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

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

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...

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Bibliographic Details
Published in:Advanced functional materials Vol. 28; no. 7
Main Authors: Liang, Ru‐Ze, Babics, Maxime, Seitkhan, Akmaral, Wang, Kai, Geraghty, Paul Bythell, Lopatin, Sergei, Cruciani, Federico, Firdaus, Yuliar, Caporuscio, Marco, Jones, David J., Beaujuge, Pierre M.
Format: Journal Article
Language:English
Published: Hoboken Wiley Subscription Services, Inc 14-02-2018
Subjects:
bulk heterojunctions
Carrier transport
Electron energy
Electrons
Energy conversion efficiency
Energy transmission
Heterojunctions
Insulators
Materials science
MIS (semiconductors)
Mixtures
Morphology
nonfullerenes
organic photovoltaics
Photoelectric effect
Photoelectric emission
Photovoltaic cells
Scanning transmission electron microscopy
small molecules
Solar cells
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Summary: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. A set of structurally analogous small‐molecule (SM) donors with distinct side‐chain manifolds shows significant differences in their performance patterns in bulk‐heterojunction (BHJ) devices with the nonfullerene SM acceptor IDTTBM. Reducing the lengthscale of the phase‐separated network between donor and acceptor effectively suppresses nongeminate recombination in the BHJ active layers and improves the carrier mobility balance.
ISSN:1616-301X
1616-3028
DOI:10.1002/adfm.201705464