Conductive paste composition and solar cell using the conductive paste composition

Abstract

A conductive paste composition, including aluminum powder; an organic carrier including an organic solvent and resin or cellulose; and phenoxy alkyl alcohol accounting for 210% of weight of the conductive paste composition. The conductive paste composition includes the phenoxy alkyl alcohol, and thus resultant conductive paste not only has enhanced surface tension, but also has an increased difference in surface tension between the resultant conductive paste and a cell to therefore alter wetting behavior between the paste and a silicon wafer, to reduce the broadening behavior of the wiring lines printed, increase the aspect ratio of printing wiring, increase the light-receiving area of the solar cells, and enhance the photovoltaic conversion efficiency of the solar cells (especially local back surface field solar cells and PERC bifacial cells).

Claims

1. A conductive paste composition, comprising: aluminum powder; an organic carrier comprising an organic solvent except for phenoxy ethanol and resin or cellulose; and phenoxy ethanol accounting for 210% of weight of the conductive paste composition.

2. The conductive paste composition of claim 1, wherein the phenoxy ethanol accounts for 28% of weight of the conductive paste composition.

3. The conductive paste composition of claim 2, wherein the aluminum powder accounts for 6085% of weight of the conductive paste composition.

4. A solar cell, comprising the conductive paste composition of claim 3.

5. The conductive paste composition of claim 2, wherein the organic carrier has viscosity of 115 Kcps.

6. The conductive paste composition of claim 2, further comprising glass frit.

7. The conductive paste composition of claim 2, wherein the organic carrier further comprises an additive selected from the group consisting of dispersing agent, leveling agent, defoaming agent, anti-precipitant, thixotropy agent and coupling agent.

8. A solar cell, comprising the conductive paste composition of claim 2.

9. The conductive paste composition of claim 1, wherein the aluminum powder accounts for 6085% of weight of the conductive paste composition.

10. A solar cell, comprising the conductive paste composition of claim 9.

11. The conductive paste composition of claim 1, wherein the organic carrier has viscosity of 115 Kcps.

12. A solar cell, comprising the conductive paste composition of claim 11.

13. The conductive paste composition of claim 1, further comprising glass frit.

14. The conductive paste composition of claim 1, wherein the organic carrier further comprises an additive selected from the group consisting of dispersing agent, leveling agent, defoaming agent, anti-precipitant, thixotropy agent and coupling agent.

15. A solar cell, comprising the conductive paste composition of claim 1.

Description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(1) Objectives, features, and advantages of the present disclosure are hereunder illustrated with specific embodiments and described below.

(2) Unless otherwise specified, the sign % used below shall mean weight %.

(3) The present disclosure provides a conductive paste comprising an organic carrier, aluminum powder, and phenoxy alkyl alcohol. The phenoxy alkyl alcohol accounts for 210%, preferably 28%, of the weight of the conductive paste. Furthermore, the phenoxy alkyl alcohol is provided preferably in the form of a solvent. Furthermore, the phenoxy alkyl alcohol is preferably phenoxy ethanol or phenoxy propanol, but the present invention is not limited thereto.

(4) Furthermore, a method of preparing a conductive paste composition according to this embodiment comprises step S1, step S2 and step S3.

(5) Step S1: mixing an organic solvent and resin or cellulose to form a uniform organic carrier. Furthermore, step S1 further entails adding an additive, as needed, to form the organic carrier.

(6) Step S2: mixing the aluminum powder, the phenoxy alkyl alcohol and the organic carrier and grinding the mixture to form a conductive paste precursor. Furthermore, step S2 further entails adding glass frit, as needed, to mix the glass frit with the organic carrier and grinding the mixture, so as to form the conductive paste precursor. In step S2, preferably, the grinding process is performed with a three-roll grinder (model number: Exakt 80E) to obtain the conductive paste precursor.

(7) Step S3: stirring the conductive paste precursor obtained in step S2 to blend and disperse it, so as to form the conductive paste composition.

(8) Furthermore, in step S1, the organic carrier has viscosity of around 115 Kcps, preferably 1015 Kcps. By controlling the viscosity of the organic carrier, it is practicable for the conductive paste composition to have an optimal viscosity.

