Pyridinium Cations Act as Charge Reservoirs in Expanded Halide Perovskite Analogs at High Pressure

ABSTRACT Introducing charge reservoirs within semiconductors is a promising strategy for controlled electronic doping. We previously showed that dmpz 2+ ( N , N ’‐dimethylpyrazinium) molecules placed within the cavities of an expanded analog of halide perovskites, (dmpz)[Sn 2 I 6 ], could serve as electron acceptors and hole‐dope the material upon compression. However, the number of such small redox‐active cations is limited, and they tend to engage in unwanted redox reactions that compromise material stability. Herein, we show that redox‐innocent pyridinium cations (H 2 apy 2+ = 3‐amidinopyridinium) contained within the cavities of an expanded perovskite, (H 2 apy)[Sn 2 I 6 ], can also act as charge reservoirs upon compression. At ambient pressure, the energy of the H 2 apy 2+ π* acceptor orbital is ≥1.84 eV above the valence‐band maximum of (H 2 apy)[Sn 2 I 6 ]. Upon compression, this energy difference is decreased to <0.2 eV (32 GPa), enabling electron transfer from the Sn‐I framework into the H 2 apy 2+ π* orbital. This electron transfer increases the valence‐band hole concentration, affording substantial electronic conductivity (7 S•cm −1 , 36 GPa). Notably, this behavior is comparable to that of (dmpz)[Sn 2 I 6 ], albeit at higher pressure, and is not matched in (H 2 bda)[Sn 2 I 6 ] (H 2 bda 2+ = butane‐1,4‐diammonium), where the organic aliphatic cations do not have π* acceptor orbitals. This work expands charge reservoir candidates in perovskite analogs to include simple, stable, and abundant aromatic molecules.