Three-Dimensional Lead Iodide Perovskitoid Hybrids with High X-ray Photoresponse

摘要

Large organic A cations cannot stabilize the 3D perovskite AMX_3 structure because they cannot be accommodated in the cubo-octhedral cage (do not follow the Goldschmidt tolerance factor rule), and they generally template low-dimensional structures. Here we report that the large dication aminomethylpyridinium (AMPY) can template novel 3D structures which resemble conventional perovskites. They have the formula (xAMPY)M_2I_6 (x = 3 or 4, M = Sn~(2+) or Pb~(2+)) which is double of the AMX_3 formula. However, because of the steric requirement of the Goldschmidt tolerance factor rule, it is impossible for (xAMPY)M_2I_6 to form proper perovskite structures. Instead, a combination of corner-sharing and edge-sharing connectivity is adopted in these compounds leading to the new 3D structures. DFT calculations reveal that the compounds are indirect band gap semiconductors with direct band gaps presenting at slightly higher energies and dispersive electronic bands. The indirect band gaps of the Sn and Pb compounds are ～1.7 and 2.0 eV, respectively, which is slightly higher than the corresponding AMI_3 3D perovskites. The Raman spectra for the compounds are diffuse, with a broad rising central peak at very low frequencies around 0 cm~(-1), a feature that is characteristic of dynamical lattices, high anharmonicity, and dissipative vibrations very similar to the 3D AMX_3 perovskites. Devices of (3AMPY)Pb_2I_6 crystals exhibit clear photoresponse under ambient light without applied bias, reflecting a high carrier mobility (μ) and long carrier lifetime (τ). The devices also exhibit sizable X-ray generated photocurrent with a high μτ product of ～1.2 × 10~(-4) cm~2 /V and an X-ray sensitivity of 207 μC・Gy~(-1)・cm~(-2).