Charge carrier transport in two-dimensional benzimidazole-based perovskites

Two-dimensional (2D) perovskites have emerged as promising candidates for field-effect transistors (FETs) due to their pronounced stability in the presence of insulating bulky organic spacer cations. However, the underlying mechanism of the charge carrier transport in these 2D perovskite semiconductors remains elusive. In this study, the temperature dependence of the charge carrier properties of benzimidazolium tin iodide perovskite ((Bn)₂SnI₄) is studied to evaluate the corresponding transport mechanism on nanoscopic and macroscopic dimensions. By combination of solvent engineering to optimize the morphology of perovskite thin films and choice of the organic imidazole-based spacer inducing hydrogen bonding with the inorganic [SnI₆]^4- octahedron layer, less ionic defects are generated resulting in suppressed ion movement. It was possible to separate the influence of mobile ions and temperature on the charge carrier transport in transistors. The decline of the charge carrier mobility with temperature decrease in the device indicates a hopping mechanism for macroscopic transport. On the other hand, the local charge transport was determined by ultrafast terahertz photoconductivity measurements revealing an increasing mobility to 17 cm² V^-1 s^-1 with temperature decrease implying a band mechanism on the nanoscopic scale. The local charge carrier mobility is associated with the particularly regular structure of the octahedral [SnI₆]^4- sheets induced by symmetric hydrogen bonding with the benzimidazolium cation. Our results provide key insights on the charge transport properties of perovskite semiconductors, which have important implications for realizing high-performance electronic devices.