Odd–Even Effects of Linear Alkyl-Based Organic Spacers for Efficient Charge Transport in Two-Dimensional Dion–Jacobson Tin Perovskites

Two-dimensional (2D) tin (Sn 2+ )-based perovskites have emerged as promising p-type semiconducting materials for (opto)electronic devices due to their favorable balance of electrical performance and structural stability. While previous studies on 2D perovskites predominantly investigated Ruddlesden–Popper (RP) perovskites with monoammonium spacers, Dion–Jacobson (DJ) perovskites with diammonium spacers have recently sparked attention in the research community. The strong hydrogen bonds at both ends of the diammonium spacer, connecting neighboring inorganic octahedral layers, promote structural stability and efficient charge transport in DJ perovskites. This study systematically investigates a series of 2D DJ Sn 2+ perovskites, [H 3 N-(CH 2 ) m -(NH) 3 SnI 4 ] ( m = 3–8), to explore the influence from the length of spacer chains on lattice structures, film crystallinity, and charge transport properties. Our findings reveal that DJ perovskites with even-numbered chains ( m = 4, 6, 8) exhibit well-ordered layered structures, whereas those with odd-numbered chains ( m = 3, 5, 7) disrupt the formation of 2D structures. Furthermore, we reveal that the precursor stoichiometry can govern the phase evolution along with the role of spacer parity. Among the even-numbered 2D DJ Sn 2+ perovskites, 1,4-butanediammonium tin iodide (BDASnI 4, m = 4) exhibits optimal lattice formation and superior charge transport properties. Moreover, the introduction of an additional self-assembly monolayer ([2-(3,6-diiodo-9H-carbazol-9-yl)ethyl]phosphonic acid, I-2PACz) between the dielectric and channel layers further enhances the interface quality and reduces the trap density. The optimized transistor exhibits significantly reduced hysteresis and boosted field-effect mobility up to 1.45 cm 2 V –1 s –1 .