FLEXIBLE TRANSPARENT ELECTRODE AND PREPARATION METHOD THEREFOR, AND FLEXIBLE SOLAR CELL PREPARED USING FLEXIBLE TRANSPARENT ELECTRODE

Abstract

A flexible solar cell is a flexible organic solar cell that can be completed at a low temperature, is easily prepared, and has a relatively low cost and relatively high efficiency. The flexible transparent electrode is prepared by selecting a plastic substrate with silver nanowires embedded therein, and thus, a flexible transparent electrode with better electrical properties, stronger adhesion and better mechanical properties can be obtained. The flexible transparent electrode prepared using the substrate with the silver nanowires embedded therein has lower sheet resistance and higher conductivity. Moreover, on a microstructure, the silver nanowires in the flexible substrate with the silver nanowires embedded therein can induce upper spin-coated silver nanowires to be more uniformly distributed, and can form nodes with the upper spin-coated silver nanowires, such that the adhesion between an upper electrode and the substrate is enhanced, which can further guarantee the good mechanical properties of the electrode.

Claims

1. A flexible transparent electrode, characterized in that a method of preparing the flexible transparent electrode comprises the following steps: spin-coating a metal nanowire on a transparent plastic, and then coating with a curing resin to obtain a flexible transparent substrate; preparing a conductive layer on the flexible transparent substrate to obtain the flexible transparent electrode.

2. The flexible transparent electrode of claim 1, characterized in that, the curing resin is a light curing resin; the conductive layer is one or more selected from the group consisting of the metal nanowire, a conductive polymer, and a metal oxide.

3. The flexible transparent electrode of claim 1, characterized in that, spin-coating the metal nanowire onto the transparent plastic, and then coating with the curing resin to obtain the flexible transparent substrate; spin-coating the metal nanowire onto the flexible transparent substrate and then coating with a metal oxide solution, heating and preparing the conductive layer onto the flexible transparent substrate to obtain the flexible transparent electrode; or spin-coating a conducting polymer solution onto the flexible transparent substrate, then coating with the metal oxide solution, heating and preparing the conductive layer on the flexible transparent substrate to obtain the flexible transparent electrode.

4. The flexible transparent electrode of claim 3, characterized in that, in the metal oxide solution, a metal oxide concentration is ranging from 5 mg/mL to 20 mg/mL; a heating temperature is from 100° C. to 150° C., and a heating time is from 10 to 30 min; when spin-coating with the metal oxide solution, a rotation speed is from 1000 rpm to 3000 rpm, and a coating time is from 10 to 100 seconds; in the metal nanowire solution, a metal nanowire concentration is ranging from 0.15 wt % to 0.5 wt %; when spin-coating with the metal nanowire solution, a rotation speed is from 1000 rpm to 3000 rpm, and a coating time is from 10 to 100 seconds.

5. A flexible solar cell, comprising a flexible transparent electrode, an active layer, a hole transporting layer, and an upper electrode layer; or comprising a flexible transparent electrode, an active layer, an electron transporting layer, and an upper electrode layer; spin-coating a metal nanowire onto the transparent plastic, and then coating with a curing resin to obtain the flexible transparent substrate; preparing the conductive layer on the flexible transparent substrate to obtain flexible transparent electrode.

6. The flexible solar cell of claim 5, characterized in that the active layer material is one or more selected from the group consisting of PBDB-T-2F, PTB7-Th, PCBM, IT-4F, and Y6; the electron transporting layer material is one or more selected from the group consisting of ZnO, TiO.sub.2, SnO.sub.2, PFN, PFN-Br, PDINO; the hole transporting layer material is one or more selected from group consisting of poly[bis(4-phenyl)(2,4,6-trimethyl) Phenyl) amine], poly 3,4-ethylenedioxythiophene/polystyrene sulfonate, nickel oxide, copper oxide, 2,2′,7,7′-tetra[N,N-bis(4-methyl(oxyphenyl)amino]-9,9′-spirobifluorene, cuprous thiocyanate, molybdenum oxide; the electrode is one or more selected from the group consisting of an Au electrode, an Ag electrode, an Al electrode, a Cu electrode, a PH1000 polymer electrode, and a metal oxide electrode.

