In this study we investigate how exposure to ambient air and light during
device processing affects the opto-electronic properties of
poly-3-hexylthiophene (P3HT) :
[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) bulk
heterojunction solar cells (BHJ). The properties of pure P3HT layers
prepared in an inert atmosphere, under ambient conditions, and additionally
degraded under light in ambient conditions were investigated using
photoluminescence (PL) and photoinduced absorption (PIA). It was observed
that exposure to air during processing leads to oxygen doping of the
polymer. Exposure to air combined with light was found to significantly
decrease the PL and PIA signals. The current-voltage (I-V) and external
quantum efficiency (EQE) characteristics of solar cells fabricated in an
inert atmosphere were compared to solar cells processed under ambient
conditions. It was observed that processing in air leads to a reduction in
the photocurrent in the devices which is attributed to electron trapping by
oxygen in the active layer.