Study On The Aluminum Conductive Paste Used In Crystalline Silicon Solar Cell

With the exhausting of traditional energies （such as coal, petroleum） and theenvironmental pollution’s worsening, new types of energies including solar cell get moreand more attention. Solar cell is a kind of idealist energy source which could convertsunlight into power directly and produces no pollution in the conversion process. In alltypes of solar cell, crystalline silicon cell is used widest for its mostly developedtechnology and highest efficiency. At present, the conversion rate of monocrystallinesilicon solar cell could get24.7%and that of polycrystalline silicon solar cell could get19.8%. Aluminum conductive paste is a key material in forming of the back surface field（BSF） of silicon solar cell, which can improve solar cell’s performance by reducing lighttransmission, charge carriers’ neutralization and prolonging their existing time. The cost ofcrystalline silicon cell could be cut down and its efficiency increased. Just for the reasonsmentioned, aluminum conductive paste used in crystalline silicon cell also becomespeople’s research focus.This thesis made a deep exploration on glass powder, which was an important part ofaluminum conductive paste. We obtained the suitable materials, proportion and meltingmethod that could produce best glass powder and further, best aluminum conductive paste.After that, we also did research on the influence of glass powder and aluminum powder’sproportion. On the basis of all these former working, we did experiments on improving thepaste’s electrical property by adding tin powder and also got very good results. At last, aresearch was done on carbon nanotubes’s fluorination, which could promote theirapplication in aluminum conductive paste.For the glass powder, our research focused mostly on the influence of meltingtemperature. We chose Bi₂O₃、B₂O₃、Al₂O₃、ZnO、SiO₂、P₂O₅、Zn3（PO₄）2·4H₂O asthe raw materials and at the proportion of45：25：2：15：3：4：6to melt glass. Then they were fused under different temperature of1000、1050、1100、1150℃for30minutes toproduce four kinds of glass powder, mixed them respectively with aluminum powder,organic binder and auxiliaries to prepare conductive paste, analyzed the pastes’ poachresistance. After the testing, We confirmed that1050℃was the best melting temperature.We also did DTA and XRD analysis to the glass sample which was produced under thetemperature of1050℃, the results showed that glass’s softening temperature was about500℃, its structure was microcrystalline.On the basis of former work, we did experiment about the influence of glass powderand aluminum powder’s proportion to the conductive paste’s property. Under the conditionof glass and aluminum’s total content was77%, We prepared five samples that with thecontent of glass is5%、3%、2%、1%、0.8%respectively, then analyzed their poachresistance properties, adhesion and electrical resistivities. The results showed that with thedecrease of glass powder, aluminum conductive paste’s poach resistance property becamebetter, the adhesion and electrical resistivity decreased. From this experiment, weconfirmed the paste which contained1%glass powder had the best comprehensiveproperty. At last, the best conductive paste was screen-printed on silicon slices andsintered into aluminum coating under850℃for30s, its microstructure was observed bySEM, the SEM results showed that the aluminum powder piled densely and the alloybetween aluminum and silicon was well formed.Based on all the above works, the experiment on improving aluminum conductivepaste’s electrical property was done by the way of adding extra tin powder. It was mixedwith the conductive paste at different proportion of0.3%,0.8%,1.3%, and then thesamples’s electrical properties were examined. The results showed that with the tinpowder’s increasing, the solar cell’s photoelectric conversion efficiency（Ncell）, shortcircuit current（Isc） and the fill factor（FF） increased after first decreasing, openvoltage（Uoc） and equivalent series resistance（Rs） decreased after first increasing, theequivalent parallel resistance（Rsh） decreased. When the tin powder’s content was1.3%, the sample’s photoelectric conversion efficiency was highest,16.34%.Carbon nanotubes were potential materials in improving aluminum conductivepaste’s property, but they were hard to disperse and dissolve, which obstructed theirapplication. Fluorination was an effectve method to improve their dispersion anddissolution. In the last chapter, we got fluorinated carbon nanotubes by using gaseousproducts from the thermal decomposition of polytetrafluoroethylene（PTFE）. Comparedwith the traditional method by using fluorine, the way in this experiment was much saferand cheaper, which could be a promising method in carbon nanotubes’ fluorination andprompted their application in aluminum conductive paste.