7. The flexible solar cell of claim 5, characterized in that the curing resin is a light curing resin; the conductive layer is one or more selected from the group consisting of a metal nanowire, a conductive polymer, and a metal oxide; spin-coating the metal nanowire onto the transparent plastic, and then coating with the curing resin to obtain a flexible transparent substrate; spin-coating the metal nanowire onto the flexible transparent substrate then coating with the metal oxide solution, heating and preparing conductive layer onto the flexible transparent substrate to obtain the flexible transparent electrode; or spin-coating with the conducting polymer solution onto the flexible transparent substrate, then coating with the metal oxide solution, heating and preparing conductive layer on the flexible transparent substrate to obtain the flexible transparent electrode.

8. The flexible solar cell of claim 7, characterized in that in metal oxide solution, a metal oxide concentration is ranging from 5 mg/mL to 20 mg/mL; a heating temperature is from 100° C. to 150° C., and a heating time is from 10 to 30 min; when spin-coating with the metal oxide solution, a rotation speed is from 1000 rpm to 3000 rpm, and a coating time is from 10 to 100 seconds; in the metal nanowire solution, a metal nanowire concentration is ranging from 0.15 wt % to 0.5 wt %; when spin-coating with the metal nanowire solution, a rotation speed is from 1000 rpm to 3000 rpm, and a coating time is from 10 to 100 seconds.

9. An Application in preparation of a flexible device with the flexible transparent electrode in claim 1.

10. The application of claim 9, characterized in that the flexible device includes flexible solar cells and flexible sensors.

Description

DESCRIPTION OF THE DRAWINGS

[0021] FIG. 1 is a schematic diagram of flexible transparent electrode fabrication process is presented in Example 1;

[0022] FIG. 2 shows SEM images of flexible transparent electrodes prepared with PET plastic substrate embedding AgNWs and normal PET plastic substrate in Example 1;

[0023] FIG. 3 shows SEM images of cross-sectional of flexible transparent electrodes prepared with PET plastic substrate embedding AgNWs and normal PET plastic substrate in Example 1;

[0024] FIG. 4 shows the adhesive force values of flexible transparent electrodes prepared with PET plastic substrate embedding AgNWs and normal PET plastic substrate in Example 1, inset: schematic illustration of adhesive force measurements;

[0025] FIG. 5 shows sheet resistance change of the FTEs prepared with PET plastic substrate embedding AgNWs and normal PET plastic substrate in Example 1 with increasing bending cycles for inward and outward bending tests (with a 4 mm bending radius);

[0026] FIG. 6 shows the photograph of Em-Ag/AgNWs:AZO-SG FTE in Example 1;

[0027] FIG. 7 shows schematic illustration of a flexible solar cells and molecular structures in Example 2;

[0028] FIG. 8 shows J-V curves under the illumination of flexible solar cells prepared with PET plastic substrate embedding AgNWs and normal PET plastic substrate in Example 2;

[0029] FIG. 9 shows flexible solar cells prepared with PET plastic substrate embedding AgNWs and normal PET plastic substrate in Example 2 versus bending cycles at a radius of 4 mm;

[0030] FIG. 10 shows J-V curves under the illumination of flexible solar cells prepared with PET plastic substrate embedding AgNWs and Em-Ag/AgNWs:AZO-SG in Example 3.

DETAILED DESCRIPTION

[0031] The flexible transparent electrode of the present invention adopts a hybrid electrode structure to combine silver nanowires with metal oxides or conductive polymers, solving the problem of low coverage of silver nanowires, and avoiding excessively high contact resistance between silver nanowires and low device efficiency. All the raw materials of the present invention are commercially available and meet the application requirements of flexible solar cells. For example, the ultraviolet curing adhesive is a conventional transparent ultraviolet curing adhesive, which is a commercially available product, such as Organtecsolar Materials Inc. The test method involved in the embodiment of the present invention is a flexible solar cell routine testing methods.

