WO2018151369A1 - Bulk heterojunction solar cell and manufacturing method therefor - Google Patents

Abstract

The present invention provides: a bulk heterojunction solar cell in which SnS2 (tin disulfide), which is used as an electron acceptor material, and poly(3-hexylthiophene-2,5-diyl) (P3HT) or poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b']dithiophene)-alt-4,7(2,1,3-benzothiadiazole)] (PCPDTBT), which serves as an electron donor, are mixed, wherein the weight ratio of SnS2 and P3HT or SnS2 and PCPDTBT is 6:4 to 8:2; and a manufacturing method therefor.

Description

Bulk heterojunction solar cell and manufacturing method thereof

The present invention relates to a bulk heterojunction solar cell and a method for manufacturing the same, and more particularly, to a hybrid bulk heterojunction solar cell containing SnS ₂ nanoparticles and a method for manufacturing the same.

It has long been known that organics have photoconductivity, photovoltaic and photovoltaic effects, and these properties have been used primarily for photographic and dry printing. Work on organic thin film solar cells was first studied by Kearns and Calvin in 1958, casting air oxidized tetramethyl-p-phenylenediamine (TMPD) onto magnesium phthalocyanine (MgPh) disks. This is the first time that organic heterojunction solar cells have been made.

However, since the technical environment around the organic photovoltaic cell was not properly prepared at that time, the efficiency was not good and there was a limit in the development of the organic photovoltaic cell. After a lot of research and development has been progressed, the organic solar cell is still a long life has not been developed.

In general, an organic solar cell is formed by stacking an ITO layer, a transparent electrode, on a glass substrate, depositing a p-type organic material used as a charge transport layer and an active layer for charge transport, and generating a built-in electric field. The n-type organic material for the stacked structure. A hole transport layer and an electron transport layer may be used to effectively transfer charges generated by absorbing light above the energy gap of an organic material.

The hole transport layer uses organic materials lower than the work function of ITO used as the anode, and the electron transport layer uses organic materials having a work function larger than aluminum (Al) used as the cathode to facilitate the transport of electrons. It is configured to be.

A general organic solar cell manufacturing process is as follows. After ITO is deposited on the glass substrate by sputtering, patterning is performed. Subsequently, after cleaning the substrate, depending on the type of organic material to be deposited, the organic material thin film is deposited by evaporation, and in the case of polymer, spin coating or screen printing is performed. To be deposited. Afterwards, aluminum is mainly used as a back electrode and is deposited by evaporation.

Recently, bulk heterojunction solar cells have been developed using inorganic nanoparticles having various sizes and shapes, such as cadmium selenide (CdSe), lead sulfide (PbS), and cadmium sulfide (CdS). However, cadmium (Cd), lead (Pb) and indium (In), etc. have a significant impact on the supply of renewable energy due to toxic or lack of resources.

In addition, bulk heterojunction solar cells using semiconductor materials such as fullerenes have a problem of low photocurrent in the long wavelength band and poor surface morphology, resulting in low power conversion efficiency (PCE). .

The present invention is to solve a number of problems including the above problems, to provide a bulk heterojunction solar cell having a high light absorption, non-toxic, low cost, excellent photoelectric conversion efficiency using abundant materials and a method of manufacturing the same. It is. The foregoing problem has been presented by way of example, and the scope of the present invention is not limited by this problem.

According to one aspect of the invention, a bulk heterojunction solar cell is provided. In the bulk heterojunction solar cell, SnS ₂ (Tin Disulfide) is used as an electron accepting material, and P3HT (Poly (3-hexylthiophene-2,5-diyl)) or PCPDTBT (Poly [2,6-) acts as an electron donor. (4,4-bis- (2-ethylhexyl) -4H-cyclopenta [2,1-b; 3,4-b '] dithiophene) -alt-4,7 (2,1,3-benzothiadiazole)]) Although mixed, the SnS ₂ and P3HT or SnS ₂ and PCPDTBT may be a weight ratio of 6: 4 to 8: 2.

According to another aspect of the present invention, a bulk heterojunction solar cell is provided. The bulk heterojunction solar cell includes a substrate; A first electrode layer formed on the substrate; A transport layer formed on the first electrode layer; An active layer formed on the transport layer; And an electrode layer formed on the active layer, wherein the active layer is formed of an electron acceptor material and an electron donor material, and the electron acceptor material is SnS ₂ (Tin Disulfide), and the electron donor material is P3HT (Poly ( 3-hexylthiophene-2,5-diyl)) or 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)]), but the electron acceptor material and the electron donor material may be mixed to have a weight ratio of 6: 4 to 8: 2.

