Preparation And Application Of Leaded Conductive Copper Paste Used In Solar Cells

With the shortage of traditional energy sources (such as coal, petroleum) andpollution of the environmental, new types of clean energies including solar energygradually brought to the people’s attention. The solar cell is a device that convertssunlight energy into electrical energy directly and produces small pollution in theconversion process. In all types of solar cells, crystalline silicon solar cell is usedwidest for its mostly developed technology and higher photoelectric conversionefficiency. Conductive silver paste is widely used for in the positive materials of thecrystalline silicon solar cells. With the silver price is rising, the cost of conductivesilver paste is constantly rising, so some base metals materials have been developedfor conductive paste. In base metals, the conductivity of copper and silver is almostequal. There is no Ag+migration defect, and the price is far lower than the silver,which makes copper become an ideal material. Conductive copper paste has become akind of promising paste. So the research for conductive copper paste of crystallinesilicon solar cells is of great significance.The conductive copper paste will be prepared by using grinding method andmixed with copper powder, PbO-B2O3system leaded glass powder and organic carrier.Than optimized the composition ratio and sintering processes. This study investigatedthe leaded glass powder and organic carrier. And the electrical conductive stabilityand reliability of copper paste were also studied. The conductive copper paste used inthe solar cells as anode material, with the I-V tester for performance testing.We selected PbO, B2O3, SiO2, Al2O3, ZnO, ZrO2and P2O5as the glass rawmaterial. PbO-B2O3system were used as the fundamental system of leaded glasspowder, they were molted at high temperature (1100℃) and quenched in deionizedwater, and through the following test methods for characterization. This leaded glasspowder were tested and characterized by X-ray diffraction (XRD), the results showedthat in2θ of20°~35°have obvious bread peaks without sharp narrow crystallinepeaks. The glass powder had typical amorphous structure, and the performance offorming glass was very good. This leaded glass powder were characterized byscanning electron microscope (SEM), the results showed that its morphology was flake and globular, which had small particle size and uniform distribution. Usethermal analyzer for differential thermal analysis (DTA) to leaded glass powder. Theresults showed that the softening temperature is about523℃and accord with thestandard of low melting point inorganic binder. With a planetary ball-mill for mill onthe lead glass powder, the results show that when the milling5h, the glass powdersize uniform which average diameter of around1~2μm.Volatilization characteristics of the commonly used organic solvent of copperpaste was studied by the method of thermostat weight loss in the temperature range of60℃~180℃and the results determined the composition of the solvent of organiccarrier for terpineol, tri-n-butyl citrate,2-(2-n-Butoxyethoxy) ethanol,2-(2-Butoxyethoxy) ethyl acetate,. In order to increase the viscosity of the slurry,avoid the powder particles aggregation, precipitation and agglomeration, and makecopper paste having rheological, thickener ethyl cellulose was added. Measure thethermal weightlessness process (TG) of ethyl cellulose and organic carrier by thermalanalyzer. The results show that ethyl cellulose volatilized in the range of350~375℃and organic carrier volatilized in the range of150~200℃.So during the process ofsintering, the copper paste should be heat-insulated in the two temperature sections toreduce the amount of residual carbon in the organic carrier film after burning. Theorganic carrier was tested and characterized by Infrared spectroscopy (FTIR) and theresult show that the organic carrier’s spectra have similar absorption peak withorganic carrier at home and abroad. The composition of organic carrier basicallysatisfied the requirement of copper paste of solar cells. The compatibility of organiccarrier and glass powder was tested by Precipitation method. When the content ofethyl cellulose was6%, there was no obvious stratification phenomenon occurred.Organic carrier has the best compatibility with glass powder.Mixed the leaded glass powder and copper powder with organic vehicleuniformly and formulated into conductive copper paste. After550℃vacuum sintering,measure the surface resistivity by four point probe tester. According to explore thecomposition and ratio of conductive copper paste, the results show that theconductivity of the copper paste is minimal when the composition and content ofcopper paste is copper powder (75%), leaded glass powder (5%) and organic carrier(20%). The sintering process of conductive copper paste has explored and the resultsshowed that copper film have optimum properties when the sintering temperature is550℃and holding time is20min. Under the condition of normal temperature andhigh temperature, the stability of conductive copper paste is studied. The accelerating failure test is also studied under the condition of constant temperature and humidity.The results show that the growth of resistivity is smaller and the conductive copperpaste with good stability and reliability.The conductive copper paste was used in cathode material of solar cell. Thenprepared solar cell and tested the solar cell with the I-V tester. Results show that theconversion efficiency of the cell is1.43%.