  Here, we focus on induced degradation and spatial inhomogeneity of organic
photovoltaic devices under different environmental conditions, uncoupled from
the influence of a hole-transport (HT) layer. During testing of devices
comprising the standard photoactive layer of P3HT as donor, blended with PCBM
as acceptor, a comparison was made between the nonencapsulated devices upon
exposure to dry air, dry air with illumination and humid air. The impact on the
active layer's photophysics is discussed, along with the device physics in
terms of integral solar cell performance and spatially resolved photocurrent
distribution with point-to-point analysis of the diode characteristics to
determine the origin of the observed behavior. The results show that even
without the widely used hygroscopic HT layer, PEDOT:PSS, humidity is still a
major factor in the short-term environmental degradation of organic solar cells
with this architecture, and not only oxygen or light, as is often reported.
Different from previous reports where water-induced device degradation was
spatially homogeneous and formation of Al2O3 islands was only seen for oxygen
permeation through pinholes in aluminum, we observed insulating islands merely
after humidity exposure in the present study. Further, we demonstrated with
laser beam induced current mapping and point-to-point diode analysis that the
water-induced performance losses are a result of the exposed device area
comprising regions with entirely unaltered high output and intact diode
behavior and those with severe degradation showing detrimentally lowered output
and voltage-independent charge blocking, which is essentially insulating
behavior. It is suggested that this is caused by transport of water through
pinholes to the organic/metal interface, where they form insulating oxide or
hydroxide islands, while the organic active layer stays unharmed.
