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Download fileHetero Bis-Addition of Spiro-Acetalized or Cyclohexanone Ring to 58π Fullerene Impacts Solubility and Mobility Balance in Polymer Solar Cells
journal contribution
posted on 2015-06-17, 00:00 authored by Tsubasa Mikie, Akinori Saeki, Naohiko Ikuma, Ken Kokubo, Shu SekiFullerene bis-adducts are increasingly
being studied to gain a high open circuit voltage (Voc) in bulk heterojunction organic photovoltaics (OPVs).
We designed and synthesized homo and hetero bis-adduct [60]fullerenes
by combining fused cyclohexanone or a five-membered spiro-acetalized
unit (SAF5) with 1,2-dihydromethano (CH2), indene,
or [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). These
new eight 56π fullerenes showed a rational rise of the lowest
unoccupied molecular orbital (LUMO). We perform a systematic study
on the electrochemical property, solubility, morphology, and space-charge-limited
current (SCLC) mobility. The best power conversion efficiency (PCE)
of 4.43% (average, 4.36%) with the Voc of 0.80 V was obtained for poly(3-hexylthiophene) (P3HT) blended
with SAF5/indene hetero bis-adduct, which is a marked advancement
in PCE compared to the 0.9% of SAF5 monoadduct. More importantly,
we elucidate an important role of mobility balance between hole and
electron that correlates with the device PCEs. Besides, an empirical
equation to extrapolate the solubilities of hetero bis-adducts is
proposed on the basis of those of counter monoadducts. Our work offers
a guide to mitigate barriers for exploring a large number of hetero
bis-adduct fullerenes for efficient OPVs.