Analysis of the optical properties of texturing patterns for design of Si solar cells

Abstract

The pronounced development in the field of solar cells has been driven by the increasing interest in “green” energy generation in recent decades. Nevertheless, to increase the deployment of solar cells the energy conversion efficiency has to be improved further. The highest energy conversion efficiency has been recorded using a Silicon solar cell. However, there are limitations such as the high reflection from the solar cell surface that limits further improvement of the energy conversion efficiency. The large refractive index contrast between air and the material of the solar cell leads to high reflection. As a consequence, reducing the reflection from the solar cell surface is a priority. This research aims at reducing reflection from the solar cell surface. To achieve this goal, modeling based analysis of a micro pillar array texturing pattern and a new and exciting texturing pattern (the hut-like pattern) are presented. The simulation method used for this study is the Finite Difference Time Domain (FDTD) method. In the discussion, the effect of key structural parameters on the reflection is analyzed to obtain an in-depth understanding of the patterns. Additionally, the inter-dependence between the different structural parameters under study is considered during the discussion. The analysis shows that the reflection from a micro pillar array solar cell decreases as the Height (H) increases. The H by Diameter (H/D) ratio analysis presented in this work determines that there is a convergence in the reflection when the H/D ratio is high. This can be useful especially for designers with low precision fabrication equipment who can target higher H/D ratio to ensure a low reflection. The high surface-to-volume ratio when the H/D ratio is high can lead to high surface recombination. High surface recombination is a major problem in textured solar cell since it diminishes the electrical performance. An alternative is to use the hut-like pattern that combines the benefits of lowering the reflection with a low surface-to-volume ratio. The low surface-tovolume ratio is expected to have a positive effect on the surface recombination (i.e. lower surface recombination). The results show excellent optical performance of the pattern. Additionally, the hut-like pattern provides a reflection lower than other texturing patterns such as pyramid, nanowires and micro pillars. Furthermore, the results of a fabricated proof of concept hut-like sample are presented which highlights the excellent optical performance of the pattern