prolonged after adding the same dose of solid additive as in Example 1.

The preparation method of the organic solar cell device containing the solid additive FCA provided by the present invention is described in detail above, and it is confirmed that the photoelectric conversion efficiency of the device can be effectively improved by adopting this method.

Specific examples are cited herein to illustrate the principles and implementations of the present invention, but these examples are not intended to limit the present invention. Any simple modifications to the present invention without departing from the principles of the present invention also fall within the protection scope of the claims of the present invention.

Claims (13)

1. A solid additive for organic polymer solar cells, characterized in that: the solid additive is an aromatic substance containing carbonyl, carboxyl, aldehyde or ester groups, and its molecular weight is 100-500 g/mol. 2 . The solid additive for organic polymer solar cells according to claim 1 , wherein the solid additive is a non-volatile substance. 3 . 3 . The solid additive for organic polymer solar cells according to claim 1 or 2 , wherein the solid additive is soluble in an organic solvent. 4 . 4. The solid additive for organic polymer solar cells according to claim 1 or 2, wherein the solid additive is 9-fluorenone-1-carboxylic acid. 5. An organic polymer solar cell device, characterized in that: the organic polymer solar cell device sequentially comprises: a transparent electrode, an electron transport/hole blocking layer, an active layer, an electron blocking/hole transport layer, and a metal electrode , wherein the active layer comprises a wide-bandgap conjugated polymer electron donor, a non-fullerene-based small molecule electron acceptor, and the solid additive according to any one of claims 1-4. 6. The organic polymer solar cell device according to claim 5, wherein the solid additive accounts for 1-25% by weight of the active layer, preferably 5-15% by weight, more preferably 8-13% by weight %. 7 . The organic polymer solar cell device according to claim 5 , wherein the thickness of the active layer is 50-1000 nm. 8 . 8 . The organic polymer solar cell device according to claim 5 , wherein: the band gap (E _g ) of the wide band gap conjugated polymer electron donor in the active layer is greater than 1.6 eV; The lerene-based small molecule electron acceptor is a conjugated small molecule compound that does not contain a fullerene group, and its band gap ranges from 1.0 to 1.6 eV. 9 . The organic polymer solar cell device according to claim 5 , wherein the material constituting the transparent electrode is a transparent or semi-transparent conductive material in the visible light region, and its light transmittance is greater than 50%. 10 . 10. The organic polymer solar cell device according to claim 9, wherein the conductive material is selected from the group consisting of tin indium oxide (ITO), aluminum doped zinc oxide (AZO), graphene, carbon nanotubes , one or more of metal nanowire films, and metal films. 11. The organic polymer solar cell device according to claim 5, wherein the material in the electron transport/hole blocking layer is an organic compound or metal oxide with electron transport ability or hole blocking ability, And the electron transport/hole blocking layer has a thickness of 1-200 nm. 12 . The organic polymer solar cell device according to claim 5 , wherein the material in the electron blocking/hole transport layer is an organic compound or metal oxide with hole transport ability or electron blocking ability, 12 . And the electron blocking/hole transporting layer has a thickness of 1-200 nm. 13 . The organic polymer solar cell device according to claim 5 , wherein the material constituting the metal electrode is selected from the group consisting of gold, silver, platinum, copper, aluminum or a combination thereof. 14 .

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