[en] Highlights: • Conventional sequential deposition is modified to be more suitable for roll-to-roll process. • Reactive intermediate shows more rapid conversion to perovskite than conventional PbI₂ intermediate. • Fully slot die coated perovskite solar cells under ambient condition shows a power conversion efficiency of 14.4%. • Roll-to-roll processed flexible perovskite solar cells show power conversion efficiency of 11%. We report organic cation additives in lead iodide solutions as a practical approach for roll-to-roll production of perovskite solar cells. Sequential deposition, which is known to be more reliable than 1 step process, is modified to be even more reliable and suitable in roll-to-roll process. Addition of less than stoichiometric amount of organic cations in PbI₂ solution effectively improves processability by working as crystallization retardant and make dried PbI₂ film more reactive for faster conversion to perovskite. The printing-friendly sequential deposition is used in air with slot die coating, an industrial up-scaling technique, to produce a perovskite solar cell on glass with a 14.4% power conversion efficiency (PCE). The process is then used in actual roll-to-roll machine in air to produce flexible perovskite solar cells with up to 11.0% PCE.