  The hybrid halide perovskite CH$_{3}$NH$_{3}$PbI$_{3}$ has enabled solar
cells to reach an efficiency of about 18\%, demonstrating a pace for
improvements with no precedents in the solar energy arena. Despite such
explosive progress, the microscopic origin behind the success of such material
is still debated, with the role played by the organic cations in the
light-harvesting process remaining unclear. Here van-der-Waals-corrected
density functional theory calculations reveal that the orientation of the
organic molecules plays a fundamental role in determining the material
electronic properties. For instance, if CH$_{3}$NH$_{3}$ orients along a
(011)-like direction, the PbI$_{6}$ octahedral cage will distort and the band
gap will become indirect. Our results suggest that molecular rotations, with
the consequent dynamical change of the band structure, might be at the origin
of the slow carrier recombination and the superior conversion efficiency of
CH$_{3}$NH$_{3}$PbI$_{3}$.
