Surprisingly High Conductivity and Efficient Exciton Blocking in Fullerene/Wide-Energy-Gap Small Molecule Mixtures.
We find that mixtures of C60 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/C60 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 C60 undergoes nanoscale (<10 nm domain size) phase segregation even at very high (>80%) BPhen fractions.
†Department of Physics, ‡Applied Physics Program, §Department of Electrical Engineering and Computer Science, and ⊥Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109, United States.
Kevin J
KJ
Bergemann
†Department of Physics, ‡Applied Physics Program, §Department of Electrical Engineering and Computer Science, and ⊥Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109, United States.
Jojo A
JA
Amonoo
†Department of Physics, ‡Applied Physics Program, §Department of Electrical Engineering and Computer Science, and ⊥Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109, United States.
Byeongseop
B
Song
†Department of Physics, ‡Applied Physics Program, §Department of Electrical Engineering and Computer Science, and ⊥Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109, United States.
Peter F
PF
Green
†Department of Physics, ‡Applied Physics Program, §Department of Electrical Engineering and Computer Science, and ⊥Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109, United States.
Stephen R
SR
Forrest
Organic photovoltaics; charge transfer; charge transport; diffusion; organic buffer layer; percolation