what's the difference of P type and N type solar cells
Sep 02, 2022
First of all, the basis of the working principle of solar cells is the photovoltaic effect of the semiconductor PN junction. The so-called photovoltaic effect is an effect in which electromotive force and current are generated when the object is illuminated, the state of charge distribution in the object changes. When sunlight or other light hits the PN junction of the semiconductor, a voltage appears on both sides of the PN junction, called the photogenerated voltage.
P-type silicon and N-type silicon
When energy is added to pure silicon (such as in the form of heat), it causes several electrons to break away from their covalent bonds and leave the atom. Every time an electron leaves, a hole is left behind. Those electrons would then wander around the lattice, looking for another hole to settle into. These electrons are called free carriers, and they can carry electric current. Mixing pure silicon with phosphorus atoms requires very little energy to escape a certain "excess" electron of the phosphorus atom (the outermost five electrons). When doped with phosphorus atoms, the resulting silicon Known as N-type ("n" means negatively charged), only a portion of the solar cell is N-type.
Another part of the silicon is doped with boron, and the outermost electron shell of boron has only three instead of four electrons, so that P-type silicon can be obtained. There are no free electrons in p-type silicon.
P-type solar cell and N-type solar cell
The boron element is diffused on the p-type semiconductor material to form a solar cell with an n/p-type structure, which is a p-type silicon wafer;
Phosphorus is injected into the N-type semiconductor material to form a solar cell with a p/n-type structure, which is an N-type silicon wafer;
At present, the mainstream product in the photovoltaic industry is P-type silicon wafers. P-type silicon wafers have a simple manufacturing process and low cost. N-type silicon wafers usually have a longer minority carrier life and higher cell efficiency, but the process is more complicated. N-type silicon wafers are doped with phosphorus elements, phosphorus and silicon have poor compatibility, and the phosphorus distribution is uneven when pulling the rod. P-type silicon wafers are doped with boron elements, and the segregation coefficients of boron and silicon are equivalent, and the dispersion uniformity is easy to control.
The high efficiency of silicon cells is currently the goal of the photovoltaic industry, because it is believed that improving efficiency means more competitiveness. However, the highest efficiency of P-type photovoltaic modules has its inherent bottleneck. When N-type photovoltaic modules obtain high efficiency, the process difficulty is increased, and the cost is also increased. The application environment of photovoltaic cells is very harsh, so their long-term stability will become a key factor to be considered in the future. Therefore, the future photovoltaic industry and applications should seek a balance in the three aspects of efficiency-cost-long-term reliability.