Effect of sol-gel derived ZnO annealing rate on light-trapping in inverted polymer solar cells

Different morphology zinc oxide (ZnO) thin films were prepared by a sol-gel method using two annealing rates and used as the electron transport layers in inverted polymer solar cells. The morphology, optical and structure properties were performed by AFM, UV-vis and XRD in order to study the effect of annealing rates. The undulating morphology of ZnO film fabricated at a slow heating rate of 9 degrees C/min possesses a rougher surface than that of ZnO film annealed at the fast heating rate of 56 degrees C/min, which provides efficient light-trapping and increases photon absorption. The resulting device shows 12.6% and 6.7% improvement in short current density and fill factor, respectively, compared with the device based on the rapidly annealed ZnO; a maximum power conversion efficiency of 2.55% was achieved. (C) 2013 Elsevier B.V. All rights reserved.