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A molecular interaction–diffusion framework for predicting organic solar cell stability


Rapid increase in the power conversion efficiency of organic solar cells (OSCs) has been achieved with the development of non-fullerene small-molecule acceptors (NF-SMAs). Although the morphological stability of these NF-SMA devices critically affects their intrinsic lifetime, their fundamental intermolecular interactions and how they govern property–function relations and morphological stability of OSCs remain elusive. Here, we discover that the diffusion of an NF-SMA into the donor polymer exhibits Arrhenius behaviour and that the activation energy Ea scales linearly with the enthalpic interaction parameters χH between the polymer and the NF-SMA. Consequently, the thermodynamically most unstable, hypo-miscible systems (high χ) are the most kinetically stabilized. We relate the differences in Ea to measured and selectively simulated molecular self-interaction properties of the constituent materials and develop quantitative property–function relations that link thermal and mechanical characteristics of the NF-SMA and polymer to predict relative diffusion properties and thus morphological stability.

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Fig. 1: Phase diagram, chemical structure, schematic of the device structure and degradation of polymer:NF-SMA devices.
Fig. 2: SIMS profiles, phase diagram, diffusion properties and activation energy of polymer:NF-SMA.
Fig. 3: Thermal and mechanical properties of neat polymers and neat NF-SMAs.
Fig. 4: Interrelations of parameters, with the χ and D dependence on Tg or Tc and EF.

Data availability

The data represented in Fig. 3a,b are provided with the paper as source data. Other datasets generated and/or analysed during the current study are available from the corresponding authors upon request.

Code availability

The code used for the simulation of the Flory–Huggins phase diagram is available from the corresponding author upon request.


  1. Zhang, G. et al. Nonfullerene acceptor molecules for bulk heterojunction organic solar cells. Chem. Rev. 118, 3447–3507 (2018).

    CAS  Google Scholar 

  2. Baran, D. et al. Reducing the efficiency–stability–cost gap of organic photovoltaics with highly efficient and stable small molecule acceptor ternary solar cells. Nat. Mater. 16, 363–369 (2016).

    Google Scholar 

  3. Du, X. et al. Efficient polymer solar cells based on non-fullerene acceptors with potential device lifetime approaching 10 years. Joule 3, 215–226 (2019).

    CAS  Google Scholar 

  4. Cha, H. et al. An efficient, ‘burn in’ free organic solar cell employing a nonfullerene electron acceptor. Adv. Mater. 29, 1701156 (2017).

    Google Scholar 

  5. Du, X. et al. Unraveling the microstructure-related device stability for polymer solar cells based on nonfullerene small–molecular acceptors. Adv. Mater. 32, 1908305 (2020).

    CAS  Google Scholar 

  6. Li, N. et al. Abnormal strong burn-in degradation of highly efficient polymer solar cells caused by spinodal donor–acceptor demixing. Nat. Commun. 8, 14541 (2017).

    CAS  Google Scholar 

  7. Ghasemi, M. et al. Delineation of thermodynamic and kinetic factors that control stability in non-fullerene organic solar cells. Joule 3, 1328–1348 (2019).

    CAS  Google Scholar 

  8. Wong, H. C. et al. Morphological stability and performance of polymer–fullerene solar cells under thermal stress: the impact of photoinduced PC60BM oligomerization. ACS Nano 8, 1297–1308 (2014).

    CAS  Google Scholar 

  9. Zhu, Y. et al. Rational strategy to stabilize an unstable high-efficiency binary nonfullerene organic solar cells with a third component. Adv. Energy Mater. 9, 1900376 (2019).

    Google Scholar 

  10. Ye, L. et al. Quantitative relations between interaction parameter, miscibility and function in organic solar cells. Nat. Mater. 17, 253–260 (2018).

    CAS  Google Scholar 

  11. Hu, H. et al. Effect of ring-fusion on miscibility and domain purity: key factors determining the performance of PDI-based nonfullerene organic solar cells. Adv. Energy Mater. 8, 1800234 (2018).

    Google Scholar 

  12. Ma, W. et al. Domain purity, miscibility, and molecular orientation at donor/acceptor interfaces in high performance organic solar cells: paths to further improvement. Adv. Energy Mater. 3, 864–872 (2013).

