Eco-Solar Factory: Multicrystalline Silicon Ingot Crystallisation from Reusable Silicon Nitride Crucibles

Transcription

1 Eco-Solar Factory: Multicrystalline Silicon Ingot Crystallisation from Reusable Silicon Nitride Crucibles Eco-Solar Factory: 40%plus eco-efficiency gains in the photovoltaic value chain with minimised resource and energy consumption by closed loop systems M.P. Bellmann, G. Stokkan, A. Ciftja, J. Denafas, F. Buchholz, T. Kaden 1

2 Content Introduction Crystallisation experiments Impurities Material performance Cell efficiencies and module performance Summary and outlook 2

3 Comparison of silica and silicon nitride based crucibles Silica based crucibles Silicon nitride crucibles 3 Drawbacks: Thermal insulator Oxygen contamination and Cost related due to single use Immediate advantages: Increased resilience, which enables them to be reused multiple times Lower oxygen content Increased mechanical resistance

4 Cost distribution for conventional mc-si ingot growth 4 Estimation based on G6 ingot dimension

5 Reaction bonded silicon nitride crucibles Silicon nitride crucibles are produced by a novel state-of-the-art slip casting technique and subsequent nitridation process (patented) which includes the following steps: Pure silicon powder, water and other chemicals are mixed together to make a slurry, which is then is poured into a plaster mould for slip. After water is absorbed by the plaster, the «greenware» crucible is produced and then removed from the plaster. Nitridation of the «greenware» crucible occurs at high temperatures (above 1000 C) and produces the final silicon nitride crucible. 5

6 Experimental DS induction furnace Crystallisation 15 kg initial silicon charge p-type HPmc-Si Seeding with FBR granules Crucibles High pure EG quartz crucibles (reference) Silicon nitride crucibles from Steuler Solar Crucibles were coated with α-si 3 N 4 and burned to prevent sticking 6

7 Crystallisation After crystallisation Ingot release from crucible 1st mc-si ingot (~15kg) 1 Si 3 N 4 crucible was used in 5 subsequent runs 7

8 Interstitial oxygen Oi concentrations are relatively stable for the ingots grown in SiO 2 crucibles Clear reduction towards the top in the ingots grown in the Si 3 N 4 crucible Shift around 8 cm suggests that Si 3 N 4 crucibles can outperform traditional SiO 2 crucibles, especially for taller ingots Initial high oxygen: some oxidation of the pre-coated Si 3 N 4 crucible is expected during burning, with formation of silicon oxynitride (SiO x N y ) 8

9 Substitutional carbon The crucible contains small amounts of silicon carbide (SiC), and it is suggested that these particles act as the main contamination source. 9

10 Nitrogen (based on NN, NNO complexes) Solid solubility limit of nitrogen 0.09 ppma Increased solubility possibly due to existence of boron, oxygen and carbon Si 3 N 4 precipitates were not detectable 10

11 Metallic impurities: Neutron Activation Analysis Same impurity levels as in reference material (EG-crucible). 11

12 Quasi-Steady-State -Photoconductance

13 Microwave detected photoconductance decay High pure EG quartz-crucibles Si 3 N 4 crucibles after a "bad run", material performance is improving again

14 Cell efficiency: standard Al-BSF 3BB technology Si 3 N 4 1 st run Si 3 N 4 4 th run 14

15 60 cell glass-glass modules The best solar cells (17.7% 17.9%) were sorted and carefully selected for a glass/glass module production giving a module output comparable to industrial type solar modules. Module Isc Imp Voc Vmp Pmp (W) (A) (A) (V) (V) A: Si 3 N B: commercial (17.5%-17.7%)

16 Summary and outlook Study suggests that the Si 3 N 4 crucible can outperform traditional SiO 2 crucibles in terms of oxygen, especially for tall ingots 5 times use has been demonstrated so far SiC existing in the crucible material. Work is ongoing to eliminate the carbon. Material performance and cell efficiencies similar as reference material (EG-SiO 2 crucibles) Module performance comparable to commercial available glass/glass modules Modules are installed outdoor for real performance measurements G2 crucibles are currently tested, G5 in preparation 16

17 Technology for a better society This project has received funding from the European Union s Horizon 2020 research and innovation programme under grant agreement No Martin.Bellmann@sintef.no