(9) Furthermore, in step 51, the cellulose (or resin) accounts for 14%, preferably 23%, of the weight of the conductive paste composition. Choices of the resin include wood rosin and polyacrylonitrile, but the present disclosure is not limited thereto. Choices of the cellulose include ethyl cellulose and propyl cellulose, but the present disclosure is not limited thereto.

(10) Furthermore, in step S1, if an additive is added, the additive accounts for around 0.22.5%, preferably 1.52%, of the total weight of the conductive paste composition. Choices of the additive include a dispersing agent, leveling agent, defoaming agent, anti-precipitant, thixotropy agent, and coupling agent, but the present disclosure is not limited thereto.

(11) Furthermore, in step S2, the phenoxy alkyl alcohol accounts for 210%, preferably 28%, of the total weight of the conductive paste composition.

(12) Furthermore, in step S2, if the glass frit is added, the glass frit accounts for 0.15%, preferably 34%, of the total weight of the conductive paste composition. Choices of the glass frit include vanadium-based, bismuth-based glass frit or the other types of glass frit, preferably the glass frit shown in Table 1 below, but the present disclosure is not limited thereto. A variant embodiment involves using just one type of glass frit or a combination of various types of glass frit.

(13) TABLE-US-00001 TABLE 1 glass frit 1 PbOZnOB.sub.2O.sub.3SiO.sub.2 glass frit 2 SiO.sub.2PbOB.sub.2O.sub.3Al.sub.2O.sub.3ZrO.sub.2 glass frit 3 Bi.sub.2O.sub.3ZnOSiO.sub.2B.sub.2O.sub.3Al.sub.2O.sub.3 glass frit 4 Bi.sub.2O.sub.3B.sub.2O.sub.3Al.sub.2O.sub.3BaOZnO glass frit 5 SiO.sub.2PbOZnOB.sub.2O.sub.3Al.sub.2O.sub.3 glass frit 6 V.sub.2O.sub.5B.sub.2O.sub.3Al.sub.2O.sub.3BaOZnO

(14) Referring to Table 2, the conductive paste composition in an embodiment is described below.

(15) TABLE-US-00002 TABLE 2 constituents conductive paste composition resin (or cellulose) 1~4% organic solvent 5~20% phenoxy alkyl alcohol 2~10% additive 0.2~2.5% glass frit 0.1~5% aluminum powder 60~85%

(16) In an embodiment illustrative of the conductive paste composition, resin (or cellulose) accounts for 14% of the weight of the conductive paste composition 1, an organic solvent accounts for 520% of the weight of the conductive paste composition, phenoxy alkyl alcohol accounts for 210% of the weight of the conductive paste composition, an additive accounts for 0.22.5 of the weight of the conductive paste composition, glass frit accounts for 0.15% of the weight of the conductive paste composition, and aluminum powder accounts for 6085% of the weight of the conductive paste composition. By confining the constituents, and proportions thereof, of the conductive paste composition to the aforesaid scope, it is practicable to obtain solar bifacial cells capable of further reducing fine-line line broadening.

(17) Choices of the organic solvent include alcohol ether-based organic solvent, ester alcohol film-forming agent (TEXANOL, EASTMAN CHEMICAL COMPANY), terpineol and diethylene glycol monobutyl ether, but the present disclosure is not limited thereto.

(18) Preparation of Conductive Paste Composition

(19) The conductive paste composition in comparisons 16 and embodiments 18 is prepared according to step S1 through step S3 and the formulas shown in Table 3 and Table 4 below.

(20) TABLE-US-00003 TABLE 3 conductive paste comparison comparison embodiment embodiment embodiment embodiment comparison composition 1 2 1 2 3 4 3 resin (or 3% 3% 3% 3% 3% 3% 3% cellulose) dispersing 1% 1% 1% 1% 1% 1% 1% agent diethylene glycol 15% 14% 13% 11% 7% 5% 0% monobutyl ether henoxyethanol 0% 1% 2% 4% 8% 10% 15% glass frit 6 2% 2% 2% 2% 2% 2% 2% glass frit 5 1% 1% 1% 1% 1% 1% 1% aluminum 9% 9% 9% 9% 9% 9% 9% powder 1 aluminum 69% 69% 69% 69% 69% 69% 69% powder 2 Total 100.0% 100.0% 100.0% 100.0% 100.0% 100% 100%

