In this paper, the use of hot solvent vapor (HSV) annealing is demonstrated to improve the performance of polymer solar cells (PSCs) fabricated by the spray process. The blend of poly(3-hexylthiophene) and [6,6]-phenyl-C-61-butyric acid methyl ester (P3HT/PCBM) is used as a photoactive layer of the solar cell. Compared to the conventional solvent vapor annealing, the HSV annealing can eliminate the formation of intra-droplet boundary during the spray process and optimize the nanostructure of the film quickly ( <= 5 min). The study of conducting atomic force microscopy (C-AFM) reveals that the HSV annealed film exhibits smooth film surface and homogenous conductivity distribution. Moreover, an enhanced light harvesting and increased crystallinity of P3HT in the active layer are observed by UV-vis absorption and X-ray diffraction (XRD). With subsequent thermal annealing, the power conversion efficiency of solar cell made from the HSV annealed film is reached at 3.61%. This HSV annealing technique can be implemented into the fabrication of high efficient large-area PSCs using the spray process. (C) 2013 Elsevier B.V. All rights reserved.