A solar cell also called photovoltaic cell (PV) or photoelectric cell is a device which converts the energy from the sunlight directly into electricity via a photovoltaic process. Multiple cells connected together make solar panels or solar modules.
A polycrystalline cell is a cut from multifaceted silicon crystal. More surface area is required in comparison with the monocrystalline.
Polycrystalline solar panels are also called Multi-crystalline solar panels. They are made of Polycrystalline cells. These panels are less expensive but less efficient in converting the sun light into electricity. However, polycrystalline technology advanced a bit as well in recent years.
By exposing the polycrystalline solar panels to the sun they have the capability to convert the energy from the sunlight (sun rays) directly into electricity via a photovoltaic process. They tend to work better in places with some shadding because of the many crystals poining in different directions collecting the photons necessary for the photovoltaic process.