What is LID(Light Induce Degradation) and PID(Potential Induced Degradation) in Solar Cell?

Two common types of degradation that affect solar cells are light-induced degradation (LID) and potential-induced degradation (PID).

In this blog post, we will explain what these phenomena are, how they occur, and how they can be prevented or mitigated.

LID (Light Induced Degradation) loss: 

LID loss refers to the power loss and other loss of performance of crystalline p-type boron-doped silicon solar cells after the first few hours of exposure to sunlight. LID loss typically varies between 1-3%. The degradation of cells by sunlight is highly dependent on the quality of the wafer manufactured and is the result of a defect known as the “boron oxygen complex”. This defect occurs owing to oxygen being trapped in the silicon as part of the “Czochralski process” during manufacture.

LID loss is a natural phenomenon that affects most crystalline silicon solar cells. It is most prominent in the first year of operation when the modules experience an initial power stabilization. The average percentage of power loss for the first year is usually advertised to be around 3%. After that, the power degradation rate is lower, typically around 0.8% per year.

LID loss can be reduced by using high-quality wafers with low oxygen content, or by applying some treatments to the wafers before cell fabrication, such as hydrogenation or annealing. LID loss can also be partially recovered by exposing the modules to elevated temperatures or reverse bias voltages.

PID (Potential Induced Degradation) loss:

PID loss refers to the degradation induced by high voltages applied to the modules in a PV system. PID loss can affect both crystalline and thin-film solar cells, but it is more common in crystalline modules operating at high voltages (near 1000 V or above), combined with high temperatures and humidity. PID loss can cause power losses of up to 25% or more.

PID loss occurs when there is a large potential difference between the module frame (grounded) and the cells (biased). This creates a leakage current that flows through the module materials, such as glass, encapsulant, and back sheet. This current can cause various types of damage to the cells, such as shunting, corrosion, delamination, or polarization. PID-affected modules often have a pattern of “black” cells near the frame that are non-functional or have reduced output.


PID loss can be prevented or mitigated by using modules that have a low susceptibility to PID, such as those with anti-PID coatings or films on the glass or back sheet. PID loss can also be reduced by using lower system voltages, avoiding negative grounding, installing bypass diodes, or applying periodic reverse bias voltages. PID loss can be partially reversed by applying positive bias voltages or heating the modules.

Conclusion:

LID loss and PID loss are two different sources of degradation that affect solar cells and reduce their performance and efficiency. LID loss is caused by sunlight exposure and affects mainly crystalline p-type boron-doped silicon solar cells. PID loss is caused by high voltages applied to the modules and affects both crystalline and thin-film solar cells. Both types of degradation can be prevented or mitigated by using high-quality materials, applying appropriate treatments, or designing PV systems with lower voltage levels. Both types of degradation can also be partially recovered by exposing the modules to elevated temperatures or reverse bias voltages.

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