[0032] In the following, the present invention will be described in detail in conjunction with embodiments:

Example 1

[0033] (1) On the surface of the PET plastic substrate (pure PET, untreated, non-conductive) spin-coated silver nanowires (length 2 um, diameter 30 nm) aqueous solution (0.25 wt %) at 2000 rpm for 40 s without heating, and then on the AgNWs scraped a layer of UV-curing resin at 20 mm/s speed, 80 nm height, then used UV lamp (distance with lamp was 18 cm, energy of UV was 335 mJ/cm) to cure for 1 min to form a PET plastic substrate embedded with silver nanowires (Em-Ag), as the substrate of flexible organic solar cells, the transmittance was similar to that of pure PET, but with a high resistance (130 Ω/sq) and cannot be directly used as a flexible electrode;

[0034] (2) Spin-coated AgNWs solution (0.25 wt %) onto the Em-Ag substrate at 2000 rpm for 40 s, without heating, and then 10-mg/mL-Al-doped ZnO (AZO) solution was spin-coated onto the obtained AgNWs film, at 2000 rpm for 1 min, followed by a thermal annealing process in air at 120° C. for 15 min, then 5-mg/mL-AZO solution was spin-coated onto the AgNWs:AZO film at 2000 rpm for 1 min, which also followed by a thermal annealing process in air at 120° C. for 15 min, with total thickness of ≈180 nm. So far, the preparation of flexible transparent electrode was completed. The thickness of the UV-curing resin layer was 80 nm and the thickness of the conductive layer was 100 nm; FIG. 1 was a schematic diagram of flexible transparent electrode fabrication process was presented, the thickness of PET plastic substrate was not included in flexible transparent electrode, flexible transparent electrode is Em-Ag/AgNWs:AZO-SG.

[0035] Replace the PET plastic substrate embedded with silver nanowires (Em-Ag) in the above step (2) with the normal PET plastic substrate (pure PET, untreated), and the rest remain unchanged to obtain a flexible transparent electrode prepared by normal PET plastic, as a comparison.

[0036] FIG. 2 shows SEM images of flexible transparent electrodes prepared with PET plastic substrate embedding AgNWs and normal PET plastic substrate. It can be clearly seen that the presence of this worm-like AZO film throughout the AgNW network (AgNWs:AZO) is more uniform.

[0037] FIG. 3 shows SEM images of cross-sectional of flexible transparent electrodes prepared with PET plastic substrate embedding AgNWs and normal PET plastic substrate (pure PET, untreated).

[0038] It can be clearly seen that the flexible transparent electrode of AgNWs:AZO, junction site in the upper and the underlying AgNWs substrate enhancing the adhesion of the electrode to the substrate.

[0039] FIG. 4 shows the adhesive force values of flexible transparent electrodes prepared with PET plastic substrate embedding AgNWs and normal PET plastic substrate (pure PET, untreated), by 90° peel measurements, the adhesion of the PET plastic substrate embedding AgNWs and normal PET plastic substrate FTEs of 72.3% relative to that of the Em-Ag/AgNWs:AZO-SG FTE. It can enhance the adhesion of the electrode to the substrate. The thickness of the UV-curing resin layer was adjusted to 50 nanometers, and the rest was the same as the above, the flexible transparent electrode was prepared, and the adhesion was tested by the same method, which was 1.18 times higher compared to that of the flexible transparent electrode prepared from the normal PET plastic substrate.

[0040] The concentration of the silver nanowire aqueous solution was adjusted to 0.3 wt %, and the rest was the same as the above, the flexible transparent electrode was prepared, and the adhesion was tested by the same method, which was 1.34 times higher compared to that of the flexible transparent electrode prepared on the normal PET plastic substrate. The spin-coated speed was adjusted to 2000 rpm/50 s, and the rest was the same as the above, the flexible transparent electrode was prepared, and the adhesion was tested by the same method, which was 1.35 times that of the flexible transparent electrode prepared on the normal PET plastic substrate.

