Nature Materials, Published online: 01 June 2026; doi:10.1038/s41563-026-02619-1Ultraviolet damage and the thermal instability of self-assembled monolayers hamper the durability of perovskite solar cells. Modifying the spacer units in these monolayers revealed the mechanisms of photodegradation and thermal degradation in non-conjugated and conjugated structures, respectively. Specifically designed spacer molecules can achieve highly efficient and stable perovskite solar cells.