 "process paragraph : : A photovoltaic cell is created with two layers of semiconductor material. The top layer are "doped" with impurities to allow a negative charge. The bottom layer are "doped" to allow for a positive charge. This produces an electric field that allows electrons to flow from negative to positve. Sunlight enters the cell. Energy from sunlight knocks electrons loose in both fields. This prevents the flow of electrons from negative to positive. Adding an external circuit allows the exchange to continue. Give the cells owner a flow of electricity. ", "event : The top layer are "doped" with impurities to allow a negative charge.", "entity : photovoltaic cell" 
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