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Reducing the efficiency–stability–cost gap of organic photovoltaics with highly efficient and stable small molecule acceptor ternary solar cells

Abstract

Technological deployment of organic photovoltaic modules requires improvements in device light-conversion efficiency and stability while keeping material costs low. Here we demonstrate highly efficient and stable solar cells using a ternary approach, wherein two non-fullerene acceptors are combined with both a scalable and affordable donor polymer, poly(3-hexylthiophene) (P3HT), and a high-efficiency, low-bandgap polymer in a single-layer bulk-heterojunction device. The addition of a strongly absorbing small molecule acceptor into a P3HT-based non-fullerene blend increases the device efficiency up to 7.7 ± 0.1% without any solvent additives. The improvement is assigned to changes in microstructure that reduce charge recombination and increase the photovoltage, and to improved light harvesting across the visible region. The stability of P3HT-based devices in ambient conditions is also significantly improved relative to polymer:fullerene devices. Combined with a low-bandgap donor polymer (PBDTTT-EFT, also known as PCE10), the two mixed acceptors also lead to solar cells with 11.0 ± 0.4% efficiency and a high open-circuit voltage of 1.03 ± 0.01 V.

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Figure 1: Chemical structures, energy levels and optical properties of materials used in this study.
Figure 2: Microstructural analysis of P3HT:IDTBR:IDFBR ternary blend.
Figure 3: Photovoltaic performances and EQE profiles of binary and ternary devices.
Figure 4: Charge carrier dynamics of inverted P3HT:IDTBR and P3HT:IDTBR:IDFBR devices.
Figure 5: Storage lifetime and photo-stability of P3HT:IDTBR:IDFBR and high-efficiency, low-bandgap polymer:fullerene devices.

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Acknowledgements

D.B. thanks Helmholtz Association for a Helmholtz Postdoc Fellowship. S.H. thanks BASF for financial support. The authors acknowledge EC FP7 Project SC2 (610115), EC FP7 Project ArtESun (604397), and EPSRC Project EP/G037515/1 and EP/K030671/1, EC FP7 Project POLYMED (612538) and Project Synthetic carbon allotropes project SFB 953.

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Contributions

D.B. and R.S.A. prepared the manuscript. S.H. and A.W. synthesized the non-fullerene acceptors. R.S.A. fabricated and characterized solar cell devices. D.B. and N.G. carried out CE and TPV measurements. M.A. performed the in situ GIWAXS and UV–Vis absorption measurements during spin coating. D.A.H. performed static GIWAXS measurements. J.A.R. did the SCLC measurements. S.L. performed the DSC measurements. R.S.A. and M.N. performed stability measurements. C.J.M.E. helped J.N. with EROI modelling. All authors discussed the results and commented on the manuscript. C.J.B. supervised charge extraction measurements. J.R.D. supervised TPV measurements, A.A. supervised in situ GIWAXS and UV–Vis measurements, A.S. supervised static GIWAXS measurements, T.K. and J.N. supervised SCLC, electroluminescence and EQE measurements. I.M. revised the manuscript and supervised and directed the project.

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Correspondence to Derya Baran, Raja Shahid Ashraf or Iain McCulloch.

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Baran, D., Ashraf, R., Hanifi, D. et al. Reducing the efficiency–stability–cost gap of organic photovoltaics with highly efficient and stable small molecule acceptor ternary solar cells. Nature Mater 16, 363–369 (2017). https://doi.org/10.1038/nmat4797

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