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 C6H5CH2CH2NH3+ (PEA+) are designed and synthesized to investigate their effect on the layered RP type H-PEA2MA2Pb3I10 (MA = CH3NH3) 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-PEA2MA2Pb3I10 layer achieves a power conversion efficiency of 5.8%, which is better than that of the reference H-PEA2MA2Pb3I10.