Turning hybrid organic-inorganic perovskites from bulk to nanoscale via desolvation

•We report a reversible top-down method to prepare nanoscale HOIPs by desolvation.•The water molecules and hydrogen bonding in the frameworks of bulk HOIPs [C4H12N2]MBr3·H2O (M = K, Rb) can be efficiently removed.•The desolvated nanoscale HOIPs can recover back to their original phases upon subsequent exposure to moisture for two days.•The mechanism of desolvation was disclosed by DFT, which demonstrate the desolvation induced substantial mechanical difference in the parent and delsovated structures.