2D layered perovskites have emerged as potential alternates to traditional 3D analogs to solve the stability issue of perovskite solar cells (PSCs). However, van der Waals gaps in reported Ruddlesden-Popper (RP) phase 2D perovskites with monoammonium cations provide weak interactions between layers, potentially destabilizing the layered perovskite structure and thus the device. Here we eradicate such gaps by incorporating diammonium cations into MAPbI3, developing a series of Dion-Jacobson phase 2D perovskites that afford a cell efficiency of 13.3% with ultrahigh device stability. Unencapsulated devices retain over 95% efficiency upon exposure to various harsh stresses including ambient air (40%–70% relative humidity RH) for 4,000 hr, damp heat (85°C and 85% RH) for 168 hr, and continuous light illumination for 3,000 hr. The improved device stability over the RP counterpart is attributed to alternating hydrogen bonding interactions between diammonium cations and inorganic slabs, strengthening the 2D layered perovskite structure. Display omitted •Dion-Jacobson (DJ) phase 2D perovskites without the van der Waals gap are developed•A maximum PCE of 13.3% is achieved from the DJ phase 2D perovskite solar cells•Unsealed devices are extremely stable, subjected to various harsh testing conditions•Hydrogen bonds at both sides of diammonium cations strengthen 2D layered structure Perovskite solar cells (PSCs) have attracted tremendous academic and industrial interests because of their rapidly increased power conversion efficiency (PCE) in the past few years, but the intrinsic instability of commonly used 3D perovskites induces the issue of low device stability. Ruddlesden-Popper (RP) phase 2D layered perovskites have recently been reported to show enhanced stability. However, weak van der Waals interactions between interlayers cannot sufficiently stabilize their 2D layered structure. By removing the van der Waals gaps in the RP case, we herein develop a series of Dion-Jacobson phase (DJ) 2D layered perovskites with higher structural stability for PSCs. A maximum PCE of 13.3% is achieved from the DJ phase 2D PSCs, and unencapsulated devices are extremely stable, retaining more than 95% of initial PCE upon exposure to ambient air (4,000 hr), damp heat (85°C and 85% RH, 168 hr), and continuous light illumination (3,000 hr). Dion-Jacobson (DJ) phase 2D layered perovskites are developed by removing the van der Waals gap between organic layers and inorganic slabs in Ruddlesden-Popper (RP) phase counterparts. The hydrogen bonding formed at both sides of diammonium cations with perovskite layers in the DJ phase 2D perovskite endows it with extremely high structural stability, compared with that at only one side in the RP phase one. The devices exhibit a PCE of 13.3% with unprecedented stability, even when subjected to very harsh testing conditions.