Photophysical Study of DPPTT-T/PC₇₀BM Blends and Solar Devices as a Function of Fullerene Loading: An Insight into EQE Limitations of DPP-Based Polymers

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• 作者：Elisa Collado-Fregoso ; Florent Deledalle ; Hendrik Utzat ; Pabitra S. Tuladhar ; Stoichko D. Dimitrov ; Alexander Gillett ; Ching-Hong Tan ; Weimin Zhang ; Iain McCulloch and James R. Durrant
• 刊名：Advanced Functional Materials
• 出版年：2017
• 出版时间：February 10, 2017
• 年：2017
• 卷：27
• 期：6
• 全文大小：1153K
• ISSN：1616-3028

文摘

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 PC₇₀BM. 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/PC₇₀BM 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.