According to another aspect of the present invention, a method of manufacturing a bulk heterojunction solar cell is provided. The method of manufacturing a bulk heterojunction solar cell includes forming an active layer on a substrate having a transparent electrode by using a hot-injection method, wherein the active layer is an electron receiving material. And the electron donor material has a weight ratio of 6: 4 to 8: 2, and the electron acceptor material includes Sn Disulfide (SnS ₂ ) nanoparticles, and the electron donor material is P3HT (Poly (3-hexylthiophene). -2,5-diyl)) or 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)]).

In the method of manufacturing a bulk heterojunction solar cell, the step of forming the active layer, the first mixture is heated to a temperature range of 110 ℃ to 130 ℃, supplying nitrogen (nitrogen), 190 ℃ to 210 ℃ of Heating up to a temperature range; And rapidly injecting a second mixture into the first mixture after the step of increasing the temperature.

According to one embodiment of the present invention made as described above, it is possible to implement a bulk heterojunction solar cell and a manufacturing method thereof having high photoelectric conversion efficiency by using a high light absorption, non-toxicity, low cost, and abundant materials. Of course, the scope of the present invention is not limited by these effects.

1 is a cross-sectional view schematically showing the structure of a bulk heterojunction solar cell according to an embodiment of the present invention.

2 is a result of analyzing the active layer of a bulk heterojunction solar cell according to an embodiment of the present invention with a transmission electron microscope (TEM).

3 is a result of analyzing the active layer of the bulk heterojunction solar cell according to an embodiment of the present invention by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS).

4 is a result of analyzing the current density and the photoelectric conversion efficiency according to the thickness of the active layer of the bulk heterojunction solar cell according to an embodiment of the present invention.

5 is a result of analyzing the current voltage characteristics and the light absorption spectrum of the bulk heterojunction solar cell according to an embodiment of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in various forms, and the following embodiments are intended to complete the disclosure of the present invention, the scope of the invention to those skilled in the art It is provided to inform you completely. In addition, the components may be exaggerated or reduced in size in the drawings for convenience of description.

1 is a cross-sectional view schematically showing the structure of a bulk heterojunction solar cell according to an embodiment of the present invention.

Referring to FIG. 1, a bulk heterojunction solar cell 100 according to an embodiment of the present invention may include a substrate 10, a first electrode layer 20, a transport layer 30, an active layer 40, and a second electrode layer 50. ) May be included. The substrate 10 may be, for example, any one of a glass, a wafer, and a flexible substrate.

The first electrode layer 20 is a transparent electrode through which the electrode is transparent, and an ITO layer having a specific gravity of 90% indium oxide (In ₂ O ₃ ) and 10% tin oxide (SnO ₂ ) may be used. However, the present invention is not limited thereto, and carbon nanotubes may be coated or PEDOT may be used. The work function of the first electrode layer 20 is 5.1 eV, 4.75 eV, 4.3 eV, and the first electrode layer 20 is formed on the substrate 10 by using any one of electron beam deposition, vacuum evaporation, and sputtering methods. Can be formed on.

The transport layer 30 may use, for example, PEDOT: PSS, which is a high concentration conductive polymer, and may be understood as a buffer layer. The transport layer 30 may be used as an electrode layer instead of the first electrode layer 20, but may be used as a transport layer for holes generated in the active layer 40 in the present invention. The transport layer 30 is formed by a spin coating method, and the work function is 5.2 eV to 5.3 eV.

The active layer 40 is formed on the substrate 10 having a transparent electrode by using a hot-injection method, and by absorbing light, electrons of the highest occupied molecular orbital (HOMO) are attracted to the LUMO (lowest unoccupied molecular). orbital) to form an exciton. Although somewhat different depending on the conductivity of the active layer 40, the active layer 40 has a thickness of about 140 nm to 150 nm. If the thickness of the active layer 40 is less than 140 nm, the efficiency of the bulk heterojunction solar cell is not high because there are few electron-hole pairs excited by the absorbed light. On the other hand, when the thickness of the active layer 40 is greater than 150nm, the thickness of the absorber layer 40 is too thick, so the movement path between electrons and holes is long, so that recombination occurs a lot, the efficiency of the bulk heterojunction solar cell is reduced. .

