Sequential all-dip-coating deposition of (CH₃)₃NPbI_3−xCl_x perovskite materials was conducted in an aqueous nonhalide lead precursor solution, which was followed by that in a (CH₃)₃NI and (CH₃)₃NCl mixed solution as part of a facile, cost-effective, and environmentally benign manufacturing process for high-efficiency perovskite solar cells. The (CH₃)₃NPbI_3−xCl_x perovskite layers deposited via the proposed process were constructed with a Cl/I ratio below ∼3%, indicating the partial insertion of Cl into the (CH₃)₃NPbI₃ perovskite lattice. The amount of Cl inserted was readily modulated by varying the (CH₃)₃NCl concentration in the (CH₃)₃NI/(CH₃)₃NCl mixed solution. Incorporating a small amount of Cl led to significant improvements in the surface morphology and crystallinity of the perovskite layer as compared to (CH₃)₃NPbI₃ fabricated under the same conditions. The perovskite solar cell devices with these (CH₃)₃NPbI_3−xCl_x perovskite films exhibited superior device performances and stabilities, resulting in an outstanding power conversion efficiency of ∼15.3%. Results show that the fabrication of (CH₃)₃NPbI_3−xCl_x perovskite material with an aqueous nonhalide lead precursor is more efficient than conventional spin-casting approach with detrimental organic solvents.