    CAS  Google Scholar 

  13. Treat, N. D. et al. Polymer–fullerene miscibility: a metric for screening new materials for high-performance organic solar cells. J. Am. Chem. Soc. 134, 15869–15879 (2012).

    CAS  Google Scholar 

  14. Zhang, C. et al. Understanding the correlation and balance between the miscibility and optoelectronic properties of polymer–fullerene solar cells. J. Mater. Chem. A 5, 17570–17579 (2017).

    CAS  Google Scholar 

  15. Ghasemi, M. et al. Panchromatic sequentially cast ternary polymer solar cells. Adv. Mater. 29, 1604603 (2017).

    Google Scholar 

  16. Li, S. et al. An unfused-core-based nonfullerene acceptor enables high-efficiency organic solar cells with excellent morphological stability at high temperatures. Adv. Mater. 30, 1705208 (2018).

    Google Scholar 

  17. Yuan, J. et al. Single-junction organic solar cell with over 15% efficiency using fused-ring acceptor with electron-deficient core. Joule 3, 1140–1151 (2019).

    CAS  Google Scholar 

  18. Yang, W. et al. Simultaneous enhanced efficiency and thermal stability in organic solar cells from a polymer acceptor additive. Nat. Commun. 11, 1218 (2020).

    CAS  Google Scholar 

  19. Ye, L. et al. Miscibility–function relations in organic solar cells: significance of optimal miscibility in relation to percolation. Adv. Energy Mater. 8, 1703058 (2018).

    Google Scholar 

  20. Treat, N. D., Mates, T. E., Hawker, C. J., Kramer, E. J. & Chabinyc, M. L. Temperature dependence of the diffusion coefficient of PCBM in poly(3-hexylthiophene). Macromolecules 46, 1002–1007 (2013).

    CAS  Google Scholar 

  21. Zhao, W. et al. Fullerene-free polymer solar cells with over 11% efficiency and excellent thermal stability. Adv. Mater. 28, 4734–4739 (2016).

    CAS  Google Scholar 

  22. Treat, N. D. et al. Interdiffusion of PCBM and P3HT reveals miscibility in a photovoltaically active blend. Adv. Energy Mater. 1, 82–89 (2011).

    CAS  Google Scholar 

  23. Ye, L. et al. Quenching to the percolation threshold in organic solar cells. Joule 3, 443–458 (2019).

    CAS  Google Scholar 

  24. Yazmaciyan, A. et al. Recombination losses above and below the transport percolation threshold in bulk heterojunction organic solar cells. Adv. Energy Mater. 8, 1703339 (2018).

    Google Scholar 

  25. Bartelt, J. A. et al. The importance of fullerene percolation in the mixed regions of polymer–fullerene bulk heterojunction solar cells. Adv. Energy Mater. 3, 364–374 (2013).

    CAS  Google Scholar 

  26. Li, S. et al. Energy-level modulation of small-molecule electron acceptors to achieve over 12% efficiency in polymer solar cells. Adv. Mater. 28, 9423–9429 (2016).

    CAS  Google Scholar 

  27. Flory, P. J. Principles of Polymer Chemistry (Cornell Univ. Press, 1953).

  28. Rubinstein, M. & Colby, R. H. Polymer Physics (Oxford Univ. Press, 2003).

  29. Batzer, H. & Kreibich, U. Connections between glass transition-temperature, thermodynamic and mechanic values for predicting material properties from the chemical-structure. Die Angew. Makromol. Chem. 105, 113–130 (1982).

    CAS  Google Scholar 

  30. Kreibich, U. & Batzer, H. Influence of the segment structure and crosslinking on the glass-transition Tg-possibilities of predicting Tg using the values of cohesive energy ecoh. Die Angew. Makromol. Chem. 83, 57–112 (1979).

    CAS  Google Scholar 

  31. Lee, C. J. Correlations of elastic modulus, cohesive energy density and heat capacity jump of glassy polymers. Polyrn. Eng. Sci. 27, 1015–1017 (1987).

