  We measure the surface of CH$_3$NH$_3$PbI$_3$ single crystals by making use
of two photon photoemission spectroscopy. Our method monitors the electronic
distribution of photoexcited electrons, explicitly discriminating the initial
thermalization from slower dynamical processes. The reported results disclose
the fast dissipation channels of hot carriers (0.25 ps), set a upper bound to
the surface induced recombination velocity ($<4000$ cm/s) and reveal the
dramatic effect of shallow traps on the electrons dynamics. The picosecond
localization of excited electrons in degraded CH$_3$NH$_3$PbI$_3$ samples is
consistent with the progressive reduction of photoconversion efficiency in
operating devices. Minimizing the density of shallow traps and solving the
aging problem may boost the macroscopic efficiency of solar cells to the
theoretical limit.