(21) TABLE-US-00004 TABLE 4 conductive paste comparison comparison embodiment embodiment embodiment embodiment comparison composition 1 2 1 2 3 4 3 resin (or 3% 3% 3% 3% 3% 3% 3% cellulose) dispersing 1% 1% 1% 1% 1% 1% 1% agent diethylene glycol 15% 14% 13% 11% 7% 5% 0% monobutyl ether phenoxyethanol 0% 1% 2% 4% 8% 10% 15% glass frit 6 2% 2% 2% 2% 2% 2% 2% glass frit 5 1% 1% 1% 1% 1% 1% 1% aluminum 9% 9% 9% 9% 9% 9% 9% powder 1 aluminum 69% 69% 69% 69% 69% 69% 69% powder 2 Total 100.0% 100.0% 100.0% 100.0% 100.0% 100% 100%

(22) Furthermore, constituents used in comparisons 16 and embodiments 18 are shown in Table 5 below.

(23) TABLE-US-00005 TABLE 5 resin (or cellulose) ETHOCEL Std 20 dispersing agent Disponer 910 glass frit 6 V.sub.2O.sub.5B.sub.2O.sub.3Al.sub.2O.sub.3BaOZnO glass frit 5 SiO.sub.2PbOZnOB.sub.2O.sub.3A1.sub.2O.sub.3 aluminum powder 1 Hunan Golden Horse Co., Ltd. FO103 aluminum powder 2 Hunan Golden Horse Co., Ltd. JM607

(24) The viscosity, line height, line width, and electrical properties of the aluminum powder-containing conductive paste composition prepared in embodiments 18 and comparisons 16 are measured, and the results are shown in Table 6 and Table 7.

(25) Viscosity

(26) The viscosity of the aluminum powder-containing conductive paste composition prepared in embodiments 18 and comparisons 16 is measured at 250.3 C., 0.5 rpm and 20 rpm with Brookfield DVII viscometer.

(27) Line Height and Line Width

(28) A screening fabric with 325 mesh and 23 m diameter wire is used as a screening template, with a designated pattern which has a line width of 150 m, and an emulsion thickness of 20 m. The aluminum powder-containing conductive paste composition prepared in embodiments 18 and comparisons 16 is printed on a blank (bifacial) PERC cell with a printer, using the same template and under the same printing condition. Then, it is dried at 150250 C. before being sent to a high-temperature sintering furnance (for removal of organic matter and aluminum layer sintering). Afterward, the line height and line width of the fine lines are measured with a 3D microscope, so as to calculate the aspect ratio (%) and line broadening ratio (%) with equations below.
aspect ratio (%)=line height (m)/line width (m)equation (1)
line broadening (%)=(sintered line width (m)designated pattern line width (m))/designated pattern line width (m))equation (2)

(29) Electrical Properties

(30) A screening fabric with 325 mesh and 23 m diameter wire is used as a screening template, with a designated pattern which has line width of 150 m, and an emulsion thickness of 20 m. The aluminum powder-containing conductive paste composition prepared in embodiments 18 and comparisons 16 is printed on a blank (bifacial) PERC cell with a printer, using the same template and under the same printing condition. Then, it is dried at 150250 C. before being sent to a high-temperature sintering furnance (for removal of organic matter and aluminum layer sintering). Front-side and back surface electrical properties of the sintering (bifacial) PERC cell are measured by a voltage current test (IV test) to test the photovoltaic conversion efficiency (Eff) (%) of the bifacial PERC cell, open-circuit voltage (Voc(V)) and short-circuit current (Isc(A)), wherein the testing machine is QuickSun 120CA produced by Finland-based Endeas.

