The intrinsically poor stability of three-dimensional (3D) α-CsPbI₃ perovskites (PVSKs) greatly hinders their application in solar cells and optoelectronics. Here, we propose a new series of compounds, quasi-2D Dion–Jacobson (DJ) CsPbI₃ PVSKs, through density functional theory (DFT) calculation. The material design is based on periodic intercalation of tailored ethylenediamine cations (EDA²⁺) between the inorganic layers. The resultant quasi-2D (EDA)Cs_n−1Pb_nI_3n+1 PVSKs exhibit fundamentally enhanced stability, owing to the strong I–H interaction of diamine cations with a shortened interlayer distance (∼3.5 Å). Their bandgaps can be widely and linearly tailored from 2.150 (n = 1) to 1.476 eV (n = ∞) with the increase of the inorganic layer number (n). In comparison to the conventional 3D counterparts, they have smaller effective masses, lower exciton energies and larger dielectric constants. Furthermore, the highest power conversion efficiency (PCE) is calculated to be 20.9% (n = 50), evidencing that the quasi-2D DJ CsPbI₃ PVSKs could be an excellent candidate for exciting applications in optoelectronic devices.