The aluminum-doped zinc oxide (AZO) thin films with nano-ridge structures were fabricated via the low-temperature ramp annealed sol-gel derived process. The power conversion efficiency, especially the short circuit current density, was dramatically improved upon using the AZO nano-ridge structured thin films as the cathode buffer layers in inverted polymer solar cells (PSCs) with comparison to the intrinsic zinc oxide (i-ZnO) planar thin films. Furthermore, the thickness of AZO nano-ridge buffer layer can be enhanced significantly to about 120 nm without sacrificing the solar cell performance, which brings convenience to PSCs manufacturing by an industrial scale production. (C) 2013 Elsevier B.V. All rights reserved.