Solvent engineering with dimethylsulfoxide (DMSO) has been shown to achieve high quality methylammonium lead iodide (MAPbI(3)) films for high performance perovskite solar cells (PSC). The morphology and composition of the intermediate PbI2-DMSO films play the key role for the success. The coordination and crystal growth of the PbI2-DMSO film however remain un-exploited. We study the way and extent of DMSO coordination and subsequent crystal growth of the PbI2-DMSO film to fabricate high quality perovskite films for enhancement of the photovoltaic performances of the cells. The DMSO is pre-coordinated or coordinated in-situ with PbI2 at a 1:1 or 2:1 M ratio. The PbI2-DMSO film from pre-coordination at 1:1 M ratio gives perovskite films of the best quality, being dense and possessing uniform size grains, high light absorption, and long charge carrier life times, among all investigated. The champion PSC achieves a high power conversion efficiency of 15.2%, significantly outperforming 13.0% of PSC based on PbI2-DMSO films from in-situ coordination at 1:1 M ratio, and 11.7% of PSC based on plain PbI2 films. (c) 2018 Elsevier Ltd. All rights reserved.