Intrinsic Properties of Two Benzodithiophene-Based Donor-Acceptor Copolymers Used in Organic Solar Cells: A Quantum-Chemical Approach

Tuuva Kastinen, Mika Niskanen, Chad Risko, Oana Cramariuc, Terttu I. Hukka

Research output: Contribution to journalArticlepeer-review

12 Scopus citations

Abstract

Conjugated donor-acceptor (D-A) copolymers show tremendous promise as active components in thin-film organic bulk heterojunction solar cells and transistors, as appropriate combinations of D-A units enable regulation of the intrinsic electronic and optical properties of the polymer. Here, the structural, electronic, and optical properties of two D-A copolymers that make use of thieno[3,4-c]pyrrole-4,6-dione as the acceptor and differ by their donor unit - benzo[1,2-b:4,5-b′]dithiophene (BDT) vs the ladder-type heptacyclic benzodi(cyclopentadithiophene) - are compared using density functional theory methods. Our calculations predict some general similarities, although the differences in the donor structures lead also to clear differences. The extended conjugation of the stiff ladder-type donor destabilizes both the highest occupied and lowest unoccupied molecular orbital energies of the ladder copolymer and results in smaller gap energies compared to its smaller counterpart. However, more significant charge transfer nature is predicted for the smaller BDT-based copolymer by natural transition orbitals than for the ladder copolymer. That is, the influence of the acceptor on the copolymer properties is "diluted" to some extent by the already extended conjugation of the ladder-type donor. Thus, the use of stronger acceptor units with the ladder-type donors would benefit the future design of new D-A copolymers. (Chemical Equation Presented).

Original languageEnglish
Pages (from-to)1051-1064
Number of pages14
JournalJournal of Physical Chemistry A
Volume120
Issue number7
DOIs
StatePublished - Feb 25 2016

Bibliographical note

Publisher Copyright:
© 2016 American Chemical Society.

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

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