highlights in this page

Dislocations in multicrystalline silicon

: Orientation image micrographs (OIM) and Individual grain images (IGI) of selected samples: Bottom, middle and top positions of corner and centre blocks from one of the reference non-seeded ingots (V

Total density of non-CSL grain boundaries vs. block height.

Dislocation density maps of wafer number 001, 301 and 601 of a corner and middle block of a non-seeded ingot (VH1) and the dislocation density maps of wafers 009, 309 and 409 from a corner block of th

The ratio of dislocation "source" grain boundaries over "sink" grain boundaries in the bottom wafers versus the dislocation cluster density in the top wafers

: Evolution of microstructure: Nucleation, multiplication and relaxation

CHEETAH short on-line course

Nucleation, growth and relaxation of dislocations in directionally solidified multicrystalline silicon

Dr.	Birgit Ryningen	9^th June 2017 11:00 –12:10 CEST
	SINTEF Department of Energy Conversion	9^th June 2017 11:00 –12:10 CEST

Multicrystalline silicon is the most promising candidate for enabling large scale production of low cost solar cells. The efficiency of such cells is fundamentally limited by the presence of crystal defects, and there is little absolute knowledge about the defect generation mechanisms, because all generation and development happens at too high temperature to be observed by conventional characterization techniques.

Crystal defects generated during the directional solidification process, particularly dislocations and sub grain boundaries, are well proven to be the factor mostly limiting the cell efficiency of multicrystalline silicon1. This means that keeping growth conditions optimal becomes extremely important. Unless the density and properties of the crystal defects are under control, any measure in other parts of the value chain, ranging from reduction of contamination, to efforts during cell processing such as gettering will have very limited effect. In contrast, recent development in crystallization process control (development of socalled High Performance Multicrystalline Silicon) has shown the large potential in efficiency improvement by reducing the amount of crystal defects.

Although directional solidification shows a large, still untapped potential and remains the most likely candidate for large scale deployment of solar energy, other silicon based technologies, e.g. deposition from the gas phase or splitting off thin layers from a single crystal may develop higher throughput combined with higher quality in the future. As with the directional solidification approach, these methods also require detailed understanding of defect generation and evolution. Understanding the fundamental characteristics of dislocation dynemics is therefore essential for these technologies as well.

In this webinar we would like to present our current understanding of dislocation nucleation, multiplication and relaxation. During growth and cool down

Post mortem characterisation (characterisation after all the dynamic processes have finished) suffers the weakness that the result being studied is a consequence of all the dynamic processes of the past; in a sense it represents the "graveyard of the dislocations". Nevertheless current understanding of microstructure evolution in silicon for solar cells is mainly based on this approach, supplemented with simulations on a global scale. This leads to controversy regarding which processes are most important in generating the observed microstructure.