Metal-free　molecular　perovskites　have　shown　great　potential　for　X-ray　detection　due　to　their　tunable　chemical　structures,　low　toxicity,　and　excellent　photophysical　properties.　However,　their　limited　X-ray　absorption　and　environmental　instability　restrict　their　practical　application.　In　this　study,　cesium-based　molecular　perovskites　(MDABCO-CsX3,　X　=　Cl,　Br,　I)　are　developed　by　introducing　Cs+　at　the　B-site　to　enhance　X-ray　absorption　while　retaining　low　toxicity.　The　effects　of　halide　modulation　on　the　physical　properties　and　device　performance　are　systematically　investigated.　Among　the　variants,　MDABCO-CsBr3　exhibited　superior　environmental　stability,　attributed　to　the　optimal　ionic　radius　and　high　chemical　stability　of　Br−.　This　stability　is　further　enhanced　by　a　higher　tolerance　factor,　which　promotes　a　stable　3D　cubic　structure　and　suppresses　ion　migration　within　the　crystal.　Consequently,　MDABCO-CsBr3-based　X-ray　detectors　demonstrated　reduced　ionic　migration,　minimal　dark　current　drift,　and　a　stable　current　response　under　X-ray　exposure,　achieving　a　high　sensitivity　of　4124　µC　Gy−1　cm−2　and　a　low　detection　limit　of　0.45　µGy　s−1.　Moreover,　the　devices　exhibit　excellent　thermal　stability,　operating　effectively　at　temperatures　up　to　130　°C.　These　results　highlight　MDABCO-CsBr3　as　a　promising　candidate　for　stable　and　efficient　X-ray　detection,　expanding　the　applicability　of　molecular　perovskites　in　advanced　radiation　detection　technologies.　©　2025　Wiley-VCH　GmbH.