Two-surface, bifacial or bifacial solar cells – interesting information about solar modules

The vast majority of the solar cells are now made from silicon. Silicon is a semiconductor and as such are its outer electrons in an energy interval called the valence band, and completely fill out the energy level of this band. Above this valence band is a forbidden band or an energy piece in which no electron can exist, and the line band is located further up. This line band is almost empty of electrons, but it is the place where the electrons of the valence band are accommodated after they have been stimulated by the absorption of photons. These electrons have more energy than the ordinary electrons of the semiconductor. The electrical conductivity of the SI described so far, which is referred to as intrinsic silicon, is extremely low. A slight contamination with phosphorus atoms leads to additional electrons in the line band, which makes the silicon n-conductive and receives a conductivity that can be influenced by changing the density of the phosphorus atoms. Alternatively, contamination with boron or aluminum atoms can lead to the SI P-leading and has a conductivity that can also be influenced. These contamination atoms absorb electrons from the valence band and leave so -called “holes”, which behave like virtual positive charges. Si solar cells are usually endowed with boron, so that they behave like a P-type-necker, and have a narrow (~ 0.5 micrometer) superficial N-type range. Between the two, the so-called PN transition is formed, in which an electric field is created, the electrons and holes split, the electrons to the surface and the holes to the inside. In this way, a photo current is generated, which is derived from metal contacts on both sides. The light that falls away from the PN transition is not split up, and the generated electron-hole pairs finally recombinate and do not generate a photo stream. The roles of the P and N regions in the cell can, as explained here, be exchanged.

Accordingly, a monofacial solar cell only generates a photocurrent when the surface where the junction was formed is illuminated.

A bifacial solar cell, on the other hand, is designed so that the cell is active on both sides and generates photocurrent when either side - front or back - is illuminated.

Additional power generation gains: Compared to P solar cells, N solar cells tend to significantly increase efficiency. Bifacial solar cells will have a broader application perspective due to the bifacial generation capacity and higher system efficiency, and are particularly suitable for snowier areas and distributed generation systems such as roofs, fences and sound barriers.

The cell backside efficiency can reach more than 19%, and the incident backlights can be used to improve the generation capacity of the system, with the unit area capacity increase up to 10%~30%.

With the glass module with bifacial cell technology, the light is captured on both the front and back of the module. Increasing the use of light increases the efficiency of the module. Up to 360 Wp total power can be achieved via the active rear of the module (290 Wp only at the front / total 320 - 360 Wp).

The efficiency gain depends on the radiation situation (atmosphere and background).

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