1 research outputs found
Surprisingly High Conductivity and Efficient Exciton Blocking in Fullerene/Wide-Energy-Gap Small Molecule Mixtures
We
find that mixtures of C<sub>60</sub> with the wide energy gap, small
molecular weight semiconductor bathophenanthroline (BPhen) exhibit
a combination of surprisingly high electron conductivity and efficient
exciton blocking when employed as buffer layers in organic photovoltaic
cells. Photoluminescence quenching measurements show that a 1:1 BPhen/C<sub>60</sub> mixed layer has an exciton blocking efficiency of 84 ±
5% compared to that of 100% for a neat BPhen layer. This high blocking
efficiency is accompanied by a 100-fold increase in electron conductivity
compared with neat BPhen. Transient photocurrent measurements show
that charge transport through a neat BPhen buffer is dispersive, in
contrast to nondispersive transport in the compound buffer. Interestingly,
although the conductivity is high, there is no clearly defined insulating-to-conducting
phase transition with increased insulating BPhen fraction. Thus, we
infer that C<sub>60</sub> undergoes nanoscale (<10 nm domain size)
phase segregation even at very high (>80%) BPhen fractions