  We have demonstrated OPV accelerated degradation studies using concentrated
sunlight, where the atmosphere, temperature and illumination intensity were
independently controlled. Testing various schemes for controlling the sample
temperature under concentrated sunlight showed that heating of P3HT:PCBM was
caused by photons at the absorbed wavelength range and dissipation of excess
photon energy, and not necessarily by IR photon absorption. Sunlight chopping
was found to be an effective method for independent temperature control under
illumination by concentrated sunlight. The first accelerated degradation tests
using sunlight concentration applied to P3HT:PCBM blends were reported.
P3HT:PCBM blends exposed to concentrated sunlight in the presence of traces of
oxygen/ humidity showed degradation induced by photo-oxidation of the P3HT
backbone within the P3HT:PCBM blend, which is significantly thermally
accelerated, in agreement with previous observations. However, this could be
demonstrated in a time scale of minutes and hours, i.e., significantly
accelerated. Exposure of well encapsulated P3HT:PCBM films to concentrated
sunlight demonstrated stability up to 3,600 sun*hours, corresponding to about
1.6 years of operating time. This result was obtained at 300 suns exposure
after merely 12 hours, demonstrating the advantage of using concentrated
sunlight for accelerated stability tests. These tests can therefore combine
extremely high acceleration factors with profound understanding of the effect
of various, independently controlled factors on the degradation mechanisms.
