This study addresses the long-standing issue of stability in solution-processed perovskite photovoltaics, a critical concern for their practical applications. The researchers demonstrate a series of ultrastable Dion–Jacobson (DJ) perovskites, specifically (1,4-cyclohexanedimethanammonium)(methylammonium)2-nPbI3n+1 (n ≥ 1), for photovoltaic applications. The scalable blade-coating technology is used to fabricate solar cells with a nominal n = 5 composition, achieving a maximum stabilized power conversion efficiency (PCE) of 19.11% under atmospheric conditions. These cells exhibit remarkable stability under moisture, thermal, and operational conditions, retaining 92% of their initial efficiency after over 4000 hours of storage at ~90% relative humidity, negligible efficiency loss after 5000 hours at 85 °C, and no significant degradation after 6000 hours at 45 °C under continuous light illumination. The stability of these cells is attributed to their unique slight-interlayer-displacement quantum-well configuration, which reduces interlayer spaces and tunes the alignment of layers, facilitating charge transport and structural stability. The use of cycloalkyl organic cations as interlayer cations further enhances flexibility and electronegativity, reducing lattice stress and improving stability. Structural analyses, including X-ray diffraction and time-resolved photoluminescence, confirm the stability and optoelectronic properties of these materials. The findings suggest that the designed DJ perovskites provide a promising pathway for constructing structurally stable 2D perovskites, with potential applications in scalable solar cells and other optoelectronic devices.This study addresses the long-standing issue of stability in solution-processed perovskite photovoltaics, a critical concern for their practical applications. The researchers demonstrate a series of ultrastable Dion–Jacobson (DJ) perovskites, specifically (1,4-cyclohexanedimethanammonium)(methylammonium)2-nPbI3n+1 (n ≥ 1), for photovoltaic applications. The scalable blade-coating technology is used to fabricate solar cells with a nominal n = 5 composition, achieving a maximum stabilized power conversion efficiency (PCE) of 19.11% under atmospheric conditions. These cells exhibit remarkable stability under moisture, thermal, and operational conditions, retaining 92% of their initial efficiency after over 4000 hours of storage at ~90% relative humidity, negligible efficiency loss after 5000 hours at 85 °C, and no significant degradation after 6000 hours at 45 °C under continuous light illumination. The stability of these cells is attributed to their unique slight-interlayer-displacement quantum-well configuration, which reduces interlayer spaces and tunes the alignment of layers, facilitating charge transport and structural stability. The use of cycloalkyl organic cations as interlayer cations further enhances flexibility and electronegativity, reducing lattice stress and improving stability. Structural analyses, including X-ray diffraction and time-resolved photoluminescence, confirm the stability and optoelectronic properties of these materials. The findings suggest that the designed DJ perovskites provide a promising pathway for constructing structurally stable 2D perovskites, with potential applications in scalable solar cells and other optoelectronic devices.