Enhancing photoluminescence quantum yield (PLQY) is one of the most important issues in photoluminescent materials. Herein, a molecule design strategy to improve the PLQY in 0D metal halides is proposed. Two new lead‐free organic–inorganic metal halide hybrids with broadband orange emissions have been prepared with a PLQY increase of 57% from (C6N2H16)SbCl5 (I) to (C6N2H16)SbCl5⋅H2O (II) by introducing H2O molecules. These two compounds have very similar inorganic frameworks, except that the incorporation of water molecules in II increases the distance between the [SbCl5] polyhedra. It is revealed that the increase of PLQY is mainly attributed to the generation of more local photoelectrons resulting from the additional water molecules. This work provides a new insight to improve the PLQY for 0D environmentally friendly organic–inorganic metal halide hybrids and is beneficial for further photoluminescent material exploration.