Additive-Morphology Interplay and Loss Channels in “All-Small-Molecule” Bulk-heterojunction (BHJ) Solar Cells with the Nonfullerene Acceptor IDTTBM

Abstract
Achieving efficient bulk-heterojunction (BHJ) solar cells from blends of solution-processable small-molecule (SM) donors and acceptors is proved particularly challenging due to the complexity in obtaining a favorable donor–acceptor morphology. In this report, the BHJ device performance pattern of a set of analogous, well-defined SM donors—DR3TBDTT (DR3), SMPV1, and BTR—used in conjunction with the SM acceptor IDTTBM is examined. Examinations show that the nonfullerene “All-SM” BHJ solar cells made with DR3 and IDTTBM can achieve power conversion efficiencies (PCEs) of up to ≈4.5% (avg. 4.0%) when the solution-processing additive 1,8-diiodooctane (DIO, 0.8% v/v) is used in the blend solutions. The figures of merit of optimized DR3:IDTTBM solar cells contrast with those of “as-cast” BHJ devices from which only modest PCEs <1% can be achieved. Combining electron energy loss spectrum analyses in scanning transmission electron microscopy mode, carrier transport measurements via “metal-insulator-semiconductor carrier extraction” methods, and systematic recombination examinations by light-dependence and transient photocurrent analyses, it is shown that DIO plays a determining role—establishing a favorable lengthscale for the phase-separated SM donor–acceptor network and, in turn, improving the balance in hole/electron mobilities and the carrier collection efficiencies overall.

Citation
Liang R-Z, Babics M, Seitkhan A, Wang K, Geraghty PB, et al. (2017) Additive-Morphology Interplay and Loss Channels in “All-Small-Molecule” Bulk-heterojunction (BHJ) Solar Cells with the Nonfullerene Acceptor IDTTBM. Advanced Functional Materials: 1705464. Available: http://dx.doi.org/10.1002/adfm.201705464.

Acknowledgements
R.-Z.L. and M.B. contributed equally to this work. This publication is based upon work supported by the King Abdullah University of Science and Technology (KAUST) Office of Sponsored Research (OSR) under Award No. CRG_R2_13_BEAU_KAUST_1 and under the KAUST Solar Center programs. The authors also acknowledge concurrent support under Baseline Research Funding from KAUST. The authors thank KAUST ACL for technical support in the mass spectrometry analyses. Dr. D. J. Jones acknowledges the Australian Renewable Energy Agency, which funds the project grants within the Australian Centre for Advanced Photovoltaics. Responsibility for the views, information or advice expressed herein is not accepted by the Australian Government.

Publisher
Wiley

Journal
Advanced Functional Materials

DOI
10.1002/adfm.201705464

Additional Links
http://onlinelibrary.wiley.com/doi/10.1002/adfm.201705464/fullhttp://minerva-access.unimelb.edu.au/bitstreams/f66ccfc6-eb5c-5a01-93b3-e25fdac0c82e/download

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