Semiconductor Solar Batteries SC-SB

Two types of solar cells are discussed in the following sections (i) semiconductor solar batteries (SC-SB) (Section 32.5) and (ii) dye-sensitized solar cells (DSSC) (Section 32.6). 

Inside the silicon semiconductor, electrons diffuse from the n-type side (with a high electron concentration) in the direction of thep-type side. Holes diffuse from the p-side in the opposite direction. This results in a region where all charge carriers are depleted (space charge region). At thep-n junction both electrons and holes accumulate electrons on one side of the junction, and holes at the other side. Thus, a double layer of electric charges is formed, which leads to a potential difference of about 0.6-0.7 V. This is the solar cell s open-circuit voltage (OCV). When both sides of the 

The maximal theoretical efficiency of solar energy conversion (for normal intensity of solar radiation) in silicon solar batteries with one p-n-junction is about 30% (Shockley-Queisser limit, described in 1961). For multijunction tandem solar batteries and for batteries with an optical light condenser the theoretical limit is higher. The practical efficiency is lower and depends on several factors, including the crystalline modification of silicon and the thickness of the semiconductor, where photons are adsorbed. For high thickness silicon batteries the efficiency reaches about 20%. For low thickness batteries made from amorphous silicon it is 5-10%. The maximum practical conversion efficiency silicon has is at a temperature of about 25 C. With rising temperatures the efficiency diminishes. The battery is often covered by a thin layer of silicium nitride that reflects UV light and prevents a temperature rise (antireflection layer). 

The first silicon solar battery was developed in 1954 at the American company Bell. Due to its high production costs, which could not compete with production costs for electric energy produced in conventional thermal power plants, this new device at first drew little attention from the scientific community. In 1954 began the era of artificial earth satelites. The first satelites were equipped with electrochemical batteries, which allowed only for a limited operational time. Soon it was realized that semiconductor solar batteries are the only alternative for the power supply of satelites (and later spaceships) with an extended operational lifetime, and extended research and development (R D) work was started in this field. In 1958 the first sattelite with a silicon solar battery Vanguard 1 was launched. The conversion efficiency of its solar battery was 10%. The battery remained operable for about 8 years. 

4 Semiconductor Solar Batteries with Nonsilicon Materials 

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