(31) TABLE-US-00006 TABLE 6 conductive paste comparison comparison embodiment embodiment embodiment embodiment comparison composition 1 2 1 2 3 4 3 viscosity 0.5 139.70 155.31 173.15 230.19 290.05 273.31 330.11 (Kcp) rpm 20.0 24.12 26.33 28.41 32.73 37.72 36.11 42.21 rpm line height 25.1 25.1 25.1 25.4 25.3 25.4 25.4 (m) line width 188.3 186.1 176.4 173.3 168.1 167.3 167.2 (m) aspect ratio 13.33 13.48 14.23 14.66 15.05 15.18 15.19 (%) line 25.53 24.07 17.60 15.53 12.07 11.53 11.47 broadening (%) front Voc 0.659 0.660 0.662 0.661 0.657 0.657 0.657 side (V) Isc 9.713 9.071 9.614 9.618 9.658 9.658 9.608 (A) Eff 21.132 21.121 21.070 21.101 21.021 21.022 21.023 (%) back Voc 0.650 0.650 0.653 0.653 0.649 0.649 0.649 side (V) Isc 6.579 6.579 6.756 6.780 6.893 6.891 6.891 (A) Eff 14.140 14.250 14.530 14.600 14.796 14.780 14.780 (%) overall 35.272 35.371 35.600 35.701 35.817 35.802 35.803 efficiency Eff (%)

(32) TABLE-US-00007 TABLE 7 conductive paste comparison comparison embodiment embodiment embodiment embodiment comparison composition 4 5 5 6 7 8 6 viscosity 0.5 139.70 170.80 193.15 253.19 286.00 300.05 330.11 (Kcp) rpm 20.0 24.12 28.93 31.1 36.11 37.72 39.7 42.21 rpm line height 25.1 25.1 25.4 25.3 25.4 25.4 25.1 (m) line width 188.3 186.4 170.3 169.1 168.3 167.3 167.2 (m) aspect ratio 13.86 14.23 14.91 14.96 15.09 15.18 13.86 (%) line 25.53 24.27 13.53 12.73 12.20 11.53 11.47 broadening (%) front Voc 0.6592 0.661 0.662 0.661 0.657 0.657 0.657 side (V) Isc 9.713 9.041 9.614 9.618 9.698 9.658 9.608 (A) Eff 21.132 21.121 21.080 21.101 21.022 21.022 21.023 (%) back Voc 0.6500 0.650 0.653 0.654 0.649 0.649 0.649 side (V) Isc 6.579 6.579 6.756 6.781 6.893 6.891 6.891 (A) Eff 14.140 14.230 14.533 14.612 14.799 14.782 14.781 (%) overall 35.272 35.351 35.613 35.712 35.82 35.80 35.804 efficiency Eff (%)

(33) As shown in Table 6, by adding the phenoxy ethanol, the aspect ratio of the conductive paste composition tends to increase, whereas the line broadening ratio tends to decrease. The line broadening ratio and aspect ratio without the addition of phenoxy ethanol (comparison 1) are around 25% and 13%, respectively. In embodiment 3, embodiment 4 and comparison 3, the line broadening ratio decreases to 1112%, whereas the aspect ratio increases to 15% or above. The viscosity increases with the proportion of phenoxy ethanol. Furthermore, although the line broadening ratio and aspect ratio in comparison 3 are satisfactory, the conductive paste composition on the screening template is unlikely to enter meshes if the viscosity of the conductive paste composition exceeds 300 Kcp @0.5 rpm (because the viscosity of the conductive paste composition preferably does not exceed 300 Kcp). Hence, the viscosity in comparison 3 is overly high and thus is unsatisfactory. With embodiment 4 being similar to comparison 3 in aspect ratio, line broadening ratio, and overall efficiency, it is inferable that if the addition ratio of phenoxy ethanol exceeds 10%, the 10% increase in the aspect ratio, line broadening ratio and overall efficiency will not bring special, remarkable effect. Therefore, a critical effect is achieved as soon as the addition ratio of phenoxy ethanol is 10%. Excessive addition of phenoxy ethanol leads to excessive viscosity, and thus the conductive paste composition on the template fails to enter meshes. Therefore, the addition ratio of phenoxy ethanol should preferably not exceed 10%.

