  Organic or inorganic (A) metal (M) halide (X) perovskites (AMX3) are
semiconductor materials setting the basis for the development of highly
efficient, low-cost and multijunction solar energy conversion devices. The best
efficiencies nowadays are obtained with mixed compositions containing
methylammonium, formamidinium, Cs and Rb as well as iodine, bromine and
chlorine as anions. The understanding of fundamental properties such as crystal
structure and its effect on the band gap, as well as their phase stability is
essential. In this systematic study X-ray diffraction and photoluminescense
spectroscopy were applied to evaluate structural and optoelectronic properties
of hybrid perovskites with mixed compositions.
