Preparation And Characterization Of Lead-free Glass Frit For Solar Cell Front Contact

The properties of silver paste for solar cell front contact is one of the keyfactors affecting the cells efficiency, reliability, and the cost in industry. In general,the silver paste comprise conductive silver powders, glass frit and organic vehicle.Traditional glass frit in silver paste usually contains lead. Lead-contained pasteshould be replaced by the lead-free paste on account of lead’s toxity to theenvironment and the human body. The key of the lead-free paste lies in lead-freeglass frit. Because bismuth in Periodic table is adjacent to lead, they have thesimilary nature. This makes it possible that bismuth will replace the position of leadin silver paste glass frit. This project in view of the lead-free solar cell front contactpaste, to research Bi₂O₃system lead-free glass as main body, discusses deep insidethe effect of the Bi₂O₃content on Bi₂O₃-B₂O₃-SiO₂and Bi₂O₃-ZnO-SiO₂glasses’crystal state, network structure, optical properties and thermal properties. The glassmaterials were characterized by means of X-ray diffraction, Infrared spectrum,Raman spectroscopy, Differential scanning calorimetry, UV-Vis and so on. In orderto validate the industrial application value of developed glass material, this projectpreparae silver-less paste to test the etching properties of glass material on SiNxanti-reflection coating during sintering process.This artical demonstrates the designed Bi₂O₃-B₂O₃-SiO₂ternary systemglasses’ amorphous state through XRD analysis of the powder samples. This projectdetermined the network constitution of the Bi₂O₃-B₂O₃-SiO₂ternary glass throughanalysis of the vibration spectra, and summed up the changing rules of the glassnetwork structure as the Bi₂O₃and B₂O₃content vary, and the corresponding changeof vibration spectra. UV-Vis spectrum analysis found that Bi₂O₃-B₂O₃-SiO₂systemglasses’ optical band gap decrease with Bi₂O₃and B₂O₃content increase, and thecorresponding cut-off wavelengths increase at the same way, the absorbency thenbecome bigger. DSC discovered glass transition temperature of the glass samplereduced with the increase of the Bi₂O₃content. Sample60Bi30B10Si glass’ softeningpoint is400℃, can meet the requirements of sintering process as silver glass frit intheory.In order to validate the glass material’s actual sintering performance, thisproject produce paste contains no silver to deposit on the silicon wafer withanti-reflection coating for sintering. Using scanning electron microscopy and energyspectrum analysis to detected the sintering cross section and etching interface, it wasfound that there is obvious change law of the N, O, Si, Bi elements distribution,which confirmed Bi₂O₃-B₂O₃-SiO₂glass can etch the SiNxcoating.