Dimensional Reduction of Cs 2 AgBiBr 6 Using Alkyl Ammonium Cations CH 3 (CH 2 ) n NH 3 + ( n = 1, 2, 3, and 6) of Varying Chain Lengths and Their Role in Structural and Optoelectronic Properties.

Tuning the dimensionality in halide perovskites provides an opportunity to obtain the properties desired for optoelectronic devices. In this work, we demonstrate the dimensional reduction of 3D halide double-perovskite Cs 2 AgBiBr 6 by systematically introducing alkylammonium organic spacer CH 3 (CH 2 ) n NH 3 + ( n = 1, 2, 3, and 6) of varying chain lengths. The single crystals of these materials were grown, and their structures were studied at 23 and -93 °C. The ethylammonium cation led to a formation of a 0D material, whereas all the other three higher alkyl ammonium spacers resulted in two-dimensional materials. The parent material possessed symmetric octahedra, whereas the modified samples led to both inter- and intra-octahedral distortion, thereby reducing the symmetry of constituent octahedra. The reduction in dimensionality led to a blue shift in the optical absorption spectrum. All these low-dimensional materials show excellent stability, and they are employed as absorbers for solar photovoltaics.