Polycrystalline silicon
Silicon cast into blocks containing many small crystal grains; cheaper to make than monocrystalline but less efficient, and now largely phased out of PV production.
Polycrystalline (multicrystalline) silicon wafers are cut from rectangular blocks produced by melting polysilicon in a crucible and letting it solidify directionally. The result is many crystal grains with visible boundaries, giving cells their characteristic blue, speckled look. Grain boundaries and higher impurity levels act as recombination centres, reducing carrier lifetime and therefore efficiency.
Multicrystalline silicon was the workhorse of the PV industry from the mid-2000s to about 2018, when it held roughly 60% of the wafer market. Its advantage was a simpler, cheaper casting process and square wafers with no wasted corners. The arrival of diamond-wire sawing, larger Czochralski pullers and PERC cell lines (which benefit more from high-quality mono wafers) erased that cost gap. By 2023 its share had fallen to a few percent (ITRPV).
- Typical module efficiency at end of mass production: 17–19%.
- Power temperature coefficient: about −0.39 to −0.42 %/°C.
Note the potential confusion: polysilicon also names the high-purity feedstock that both mono and multi wafers are made from, and that feedstock remains essential.
Related terms
All terms →- Monocrystalline silicon
Silicon grown as a single continuous crystal, usually by the Czochralski method, giving the highest-efficiency and now dominant wafer type for PV.
- Solar cell
A semiconductor device, usually a doped silicon wafer with metal contacts, that converts sunlight directly into direct-current electricity via the photovoltaic effect.
- PERC (Passivated Emitter and Rear Cell)
A silicon cell design that adds a passivating dielectric layer to the rear surface, reducing recombination and reflecting light back into the cell.
- Temperature coefficient
The percentage change in a PV module power, voltage or current per degree Celsius of cell temperature away from 25 °C.