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The difference between p-type and n-type crystalline solar cells

Release:2017/04/25 Company News

The raw material that precedes the the pulling and cutting of silicon wafers is the same for both p and n-type cells. This raw silicon feedstock is “grown” into ingots (Czochralski process) or cast as bricks and then thinly sliced. These wafers form the basis of a solar cell. It is at this point that p and n-type cells diverge. To create a semiconductor junction that will induce current flow the wafers are doped (coated) with either boron (p-type) or phosphorus (n-type).

The creation of a solar module from raw material to finished product. Image courtesy PVInsights.com

 

The advantages of n-type cells

 

Monocrystalline p-type solar modules use cells/wafers that are Czochralski-grown (and block cast p-type polycrystalline cells/wafers to a lesser extent) suffer from light induced degradation (LID). LID occurs when oxygen impurities in the silicon wafer react with the doped boron in the first few hours/weeks of illumination of the cell. This effect can reduce cell efficiencies from 2-4% right off the bat. In comparison, n-type cells that rely on phosphorus doping do not see similar drops in efficiency and power output.

 

Cell efficiencies by technology. Both IBC and HIT modules use N-type cells. Image courtesy PVMaganize.

 

Typically, n-type wafers are less sensitive to impurities in the raw silicon. This means producers of n-type cells can rely on using lower quality wafers and still maintain high efficiencies without the impact of LID. Although high efficiency n-type modules cannot currently compete on a cost basis with standard efficiency polycrystalline p-type modules, n-type modules such as thePanasonic HIT 325W are becoming competitive with high efficiency p-type monos that require high grade silicon to produce.

 

Performance characteristics of Panasonic N-type HIT cells compared to a standard module.

Panasonic n-type cells are composed of monocrystalline and amorphous silicon layers. Amorphous silicon layers in the cells prevent recombinations of electrons, minimizing power loss.

 

Why consider using module with n-type cells

 

In short, higher efficiency = lower levelized cost of energy (LCOE) in $/kWh. In the end, higher efficiency modules mean more power per square foot. More power means less modules. Less modules means less space, lower BOS cost and less labor. These reduced costs drive the overall price of the solar electricity generated down. As the price of solar per kWh drops, PV will continue to increase its share of the US energy mix.

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