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

Ru-Ze Liang, M. Babics, A. Seitkhan, K. Wang, P.B. Geraghtyl, S. Lopatin, F. Cruciani, Y. Firdaus, M. Caporuscio, D.J. Jones, P. Beaujuge
Advanced Functional Materials, 28, 1705464, (2018)

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

Keywords

small moleculaes, nonfullerene, solar cell, morphology

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 mobiliies and the carrier collection efficiencies overall.

Code

doi.org/10.1002/adfm.201705464

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