The first practical photovoltaic cell was developed in 1954 at Bell Laboratories .They used a diffused silicon p–n junction that reached 6% efficiency, compared to the selenium cells in fabrication of solar cell.
Most practical solar cells are silicon based ,because it is cheap and abundant material.
STEPS of fabrication of solar cell
- First step is refining silicon
- Silicon dioxide (SiO2) is the most abundant mineral in the earth’s crust.
- The manufacture of the hyper pure silicon for photovoltaics starts with locating a source of silicon dioxide in the form of sand.
- The silica is reduced (oxygen removed) through a reaction with carbon in the form of coal, charcoal and heating to 1500-2000 °C in an electrode arc furnace.
- Silicon di oxide + Carbon = Silicon + Carbon di oxide
- The resulting silicon is 98% pure. It contains Fe, Al, and B , to remove these traces , further purification is done ,Powdered Si is reacted with anhydrous HCl at 300 C to form SiHCl3
- During this reaction impurities such as Fe, Al, and B react to form their halides (e.g. FeCl3, AlCl3, and BCl3).
- The SiHCl3 has a low boiling point of 31.8 C and distillation is used to purify the SiHCl3 from the impurity halides.
- Finally, the pure SiHCl3 is reacted with hydrogen at 1100 C for ~200 – 300 hours to produce a very pure form of silicon.
- Above reaction takes place inside large vacuum chambers and the silicon is deposited onto thin polysilicon rods (small grain size silicon) to produce high-purity polysilicon rods of diameter 150-200mm.
- Silicon used for solar cells can be single crystalline, multi crystalline, polycrystalline or amorphous. The key difference between these materials is degree to which the semiconductor has a regular, perfectly ordered crystal structure.
- AFTER GETTING THE REQUIRED SILICON FROM ABOVE MENTIONED CHEMICAL PROCEDURE , different methods of solar cells fabrication are applied , each method involves doping of silicon to make p-n junction , and required processes to make a furnished solar cell.