Here, we demonstrate that light and oxygen-induced degradation is the main reason for
the low operational stability of methylammonium lead triiodide (MeNH3PbI3) perovskite
solar cells exposed to ambient conditions. When exposed to both light and dry air,
unencapsulated MeNH3PbI3 solar cells rapidly degrade on timescales of minutes to a few
hours. This rapid degradation is also observed under electrically bias driven current flow in
the dark in the presence of O2. In contrast, significantly slower degradation is observed
when the MeNH3PbI3 devices are exposed to moisture alone (e.g. 85% relative humidity in
N2). We show that this light and oxygen induced degradation can be slowed down by the
use of interlayers that are able to remove electrons from the perovskite film before they
can react with oxygen to form O2
-
. These observations demonstrate that the operational
stability of electronic and optoelectronic devices that exploit the electron transporting
properties of MeNH3PbI3 will be critically dependent upon the use of suitable barrier
layers and device configurations to mitigate the oxygen sensitivity of this remarkable
material.