The central part of a solar panel is a semiconductor diode, a two-layer electrical component that conducts current in one direction (and only one direction) from the bottom semi-conductor layer to the top semi-conductor layer. It’s a one way street. Both layers are made of a semi-conductor material, typically silicone with some added impurities to create a situation where an electrical field can form at the intersection between the two layers.
P-Type Silicon Layer
The thicker bottom layer, referred to as the p-type layer, is doped (impurities added) with a small amount of something like boron, which gives the silicon layer a positive (p-type) character. This p-type characteristic means the molecular structure of boron-doped silicon naturally contains an extra hole (positive charge carriers). Freely floating electrons (negative charge carriers) that pass by are drawn in and fill this hole, and in doing so the electron releases its stored energy. The electron remains in this hole until they are energized and knocked free by some external force (like the introduction of photons). It’s kind of a transient home.
N-Type Silicon Layer
The thinner top layer, referred to as the n-type layer, is doped with something like phosphorous, which gives the silicon layer a negative (n-type) character. This n-type characteristic means the molecular structure of phosphorous-doped silicon naturally contains an extra electron. This extra electron can be knocked free by some external force.
P-N Junction
Where the top (n-type) and bottom (p-type) doped-silicon layers meet is called the p-n junction. This is the boundary across which the electric current flows once energy in the form of photons (from sunlight) is introduced. As sunlight shines into the solar panel some photons are absorbed into the p-n junction, which energizes and knocks free some electrons from both silicon layers. This knocking free of electrons is the photovoltaic effect. The newly free and energized electrons from the top n-type silicon layer and the holes from the p-type silicon layer meet up at the p-n junction and the electrons essentially cross over from the top to the bottom. Don’t confuse the direction of the electrons with the direction of the current. They move in an opposite direction. The electrons move from top to bottom, yet the electrical current moves from the bottom to the top. The mass exodus of electrons jumping over the p-n junction creates a void in the top n-type silicon layer – the phosphorous-doped silicon molecules are sorely missing their extra electron, but they can’t pull it back across the p-n junction as that’s only a one-way street. They need to get it from somewhere else. In a complete functioning system, this bottom and top silicon layer are not only connected by the p-n junction, but also by a wire (a highly conductive material) going out of the bottom of the solar panel, over to the electrical application (where the energy from the system is captured), and then back into the top of the solar panel. It’s a loop, or a complete circuit. The newly freed and energized electrons from the bottom p-type silicon layer that didn’t find a hole to rest in are drawn down and out of the solar panel and around the circuit and eventually back into the top of the solar panel to serve as the extra electrons in the top layer of electron depleted phosphorous-doped silicon molecules.
Metallic Terminals
On the top and bottom of these sandwiched layers of Silicon, a highly conductive metallic material of some kind is present. The electrical current flowing from the bottom p-type layer to the top n-type layer seeks the path of least resistance and naturally heads for highly conductive metal terminal on the top of the solar panel and follows the attached wires out.
Wiring
The wires go from the solar panel and attach to some sort of electrical application (a battery bank where the energy is stored, or directly connects to an electrical appliance) and then other wires come back and attach to the metallic terminal on the bottom of the solar panel, forming a self-contained circuit of flowing electrical current in one direction and flow of electrons in the other direction. Newly energized (by photons in the sunlight) electrons flow thru this circuit out of the bottom of the solar panel (the p-type side), out to the electrical application (where they give up their energy), and then return as un-energized electrons thru the top metallic terminal and back into the top n-type silicon layer and recombine at the molecular level with the silicon (essentially replacing other electrons that were energized and knocked free by the photons and crossed over the p-n junction). The cycle repeats so long as photons (energy) are being introduced into the system (as long as the sun is shining). There are no moving parts to this system and no physical material is consumed or emitted.
Protective Coating
The solar panel is typically encased by some form of glass to protect it from the environment.
Anti-reflective Coating
The object is to capture as much sunlight (and photons) as possible, so an anti-reflective coating is applied under the glass to minimize the reflective properties of the solar panel materials.
