Atomic-Scale Tailoring of Organic Cation of Layered Ruddlesden-Popper Perovskite Compounds.

Layered Ruddlesden-Popper (RP) phase perovskite compounds have emerged as promising photovoltaic materials for solar cell applications, but they suffer from poor absorption and strong exciton-binding energy. Herein, fluoro-, chloro-, and bromo-substitutions on the 4-position of the phenyl group in the component CHCHCHNH (PEA) are designed and synthesized to investigate their effect on the layered RP type H-PEAMAPbI (MA = CHNH) perovskite as an example. Single-crystal X-ray diffraction and temperature-dependent photoluminescence spectroscopy characterization reveal the electron-withdrawing halogen in organic cations decreases the distortion of inorganic sheets and significantly reduces the impact of two-dimensional quantum and dielectric confinement. This is further verified with an increased visible absorption and lower exciton-binding energy for these new layered RP-type perovskite compounds. A planar structured perovskite solar cell using an F-PEAMAPbI layer achieves a power conversion efficiency of 5.8%, which is better than that of the reference H-PEAMAPbI.