Modulation And Related Mechanism Of Dislocations In Cast Quasi-single Crystalline Silicon

Photovoltaic(PV)is one of the most widely used clean and renewable energy.The development of PV market is based on the continuous progress of low-cost and high-quality crystalline silicon materials,which always occupy more than 90%of market share.In the era of Czochralski silicon(CZ-Si)and cast multi-crystalline silicon(mc-Si),the development of cast quasi-single crystalline silicon(QSC-Si)has big opportunity to break through the status quo and lead the trend of the industry.Therefore,studies of QSC-Si relative to the key problems encountered in its industrialization process is of great significance for the development and progress of the PV industry.In this thesis,some growth methods of QSC-Si to control the generation of dislocations has been explored.The primary coverage of this thesis is as follows:(1)The parameters of the experimental ingot furnace are adjusted.The problem of cracks at the top of ingot caused by the rapid lifting of the heat preservation cover and the large solidification stress in the later stage of crystal growth is successfully solved.Moreover,the semi-melting growth of casting crystalline Si was demonstrated by reducing temperature,reducing melting time and increasing the height of initial insulation cover.These results provide powerful technological conditions for seed-assisted cast QSC-Si.(2)The dislocation behaviour in the<110>-oriented cast QSC-Si is investigated.Higher quality ingot with uniform minority carrier lifetime can be obtained by semi-melt growth of<110>-oriented seed,in which dislocations are confined at the area of seed junctions.The<110>-orientation is the slip direction for dislocations,which prevents dislocations generated at the seed junctions from extending to the whole ingot.Thus,the ingot quality in most regions is effectively improved.However,the results show that the high dislocation density area in the tread-like region will lead to serious reverse leakage current,which will reduce the efficiency of the cast SC-Si solar cells.(3)The effect of grain boundary engineering on the dislocation generation in the cast QSC-Si is investigated.The E13a relationship between adjacent seeds is satisfied by 1800°alternately rotating the seed crystal around the[510]axis.Thus,the origin of dislocations and sub-grain boundaries at the seed junctions due to the slight misorientation is effectively suppressed,and the dislocation density in the cast SC-Si ingot is greatly reduced,leading the ingot quality ingot and the efficiency of the cast SC-Si solar cells higher in the industrial circles.However,the results show that the vertical growth of ?13a grain boundary will cause twin formation during the growth process,which will give a bad influence on the wafer texturization during the following solar cell fabrication.