Colloidal perovskite nanocrystals (NCs) have shown promise in visible and near-infrared light emission compared with conventional quantum dots because of their sharp and highly efficient emission. Light-driven halide exchange offers high degrees of tunability of perovskite NC composition and photoluminescence properties. A remaining challenge is the incomplete change between bromide and chloride due to the presence of radical quenchers. Herein, an optimized in situ halide exchange method of perovskite NCs is reported. Chloroform is used as the solvent and the precursor to effectively generate halide radicals and ions under ultraviolet light irradiation in an inert atmosphere. This strategy achieves complete crystal transformation in colloidal perovskite NCs such as CsPbBr3-to-CsPbCl3 and Cs4PbBr6-to-CsPbCl3. The exchange reaction rate can be further tuned by the presence of B-site dopants such as Zn2+ and Ce3+. The dopant cations are partially remained in the exchanged perovskite NCs, indicating the predominance of thermodynamic control in the crystal transformation.