Study On Soldering Defects Of Crystalline Silicon Cells And Aging Failure Mechanism Of Free Bus-bars Photovoltaic Modules

Soldering defects are the major factors causing the failure of crystalline silicon cells,and free bus-bars cells and photovoltaics(PV)modules are an important way to reduce the cost of cells and modules.In this paper,based on the study of soldering defects of crystalline silicon cells and aging attenuation mechanism of PV modules,the design of the free bus-bars PV modules and the failure rules of the free bus-bars PV modules in various environments are mainly discussed.To forcast the failure mechanism of free bus-bars PV module during soldering process and damp-heat test,we have investigated the formation and distribution of cracks of conventional crystalline silicon cells during soldering process and the corrosion of conventional crystalline silicon cells and the degradation of conventional PV modules during damp-heat test.By comparing the performance of the free bus-bars silicon cells and PV modules during thermal cycle aging test,we obtained the failure mechanisms of the free bus-bars PV modules.The main results are as following1.Single-crystalline cells are more prone to producing crack defects than multi-crystalline cells during soldering process.Under the same electromagnetic induction soldering process,the cracks occupy 80.2%of the total number of defects in the single-crystalline cells,and the main crack is oblique crack and occupies a ratio of 44.9%.The cracks occupy 59.4%of the total number of defects in the multi-crystalline cells,and the main crack is short crack perpendicular to the main bus-bars and occupies a ratio of 44.9%.Therefore,the free bua-bars PV modules choose the multi-crystalline silicon cells in this paper.2.The ability of anti-aging test of double-glass PV module is significantly better than that of single-glass PV module during aging test.In the 3000 hours of damp-heat aging process,the output power decay rate of double-glass PV module is 0.07-0.16%per 500 hours.While the output power decay rate of single-glass PV module up to 1.63%.In the 400 cycles of thermal cycling aging process,the final decay rate of the output power of the double-glass PV module was 4.41%,while the single-glass PV module was failure at 227 cycles and its output power decay rate was 10.75%Therefore,the free bua-bars PV modules choose the double-glass module in this paper3.In addition,the degree of corrosion of multi-crystalline cell is different under different experimental conditions,but the failure mechanism is same.First of all,the corrosion of aluminum paste layer leads to looser structure and produces smooth oxide.The corrosion of back electrode leads to discoloration and produce smooth oxide.The edge of soldered joints was occurred firstly,and the corrosion area would propagate to the center of soldered joints along the interface between Ag electrode and Sn37Pb.3.The failure mechanism of cells in the free bus-bars PV module is different in the different environment.During the damp-heat test,corrosion of the back aluminum layer causes the looser structure,and corrosion of the back electrode leads the surface to change color.The corrosion at the soldering joints would occur firstly in the edge part,and the corrosion area would extend along the interface between Ag electrode and Sn37Pb alloy to the center.During thermal cycling,the main failure mode of multi-silicon cells is poor soldering,especially the poor soldering of both ends of cells.In addition,the cells of single-glass PV module are prone to producing cracks.4.Based on the research results of this paper and the production level of PV module,we design a suitable free bus-bars PV module.The materials and structure of the free bus-bars PV module are as following:multi-crystalline silicon cell,special front electrode and special back electrode,rectangular cross-section ribbon and double-glass PV module.