In this case, not only the loss in the active layer 40 and the electrode interface should be minimized, but also the path should be formed so that the electrons and holes separated in the active layer 40 can move to the electrode without being short-circuited. At this time, even within the electron donor material and the electron acceptor material, the movement speed of holes and electrons should be fast enough.

In order to solve this problem, in the bulk heterojunction solar cell 100 according to an embodiment of the present invention, the active layer 40 separates electrons and holes from excitons generated by absorbing light, and as an electron donor material, For example, P3HT (Poly (3-hexylthiophene-2,5-diyl)) or 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)]) may be used. As the acceptor material, LUMO is lower than the electron donor material. For example, SnS ₂ (Tin Disulfide) nanoparticles may be used. That is, the exciton generated by absorbing light from the electron donor material moves to the interface of the electron acceptor and then passes the electron to the electron acceptor to separate the electron and the hole pair.

SnS ₂ (Tin Disulfide) used as electron acceptor in active layer 40 is P3HT (Poly (3-hexylthiophene-2,5-diyl)) or 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)]) These two materials mix well together. At this time, the weight ratio of the electron receiving material and the electron donor material must satisfy 6: 4 to 8: 2 to improve the efficiency of transmitting and receiving electrons according to light absorption. In the present invention, when the weight ratio of the electron acceptor material and the electron donor material is 7: 3, the optimum efficiency is obtained. That is, the SnS ₂ and the P3HT or the SnS ₂ and the PCPDTBT may satisfy a weight ratio of 6: 4 to 8: 2.

The second electrode layer 50 may be formed on the active layer 40 using a vacuum evaporator method. The second electrode layer 50 may include, for example, aluminum (Al) metal.

On the other hand, a method of manufacturing a bulk heterojunction solar cell according to an embodiment of the present invention will be described in detail with reference to the following experimental example and FIGS.

Hereinafter, an experimental example to which the above-described technical concept is applied will be described to help understanding of the present invention. However, the following experimental examples are only for helping understanding of the present invention, and the present invention is not limited to the following experimental examples.

As a sample according to the experimental example of the present invention, PEDOT: PSS (polyethylenedioxythiophene doped with polystyrene-sulfonic acid) was formed at about 70 nm on a glass substrate coated with ITO by using a spin coating method. Here, the spin coating condition was carried out at a speed of 4000rpm for about 30sec. The SnS ₂ used in the active layer is then mixed by mixing the first mixture and the second mixture in a flask having two openings using a hot-injection method. Nanoparticles were formed. Here, after putting the first mixture containing SnCl ₄ (anhydrous tin (IV) chloride) and OLA (oleylamine), and heated to a temperature range of 110 ℃ to 130 ℃, supplying nitrogen (nitrogen), 190 ℃ It heated up to the temperature range of 210 degreeC.

After the temperature increase, the first mixture was rapidly reacted by injecting the second mixture containing OLA and TAA (thioacetamide). The reaction was carried out in a nitrogen atmosphere, and reacted for about 12 hours and then cooled to room temperature. Finally, the mixture was centrifuged at a rate of 10000 rpm for about 10 minutes using a mixture of chlorobenzene and ethanol. The chlorobenzene and ethanol were used to disperse SnS ₂ nanoparticles (SnS ₂ : P3HT), and after repeated centrifugation, washed repeatedly to give SnS ₂ Nanoparticles were prepared.

In addition, SnS ₂ After the nanoparticles were prepared, the drying process was performed at about 140 ° C. for about 30 minutes. SnS ₂ on the PEDOT: PSS formed substrate after drying Nano particles were dropped to form an active layer. Thereafter, an aluminum electrode having a thickness of about 100 nm was formed on the active layer by using a vacuum evaporation method to prepare a bulk heterojunction solar cell sample.

The prepared sample was subjected to ultraviolet-visible absorption spectroscopy, photoluminescence spectroscopy (PL), x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD), transmission electron microscopy (TEM) and HR-TEM. The analysis was performed. The wjsfalfeh and open voltage characteristics of bulk heterojunction solar cell samples were analyzed using sampCurrent density-voltage (J-V) and solar simulator (Keithley 69911).

In another embodiment of the present invention, the electron donor material of the active layer was changed from P3HT to PCPDTBT, and SnS ₂ nanoparticles (SnS ₂ : PCPDTBT) were prepared in the same manner as described above to analyze current density and absorption rate.

