Plastic material with the maximum allowable incident wavelengths could be used. For example, polycarbonate thin sheets. It is robust in nature.

PMMA,PDMS materials may be used as encapsulation layer.it is better Mechanical Reliability and flexibility.

Hello Azzouni Tarek,

You can not use the above methods. The moisture can get through the devices which degrade the devices leading to the failure of your cells.

What you need

Low permeability of materials such as glass or thin metals as a cap.

Within the cap, you need to have moisture absorbance such as CaO or MgO tablets.

If you interested, you could buy a small model OPV. And dismantled it.

You will have first experience of that.

Hope it helps.

Dr Wang