Kinetic Monte Carlo and Drift-Diffusion simulations to investigate the effects of interfaces in organic photovoltaic cells including a realistic blend morphology

Paolo Lugli^a, Tim Albes^a, Alessio Gagliardi^a

^aDept. Electrical and Computer Eng., Technische Universitaet Muenchen, Karlstrasse 45, Munich, 80333, Germany

International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics 2015 (HOPV15)

Roma, Italy, 2015 May 11th - 13th

Organizer: Filippo De Angelis

Poster, Alessio Gagliardi, 187
Publication date: 5th February 2015

Organic photovoltaic (OPV) cells are an interesting technology with a wide development potentiality thanks to the possibility of chemically tuning the materials with ease. Moreover, the fabrication is far simpler than the one for conventional inorganic semiconductor solar cells [1-2]. Despite that, the light-to-current conversion of the device is rather complex being the interplay among many different processes and it is dominated by interfaces. Indeed interfaces are ubiquitous inside an OPV cell, due to the need of efficiently splitting photogenerated excitons. Similarly important are the contact interfaces, fundamental for an efficient charge collection and in determining the open circuit voltage. Investigating such problems from a theoretical point of view is quite challenging. The standard simulation method is based on drift-diffusion within the so called "effective medium" approximation [3-4], where the complexity of the morphology is approximated by a single homogeneous material with mixed properties derived from the hole and electron transport material parameters. Recently a large effort has been devoted to overcome this limitation using kinetic monte carlo (kMC) methods which allows to include the effective morphology in the simulation [5-7]. The main limitation in kMC simulations is the computational cost that in many cases does not permit to simulate the entire system. We present a critical discussion comparing the effects of interfaces in drift-diffusion and kMC approaches within OPV, where the entire active layer is included in the simulation [8]. In particular we investigate the effect of different contact workfunctions for charge collection and the impact to the overall device performance.
Fig.1: (Left) different morphologies obtained using the Kawasaki spin-exchange algorithm. (Right) J-V characteristics for different morphologies calculated using kMC, the larger the number of Monte Carlo steps (MC number) the finer is the intermix in the blend.
[1] Søndergaard, R., et al., Materials Today, 2012. 15(1): p. 36-49. [2] Kang, J.-W., et al., Solar Energy Materials and Solar Cells, 2012. 103: p. 76-79. [3] Fallahpour, A.H., et al., J. Applied Physics, 116 184502 (2014). [4] Fallahpour, A.H. et al., Journal of Computational Electronics, 2014: p. 1-10. [5] P. Giazitzidis, et al., Org. Electron. 15, 1043–1049 (2014). [6] C. Groves, et al., Nano Lett.10, 1063–1069 (2010). [7] R. G. E. Kimber, et al., Phys. Rev. B 86, 235206 (2012). [8] T. Albes et al., 40th IEEE Photovoltaic Specialists Conference, conference proceeding (2014).

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