Friedrich-Alexander-Universität Erlangen-Nürnberg

Simulation of Optical Waves in Thin-Film Solar Cells

Simulation of Optical Waves in Thin-Film Solar Cells

A sophisticated light management significantly contributes to the overall performance of thin-film solar cells based on amorphous (a-Si:H) and microcrystalline silicon (ìc-Si:H). Thus, an important issue in designing highly efficient solar cells is to optimize both light in-coupling and light trapping by considering several factors. These include the size and composition of the layers, the material data, the topology of the nano-textured interfaces, and the incident angle of light. Simulations are a suitable tool to analyze all optical effects like interferences, near-field properties, and plasmonic effects. Therefore, an accurate discretization of the computational domain is needed which leads to a huge number of grid points. To meet the large computational requirements parallel calculations on high performance computers (HPC) are needed.

Solar Cell Model

The simulations are helpful in enhancing the light trapping in silicon thin-film solar cells. An example of a modeled μc-Si:H solar cell is shown in Fig. 1. Rough interfaces between the layers lead to a reduction of the reflexion losses at the glass/ TCO layer and extend the path of the light in the solar cell by inner reflexion. Structures of various glass/TCO coatings, which are developed in the laboratory, can be integrated in the solar cell model. This enables us to compare the efficiency of solar cells consisting of different sets of interfaces without manufacturing a whole solar cell, and allows us to analyze the reflexion and light scattering behavior. Fig. 2 shows the quantum efficiency under different incident angles for a circularly polarized wave. The results are based on an implemented iterative solver which solves Maxwell's equations with the finite integration technique (FIT).

Figure 1: 3-dimensional structure of a μc-Si:H solar cell with rough interfaces described by atomic force microscope (AFM) scan data. The dimensions of the x-y plane are 3.5 μm by 3.5 μm. The modeled height is 2.4 μm.
Figure 2: Quantum efficiency of a simulated ìc-Si:H under perpendicular and oblique circularly polarized light. JSC = 18.44 mA/cm² (0°), JSC = 16.48 mA/cm² (30°), and JSC = 9.26 mA/cm² (60°).
Figure 3: Electrical field distribution |E|² for λ = 500 nm (left) and λ = 800 nm (right) at α = 30° for circularly polarized light.


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