Novel (110) Double-Layered Guanidinium-Lead Iodide Perovskite Material: Crystal Structure, Electronic Structure, and Broad Luminescence

In this work, a new crystalline structure of two-dimensional (2D) Ruddlesden-Popper guanidinium lead iodide [C(NH2)3]2PbI4 with a particular organic cation orientation is proposed. Density functional theory calculations indicate that this structure of [C(NH2)3]2PbI4 is more energetically stable than the reported structure belonging to the Pmna space group. The crystalline and electronic structures of the new [C(NH2)3]2PbI4 are calculated by various functionals with and without spin-orbit coupling (SOC). Powder X-ray diffraction on [C(NH2)3]2PbI4 powder and thin film materials confirm the Pmna structure. A weak, but sharp, free excitonic peak combined with a strong broadened emission feature due to the corrugated 2D layers is observed by the absorption measurement of the thin film samples and by photoluminescence spectra. The present article shows that the complementarity between experiment and simulation improves the structural and optical understanding of this new 2D [C(NH2)3]2PbI4 material. Furthermore, this material is crucial to the study of both free excitonic effects and strong exciton-phonon coupling in a double-layer confinement. In addition, our results indicate that the relativistic effect of electrons with nonzero angular momentum via SOC in this compound plays a central role in its electronic properties.