The fabrication of high-performance, hole-conductor-free, printable mesoscopic perovskite solar cells (PMPSCs) is still a major challenge because it is difficult to realize the free diffusion of precursors throughout the micrometer-scale porous structure. Here, a facile and efficient additive manufacturing technique is proposed with melamine hydroiodide (MLAI) as an additional material. We systematically investigated the impact of MLAI on the crystallization, morphology, and defects of the perovskite film and the performance of the PMPSCs. The results revealed that the MLAI effectively optimized the morphology of perovskite and improved the pore-filling as well as passivated the defects of the perovskite film, thus hysteresis was reduced and the performance of the devices was enhanced. Based on the addition of MLAI, the power conversion efficiency (PCE) was obtained as 13.86%, which was 18.5% higher than that of the additive-free device. The additive engineering technique exhibits immense potential for large-scale production and application of PMPSCs.