Photovoltaic Solar Modules of Different Types and Designs for Energy Supply

Properties Of Silicon Photovoltaic Converters

Photovoltaic conversion of solar radiation into electrical energy occurs in semiconductor photovoltaic (PV) cells. PV cells based on crystalline silicon are most widely used.

Semiconductors can exist as intrinsic as well as doped, in case existing in the material any impurities. Accordance with the type of impurities nature of the charge carriers may be of different type. Doped semiconductors can be N-type (with electrons as main charge carriers) or P-type (with holes that behave like positively charged particles as the main charge carriers).

In the electric field, both free electrons and electrons, jumping from the valence band, move against the direction of the electric field, since they have a negative electric charge. This means that the free places move in the direction of the electric field. Vacant place, thus, behaves like a particle with a positive charge and mass, which differs from the mass of the free electron. This quasiparticle is usually called a “hole” (Strebkov, 2010a; Strebkov, 2010b; Strebkov, 2010c; Kharchenko et al., 2010; Kharchenko et al., 2019; Panchenko et al., 2015; Strebkov et al., 2013).

In the intrinsic semiconductor, the escape of one electron from the valence band leads to the formation of one hole, the number of free electrons and holes is equal. The crystal as a whole remains electrically neutral. If the electron-hole pair is formed by a falling photon (that is, a quantum of light), then the photon energy should be equal to or larger than the band gap width. Photons with lower energy pass through the semiconductor and photons with higher or equal energy generate electron-hole pairs. The band gap in silicon is approximately ΔE_G ≈ 1,1 eV. That is, silicon is transparent to photons of lower energies that pass through the material without hindrance. The wavelengths corresponding to these energies are greater than about λ ≥ 1100 nm.

If we replace Si atoms in a silicon crystal with atoms of some elements of the fifth group of the periodic system, which have 5 valence electrons (for example, As, P, Sb), then four of these valence electrons form covalent bonds with neighboring silicon atoms. The fifth electron will be weakly bound to the impurity atom. This doped semiconductor is called an n-type semiconductor (“negative”). When a relatively small amount of energy is supplied, this electron “breaks away” from the atom. These pentavalent atoms are called donors, since they supply free electrons. As a result of the interaction of photons of solar radiation with a semiconductor, electron-hole pairs are formed.