On the other hand, in comparison with this, by controlling the spin coating conditions in the active layer manufacturing process, a bulk heterojunction solar cell having a different thickness of the active layer was manufactured to measure current density and photoelectric conversion efficiency.

2 is a result of analyzing the active layer of a bulk heterojunction solar cell according to an embodiment of the present invention with a transmission electron microscope (TEM).

Referring to FIG. 2 (a) and (b), as was analyzed and SnS ₂ nanoparticle by TEM and HR-TEM, SnS ₂ nanoparticle is shown to clarify the lattice pattern, distorted hexagonal shape of SnS ₂ nano Since no dislocations exist in the particles, it was confirmed that the prepared SnS ₂ nanoparticles were very crystalline.

Referring to (c) of FIG. 2, the size of SnS ₂ nanoparticles is calculated based on 100 particles in a TEM image, and has a size distribution of about 3 nm to 8 nm and an average of about 5.2 nm. Particles were found to be the most distributed.

3 is a result of analyzing the active layer of the bulk heterojunction solar cell according to an embodiment of the present invention by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS).

Referring to FIG. 3, the crystal structure of SnS ₂ nanoparticles was analyzed by XRD. In FIG. 3 (a), diffraction peaks were observed at 2theta values of 17 °, 30 °, 51 °, and 60 °, and JCPDS. card No. According to 0-040-1466, the SnS ₂ nanoparticles of the present invention were found to have hexagonal structures having (002), (100), (110, and (200) crystal faces, respectively, in the diffraction peaks. The hexagonal structure is clearly shown in (b) of FIG. 2 as a result of analysis by HR-TEM.

Of Figure 3 (b) is a result of analyzing the optical properties of SnS ₂ nanoparticle by UV-vis and PL spectroscopy, SnS ₂ nano-particles shows a light absorption rate in accordance with various reaction times of from 1 hour to 13 hours. Absorption of SnS ₂ nanoparticles at a reaction time of about 9 hours and a wavelength of about 440 nm was red-shifted relative to the bulk value. The bandgap of the SnS ₂ nanoparticles reacted for 9 hours is about 2.8 eV, which is about 0.4 eV larger than the bulk value. This seems to be due to the quantum size effect. Strong quantum nanocrystals have been found to be photoluminescent with high quantum efficiency, and the emission and absorption peaks are adjustable in size. Therefore, the SnS ₂ nanoparticles of the present invention can be seen that the optical properties are improved, it can be applied to LED, Solar cell and the like.

3 (c) is an analysis of the chemical composition of the SnS ₂ nanoparticles by XPS, looking at the irradiated spectrum, it was confirmed that the Sn, S and C peaks were found mainly in the nanocrystals SnS ₂ nanoparticles are stable It can be confirmed that it is formed.

4 is a result of analyzing the current density and the photoelectric conversion efficiency according to the thickness of the active layer of the bulk heterojunction solar cell according to an embodiment of the present invention.

Referring to (a) of FIG. 4, the thickness of the active layer (SnS ₂ : P3HT = 7: 3) containing SnS ₂ nanoparticles is adjusted by varying the speed of spin-casting from 1000 rpm to 5000 rpm. The result of control. As the spin speed increases, the thickness of the active layer gradually decreases.

Experimental Example	Active layer thickness (nm)	Voc (V)	Jsc (㎃ / ㎠)	FF (fill factor)	Photoelectric conversion efficiency (%)
Comparative Example 1	161	0.56	0.46	0.59	0.15
Comparative Example 2	153	0.55	0.55	0.61	0.18
Example 1	146	0.55	1.18	0.61	0.39
Comparative Example 3	131	0.55	0.62	0.58	0.19
Comparative Example 4	127	0.57	0.75	0.59	0.25

Referring to Table 1 and FIGS. 4B and 4C, the bulk heterojunction solar cell sample of Example 1 has an active layer thickness of about 146 nm, an open voltage of 0.55 V, and a short circuit current of 1.18 mA / cm 2. FF was 0.61, and the photoelectric conversion efficiency was 0.39%, which was higher than that of Comparative Examples 1 to 4.

It can be seen that the short circuit current increases as the thickness of the active layer decreases, and the absorption of photons becomes higher as the thickness of the active layer becomes thinner. On the other hand, as the thickness of the active layer increases, the short-circuit current decreases, which seems to decrease with increasing recombination rate before each electron-hole pair is collected at the electrode. In other words, when the thick active layer is moved to collect electrons or holes, the path is long and the possibility of recombination due to defects is increased.