    CAS  Google Scholar 

  32. Roberts, R. J., Rowe, R. C. & York, P. The relationship between Young’s modulus of elasticity of organic solids and their molecular structure. Powder Technol. 65, 139–146 (1991).

    CAS  Google Scholar 

  33. Root, S. E., Alkhadra, M. A., Rodriquez, D., Printz, A. D. & Lipomi, D. J. Measuring the glass transition temperature of conjugated polymer films with ultraviolet–visible spectroscopy. Chem. Mater. 29, 2646–2654 (2017).

    CAS  Google Scholar 

  34. Sharma, A., Pan, X., Campbell, J. A., Andersson, M. R. & Lewis, D. A. Unravelling the thermomechanical properties of bulk heterojunction blends in polymer solar cells. Macromolecules 50, 3347–3354 (2017).

    CAS  Google Scholar 

  35. Balar, N. et al. The importance of entanglements in optimizing the mechanical and electrical performance of all-polymer solar cells. Chem. Mater. 31, 5124–5132 (2019).

    CAS  Google Scholar 

  36. Sperling, L. H. Introduction to Physical Polymer Science (John Wiley & Sons, 2005).

  37. Lodge, T. P. Reconciliation of the molecular weight dependence of diffusion and viscosity in entangled polymers. Phys. Rev. Lett. 83, 3218–3221 (1999).

    CAS  Google Scholar 

  38. Thomas, N. L. & Windle, A. H. A theory of case II diffusion. Polymer 23, 529–542 (1982).

    CAS  Google Scholar 

  39. Matsuoka, S. (ed.) Relaxation Phenomena in Polymers (Hanser, 1992).

  40. Balar, N. & O’Connor, B. T. Correlating crack onset strain and cohesive fracture energy in polymer semiconductor films. Macromolecules 50, 8611–8618 (2017).

    CAS  Google Scholar 

  41. Stafford, C. M. et al. A buckling-based metrology for measuring the elastic moduli of polymeric thin films. Nat. Mater. 3, 545–550 (2004).

    CAS  Google Scholar 

  42. Virkar, A. A., Mannsfeld, S., Bao, Z. & Stingelin, N. Organic semiconductor growth and morphology considerations for organic thin-film transistors. Adv. Mater. 22, 3857–3875 (2010).

    CAS  Google Scholar 

  43. Kim, J.-S. et al. Tuning mechanical and optoelectrical properties of poly(3-hexylthiophene) through systematic regioregularity control. Macromolecules 48, 4339–4346 (2015).

    CAS  Google Scholar 

  44. Collins, B. A. et al. Molecular miscibility of polymer−fullerene blends. J. Phys. Chem. Lett. 1, 3160–3166 (2010).

    CAS  Google Scholar 

  45. Standard Test Methods for Photovoltaic Modules in Cyclic Temperature and Humidity Environments ASTM E1171-15 (ASTM International, 2015).

  46. White, J. R. On internal stress and activation volume in polymers. J. Mater. Sci. 16, 3249–3262 (1981).

    CAS  Google Scholar 

  47. Mehrer, H. Diffusion in Solids: Fundamentals, Methods, Materials, Diffusion-Controlled Processes (Springer Science & Business Media, 2007).

  48. Deppe, D. D., Miller, R. D. & Torkelson, J. M. Small molecule diffusion in a rubbery polymer near Tg: effects of probe size, shape, and flexibility. J. Polym. Sci., B: Polym. Phys. 34, 2987–2997 (1996).

    CAS  Google Scholar 

  49. Carpenter, J. H. et al. Competition between exceptionally long-range alkyl sidechain ordering and backbone ordering in semiconducting polymers and its impact on electronic and optoelectronic properties. Adv. Funct. Mater. 29, 1806977 (2019).

    Google Scholar 

  50. Alkhadra, M. A. et al. Quantifying the fracture behavior of brittle and ductile thin films of semiconducting polymers. Chem. Mater. 29, 10139–10149 (2017).

    CAS  Google Scholar 

  51. Kozub, D. R. et al. Polymer crystallization of partially miscible polythiophene/fullerene mixtures controls morphology. Macromolecules 44, 5722–5726 (2011).

