Quasi 3D electronic structures of Dion-Jacobson layered perovskites with exceptional short interlayer distances

In the field of perovskite solar cells (PSCs), 3D/2D heterostructures are promising candidates to obtain highly efficient and stable devices. Herein, inspired by dications that have afforded rare layered perovskites called Dion-Jacobson (DJ), with short interlayer distances, we designed and synthesized the new 2-iodopropane-1,3-diamonium dication (DicI), and we successfully obtained multi-n 2D layered perovskites (DicI)(MA)(n-1)PbnI3n+1 (n = 1-4, MA(+) = methylammonium). As a result of a suitable size of the dication which fits well, in projection to the layer planes, in the square defined by four adjacent apical iodides, as well as halogen bonding between organic iodine and apical iodides (I-(ap)) of perovskite layers, a perfect eclipsed configuration between adjacent layers takes place, yielding unprecedented short I-(ap)center dot center dot center dot ((ap)) distances, as small as 3.882 angstrom in (DicI)(MA)(2)Pb3I10. Density functional theory (DFT) calculations highlight unusually strong valence band dispersion along the Gamma -> Z direction. Effective masses for out-of-plane motions of holes are estimated on par with values computed for 3D perovskites, and similar to in-plane effective masses in 2D multilayered perovskites. This indicates that these layered compounds feature quasi 3D electronic structures, hence appearing as promising candidates for PSC heterostructures.