Thin film solar cells based on amorphous silicon require efficient light trapping due to the reduced thickness of the cell. Antireflective coatings may reduce the reflectance, but microstructuring the surface has been shown to be more efficient for a broader wavelength range. In this project, structured PMMA substrates were prepared by a micro-imprinting process. Using PMMA in the solar cell design adds strength to a thin film solar cell and provides easy handling. The process presented here is deemed viable for larger scale production.

Five different masters were used for obtaining microstructured PMMA substrates. Four masters were synthesized by anodic anodization of aluminum and the fifth master was prepared by anisotropic etching in crystalline silicon. Indium tin oxide, amorphous silicon and aluminum layers were deposited on the imprinted surfaces in order to imitate a solar cell structure. Reflection and transmission measurements were conducted and the surfaces were examined by AFM and SEM in order to model the surfaces. The surface models were used for simulating the optical properties with Lumerical FDTD Solutions.

Based on the reflection measurements, it was shown that the reflection of the AM1.5 solar spectrum could be lowered to 13.1% for imprints with 300 nm a-Si and Al compared to a planar surface with similar layers that reflect 46.7% of the incident solar spectrum. The reflection could be lowered further to ~9% by adding an antireflective ITO layer.