There is an issue I'm facing that is very tricky.
A solar cell that is encapsulated in Sylgard 184 Silicone Elastomer with a front borofloat front glass. This cell is used to measure a light intensity.
The cell is enclosed in a chamber that can vary the temperature. The room ambient temperature is 25°C and humidity is 50%.
The cell has a temperature sensor applied to it that measures the cell's temperature.
The cell is shunted with a resistor (which has low temperature coefficient) in order to measure it's Isc value, and the whole is compensated in temperature, and is expected to behave linearly over temperature.
It does behave linearly when we raise the temperature, but when cooling, it goes off the chart and I can't really explain why.
One possibility is that as the cell cools, humidity diffuses into the silicone, which somehow changes its characteristics (refraction/transmission?) when the system cools down.
Perhaps, humidity seeps between the elastomer and the glass (a bonding agent is used) and when cooled, the dew point is reached causing the interface glass->elastomer to become glass->water->elastomer, changing the refractive index of the system.. ?
A clear change in behavior is noticed at around 25°C, which is the ambient temperature at which the cell rests when not performing tests.