Comparative study of patterned TiO2 and Al2O3 layers as passivated back-contact for ultra-thin Cu(In, Ga)Se2 solar cells

In this work, a low cost passivated back-contact for ultra-thin Cu(In, Ga)Se
₂
-based (CIGS) solar cells to improve the carrier collection is developed. The current loss due to rear-interface recombination was first estimated with an accurate opto-electrical model. We compared the use of a sol-gel TiO
₂
and an ALD-Al
₂
O
₃
layer for the back-contact passivation. 400-420 nm CIGS cells were fabricated on the oxide/Mo substrate with point-contacts patterned by nanoimprint lithography. The use of a patterned-Mo/Al
₂
O
₃
back-contact leads to an increase of the cell performance compared to the standard Mo back-contact. The passivation effect is discussed and is characterized by photoluminescence.