[0041] The sheet resistance of the Em-Ag/AgNWs:AZO-SG FTE calculated from the statistical results was 18 Ω/sq (measured with a four-probe instrument), which is comparable to that of the conventional and much lower than those of the FTEs (30 Ω/sq) prepared on the normal PET plastic substrate. This result is also consistent with their respective conductivity values, the Em-Ag/AgNWs:AZO-SG FTEs can improve the electrical performance of the electrode.

[0042] FIG. 5 shows sheet resistance change of the FTEs prepared with PET plastic substrate embedding AgNWs and normal PET plastic substrate (pure PET, untreated) with increasing bending cycles for inward and outward bending tests. The bending durability of the FTEs in the inward or outward direction was evaluated via the ratio of the sheet resistance to the initial resistance with the evolution of bending cycles at a bending radius of 4 mm. As shown in FIG. 5, the Rsh/R0 of the AgNWs:AZO-SG grown on the bare PET substrate was slightly increased after 1200 bending cycles in the inward direction, indicating that the increase in adhesion was conducive to improving the mechanical properties of the electrode.

[0043] FIG. 6 shows the photograph of Em-Ag/AgNWs:AZO-SG FTE, the electrode in the present has a high transmittance of 84% in common text, and transmittance of the pure PET plastic substrate is 89%.

Control Example

[0044] On the surface of the PET plastic substrate (pure PET, untreated, consistent with Example 1) scraped a layer of UV-curing resin, after dried, spin-coated AgNWs solution (0.25 wt %) at 2000 rpm for 40 s without heating, then used UV lamp (distance with lamp is 18 cm, energy of UV is 335 mJ/cm) to cure for 1 min to form a PET plastic substrate embedded with silver nanowires, as the substrate of flexible organic solar cells; Spin-coated AgNWs solution (0.25 wt %) onto the substrate at 2000 rpm for 40 s, without heating, and then 10-mg/mL-Al-doped ZnO (AZO) solution was spin-coated onto the obtained AgNWs film, at 2000 rpm for 1 min, followed by a thermal annealing process in air at 120° C. for 15 min, then 5-mg/mL-AZO solution was spin-coated onto the AgNWs:AZO film at 2000 rpm for 1 min, which also followed by a thermal annealing process in air at 120° C. for 15 min, to prepare the flexible transparent electrode. The thickness of the UV-curing resin layer was 80 nm and the thickness of the conductive layer was 100 nm. At the same test, the sheet resistance was 28 Ω/sq, at a bending radius of 4 mm after 1200 bending cycles in the inward direction, the sheet resistance was 1.3 times that was similar to pure PET.

[0045] On the surface of the PET plastic substrate (pure PET, untreated, consistent with Example 1) spin-coated AgNWs solution (0.25 wt %) at 2000 rpm for 40 s without heating, and then spin-coated AgNWs solution (0.25 wt %) onto the substrate at 2000 rpm for 40 s again, without heating, and then 10-mg/mL-Al-doped ZnO (AZO) solution was spin-coated onto the obtained AgNWs film, at 2000 rpm for 1 min, followed by a thermal annealing process in air at 120° C. for 15 min, then 5-mg/mL-AZO solution was spin-coated onto the AgNWs:AZO film at 2000 rpm for 1 min, which also followed by a thermal annealing process in air at 120° C. for 15 min, to prepare the flexible transparent electrode. The thickness of the UV-curing resin layer was 80 nm and the thickness of the conductive layer was 100 nm. At the same test, the sheet resistance was 24 Ω/sq, at a bending radius of 4 mm after 1200 bending cycles in the inward direction, the sheet resistance was 1.4 times that was worse than the pure PET.

[0046] On the surface of the Em-Ag spin-coated conductive polymer PH1000 at 1400 rpm for 60 s, followed by a thermal annealing process at 100° C. for 15 min, and then spin-coated PETE at 5000 rpm/30 s to obtain a flexible transparent electrode; At the same test, the sheet resistance was 90 Ω/sq, the transmittance was only 75%, worse than the AgNWs:AZO hybrid layer.

