Abstract

Organic solar cells present a promising alternative for the generation of solar energy at lower material and production costs compared to widely used silicon-based solar cells. The major drawback of organic solar cells currently is a lower rate of energy conversion. Thus many research projects aim to improve the achievable efficiency. In this work a phase field model is used to mathematically describe the morphology evolution of the active layer composed of polymer as electron-donor and fullerene as electron-acceptor. The derivation of a chemical potential term and a surface energy term for the polymer-fullerene solution using the Flory-Huggins theory forms the basis to employ the Cahn-Hilliard equation. After including several specifics of the application in this non-linear partial differential equation of fourth order, an implementation of the model using the FEM solver software FEniCS provides some simulation results that qualitatively match results from the literature.

Highlights

  • Since the enactment of the German Renewable Energy Law (Erneuerbare-Energien-Gesetz) in the year 2000 solar energy successively increased its share of the German energy mix from initially 0 to currently approximately 7 % [5]

  • As it has already been possible to print the active layer of organic solar cells on flexible and semi-transparent support material, this class of solar cells could extend the area of application from currently mainly house roofs and flat areas to building fronts, car windows, backpacks, clothing, and many more

  • While research on organic solar cells started with approximately 2 % efficiency in the early 2000s, the efficiency record could be increased to approximately 10 % until 2012 and ranges at 16 % to date

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Summary

Introduction

Since the enactment of the German Renewable Energy Law (Erneuerbare-Energien-Gesetz) in the year 2000 solar energy successively increased its share of the German energy mix from initially 0 to currently approximately 7 % [5]. While research on organic solar cells started with approximately 2 % efficiency in the early 2000s, the efficiency record could be increased to approximately 10 % until 2012 and ranges at 16 % to date The Ginzburg-Landau energy functional forms the basis for the Cahn-Hilliard equation and is given by Figure 1: Schematic model of an organic solar cell [12, Fig. 1]. The class of organic solar cells considered in this work makes use of a polymer in the role of an electron-donor, a fullerene as an electron-acceptor and a solvent to initially form a homogeneous solution.

Flory-Huggins energy model
Entropy
Enthalpy
Interpretation
Surface energy
The Cahn-Hilliard equation
Numerical implementation
Results
Conclusion
Full Text
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