Influence of Polymer Aggregation and Liquid Immiscibility on Morphology Tuning by Varying Composition in PffBT4T-2DT/Nonfullerene Organic Solar Cells

Zeinab Hamid, Andrew Wadsworth, Elham Rezasoltani, Sarah Holliday, Mohammed Azzouzi, Marios Neophytou, Anne A. Y. Guilbert, Yifan Dong, Mark S. Little, Subhrangsu Mukherjee, Andrew A. Herzing, Helen Bristow, R. Joseph Kline, Dean M. DeLongchamp, Artem A. Bakulin, James R. Durrant, Jenny Nelson, Iain McCulloch

Research output: Contribution to journalArticlepeer-review

22 Scopus citations

Abstract

The temperature-dependent aggregation behavior of PffBT4T polymers used in organic solar cells plays a critical role in the formation of a favorable morphology in fullerene-based devices. However, there is little investigation into the impact of donor/acceptor ratio on morphology tuning, especially for nonfullerene acceptors (NFAs). Herein, the influence of composition on morphology is reported for blends of PffBT4T-2DT with two NFAs, O-IDTBR and O-IDFBR. The monotectic phase behavior inferred from differential scanning calorimetry provides qualitative insight into the interplay between solid–liquid and liquid–liquid demixing. Transient absorption spectroscopy suggests that geminate recombination dominates charge decay and that the decay rate is insensitive to composition, corroborated by negligible changes in open-circuit voltage. Exciton lifetimes are also insensitive to composition, which is attributed to the signal being dominated by acceptor excitons which are formed and decay in domains of similar size and purity irrespective of composition. A hierarchical morphology is observed, where the composition dependence of size scales and scattering intensity from resonant soft X-ray scattering (R-SoXS) is dominated by variations in volume fractions of polymer/polymer-rich domains. Results suggest an optimal morphology where polymer crystallite size and connectivity are balanced, ensuring a high probability of hole extraction via such domains.
Original languageEnglish (US)
Pages (from-to)1903248
JournalAdvanced Energy Materials
DOIs
StatePublished - Jan 29 2020

Bibliographical note

KAUST Repository Item: Exported on 2020-10-01
Acknowledgements: Z.H. thanks the EPSRC for a doctoral studentship. The authors thank KAUST for financial support and acknowledge EPSRC Projects EP/G037515/1, EP/M005143/1, and EP/L016702/1, and EC FP7 Project SC2 (610115), ECH2020 (643791). J.N. acknowledges funding from the EPSRC (Grant No. EP/P005543/1) and the European Research Council (Project CAPaCITy, Grant Agreement No. 742708). A.A.B. is a Royal Society University Research Fellow. E.R. thanks the Fonds de Recherche du Quebec-Nature et technologies (FRQNT) for a postdoctoral fellowship. A.A.Y.G. thanks the EPSRC for award of a postdoctoral fellowship (Grant No. EP/P00928X/1). M.A. thanks the EPSRC for a doctoral studentship. Portions of this research were carried out at the 7-ID Spectroscopy Soft and Tender (SST-1), 11-BM Complex Materials Scattering (CMS) beamlines of the National Synchrotron Light Source II, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory under Contract No. DE-SC0012704, and at beamline 11.0.1.2 of the Advanced Light Source, which is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. D. Fischer, C. Jaye, E. Gann, R. Li (NSLS-II) and C. Wang (ALS) are acknowledged for assisting with the experiments.

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