Long-Term
Stabilization of Organic Solar Cells Using Hindered Phenols as Additives
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Abstract
We
report on the improvement of long-term stability of organic solar
cells (OPV) using hindered phenol based antioxidants as stabilizing
additives. A set of seven commercially available hindered phenols
are investigated for use in bulk-heterojunction OPV. Polymer:fullerene
films based on poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric
acid methyl ester (PCBM) are characterized with respect to the initial
power conversion efficiency and the long-term stability improvement
under illumination in ambient conditions. FTIR spectroscopy is used
to trace chemical degradation over time. OPV performance is recorded
under ISOS-3 conditions, and an improved long-term performance of
OPV devices, manifested in increased accumulated power generation
(APG), is found for octadecyl 3-(3,5-di-<i>tert</i>-butyl-4-hydroxyphenyl)propionate.
Using this additive, APG is increased by a factor of 3 compared to
the reference. Observed differences in the stabilization of tested
additives are discussed in terms of energetic trap states formation
within the HOMO/LUMO gap of the photoactive material, morphological
changes, and chemical structure