Each of the monocrystalline silicon cells manufactured, regardless of the manufacturing technology used, is susceptible to the adverse LID effect. This phenomenon has been known for many years, but only with the introduction of high-performance modules has it become more severe. What is the LID effect? What are its negative effects? How are manufacturers dealing with this challenge? This is discussed later in the article, using the example of German photovoltaic panel manufacturer AE Solar.[1]

An extension of the commonly used abbreviation LID is Light Induced Degradation, or in Polish, degradation (of a photovoltaic cell) caused by incident sunlight, induced by an induced voltage. The LID effect occurs during the operation of a photovoltaic system exposed to high sunlight and high temperatures. The result can be a loss of up to 5% of relative efficiency. For example, boron oxide, which is present in the silicon cell due to boron doping, is responsible for the degradation process, as well as trace amounts of oxygen present, which is a side effect of the growth of silicon wafers during their manufacture. Then, already in operation, the oxygen combines with the boron used in the cell to form boron oxide (B-O). Higher concentrations of boron result in lower base resistivity, which increases the occurrence of LID. 

Failure to counteract the LID effect in any way can cause degradation of cell performance in the first month of operation of up to 10%. For this reason, module manufacturers perform a cell regeneration (annealing) process, which they carry out by subjecting the cell to high temperatures with light or applied current. However, this process is time-consuming, and the optimal level of regeneration for each cell is different. For this reason, manufacturers have tried to find another method to neutralize the effects of this effect or reduce its magnitude.[2]

AE Solar engineers struggling with the LID problem decided to use a series of studies on permanent instability in monocrystalline gallium-doped PERC-type silicon cells. The main positive effect of changing the doping material from boron to gallium is that there is no degradation or even a slight improvement in performance during the cell stabilization process. Under the same conditions, boron-doped cells suffered about 5% degradation in efficiency, after which (after performing a full regeneration process) their efficiency returned to normal. Using its knowledge, AE Solar has developed a new series of AURORA photovoltaic panels, which includes gallium-doped PERC-type modules resistant to the adverse LID phenomenon. [3]

Click to find out more about AE Solar

Author: Przemyslaw Lis
Bibliography:
[1] - Nicholas E. Grant, Jennifer R. Scowcroft, Alex I. Pointon, Mohammad Al-Amin, Pietro P. Altermatt, John D. Murphy – Lifetime instabilities in gallium doped monocrystalline PERC silicon solar cells

[2] – Jay Lin – „Why can’t LID effects be completely removed in PERC cells?”

[3] -  Vidhyashankar Venkatachalaperumal, Afshin Bakhtiari - LIGHT-INDUCED DEGRADATION