The inverted bulk-heterojunction solar cell on the polyester (PET) substrate with a nonannealing active layer is investigated. The atomic force microscope images show that the morphology of the nonannealing active layer of the inverted plastic solar cell evolves with time. which improves the performance of the solar cell. Our investigations show that the grain size of the active layer increases with time, resulting in improvements in the fill factor (from 34.8 to 62.8%) and shunt resistance (from 107 to 505 Omega cm(2)) as well as it reduction in the series resistance (from 4.82 to 0.96 Omega cm(2)). The easily processed inverted device with a nonannealing active layer on the indium tin oxide-coated PET substrate exhibits a high power conversion efficiency of similar to 3.66%. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3184341] All rights reserved.