In this work, we investigated the influence of postproduction annealing on the solar cells based on polymer and zinc oxide (ZnO) nanorod composites. We discussed the morphological, crystalline, optical and electrical properties of devices with and without postproduction annealing. The experimental results showed that the postproduction annealing treatment worsened the performance of solar cells. The device without postproduction annealing has a power convention efficiency (PCE) of 1.06% and a short circuit voltage current density (Jsc) of 8.0 mA under Air Mass 1.5, 100-mW/cm2 illumination. After postproduction annealing at 150 for 3 minutes, Jsc decreased from 8.0 to 0.52 mA and PCE from 1.06 to 0.31%. The field emission scanning electron microscopy (FESEM) images of the postproduction annealing device show that the polymer aggregated on top of nanorods and formed crystallities with its main chains parallel to the substrate. As a result, the polymer cannot well fill the spacing of ZnO nanorods and more pores were created. Moreover, some nanorods were broken due to the stress from the polymer shrinking as the polymer cooled down to room temperature. Therefore, the electron transport path in ZnO nanorod was broken, leading to the significant reduction of PCE and Jsc.