  Encapsulation of electronic devices based on organic materials that are prone
to degradation even under normal atmospheric conditions with hermetic barriers
is crucial for increasing their lifetime. A challenge is to develop
'ultrabarriers' that are impermeable, flexible, and preferably transparent.
Another important requirement is that they must be compatible with organic
electronics fabrication schemes (i.e. must be solution processable, deposited
at room temperature and be chemically inert). Here, we report lifetime increase
of 1,300 hours for poly(3-hexylthiophene) (P3HT) films encapsulated by uniform
and continuous thin (~10 nm) films of reduced graphene oxide (rGO). This level
of protection against oxygen and water vapor diffusion is substantially better
than conventional polymeric barriers such as CytopTM, which degrades after only
350 hours despite being 400 nm thick. Analysis using atomic force microscopy,
x-ray photoelectron spectroscopy and high resolution transmission electron
microscopy suggest that the superior oxygen gas/moisture barrier property of
rGO is due to the close interlayer distance packing and absence of pinholes
within the impermeable sheets. These material properties can be correlated to
the enhanced lag time of 500 hours. Our results provide new insight for the
design of high performance and solution processable transparent 'ultrabarriers'
for a wide range of encapsulation applications.
