High Members of the 2D Ruddlesden-Popper Halide Perovskites: Synthesis, Optical Properties, andSolar Cellsof ( CH3( CH2)3NH3)2( CH3NH3)4Pb5I16

Here, we present the fifth member (n = 5) of the Ruddlesden-Popper (CH3(CH2)(3)NH3)(2)( CH3NH3) n-1PbnI3n+ 1 family, which we successfully synthesized in high yield and purity. Phase purity could be clearly determined from its X-ray powder diffraction patterns, which feature the (0k0) Bragg reflections at low 20 angles. The obtained pure n = 5 compound was confirmed to be a direct band-gap semiconductor with E-g = 1.83 eV. The direct nature of the band gap is supported by density functional theory calculations. Intense photoluminescence was observed at room temperature at 678 nm arising from the band edge of the material. High-quality thin films can be prepared by the hot-casting method from solutions with a pure-phase compound as a precursor. The planar solar cells fabricated with n = 5 thin films demonstrate excellent power-conversion efficiency of 8.71% with an impressive open-circuit voltage of similar to 1 V. Our results point to the use of layered perovskites with higher n numbers and pure chemical composition.