    CAS  Google Scholar 

  52. Abraham, M. J. et al. GROMACS: high performance molecular simulations through multi-level parallelism from laptops to supercomputers. SoftwareX 1-2, 19–25 (2015).

    Google Scholar 

  53. Jorgensen, W. L., Maxwell, D. S. & Tirado-Rives, J. Development and testing of the OPLS all-atom force field on conformational energetics and properties of organic liquids. J. Am. Chem. Soc. 118, 11225–11236 (1996).

    CAS  Google Scholar 

  54. Frisch, M. J. et al. Gaussian 16 Rev. C.01 (Wallingford, 2016).

  55. Ryno, S. M. & Risko, C. Deconstructing the behavior of donor–acceptor copolymers in solution & the melt: the case of PTB7. Phys. Chem. Chem. Phys. 21, 7802–7813 (2019).

    CAS  Google Scholar 

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Y.Q., Z.P., H.H., H.A. and initial work by M.G. was supported by Office of Naval Research (ONR) grant no. N000141712204 and KAUST’s Center Partnership Fund (no. 3321). N.B. and B.T.O. acknowledge support by a National Science Foundation (NSF) grant (no. CMMI-1554322). T.K., A.A. and recent work by M.G. was supported by NCSU start-up funds to A.A., J.R. and W.Y. acknowledge support by an NSF grant (no. CBET-1639429). C.R. and W.M. acknowledge the support of the ONR (N00014-18-1-2448) and the NSF under Cooperative Agreement no. 1849213; supercomputing resources were provided by the Department of Defense (DoD) through the DoD High-Performance Computing Modernization Program (project no. ONRDC40433481) and by the University of Kentucky Information Technology Department and Center for Computational Sciences. SIMS measurements were performed at the Analytical Instrumentation Facility at NCSU, which is partially supported by the State of North Carolina and the National Science Foundation. C. Zhou is acknowledged for providing support for SIMS measurements. The DSC instrument was purchased with UNC-GA ROI funds. C. Zhu, A. Hexemer and C. Wang of the ALS provided instrument maintenance. E. Gomez and J. Litofsky are acknowledged for providing the initial Flory–Huggins program code. L. Ye and M. Balik (NCSU) are acknowledged for fruitful discussion and input. A. Dinku is acknowledged for maintaining shared ORaCEL facilities and sharing some PBDB-T2F:Y6 stability data for reference. F. He and T. Zhao are acknowledged for help with attaining molecular weight data via high temperature gel permeation chromatography. H. Yan is acknowledged for providing ITIC-4Cl NF-SMA. I. Angunawela is acknowledged for performing complementary shelflife measurements of P3HT:EH-IDTBR devices.

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Authors and Affiliations



H.A. and B.T.O. conceived the scientific framework with the help of M.G. M.G. designed experimental protocols, coordinated the experimental work, performed the SIMS, DSC measurements and analysed the SIMS and DSC data with the help of Z.P. Z.P. performed the complementary SIMS measurements of P3HT:NF-SMA. M.G. fabricated solar cell devices and performed subsequent stability tests with the help of H.H., T.K. and Y.Q., and with supervision by A.A. B.T.O. and N.B. designed the mechanical test experiments. N.B. prepared the films needed for mechanical test measurements and performed DMA and elastic modulus measurements. H.H. fabricated the complementary FTAZ:IT-M devices. J.J.R. synthesized the FTAZ polymers, supervised by W.Y. M.B. synthesized P3HT, supervised by I.M. W.M. performed molecular dynamics simulations, supervised by C.R. M.G., H.A. and B.T.O. drafted the paper. All authors contributed to the editing and interpretation.

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Correspondence to Brendan T. O’Connor or Harald Ade.

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The authors declare no competing interests.

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Peer review information Nature Materials thanks Mats Andersson, Andrew T. Kleinschmidt, Darren Lipomi and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–13, equations (1)–(15), Tables 1–9 and Discussion.

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Source data

Source Data Fig. 3

DSC thermograms of neat polymers and NF-SMAs and time-temperature superposition of neat polymers.

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Ghasemi, M., Balar, N., Peng, Z. et al. A molecular interaction–diffusion framework for predicting organic solar cell stability. Nat. Mater. 20, 525–532 (2021).

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