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Field-effect transistors (FETs) provide an ideal and versatile platform to study electronic properties of perovskite semiconductors. However, the fabrication of reliable perovskite FETs has remained an enormous challenge due to the severe ion migration, which can screen the applied gate electric field, resulting in poor device performance. Two-dimensional (2D) perovskites with bulky spacer cations are promising candidates for FET application due to the suppressed ion movement by large size insulating ligands. Unfortunately, to date, most research on organic cations is based on trial-and-error tests by picking the spacers randomly to incorporate into layered perovskites and devices. The correlation between chemical nature of the organic cations, film morphology, crystallinity, molecular organization, and charge carrier transport in 2D layered perovskites is still not well understood, thus, significantly limiting the development of 2D perovskite FETs.
In this report, we selected five different lengths of the linear alkyl ammonium organic cation to incorporate in 2D Sn-based perovskites. It is found that the chain length of the cation spacer and the film processing parameters significantly influence the film morphology and crystal orientation, which in turn affect local charge carrier mobility, as confirmed by terahertz spectroscopy, and finally determine the charge carrier transport in FET devices. Additionally, temperature-dependent charge transport measurements reveal a switch from negative mobility coefficient dominated by ion migration to a thermally activated regime with positive coefficient with increasing temperature. Such transport behaviour has not been observed so far for 2D layered perovskite FETs. We believe this work provides a general guideline on rational design principles of organic spacer cations in 2D perovskite for FET applications.
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