An antisolvent (iodobenzene, IB) was used to assist the formation of closely packed CH3NH3PbI3 (MAPbI(3)) thin films during the one-step spin-coating process using different volumes of IB. The morphological, structural, optical and excitonic properties of MAPbI(3) thin films were analyzed using a contact-mode atomic-force microscope, X-ray diffractometer, broadband absorbance spectrometer and optical microscope-based time-resolved photoluminescence spectrometer. The properties of the resultant MAPbI(3) thin films can be manipulated by using different IB volumes, which dominates the device performance of MAPbI(3) based photovoltaic cells. The experimental results show that the grain size (or particle size) of MAPbI(3) thin films influences the collection of photoexcited carriers and the contact at the 6,6-Phenyl C-61 butyric acid methyl ester (PCBM)/MAPbI(3) interface, thereby resulting in a trade-off between the fill factor (FF) and short-circuit current density (J(SC)). In addition, it is predicted that the power conversion efficiency (PCE) can be further improved by increasing the crystallinity of the MAPbI(3) thin film while keeping the small grain size. (C) 2018 Elsevier B.V. All rights reserved.