Ultrafast terahertz photoconductivity of photovoltaic polymer-fullerene blends: A comparative study correlated with photovoltaic device performance

Zuanming Jin, Dominik Gehrig, Clare Dyer-Smith, Edwin J. Heilweil, Frederic Laquai, Mischa Bonn, Dmitry Turchinovich*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

38 Scopus citations

Abstract

Ultrafast photoinduced carrier dynamics in prototypical low band gap polymer:fullerene photovoltaic blend films PTB7:PC70BM and P3HT:PC70BM is investigated using ultrafast terahertz (THz) spectroscopy. The subpicosecond and few-picosecond decays of THz-probed photoconductivities for both compounds are observed, attributed to the rapid formation of polaron pairs by exciton-exciton annihilation and subsequent polaron pair annihilation, respectively. The transient THz photoconductivity spectra of PTB7:PC70BM are well described by the Drude-Smith (DS) model, directly yielding the important charge transport parameters such as charge carrier density, momentum scattering time, and effective localization. By comparison with P3HT:PC70BM, we find that in PTB7:PC70BM the mobile charge carrier photoconductivity is significantly enhanced by a factor of 1.8 and prevails for longer times after charge formation, due to both improved mobile charge carrier yield and lower charge localization. In PTB7:PC70BM, a strong dependency of electron momentum scattering time on electron density was found, well parametrized by the empirical Caughey-Thomas model. The difference in ultrafast photoconductivities of both P3HT:PC70BM and PTB7:PC70BM is found to correlate very well with the performance of photovoltaic devices based on those materials. (Chemical Equation Presented).

Original languageEnglish (US)
Pages (from-to)3662-3668
Number of pages7
JournalJournal of Physical Chemistry Letters
Volume5
Issue number21
DOIs
StatePublished - Nov 6 2014

ASJC Scopus subject areas

  • Materials Science(all)

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