The structure and working principle of Solar Energy Storage Battery
Light can be divided into different wavelengths, and we can see this through rainbows. Due to the wide range of photon energies of light incident on the cell, some photons do not have enough energy to form electron-hole pairs. They just go through the battery as if the battery were transparent. But some other photons are very energetic. Only a certain amount of energy—measured in electron volts (eV), determined by the battery material (about 1.1 eV for crystalline silicon)—can allow electrons to escape. We call this energy value the bandgap energy of the material. If the energy of the photon is greater than the required energy, the excess energy is lost (unless the photon has twice the energy required, multiple electron-hole pairs can be created, but the effect is not critical). These two effects alone account for about 70 percent of the radiant energy lost in the cell.
To use more photons, why don't we choose a material with a very low bandgap? Unfortunately, the band gap also determines the electric field strength (voltage). If the bandgap is too low, you will lose some voltage while increasing the current (by absorbing more electrons). Remember, power is the product of voltage and current. The optimal bandgap energy must balance these two effects. For a cell made of a single material, this value is about 1.4 electron volts.
We have other energy losses. Electrons must flow from one side of the battery to the other through an external circuit. We can coat the bottom of the battery with a layer of metal to ensure good conductivity. However, if we fully metallized the top of the cell, the photons would not be able to pass through the opaque conductor, losing all current (in some cells, the transparent conductor is only used on the top surface, not everywhere). If we only put contacts on both sides of the battery, the electrons need to travel a long distance (for the electrons) to reach the contacts. You know, silicon is a semiconductor, and its current transmission performance is not as good as that of metal. Its internal resistance (called series resistance) is quite high, and high resistance means high losses. To minimize these losses, the battery is covered with a metal contact mesh that shortens the distance the electrons travel, covering only a small portion of the battery's surface. Even so, some photons are blocked by the grid. The grid can't be too small, or its own resistance will be too high.
There are several other steps that need to be taken before actually using the battery. Silicon is a shiny material, which means it has good reflective properties. The reflected photons cannot be used by the battery. Because of this, an anti-reflective coating on top of the cell can reduce reflection losses to less than 5%.