“…In an attempt to improve electric conduction and minimize the dark current, several materials have been explored for this purpose, such as Al 2 O 3 , Nb 2 O 5 , ZrO 2 , SnO 2, In 2 O 3 and CeO 2 9,10 . In photovoltaic devices the Nb 2 O 5 forms an energy barrier due to its energy gap being larger when compared to other semiconductors, causing the increase of the open circuit potential, thus suggesting the reduction in the speed of the reactions of charge recombination 11,12,13 . For that reason Nb 2 O 5 layers have also been used as blocking layers of other oxides, preventing electron back-transfer 14 .…”