Single-halogen CsPbI₃ is a promising candidate for red light-emitting diodes due to its high photoluminescence quantum yield, narrow emission line width, and facile solution processability. However, the bandgap of CsPbI₃ is not in the range of the display-oriented pure red band (620–660 nm). In this study, the introduction of a phenylbutylammonium bromide (PBABr) ligand can not only tune the bandgap of the resulting low-dimensional CsPbI₃ films but also induce the formation of a concentrated quantum-well structure at n = 3 domains, which contributes to better energy transfer and charge transport. As a result, low-dimensional PBABr capped CsPbI₃ films with tunable emissions covering the pure red band were obtained and the corresponding efficient electroluminescent devices were achieved. By further optimizing the device structure and interface, a highly efficient red (653 nm) light-emitting diode device was fabricated with a maximum EQE of 14.3% and a maximum brightness of 543 cd m⁻². This work provides a facile one-step strategy by bromine-terminated ligand treatment to realize low-dimensional CsPbI₃ films with desirable optical properties and preferred quantum-well distribution for display applications.