Abstract We incorporated triphenylsulfonium triflate (TPST), a sulfonium‐based additive consisting of polar triflate and bulky hydrophobic phenyl rings, to the PbI2 precursor solution for preparation of less‐defect perovskite film via two‐step fabrication. TPST induced localized alterations in the array of the PbI2 structure due to its large size, thereby forming a more discontinuous and coarser surface with a greater number of pinholes and subsequently facilitating more efficient organic–inorganic reactions. As a result, we achieved the production of thick perovskite films with enlarged granules and decreased PbI2 residuals in the two‐step fabrication process. Furthermore, TPST facilitated the passivation of bulk film defects by increasing the binding energy with the defects. Consequently, the ITO/SnO2 np‐based device and the FTO/CBD SnO2‐based device obtained the best PCEs of 23.88% and 24.30%, respectively. Furthermore, the moisture stability of the perovskite was improved by the hydrophobic character of the TPST additive.
