Preparation Of Silver-coated Copper Wire For High Electrical Performance At Low Sintering Temperature

The preparation of front electrodes in crystalline silicon solar cells is based on screen printing technology which has some negative effects on conversion efficiency.High shading loss and sintering temperature are the main factors.Based on this,this article has supplied a new preparation technology of front electrodes in solar cells.Ag-Cu nanocomposites are prepared by liquid chemical reduction and electrodeposition.The effects of reduction environment、silver nitrate、reduction time、polyvinyl pyrrolidone(PVP)and voltage have been discussed on the quality of Ag coatings.And the best preparation condition of Ag coatings is confirmed at last.Because of the low melting points of nanocomposites,the paper has also carried on the discussion to low sintering process between Ag-Cu nanocomposites and silicon wafer.The research contents and results are as follows.(1)Under ultrasonic environment,we have prepared a series of Ag-Cu nanocomposites with different experiment condition by liquid chemical reduction.The study explores the best preparation condition by measuring the morphology and thickness of Ag coating through SEM and EDS.We can get Ag coating with good compactness and uniformity when we control the dosage of silver nitrate at 24mmol/L、the molar ratio of silver nitrate and PVP at 10:1 and the reaction time at 1h.the size prepared is about 100nm.(2)Ag-Cu coatings were prepared by electrodeposition and the growth mechanism of dendritic silver nanoparticles has been discussed based on Diffusion Limited Aggregation(DLA)model.This paper study the effect of applied voltage,electrolyte concentration and deposition time on Ag-Cu coatings systematically.The applied voltage and electrolyte concentration can affect the electrolytic growth morphology of sediment and properties through changing the deposit rating of iron.Fast deposit speed weakens shielding effect that outer particles to inners which make Ag-Cu coatings more densely.And at the same time,applied voltage also has something to do with hydrogen evolutional speed.Over hydrogen evolutional speed will ruin the growth mechanism of fractal structure.The silver particles prepared will small in size and the size is less than50nm when we control the dosage of silver nitrate at 24mmol/L、the voltage at 3.5V and the reaction time at 1h.(3)The study explores the sintering property of the Ag-Cu nanocomposites prepared by chemical plating and electrodeposition and both of them have formed good melting contact between silicon wafer after low temperature sintering.Ag coatings are uniformly distributed after sintering process and the thickness of Ag coatings are about2μm.The smaller the size of silver nanoparticles is,the lower the sintering temperature is.Ag-Cu nanocomposites prepared by electrodeposition can get great ohmic contact performance at 280℃sintering process.And the ohmic contact rates is 0.08Ω·cm~2.