  This work is aimed to study mixed-cation (hybrid methyl ammonium plus
inorganic cations) halide perovskites using first principles Density Functional
Theory (DFT) formalism in order to find their potential applications in
perovskite based photovoltaics. This is an addition to the two previous studies
performed by the author on high-throughput screening of hybrid halide and
inorganic halide perovskites. This work involves mixing certain amounts of the
inorganic cation to the organic site (methyl ammonium) and study the electronic
structure of the resultant. 63 perovskites have been simulated in their
calculated stable phases and their band gaps have been predicted. Band gaps are
important parameters to predict as these indicate their potential to be used as
opto-electronic devices. From the calculated band gaps, 37 perovskites are
predicted to be suitable for single junction as well as multi junction solar
cell application, 7 are not suitable for either single or multi junction solar
cells, and the rest 21 are suitable for multi junction but not for single
junction solar cells. The study also shows interesting transition in the nature
of the band gaps from indirect to direct and vice-versa caused at about 50% of
inorganic cation mixing.
