  Perovskite-based optoelectronic devices have shown great promise for solar
conversion and other optoelectronic applications, but their long-term
performance instability is regarded as a major obstacle to their widespread
deployment. Previous works have shown that the ultralow thermal conductivity
and inefficient heat spreading might put an intrinsic limit on the lifetime of
perovskite devices. Here, we report the observation of a remarkably efficient
thermal conductance, with conductivity of 11.2 +/- 0.8 W m^-1 K^-1 at room
temperature, in densely-packed perovskite CH3NH3PbI3 films, via noncontact
time-domain thermal reflectance measurements. The temperature-dependent
experiments suggest the important roles of organic cations and structural phase
transitions, which are further confirmed by temperature-dependent Raman
spectra. The thermal conductivity at room temperature observed here is over one
order of magnitude larger than that in the early report, suggesting that
perovskite device performance will not be limited by thermal stability.
