4 research outputs found
Hetero Bis-Addition of Spiro-Acetalized or Cyclohexanone Ring to 58Ļ Fullerene Impacts Solubility and Mobility Balance in Polymer Solar Cells
Fullerene bis-adducts are increasingly
being studied to gain a high open circuit voltage (<i>V</i><sub>oc</sub>) in bulk heterojunction organic photovoltaics (OPVs).
We designed and synthesized homo and hetero bis-adduct [60]Āfullerenes
by combining fused cyclohexanone or a five-membered spiro-acetalized
unit (SAF<sub>5</sub>) with 1,2-dihydromethano (CH<sub>2</sub>), indene,
or [6,6]-phenyl-C<sub>61</sub>-butyric acid methyl ester (PCBM). These
new eight 56Ļ 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 <i>V</i><sub>oc</sub> of 0.80 V was obtained for polyĀ(3-hexylthiophene) (P3HT) blended
with SAF<sub>5</sub>/indene hetero bis-adduct, which is a marked advancement
in PCE compared to the 0.9% of SAF<sub>5</sub> 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
Facile and Exclusive Formation of Aziridinofullerenes by Acid-catalyzed Denitrogenation of Triazolinofullerenes
Variously substituted [6,6]closed aziridinofullerenes were exclusively obtained from acid-catalyzed denitrogenation of triazolinofullerenes without formation of relevant [5,6]open azafulleroids, which are the major products on noncatalyzed denitrogenation. The mechanistic consideration by DFT calculations suggested a reaction sequence involving initial pre-equilibrium protonation of the triazoline N<sub>1</sub> atom, generation of aminofullerenyl cation by nitrogen-extrusion, and final aziridination
Stereochemistry of Spiro-Acetalized [60]Fullerenes: How the <i>Exo</i> and <i>Endo</i> Stereoisomers Influence Organic Solar Cell Performance
Exploiting bis-addition products
of fullerenes is a rational way to improve the efficiency of bulk
heterojunction-type organic photovoltaic cells (OPV); however, this
design inherently produces regio- and stereoisomers that may impair
the ultimate performance and fabrication reproducibility. Here, we
report unprecedented <i>exo</i> and <i>endo</i> stereoisomers of the spiro-acetalized [60]Āfullerene monoadduct with
methyl- or phenyl-substituted 1,3-dioxane (<b>SAF</b><sub><b>6</b></sub>). Although there is no chiral carbon in either the
reagent or the fullerene, equatorial (<i>eq</i>) rather
than axial (<i>ax</i>) isomers are selectively produced
at an <i>exo-eq</i>:<i>endo</i>-<i>eq</i> ratio of approximately 1:1 and can be easily separated using silica
gel column chromatography. Nuclear Overhauser effect measurements
identified the conformations of the straight <i>exo</i> isomer
and bent <i>endo</i> isomer. We discuss the origin of stereoselectivity,
the anomeric effect, intermolecular ordering in the film state, and
the performance of polyĀ(3-hexylthiophene):substituted <b>SAF</b><sub><b>6</b></sub> OPV devices. Despite their identical optical
and electrochemical properties, their solubilities and space-charge
limited current mobilities are largely influenced by the stereoisomers,
which leads to variation in the OPV efficiency. This study emphasizes
the importance of fullerene stereochemistry for understanding the
relationship between stereochemical structures and device output
Highly Ordered <i>n</i>/<i>p</i>āCo-assembled Materials with Remarkable Charge Mobilities
Controlling
self-organization and morphology of chemical architectures
is an essential challenge in the search for higher energy-conversion
efficiencies in a variety of optoelectronic devices. Here, we report
a highly ordered donor/acceptor functional material, which has been
obtained using the principle of ionic self-assembly. Initially, an
electron donor Ļ-extended tetrathiafulvalene and an electron-acceptor
perylene-bisimide were self-organized separately obtaining <i>n</i>- and <i>p</i>-nanofibers at the same scale.
These complementary <i>n</i>- and <i>p</i>-nanofibers
are endowed with ionic groups with opposite charges on their surfaces.
The synergic interactions establish periodic alignments between both
nanofibers resulting in a material with alternately segregated donor/acceptor
nanodomains. Photoconductivity measurements show values for these <i>n</i>/<i>p</i>-co-assembled materials up to 0.8 cm<sup>2</sup> V<sup>ā1</sup> s<sup>ā1</sup>, confirming the
effectiveness in the design of these heterojunction structures. This
easy methodology offers great possibilities to achieve highly ordered <i>n</i>/<i>p</i>-materials for potential applications
in different areas such as optoelectonics and photovoltaics