  Defect engineering is applied to hybrid (CH$_3$NH$_3$)PbI$_3$
organic-inorganic perovskites. These materials have become one of the most
promising low-cost alternatives to traditional semiconductors in the field of
photovoltaics and light emitting devices. We use here Helium ion irradiation at
low energy as a tool for the controlled introduction of point defects in both
single crystals and polycrystalline thin films. The irradiation defects modify
the opto-electronic properties as probed using photoluminescence spectroscopy
from 10K to room-temperature. 2 Contrary to usual semiconductors, we observe a
very good resilience of the PL properties with irradiation, even associated to
an enhancement of the optical emission at low temperature. We discuss these
results in relation with the tetragonal to orthorhombic low-temperature phase
transition below T=160 K. A comparison between spectra from single crystals and
polycrystalline films, both with and without irradiation defects, allow a
better understanding of the light emission mechanisms in both kinds of samples.
We thereby evidence radiation hardness of these materials and the specificity
of defects and their impact over light emission properties.
