Pulse NMR Measurement of Encapsulation Resin (EVA) for Solar Cells

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Summary

Ethylene-vinyl acetate copolymer (EVA) is the resin that is used most often as an encapsulant for solar cells. The pulse NMR of non-crosslinked EVA and crosslinked EVA was measured, and the difference in mobility that is attributable to crosslinking was compared.

Example of analysis

Comparison of mobility between non-crosslinked EVA and crosslinked EVA by C pulse NMR.
Sample: Ethylene-vinyl acetate copolymer (EVA)

Analysis conditions
Equipment: Broad line nuclear magnetic resonance JNR-MU25 (25MHz) (available from JEOL)
Method: Carr Purcell Meiboom Gill Method
Conditions: 90°pulse 2.0μs; repeating time: 4s; times of integration: 8 times
Temp.: 150℃(melting conditions)

  • From the decay curve (Fig. 1) obtained by pulse NMR measurement, the difference in mobility due to crosslinking can be compared.
  • It can be seen that after crosslinking, decay was faster than before crosslinking, indicating that mobility was low.
  • Furthermore, an analysis of the decay curve through waveform separation processing reveals the decay abundance ratio of the components having molecular mobility and the relaxation time T2 (mobility).
<Results of analysis>
  Abundance ratio(%) T2(ms)
  Before crosslinking After crosslinking Before crosslinking After crosslinking
Component 1 39.8 49.5 3.32 1.72
Component 2 39.8 37.2 20.6 14.0
Component 3 20.4 13.3 124 91

It can be seen that the component having low molecular mobility (Component 1) showed a higher abundance ratio and a lower T2 value in the crosslinked sample. (This indicates that as the T2 value falls, the molecules becomes less mobile, resulting in lower mobility.

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