Assertion: solar cell's layer | /r/MadeOf | traces of elements
Facets:
value: to give a negative electric charge
type: PURPOSE
Source sentences:
text: A solar, or photovoltaic, cell is a two-layer sandwich of silicon; one layer, called N-type, contains traces of elements such as arsenic to give the material a negative electric charge; the second layer, called P-type, is laced with other elements that give a positive charge.