5 is a result of analyzing the current voltage characteristics and the light absorption spectrum of the bulk heterojunction solar cell according to the embodiments of the present invention.

Referring to Figure 5 (a), it is the result of analyzing the current density and light absorption spectrum of the bulk heterojunction solar cell manufactured by different types of active layers, respectively. Example 1 is a sample of a bulk heterojunction solar cell with an active layer containing SnS ₂ nanoparticles (SnS ₂ : P3HT), and Example 2 is provided with an active layer containing SnS ₂ nanoparticles (SnS ₂ : PCPDTBT) Bulk heterojunction solar cell sample. The sample of Example 1 and the sample of Example 2 differ only in the electron donor material, and it can be seen that the sample of Example 2 using PCPDTBT as the electron donor material has a higher current density than the sample of Example 1 using P3HT. there was. The bandgap of PCPDTBT is 1.4eV, which is a relatively lower bandgap polymer than the bandgap 2eV of P3HT. Referring to FIG. 5B, the sample of Example 2 using PCPDTBT has a higher absorption rate in the visible light spectrum than the sample of Example 1 using P3HT and the sample of Comparative Example 5 using SnS ₂ only. It seems to have improved.

As described above, the present invention may form an active layer by mixing P3HT and PCPDTBT with SnS ₂ , which is an electron accepting material, as an electron donor material. The bulk heterojunction solar cell including the active layer may have a photoelectric conversion efficiency of up to 0.77% under AM 1.5G conditions.

In addition, the active layer thickness of the present invention affects the number of photons absorbed by the active layer and improves the penetration path for carrier transport and collection. By using SnS ₂ nanoparticles as electron accepting materials, it is possible to form improved device properties after altering the insulating surface ligand of the SnS ₂ particles. The inclusion of low bandgap polymers in the device structure can increase light absorption in the active layer to further improve device performance.

Therefore, a bulk heterojunction solar cell having excellent light absorption characteristics, non-toxicity, low cost, and improving the photoelectric conversion efficiency can be realized by forming an absorption layer using abundant materials.

Although the present invention has been described with reference to one embodiment shown in the drawings, this is merely exemplary, and those skilled in the art will understand that various modifications and equivalent other embodiments are possible therefrom. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

Claims (4)

1. SnS ₂ (Tin Disulfide) is used as an electron acceptor, and P3HT (Poly (3-hexylthiophene-2,5-diyl)) or PCPDTBT (Poly [2,6- (4,4-bis-) acts as an electron donor. (2-ethylhexyl) -4H-cyclopenta [2,1-b; 3,4-b '] dithiophene) -alt-4,7 (2,1,3-benzothiadiazole)]), but the SnS ₂ and P3HT or SnS ₂ and PCPDTBT is characterized in that the weight ratio of 6: 4 to 8: 2,

   Bulk heterojunction solar cell.
2. Board;

   A first electrode layer formed on the substrate;

   A transport layer formed on the ITO layer;

   An active layer formed on the transport layer; And

   A second electrode layer formed on the active layer;

   Including,

   The active layer is composed of an electron acceptor material and an electron donor material, and the electron acceptor material is SnS ₂ (Tin Disulfide), and the electron donor material is P3HT (Poly (3-hexylthiophene-2,5-diyl)) or 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)]), wherein the electron acceptor material and the electron donor material are mixed to have a weight ratio of 6: 4 to 8: 2,

   Bulk heterojunction solar cell.
3. Forming an active layer on a substrate having a transparent electrode using a hot-injection method;

   The active layer has a weight ratio of the electron acceptor material and the electron donor material of 6: 4 to 8: 2,

   The electron acceptor material includes Sn Disulfide (SnS ₂ ) nanoparticles, and the electron donor material is P3HT (Poly (3-hexylthiophene-2,5-diyl)) or 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)]) Characterized in that,

   Method of manufacturing bulk heterojunction solar cell.
4. The method of claim 3, wherein

   Forming the active layer,

   Heating the first mixture to a temperature range of 110 ° C. to 130 ° C., supplying nitrogen and raising the temperature to a temperature range of 190 ° C. to 210 ° C .; And

   Reacting by rapidly injecting a second mixture into the first mixture after the temperature raising step;

   Characterized in that it comprises a,

   Method of manufacturing bulk heterojunction solar cell.

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