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Due to intrinsic defects, zinc oxide nanoparticles may induce interfacial recombination when used as the electron extraction layer in an inverted polymer solar cell. On page 1333, Franky So, John R. Reynolds, and co-workers demonstrate that UV-ozone treatment is an effective way to passivate defects in ZnO NPs and reduce interface recombination in a polymer solar cell. As a result, the power conversion efficiency of inverted PDTGTPD: PC71BM cells is improved to 8.1%.