The versatile structure of organic–inorganic layered perovskites has enabled the fabrication of strongly luminescent material sources with narrow emission. However, although demonstrated to be beneficial for many applications, their structural tunability to achieve broadband emission and thus white light is often limited to changes in the organic cation. Herein, the role of solvent–organic cation interactions on the structural arrangement of the organic and inorganic building blocks in a room‐temperature synthesis is investigated. It is shown that changes in the solvent properties coupled with the molecular configuration of the organic cation can disrupt the conventional platelet‐like shape of layered perovskites, leading to disconnected corner‐sharing ribbons of octahedra, from which micrometer‐elongated crystals with nanoscale grooves are formed. With an 18% white light photoluminescence quantum efficiency, the crystal shape enables localized Mn doping at the groove interfaces. These findings highlight the crucial role of the interaction among solvent molecules and organic cations in shaping the assembly of the structural framework and their optical properties.