On The Feasibility Of Using Sn Based Solders As Electrode Materials For A-Si/C-Si Photovoltaic Cells

Crystalline silicon solar cells are the mainstream products in the current PV market.Due to the limitation of materials and technology,the improvement of cell efficiency and reduction of cost is limited.In recent years,a-Si/c-Si PV cells,as a new type of structure solar cell proposed by researchers,has been rapidly developed with its advantages of high conversion efficiency.The grid line electrode is on the most outer layer of indium tin oxide film(ITO)in the structure of a-Si/c-Si PV cell.In current research,generally,grid electrode was fabricated by printing low temperature sintered silver paste on ITO film and curing procedure.But the high cost of low temperature sintered silver paste hindered the promotion and application of a-Si/c-Si PV cells.Aimed at such problem,the feasibility of using low temperature Sn based solder instead of low temperature sintered silver paste to fabricate a-Si/c-Si PV cell is explored.The aim is to reduce the cost of cells and without the loss of conversion efficiency.The main contents are as follows: interaction between Sn based solder,Sn-58 Bi,Sn-50Bi-2Zn,Sn-37 Pb,Sn-53 In alloy and ITO thin films;study on electrical properties of Sn based solder and its contact with ITO thin films;attempting to print grid electrode with Sn-58 Bi conductive paste on ITO thin films.The results show that the molten Sn based solder can adhered on the surface of ITO wafer.The interaction between Sn based solder and ITO thin films result in a certain interfacial strength.The oxidation of the solder in the air makes a poor wetting property on the ITO thin film.Only with use of external force,the molten Sn based solder can wetting and spreading on the ITO films.It is found that the interfacial strength between Sn-58 Bi,Sn-53 In alloy and ITO thin films is stronger than other groups.The analysis of the interaction mechanism between the interface shows that there is no chemical reaction between the solder and ITO films,and no new interface layer is formed.The results of atomic force microscope(AFM)analysis indicated that there is a significant profile,formed by ITO accumulation,between the interaction and the non-interaction region.The greater the accumulation height is,the higher the bond strength.In the electric performances,the bulk resistivity of Sn-58 Bi,Sn-50Bi-2Zn,Sn-37 Pb and Sn-53 In is generally lower than low temperature sintered silver paste,and so is the contact resistance between the Sn based alloy,silver paste and ITO thin films.The attempt to print grid electrode with Sn-58 Bi conductive paste on ITO thin films shows that the molten Sn-58 Bi alloy powder condense into independent sphere on the ITO.The conductive paste ultimately failed to form a continuous grid wire electrode on ITO glass.However,in the atmosphere of 95% nitrogen and 5% hydrogen mixture or 99.999% argon and.The size of balls after Sn-58 Bi alloy melting solidification is larger than that of air.It is shown that the powder in the slurry has better melting and polymerization in these two kinds of atmosphere.