Crystalline silicon
[5][6] In 2013, conventional crystalline silicon technology dominated worldwide PV production, with multi-Si leading the market ahead of mono-Si, accounting for 54% and 36%, respectively.
[3]: 41 The conversion efficiency of PV devices describes the energy-ratio of the outgoing electrical power compared to the incoming radiated light.
They were 7% above the efficiency of commercially produced modules (23% over 16%) which indicated that the conventional silicon technology still had potential to improve and therefore maintain its leading position.
This coke-fired smelting process occurs at high temperatures of more than 1,000 °C and is very energy intensive, using about 11 kilowatt-hours (kW⋅h) per kilogram of silicon.
[3]: 29 With the exception of amorphous silicon, most commercially established PV technologies use toxic heavy metals.
CIGS often uses a CdS buffer layer, and the semiconductor material of CdTe-technology itself contains the toxic cadmium (Cd).
In the case of crystalline silicon modules, the solder material that joins the copper strings of the cells, it contains about 36% of lead (Pb).
[13] Martin Green, Andrew Blakers, Jianhua Zhao and Aihua Wang won the Queen Elizabeth Prize for Engineering in 2023 for development of the PERC solar cell.
[16] Panasonic and several other groups have reported several advantages of the HIT design over its traditional c-Si counterpart: Owing to all these advantages, this new hetero-junction solar cell is a considered to be a promising low cost alternative to traditional c-Si based solar cells.
Typically in good quality, CZ/FZ grown c-Si wafer (with ~1 ms lifetimes) are used as the absorber layer of HIT cells.
Direct deposition of doped a-Si layers on c-Si wafer is shown to have very poor passivation properties.
[29] This is because of the presence of hetero-junction between the intrinsic a-Si layer and c-Si wafer which introduces additional complexities to current flow.
[26][30] In addition, there has been significant efforts to characterize this solar cell using C-V,[31][32] impedance spectroscopy,[31][33][34] surface photo-voltage,[35] suns-Voc[36][37] to produce complementary information.
[41] Dopant atoms such as phosphorus and boron are often incorporated into the film to make the silicon n-type or p-type respectively.
[41] This monocrystalline material, while useful, is one of the chief expenses associated with producing photovoltaics where approximately 40% of the final price of the product is attributable to the cost of the starting silicon wafer used in cell fabrication.
Additionally, other methods for forming smaller-grained polycrystalline silicon (poly-Si) exist such as high temperature chemical vapor deposition (CVD).
The application of amorphous silicon to photovoltaics as a standalone material is somewhat limited by its inferior electronic properties.
Protocrystalline Si also has a relatively low absorption near the band gap owing to its more ordered crystalline structure.
The typical method used in industry requires high-temperature compatible materials, such as special high temperature glass that is expensive to produce.
In both of these methods, amorphous silicon is grown using traditional techniques such as plasma-enhanced chemical vapor deposition (PECVD).
The aluminum that diffuses into the amorphous silicon is believed to weaken the hydrogen bonds present, allowing crystal nucleation and growth.
[48] Experiments have shown that polycrystalline silicon with grains on the order of 0.2–0.3 μm can be produced at temperatures as low as 150 °C.
The laser fluence must be carefully controlled in order to induce crystallization without causing widespread melting.
Polymer-backed solar cells are of interest for seamlessly integrated power production schemes that involve placing photovoltaics on everyday surfaces.
[50] Plasma torch annealing is attractive because the process parameters and equipment dimensions can be changed easily to yield varying levels of performance.
While this method is applied frequently to silicon on a glass substrate, processing temperatures may be too high for polymers.
