Continuous Production of Photovoltaic Silicon Ribbons by the New Pendant Drop Growth (PDG) Method

Summary

The PDG apparatus and procedure were significantly improved during this contract. New theoretical considerations enable us to establish the stability of our process as well as the possibility of manufacturing ribbons thinner than the lip thickness, about up to 0,5 mm.

Through the study of materials available for our crucibles, we could work out the ideal crucible, which is made of dense graphite and internaly lined with SiC or pyrocarbon.

We have also markedly improved the crucible powder feeding system involving a vibrating bowl. The rate of output is constant within ±.1.5 from 1 up to 100 g/hr. The response to a temperature adjustement of the crucible is immediate.

We have manufactured up to 500 mm long and 50 mm wide ribbons at extrusion rate of as much as 90 cm/hr. We could not manage to obtain thinner than 1 mm ribbons without losing width, but now we know the reasons for a such failure new crucibles have machined after the contract for this purpose.

The amount of crystals is convenient in both crystalline and electrical respects. The required annealing of our ribbons prior to submitting them to photovoltaic test prevented us from recording photovoltaic outputs exceeding 4.5% because of impurity from the ribbon surfaces inwards.

Lastly, our actual cost estimates allow us to contemplate a ribbon production at a price lower than 500 FF per square meter for 0.5 thickness.

This contract enabled us to define the subsequent research trends :

• reduction of thickness

• automation

• study and control of ribbon cooling

• reduction of drawing lip external wetting.