Terahertz short-range mobilities in neat and intermixed regions of polymer:fullerene blends with controlled phase morphology

Krauspe, Philipp Jonathan; Tsokkou, Demetra; Causa, Martina; Buchaca-Domingo, Ester; Fei, Zhuping; Heeney, Martin; Stingelin, Natalie; Banerji, Natalie (2018). Terahertz short-range mobilities in neat and intermixed regions of polymer:fullerene blends with controlled phase morphology. Journal of materials chemistry. A, 6(44), pp. 22301-22309. Royal Society of Chemistry 10.1039/C8TA08061E

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The molecular-level arrangement of the donor and acceptor (i.e. the local morphology) in organic solar cells governs charge separation and charge transport via its effect on the mobility of charges. However, the nanometre-scale mobility in such systems, which can be measured using terahertz (THz) spectroscopy, has been little investigated at relevant low excitation densities, due to extremely weak signals. Here, we study the mobility over short distances and at ultrashort times using time-resolved optical-pump-THz-probe (OPTP) spectroscopy on pBTTT:PCBM blends. This complements our previous results obtained with transient absorption (TA) and electro-modulated differential absorption (EDA) techniques. In the pBTTT:PCBM system, the co-existence of fullerene-/polymer-rich (‘neat’) and co-crystalline (‘intermixed’) regions can be controlled through choice of composition (weight ratio of the two components, use of processing additive). We demonstrate high short-range mobilities that help charges separate, and we show how this mobility of photogenerated charges develops in time, in particular as the charges move between different phase regions of the blend. By reducing the pump fluence below the threshold for nonlinear recombination mechanisms, we access these properties at solar cell operating conditions. Overall, we explain the necessity of different local phases through their influence on charge lifetime and mobility.

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Departement of Chemistry and Biochemistry

UniBE Contributor:

Krauspe, Philipp Jonathan; Causa, Martina and Banerji, Natalie

Subjects:

500 Science > 570 Life sciences; biology
500 Science > 540 Chemistry
500 Science > 530 Physics

ISSN:

2050-7488

Publisher:

Royal Society of Chemistry

Language:

English

Submitter:

Gareth John Moore

Date Deposited:

07 Dec 2018 12:42

Last Modified:

07 Dec 2018 12:42

Publisher DOI:

10.1039/C8TA08061E

BORIS DOI:

10.7892/boris.121522

URI:

https://boris.unibe.ch/id/eprint/121522

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