Solution-processed amorphous niobium oxide as a novel electron collection layer for inverted polymer solar cells

Amorphous niobium oxide (NbOx) as an electron collection layer in inverted polymer solar cells was prepared by a solution process. The power conversion efficiency of inverted polymer solar cells based on a blend of poly(3-hexylthiophene) and [6,6]-phenyl C61 butyric acid methyl ester was improved to 2.22% by inserting an NbOx layer between the active layer and indium tin oxide electrode. An energy level diagram of component materials in the inverted polymer solar cell indicated that the NbOx layer works as both an electron collection layer and hole blocking layer in polymer solar cells.