Solar cells' stability is measured as function of time. When we plot time against the stability of solar cells, it is called Decay Curve. The curve varies depending upon the situations or environment in which the stability has been measured. Decay curve is very useful but it does not give much detail about underlying degradation mechanisms. Decay Curve is a graph obtained when we plot stability of a solar cell in electrical measurements at regular intervals, hence it gives us information about how fast or slow degradation process is under specific circumstances. It also gives clues about what role factors like oxygen, water, temperature, etc. play in degradation of a solar cell.

Terms Used in a Decay Curve :-

• E0 : Initial efficiency of a solar cell. It decreases over time.

• T80 : The time it takes to reduce the initial efficiency to 80%. It is sometimes taken as a measure of the useful lifetime of a device.

• Burn-In Phase : It has been observed that there is a rapid initial decrease in the power-conversion efficiency, which is followed by a more stable phase. This initial stage is called the burn-in phase. It is not always considered part of the proper decay curve.

• Ts : The time at the end of the burn-in phase is T-s.

• Ts80 : The time it takes to reduce the efficiency to 80% from the T-s time.