With the increase in solar power installations and concurrent attention to their maintenance and life cycle, it has been found that solar cells, both monocrystalline (thin-film) and polycrystalline, wafers, and coated films, etc. can become structurally modified over time. This phenomena is typically referred to as “light induced degradation,” and is sometimes referred to as the Staebler-Wronski effect. Light induced degradation has been discussed in various publications including, for example, Experimental Study of the Factors Governing the Staebler-Wronski Photodegradation Effect in a-Si:H Solar Cells, Annual Subcontract Report, 1 Apr. 1995-30 Jun. 1996 (October 1996) and National Staebler-Wronski Effect in Amorphous Silicon and Its Alloys, Opto-Electronics Review 12(1), 21-32 (2004).
It has been found that receiving a medium to large amount of light or sunlight with no load or very little load (referred to as “no load” herein) can physically damage solar cells and reduce the power output of the solar cells over their lifetime by 10% to 15% percent or more. Often, from the time solar cells leave a factory to the time when they are connected to the power grid, there is a loss of power of up to 20% per solar module. But even after such connection, damage may continue in the field due to open circuit conditions (VOC) in early morning hours and other factors.
The cause of light induced degradation is not very well understood currently. The problem often occurs during and immediately after manufacturing the solar cells. One possible effect of the problem is an undesirable buildup of unipolar or dipolar charges near the junction layer of the solar cell. The buildup, or static barrier, results in reduction of the solar cell output voltage by as much as 20%, depending on the prevalent mix of wavelengths and temperature to which the solar cells are exposed. Undesirable effects are compounded by the above-mentioned physical damage to the solar cell and can lead to very substantial losses in the production of electricity, as the static barrier reduces the energy output of the solar cell and further contributes to its heating up.