Full 3D simulation of phase separation in solution-processed organic solar cells

Vikas Negi^a, Olga Wodo^b, Jacobus Franeker^a^,^c, Rene Janssen^a^,^c, Peter Bobbert^a^,^d

^aMolecular Materials and Nanosystems, Eindhoven University of Technology, Netherlands, Netherlands

^bDepartment of Materials Design and Innovation and Department of Mechanical and Aerospace Engineering, University at Buffalo, Buffalo, NY

^cInstitute for Complex Molecular Systems, Eindhoven University of Technology, NL, Den Dolech 2, 5600 MB, Eindhoven, NL, Netherlands

^dEindhoven University of Technology, Department of Applied Physics, 5600MB, Eindhoven, Netherlands

International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV18)

Benidorm, Spain, 2018 May 28th - 31st

Organizers: Emilio Palomares and Rene Janssen

Oral, Vikas Negi, presentation 130
DOI: https://doi.org/10.29363/nanoge.hopv.2018.130
Publication date: 21st February 2018

Computer simulations provide unique insight into the role of processing conditions in determining the photoactive layer morphology and ultimately the device performance of organic solar cells. They further enable us to visualize the full 3D morphology evolution, which is currently beyond the resolution of standard optical experimental techniques. We present 3D phase field simulation results of phase separation during spin-coating in solution-processed organic solar cells using high performance computing facilities. We are able to access the length and time scales associated with evaporation-induced phase separation in a ternary blend consisting of PDPP5T (diketopyrrolopyrrole-quinquethiophene) and PC₇₁BM ([6,6]-Phenyl-C71 butyric acid methyl ester) dissolved in chloroform. A finite-element based approach is used to solve the governing Cahn-Hilliard-Cook equations in a 3D domain.¹ The kinetic and thermodynamic model parameters are obtained from experiments.^2,3

Our model successfully captures the liquid-liquid phase separation in this system and the subsequent domain coarsening, leading to formation of PC₇₁BM-rich droplets suspended in a polymer matrix.⁴ The simulated morphologies agree quite well with experiments, reproducing the intriguing scaling law found between the dominant length scale and the normalized evaporation rate.^3,4 We find that thermal fluctuations play a crucial role in determining the early-stage length scales of phase separation.⁴

References

[1] O. Wodo, B. Ganapathysubramanian; Comput. Mater. Sci. 2012, 55, 113-126.

[2] S. Kouijzer, J. J Michels, M. van den Berg, V. S. Gevaerts, M. Turbiez, M. M. Wienk, R.A. J. Janssen; J. Am. Chem. Soc. 2013, 135, 12057–12067.

[3] J.J. Van Franeker, D. Westoff, M. Turbiez, M. M. Wienk, V. Schmidt, R. A. J. Janssen; Adv. Func. Mater. 2015, 25, 855-863.

[4] V. Negi, O. Wodo, J.J. Van Franeker, R.A. J. Janssen, P.A. Bobbert; ACS Appl. Energy Mater. 2018, manuscript accepted.

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