Pressure is a powerful tool to modulate hybrid metal halides (HMHs), but its effects are often reversed upon decompression. Here, using the unsaturated m-aminophenylacetylene (m-APA) cation, we report pressure-induced polymerization (PIP) as a strategy for irreversible band-structure engineering in three heterostructures as HMH crystals: (m-APA)2Pb3I8, (m-APA)2PbBr4, and (m-APA)PbCl3. Distinct polymerization pathways yield novel ambient-stable phases with narrowed band gaps and reconfigured band alignments. The resulting polymeric cations exhibit varied sp2/sp3-C ratios, which significantly tune the electronic coupling across organic-inorganic interfaces. Specifically, P-(m-APA)2Pb3I8 retains type I alignment with gap narrowing driven by chemical pressure on the inorganic sublattice, while P-(m-APA)2PbBr4 undergoes a type I to type II transition, and P-(m-APA)PbCl3 transforms from type II to reversed-type I via organic band-edge reconstruction. This work demonstrates PIP as a novel and general approach to permanently tailor the electronic structures of HMHs, enabling functional design through the controlled covalent transformation of organic cations under high pressure.
Xu et al. (Mon,) studied this question.