This study reports on the electron-hole diffusion lengths in mixed halide and triiodide perovskite absorbers, revealing that the mixed halide perovskite has diffusion lengths exceeding 1 micrometer, significantly longer than its absorption depth. In contrast, the triiodide perovskite has diffusion lengths of about 100 nanometers. These findings justify the high efficiency of planar heterojunction perovskite solar cells and highlight the importance of optimizing diffusion lengths for future perovskite absorber development. The research uses photoluminescence quenching measurements to determine these diffusion lengths. The mixed halide perovskite's longer diffusion length is attributed to a longer recombination lifetime, consistent with its superior performance in meso-superstructured and planar heterojunction solar cells. The study also demonstrates that the diffusion lengths in the mixed halide perovskite are significantly longer than those in the triiodide perovskite, which limits the efficiency of the latter in thin-film configurations. The results indicate that the mixed halide perovskite can achieve high efficiency without the need for meso or nanostructures, while the triiodide perovskite requires such structures for efficient charge collection. The study also shows that the addition of chloride ions to the triiodide perovskite significantly increases the electron-hole diffusion length, primarily due to reduced non-radiative recombination. These findings have important implications for the development of high-efficiency perovskite solar cells.This study reports on the electron-hole diffusion lengths in mixed halide and triiodide perovskite absorbers, revealing that the mixed halide perovskite has diffusion lengths exceeding 1 micrometer, significantly longer than its absorption depth. In contrast, the triiodide perovskite has diffusion lengths of about 100 nanometers. These findings justify the high efficiency of planar heterojunction perovskite solar cells and highlight the importance of optimizing diffusion lengths for future perovskite absorber development. The research uses photoluminescence quenching measurements to determine these diffusion lengths. The mixed halide perovskite's longer diffusion length is attributed to a longer recombination lifetime, consistent with its superior performance in meso-superstructured and planar heterojunction solar cells. The study also demonstrates that the diffusion lengths in the mixed halide perovskite are significantly longer than those in the triiodide perovskite, which limits the efficiency of the latter in thin-film configurations. The results indicate that the mixed halide perovskite can achieve high efficiency without the need for meso or nanostructures, while the triiodide perovskite requires such structures for efficient charge collection. The study also shows that the addition of chloride ions to the triiodide perovskite significantly increases the electron-hole diffusion length, primarily due to reduced non-radiative recombination. These findings have important implications for the development of high-efficiency perovskite solar cells.