(34) Furthermore, as indicated by comparison 1 and comparison 2, if a mere 1% of phenoxy ethanol is added, there will not be any significant improvement in the aspect ratio, line broadening ratio and overall efficiency. Referring to comparison 1 and embodiment 1, the aspect ratio, line broadening ratio and overall efficiency in embodiment 1 are significantly improved. For instance, the introduction of 1% phenoxy ethanol (comparison 2) causes the line broadening ratio in comparison 1 (0% phenoxy ethanol) to decrease by around 1% and the overall efficiency in comparison 1 (0% phenoxy ethanol) to increase by around 0.1%. The introduction of 2% phenoxy ethanol (embodiment 1) causes the line broadening ratio in comparison 1 (0% phenoxy ethanol) to decrease by around 8% and the overall efficiency in comparison 1 (0% phenoxy ethanol) to increase by around 0.33%. Therefore, the addition ratio of phenoxy ethanol should preferably be above 2%.

(35) As shown in Table 6, embodiment 3 is good at the aspect ratio, line broadening ratio and overall efficiency, especially overall efficiency which increases to 35.817%. Hence, embodiment 3 achieves the most preferable implementation.

(36) Table 7 indicates the same tendency as Table 6. For instance, although comparison 6 involves adding 15% phenoxy propanol, its aspect ratio is 13.86%, that is, the same as the aspect ratio achieved without the addition of phenoxy propanol (in comparison 4 (0% phenoxy propanol)). Furthermore, comparison 6 achieves viscosity which exceeds 300 Kcp @0.5 rpm and thus is unsatisfactory. By contrast, both the aspect ratio (15.18%) and the viscosity (300.05 Kcp) in embodiment 8 (10% phenoxy propanol) are preferable; hence, the addition ratio of phenoxy propanol should preferably not exceed 10%. Furthermore, like what is indicated in Table 6, the addition of 1% phenoxy propanol (comparison 5) causes the line broadening ratio in comparison 4 (0% phenoxy propanol) to decrease by around 1.3% and the overall efficiency in comparison 4 (0% phenoxy propanol) to increase by around 0.08%. The addition of 2% phenoxy propanol (embodiment 5) causes the line broadening ratio in comparison 4 (0% phenoxy propanol) to decrease by around 12% and the overall efficiency in comparison 4 (0% phenoxy propanol) to increase by around 0.34%. Therefore, the addition ratio of phenoxy propanol should preferably be above 2%.

(37) Therefore, even if phenoxy ethanol is replaced with phenoxy propanol (or the other type of phenoxy alkyl alcohol), the similar effect will be achieved. Furthermore, the addition ratio of phenoxy propanol should preferably be 210%, preferably 28%, and most preferably 8% (in embodiment 7 the overall efficiency is 35.82%).

(38) Therefore, as indicated in Table 6 and Table 7, the addition ratio of phenoxy alkyl alcohol is preferably 210%, preferably 28%, and most preferably 8% (embodiments 3, 7).

(39) Since fine-line printing is especially suitable for bifacial cell conductive paste, if back-side aluminum layer wirings are narrow, back-side light-receiving area will increase. As indicated in Table 6 and Table 7, in the course of the measurement of the front side, although the short-circuit current (Isc) may decrease because the back aluminum layer area decreases and thus light reflecting off the aluminum layer decreases, the wirings formed from the phenoxy alkyl alcohol-containing conductive paste composition have low line broadening and high aspect ratio, their back-side measured efficiency increases because of a reduction in light-blocking area, thereby giving rise to an increase in the summation of front-side and back-side efficiency.

(40) In conclusion, the present disclosure is advantageous in that the use of phenoxy alkyl alcohol reduces the line broadening issue of fine line printing, enhances the aspect ratio of wirings, increases the photovoltaic conversion efficiency, thereby allowing phenoxy alkyl alcohol to be applicable to solar cells which employ fine line printing, for example, PERC bifacial cells and local back surface field solar cells.

(41) The present disclosure is disclosed above by preferred embodiments. However, persons skilled in the art should understand that the preferred embodiments are illustrative of the present disclosure only, but shall not be interpreted as restrictive of the scope of the present disclosure. Hence, all equivalent modifications and replacements made to the aforesaid embodiments shall fall within the scope of the present disclosure. Accordingly, the legal protection for the present disclosure shall be defined by the appended claims.