Organic–inorganic
hybrid perovskites have shown tremendous
potential for optoelectronic applications. Ion migration within the
crystal and across heterointerfaces, however, imposed severe problems
with material degradation and performance loss in devices. Encapsulating
hybrid perovskite with a thin physical barrier can be essential for
suppressing the undesirable interfacial reactions without inhibiting
the desirable transport of charge carriers. Here, we demonstrated
that nanoscale, pinhole-free Al2O3 layer can
be coated directly on the perovskite CH3NH3PbI3 using atomic layer deposition (ALD). The success can be attributed
to a multitude of strategies including surface molecular modification
and hybrid ALD processing combining the thermal and plasma-enhanced
modes. The Al2O3 films provided remarkable protection
to the underlying perovskite films, surviving by hours in solvents
without noticeable decays in either structural or optical properties.
The results advanced the understanding of applying ALD directly on
hybrid perovskite and provided new opportunities to implement stable
and high-performance devices based on the perovskites.