| The front silver conductive paste is composed of silver particles, glass frits, organic carrier and additives. It plays a very important role in improving the photoelectric conversion efficiency. Currently, the major technology and production sales of the front silver paste are in the hands of foreign countries. Research about the front silver paste is late in domestic. Nano silver powder has small particle size, low melting point, which can acquire good ohmic contact. A new activation method to preseed silver nuclei on glass frit used for silver paste has been developed. Electroless silver plating on the glass frit was successfully realized by adding the activated glass frit into two kinds of electoless plating baths. This article investigated the advantages and disadvantages of different silver plating method and optimized this method. What’s more, the front silver conducting film is also prepared with composed powder. The particle sizes of Ag particles deposited on glass frits were identified by X-ray diffraction (XRD, D/Max2500) using Cu Ka radiation. The morphologies (distribution and particle size) of Ag particles on glass frits and the silver-conducting films were observed by environmental scanning electron microscope (ESEM, Quanta-200). The content of Ag in Pd-based glass frits coated with Ag material was determined by atomic absorption spectrophotometer (HG-9602).The photo-voltaic parameters of finished cells were tested by a solar cell testing system (DLSK-FXJ7) and four point probe instrument. Main results for this study are as follows:1、The activation of glass frit was accomplished by using glycol to reduce Ag+to Ag0on the surface of glass frit. Electroless silver plating on the glass frit was successfully realized by adding the activated glass frit into two kinds of electroless plating baths. The stability of the plating solution was investigated:with the increasing amount of ammonia, the complexation ability became stronger. Meanwhile, as the pH value of the increased along with the dosage of ammonia, the stability of the plating solution became worse. When the dosage of ammonia is100ml·L-1, the stability is the best. As the temperature of increased, the decompositing ability of the solution enhanced. Ultrasonic wave involved in the plating process had great effects on liquid stirring and could quicken the reaction and dispersion. The increasing of the pH value could enhance the reduction ability of formaldehyde, leading to decomposition of plating solution.2、The feasibility of preparing the composite powder by traditional method was also discussed. The disadvantages of this method were following:(1) roughening treatment was needed before the silver plating; otherwise it was not easy to have uniform coating, generating more free silver particles. What’s more, roughening treatment would lead to a certain degree of selective corrosion, changing the composition of the glass frits.(2) A large amount of hydrochloric and sodium chloride was used. Due to the impurities especially the chloridion was easily absorbed to sensitization layer, it was difficult to clean chloridion after pretreatment. Through laboratory study, it was found that a lot of chloridion existed in glass frits after washing20times, which was harmful to photoelectric conversion efficiency. Meanwhile, too much washing could lead to the oxidation of stannous ions, affecting the quality of coatings.(3) The palladium used in activation process was costly.(4) The tin would lead to a certain degree of harm to the human body.3、The paper dealed with the effect of activation temperature, dosage of dispersants, pH value, loading capacity etc on the morphology of composite powder. When the activation temperature was5℃, nano-silver particles were very little and mainly quoted on cracked sections. When the activation temperature was15℃, the number of nano-silver particles increases. When the activation temperature was25℃, the nano-silver particles had the largest density and were distributed evenly and uniform. The pH value had a great effect on the particle size of nano-silver particles. When the loading capacity was30g/L, activation temperature was25℃, and the pH values were adjusted to11.8,12.6and13.4, the grain sizes of the nano-silver particles, calculated by Scherrer formula, are about30nm,60nm and100nm. In addition, the reaction time, reactant concentration, loading capacity, adding mode, additives and ultrasonic wave could also affect the morphology and the silver content of composite powder.4、The electrical performance of the conducting films obtained from silver pastes containing glass frits or composite powders were investigated:the nano-silver particles played a important role in decreasing the hole ratio and enhancing the optical and electrical properties. The average photoelectric conversion efficiency was improved0.1%by using the composite powder. What’s more, the morphology of the composite powder had a great effect on the electrical performance and the appearance of the conducting films. When the spheroid nano-silver particles were evenly distributed, had a high proportion and surface density, the sheet resistance became lower and the solar cells would have high photoelectric conversion efficiency. |
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