How silicon solar cells work There are 4 electrons in the outer shell of the silicon atom.The bondage of the nucleus is relatively small.If the electrons get enough energy,they will get rid of the bondage of the nucleus and become a free electron,while leaving a hole in the original position.Electrons are negatively charged;holes are positively charged. Valence electrons covalent bond In pure silicon crystals,the number of free electrons and holes is equal.How silicon solar cells work There are 4 electrons in the outer shell of the silicon atom. The bondage of the nucleus is relatively small. If the electrons get enough energy, they will get rid of the bondage of the nucleus and become a free electron, while leaving a hole in the original position. Electrons are negatively charged; holes are positively charged. In pure silicon crystals, the number of free electrons and holes is equal. Si + 4 + 4 + 4 + 4 covalent bond Valence electrons