Photophysical Study of DPPTT-T/PC70 BM Blends and Solar Devices as a Function of Fullerene Loading: An Insight into EQE Limitations of DPP-Based Polymers

Elisa Collado-Fregoso, Florent Deledalle, Hendrik Utzat, Pabitra S. Tuladhar, Stoichko D. Dimitrov, Alexander Gillett, Ching Hong Tan, Weimin Zhang, Iain McCulloch, James R. Durrant

Research output: Contribution to journalArticlepeer-review

11 Scopus citations

Abstract

Diketopyrrolopyrrole (DPP)-based polymers have been consistently used for the fabrication of solar cell devices and transistors due to the existence of intermolecular short contacts, resulting in high electron and hole mobilities. However, they also often show limited external quantum efficiencies (EQEs). In this contribution, the authors analyze the limitations on EQE by a combined study of exciton dissociation efficiency, charge separation, and recombination kinetics in thin films and solar devices of a DPP-based donor polymer, DPPTT-T (thieno[3,2-b]thiophene-diketopyrrolopyrrole copolymer) blended with varying weight fractions of the fullerene acceptor PCBM. From the correlations between photoluminescence quenching, transient absorption studies, and EQE measurements, it is concluded that the main limitation of photon-to-charge conversion in DPPTT-T/PCBM devices is poor exciton dissociation. This exciton quenching limit is related not only to the low affinity/miscibility of the materials, as confirmed by wide angle X-ray diffraction diffraction and transmission electron microscopy data, but also to the relatively short DPPTT-T singlet exciton lifetime, possibly associated with high nonradiative losses. A further strategy to improve EQE in this class of polymers without sacrificing the good extraction properties in optimized blends is therefore to limit those nonradiative decay processes.
Original languageEnglish (US)
Pages (from-to)1604426
JournalAdvanced Functional Materials
Volume27
Issue number6
DOIs
StatePublished - Dec 27 2016

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