In both ThEA and PEA, the protons at -NH3 + and the alkyl bridge exhibit sequential downfield shifts as seen in the BA system (Figure and), suggesting the spacers primarily interact with the inorganic ions through the ammonium head. In contrast, only the proton at the 3-carbon in ThEA (marked with a yellow circle) exhibits appreciable downfield shifts (Figure ), whereas the protons at ortho-and parapositions of PEA undergo such downfield shifts (Figure and Figure ). This suggests that the respective chemical interaction between the spacer and precursor ions manifests different molecular geometry of ThEA and PEA in the solutions. Specifically, ThEA renders an asymmetric molecular geometry, where both the ammonium head and 3-carbon in the thiophene ring interact with the inorganic ions (Figure ). In contrast, PEA can offer symmetric molecular geometry that the phenyl ring faces on the inorganic ions (Figure ). We hypothesize that such molecular geometry can be maintained even during the crystallization process. This in turn manifests the distinctive ring alignments at the HP surfaces for each case, thus bestowing a stark difference in phase stability upon ambient exposures. The upright geometry of ThEA cannot protect the HP lattice and compromise the lattice stability (Figure ). In contrast, PEA's 'umbrella' geometry can effectively block the environmental O2 and H2O, thus effectively protecting the inorganic lattice and improving the phase stability (Figure ) -consistent with the conclusion based on PL, CL and GIWAXS observations. Similar symmetric molecular geometry is anticipated from the 1 H NMR spectra of the DPA-based system (Figure and S16c), which strongly agrees with our observations.