Synthetic strategies for modifying dielectric properties and the electron mobility of fullerene derivatives

Fatemeh Jahani Bahnamiri

Research output: ThesisThesis fully internal (DIV)

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The goal of this PhD research project was to develop fullerene derivatives with enhanced dielectric properties for photovoltaic applications. Organic solar cells suffer from relatively low power conversion efficiency mainly due to charge recombination, which stems from the low dielectric constant of these materials. Donor and acceptor combinations are necessary to avoid this, but that approach leads to other types of losses. Increasing the dielectric constant would be the fundamental way to cure the problem.

In this thesis the effects of several synthetic strategies on the dielectric constant of fullerene derivatives are described. These strategies includes installing strong permanent dipole groups, incorporating flexible ethyleneoxy-type side chains with small dipoles, installing side chains with highly polarizable heavy atoms such as bromine and iodine and, finally, installing side chains which inherently have a high dielectric constant, such as cyclic carbonates.

Theoretical calculations predicted enhanced charge separation upon replacing PCBM by fullerenes with side groups containing strong permanent dipoles, but interestingly their experimentally determined dielectric constant remained similar. Among the proposed strategies, installing ethyleneoxy-type side chains is shown to be a promising way to increase the dielectric constant by ~46 percent without devaluation of optical properties, electron mobility, and orbital energy levels of the compound. However, the length of these chains did not show a considerable effect on dielectric constant.
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • University of Groningen
  • Hummelen, Kees, Supervisor
  • Loi, Maria, Assessment committee
  • Minnaard, Adriaan, Assessment committee
  • Sijbesma, Rint P., Assessment committee, External person
Award date30-Jun-2016
Place of Publication[Groningen]
Print ISBNs978-90-367-8930-1
Electronic ISBNs978-90-367-8928-8
Publication statusPublished - 2016

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