The Study And O(?)Timized Of The Back Surface Field For Crystalline Silicon Solar Cell

The aluminum back surface field is a key structure used to improve efficiency of silicon solar cells. Solar cell output performances largely determined by the quality of the aluminum back surface field. In order to increase the cost-effective, there is a strong trend to reduce the wafer thickness. When the minority diffusion length exceed cell thickness, back surface recombination is very effective to the cell efficiency. The minority carrier life time and the open circuit voltage can be improved; the series resistance and back surface recombination can be reduced if the aluminum back surface field can be used. So it necessary to explore the effect of the back surface field depth and concentration to the cell efficiency and the relationship the depth and the concentration among the substrate.The aluminum paste was printed on the semi-finished silicon solar cells by screen printing technique, different firing condition were compared by I-V testing. The back surface field carrier concentration and depth were analysis by ECV between different aluminum pastes. The experiment result shows that the minority carrier lifetime is an effective means to analysis the back surface passivation quality. Solar cell series resistance and the passivation quality closed related to firing temperature. The open circuit voltage not increased with the doping concentration of the aluminum back surface field, the short circuit voltage did not decreased with the back surface field junction depth. To further study the aluminum back surface field characteristic, the physical model of crystalline solar cells model N+PP+structure was established in the simulation software PC ID, the aluminum back surface field concentration profile and depth and the substrate characteristic how to affect the aluminum back surface field,were systematically simulated and studied. The simulation result shows that the aluminum back surface field concentration a bit lower and the junction depth deeper seems to be more effective to high efficiency solar cell. The higher of the depth factor, the higher of cell efficiency, but it needs higher sintering temperature and much more time. This can increase the P+layer thickness and consume the aluminum on the back surface. The series resistance increased if the aluminum on the back surface reduced and the thickness of P+layer will affect the bow of the cell. So the highly doped shallow junction is more suitable for the needs of the industrial production of batteries. Silicon solar cells with its P+depth is about5-7μm, and the optimization concentration is7×1018cm-3～9×101cm-3, when concentration is above5×1019cm-3, the optimization depth of P+is less than1μm. The above optimized criteria for the back surface field is suitable for all the substrates.