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
Tuladhar, Pabitra S.
Dimitrov, Stoichko D.
Tan, Ching Hong
Durrant, James R.
KAUST DepartmentPhysical Sciences and Engineering (PSE) Division
Chemical Science Program
KAUST Solar Center (KSC)
KSC; King Abdullah University of Science and Technology; Thuwal 23955-6900 Saudi Arabia
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AbstractDiketopyrrolopyrrole (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.
CitationCollado-Fregoso E, Deledalle F, Utzat H, Tuladhar PS, Dimitrov SD, et al. (2016) 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. Advanced Functional Materials: 1604426. Available: http://dx.doi.org/10.1002/adfm.201604426.
SponsorsThe authors gratefully acknowledge the Engineering and Physical Science Research Council, EPSRC (EP/IO1927B/1, EP/M023532/1, and EP/K011987/1) for funding. E.C.-F. also thanks CONACyT (scholarship 309929) and the Kernahan Fund from Imperial College London for funding. The authors are also grateful to Prof. Jenny Nelson, Prof. Sophia Hayes, and Michelle Vezie for fruitful discussions and Pabitra Shakya for device fabrication.
JournalAdvanced Functional Materials