In state-of-the-art crystalline silicon solar cells technology, based on p-type silicon, a back surface field (BSF) is implemented. This BSF is implemented, because in this way:
The barrier for hole collection at the back contact is reduced, increasing the surface recombination velocity at the back contact.
The barrier for electron collection at the back contact is reduced, decreasing the surface recombination velocity at the back contact.
A barrier is created for hole collection at the back contact, increasing the surface recombination velocity at the back contact.
A barrier is created for electron collection at the back contact, decreasing the surface recombination velocity at the back contact.
The correct answer is:
A barrier is created for hole collection at the back contact, increasing the surface recombination velocity at the back contact.
To arrive at this answer, we need to understand the purpose of the back surface field (BSF) in state-of-the-art crystalline silicon solar cells. The BSF is designed to reduce the surface recombination velocity at the back contact. Surface recombination is a process where charge carriers (electrons and holes) are lost at the surface of a material, reducing the overall efficiency of a solar cell.
In p-type silicon solar cells, the primary goal is to collect the photo-generated holes (positive charge carriers) at the back contact. The BSF helps in this process by creating a barrier for hole collection at the back contact. This barrier prevents the holes from recombining with the electrons at the back surface, thus reducing the surface recombination velocity.
On the other hand, the BSF does not affect the electron collection at the back contact. The electrons generated by the absorbed sunlight are already collected efficiently by the heavily doped n+ region in the front surface of the solar cell.
Therefore, the correct statement is:
A barrier is created for hole collection at the back contact, increasing the surface recombination velocity at the back contact.
The correct answer is:
A barrier is created for hole collection at the back contact, increasing the surface recombination velocity at the back contact.