Interdigitated nanostructures can increase power conversion efficiency (PCE) by providing large interfaces for the dissociation of excitons and arrays for carrier transportation without recombination. Here, we reappraise the validity of donor-acceptor nanostructures composed of well-aligned porphyrin-fullerene nanopillars based on their contribution to the PCE compared with bulk heterojunction (BHJ) and bilayer (BL) organic photovoltaic solar cells (OPVs) with high efficiencies. Contrary to expectations, the results showed that poly (3-hexyithiophene) (P3HT):[6, 6]-phenyl C-61 butyric acid methyl ester (PCBM) interdigitated nanostructures hardly enhanced the PCE. We suggested three reasons focused on the morphological characteristics: the misbalanced carrier transit time caused by differences in the travel distances and carrier mobilities, detrimental effects on carrier transportation due to the overlap of the pathways to the electrodes, and the dependence of the PCE on the shapes and sizes of the nanostructures. (C) 2015 Elsevier B.V. All rights reserved.