Encapsulation of Cu(InGa)Se2 solar cells with ALD Al2O3 flexible thin-film moisture barrier: Stability under 1000 hour damp heat and UV exposure

Single or double layers of Al₂O₃ deposited by atomic layer deposition are shown to be excellent transparent front moisture barriers for CuInGaSe₂ devices. We studied two configurations; one where the Al₂O₃ was deposited directly on the substrate, and the other where it was deposited onto a flexible UV-PET and laminated on to the substrate. We have exposed samples with ALD barrier, and other barriers for comparison, to accelerated degradation including 1000 hr damp-heat, 1200 hour UV, and 10 freeze-thaw cycles. The V_OC and FF are essentially unaffected for cells with the ALD barrier, indicating it is highly effective in preventing moisture from reaching the junction of the CuInGaSe₂ cells. The J_SC decreases due to yellowing of an epoxy which was used to bond the encapsulant to the substrate for these experimental devices. This is unrelated to the ALD barrier. The excellent stability in D-H exposure indicates the 55 nm ALD layers, directly applied to the device with 3 μm high grids, has very good conformal coverage.