  Excellent conversion efficiencies of over 20 % and facile cell production
have placed hybrid perovskites at the forefront of novel solar cell materials
with CH3NH3PbI3 being its archetypal compound. The question why CH3NH3PbI3 has
such extraordinary characteristics, particularly a hugely efficient light
absorption, is hotly debated with ferroelectricity being a promising candidate.
This does, however, afford the crystal structure to be non-centrosymmetric and
we herein present crystallographic evidence as to how the symmetry breaking
occurs on a crystallographic, and therefore long-scale, level. While the
molecular cation CH3NH3+ is intrinsically polar, it is heavily disordered and
cannot be the sole reason for ferroelectricity. We show that it, nonetheless,
plays an important role as it distorts the neighboring iodide positions from
their centrosymmetric positions.