Example 2

[0047] The flexible transparent electrode prepared in Example 1 is placed in a nitrogen glove box, and spin-coated the active layer solution onto the surface of the conductive layer. The components of the solution were PBDB-T-2F, Y6, the solvent was pure CF, and the concentration was 16 mg/mL of solution, the spin-coating rate was 3000 rpm for 30 s, after dripping, by a thermal annealing process at 110° C. for 10 min, to prepare the active layer; In the coating machine, the MoO.sub.3 hole transporting layer is vapor-deposited on the surface of the active layer and Al electrode, the thickness is 10 nm and 100 nm, respectively. So far, the preparation of the flexible solar cell is completed. It is a flexible organic solar cell prepared with a PET plastic substrate embedded with silver nanowires. The schematic illustration is shown in FIG. 7.

[0048] The flexible transparent electrode prepared on the normal PET plastic substrate in Example 1 was placed in a nitrogen glove box, and the same preparation steps were performed to obtain a flexible organic solar cell by the normal PET plastic substrate, in comparison.

[0049] The PET plastic substrate of Example 1 was replaced with a PEN plastic substrate, and the same preparation steps were performed to obtain a flexible organic solar cell prepared from a PEN plastic substrate embedded with silver nanowires, with the efficiency (PCE) of 14.93%.

[0050] Table 1 and FIG. 8 are the photovoltaic performance parameters and J-V curves under the illumination of flexible solar cells prepared with PET plastic substrate embedding AgNWs and normal PET plastic substrate.

[0051] It can be seen that the performance of flexible organic solar cells made of normal PET plastic substrates has declined, and the battery repeatability is not good. The efficiency of flexible organic solar cells made of PET plastic substrates embedded with silver nanowires is 15.21%, which is also the highest reported efficiency of single-junction flexible organic solar cells is close to (15.78%) of organic solar cells with rigid substrates (the substrate is glass, the electrodes are indium tin oxide, and the rest are the same).

TABLE-US-00001 TABLE 1 Photovoltaic performance parameters of PET plastic substrate embedding AgNWs and normal PET plastic substrate V.sub.OC J.sub.SC FF PCE Electrode (V) (mA/cm.sup.2) (%) (%) PET plastic substrate 0.832 25.05 72.97 15.21 embedding AgNWs normal PET plastic substrate 0.824 25.43 69.77 14.61

[0052] FIG. 9 shows flexible solar cells prepared with PET plastic substrate embedding AgNWs and normal PET plastic substrate versus bending cycles at a radius of 4 mm (the upper electrode as the inside);

[0053] It can be seen that the various properties of flexible organic solar cell prepared with a normal plastic substrate drop sharply. At a bending, the sheet resistance was 1.3 times that was similar to pure PET, the flexible OSCs based on Em-Ag/AgNWs:AZO-SG FTEs maintained 93% of its initial value when radius of 4 mm after 1200 bending cycles in the inward direction, demonstrating the well-maintained photovoltaic parameters. It was successfully developed in order to overcome the shortcomings of poor bending performance of batteries prepared in the prior arts, and achieves unexpected technology.

Example 3

[0054] On the surface of the Em-Ag spin-coated conductive polymer PH1000, then spin-coated PETE, and then spin-coated 5-mg/mL-AZO solution followed by a thermal annealing process at 120° C. for 15 min, at 2000 rpm/60 s to obtain a flexible transparent electrode was placed in a nitrogen glove box, and then the same battery preparation steps as in Example 2 were performed to obtain flexible organic solar cells.

[0055] Table 2 and FIG. 10 are the photovoltaic performance parameters and J-V curves of Em-Ag/AgNWs:AZO-SG in Example 2 and Em-Ag/PH1000 in Example 3.

[0056] The results indicate that the FTE design with an integrated underlying substrate and upper electrode layer effectively enhanced the optoelectronic and mechanical properties of the flexible OSCs.

TABLE-US-00002 TABLE 2 Photovoltaic performance parameters of Em-Ag/AgNWs:AZO-SG in Example 2 and Em-Ag/PH1000 in Example 3 V.sub.OC J.sub.SC FF PCE Electrode (V) (mA/cm.sup.2) (%) (%) Em-Ag/AgNWs:AZO-SG 0.832 25.05 72.97 15.21 Em-Ag/PH1000 0.826 21.90 67.38 12.19