  Organic-inorganic halide perovskites, especially methylammonium lead halide,
have recently led to a remarkable breakthrough in photovoltaic devices.
However, due to the environmental and stability concerns of the heavy metal,
lead, in these perovskite based solar cells, research in the non-lead
perovskite structures have been attracting increasing attention. In this study,
a layered perovskite-like architecture, (NH4)3Bi2I9, was prepared in solution
and the structure was solved by single crystal X-ray diffraction. The results
from DFT calculations showed the significant lone pair effect of the bismuth
ion and the band gap was measured as around 2.04 eV, which is lower than the
band gap of CH3NH3PbBr3. Conductivity measurement was also performed to examine
the potential in the applications as an alternative to the lead containing
perovskites.
