We present a number of polyfluorene based conjugated polymers with crosslinkable acrylate and oxetane units. These
polymers can be crosslinked by free radical polymerization in the case of acrylates and by cationic ring opening
polymerization for oxetanes. Upon polymerization densely crosslinked networks are formed which are completely
insoluble. We show that the diffusion coefficient of C60 in polyfluorene is reduced by a factor of 1000 by crosslinking.
MIS-CELIV measurements are used to monitor changes in the charge carrier mobility upon crosslinking. It shows that
using appropriate conditions, e.g. low initiator concentrations or thermal crosslinking, the charge carrier mobility is not
reduced by crosslinking. Solution processed three layer organic solar cells were realized with a crosslinkable fluorene
based copolymer containing acrylate groups. The efficiency is increased from 1.4% for the reference to 1.8% in the three
layer cell with a crosslinked exciton blocking layer. A critical issue of BHJ cells is the instability of the morphology of
the polymer:fullerene blend over long operation times at elevated temperature. We present a crosslinkable derivative of
the low bandgap polymer PFDTBT which contains oxetane units. BHJ cells with the crosslinked PFDTBT derivative and
PCBM were tested in accelerated aging experiments at 100 °C for times up to 100 h. Stabilization was clearly observed
in crosslinked BHJ cells compared to the non-crosslinked reference. We show for the first time that oxetane containing
polymers can be thermally crosslinked without any added initiator. Initiator free crosslinking is particularly attractive as
it avoids the formation of decomposition products, and thus potential electron traps and quenching sites from the
initiator.