Influence On Performance Of Multi-crystalline Silicon By Transforming Thermal Field Of Multi-crystalline Silicon Ingot Furnace

Multi-crystalline silicon solar cells having high photoelectric conversionefficiency and low cost advantages occupy a major market share of the photovoltaicindustry. Casting process of multi-crystalline silicon ingot is an important work. Themain factors, such as impurities, grain boundaries and dislocations, affect the qualityof multi-crystalline silicon. The thermal field of multi-crystalline silicon ingotfurnace has a great influence on creating grain boundaries and dislocationsreproduce Therefore, how to controlling the orientation of the crystal growth ofmulti-crystalline silicon and how to growing high quality ingot with uniform sizegrain and low dislocation density are important issue to study.Since the heat radiation on the crucible side from graphite heater is notbalanced, temperature of the around crucible are more than the center, so the lateraltemperature gradient field of the growth process of multi-crystalline is too large，andthe solid-liquid surface is not horizontal, and presents a convex. The non-uniformthermal radiation is easy to make the seed of the crucible edge melting, and the areaof seed changes to small, all that directly affects the quality of the ingot.Therefore, this paper researches specifically on the thermal field distribution ofmulti-crystalline silicon ingot furnace, and make some adjustments to enhancethermal dissipation capability from the crucible bottom. Putting thermal insulationon the around crucible to reduce the lateral thermal temperature gradient field,ensuring that heat pass through the vertical direction. By comparing the minoritycarrier lifetime of multi-crystalline of ingot from the transformation of the thermalfield and the undo, some conclusions are as following:1. The bottom lateral thermal gradient reduces after transformation the thermalfield, and the bottom seed retention area improves. The height of the seed remainingfrom the center to the edge reduces slowly to help the next vertically oriented crystalgrowth. All this provides a good foundation conducive to the growth of ahigh-quality crystalline silicon.2. Transforming thermal field is useful to upgrade the cooling effect ofmulti-crystalline silicon ingot, and to ensure that heat pass through the vertical direction. It can get the vertical growth crystal. The solid-liquid interface can changefrom the convex to the lateral after the transformation; it is desirable to improve theminority carrier lifetime of ingot edge. The average minority carrier lifetime of theentire ingot increases from5.92us to7.08us, the average photoelectric conversionefficiency of the multi-crystalline silicon solar cells increases from17.49%to17.71%.3. Analyzing effects of the bottom solid-liquid interface on crystal growthprocess, the results show that the greater fluctuations in solid-liquid interfaces are,the greater crystal growth disordered are,So the smooth of the solid-liquid interfacein crystal growth process is conducive to grow the stable and orderly crystal, also toproduce multi-crystalline silicon of uniform grain size and high minority carrierlifetime.