Fabrication of anti-reflection coating by electron-beam oblique-angle deposition
Date Issued
2009
Date
2009
Author(s)
Lin, Ching-Yao
Abstract
Anti-reflection (AR) coating on crystalline silicon solar cell can reduce the reflection of incident sun light and increase the efficiency of solar cell. However, a typical single layer AR on crystalline silicon solar cell coating has narrow low reflection band and sensitive to incident angle of light. A gradient-index AR coating is a modified AR coating with broad band low reflection and insensitive to incident angle of light. The refractive index of gradient-index AR coating is gradually varying as the thickness of coating. Hence, it is difficult to fabricate gradient-index AR coating. In this thesis, a fabrication technique called electron-beam (e-beam) oblique-angle deposition is used for fabricating gradient-index AR coating on silicon. E-beam oblique-angle deposition is used e-beam evaporation system only. And this technique can produce nanoporous thin film with a specific refractive index by varying the angle between incident vapor flux of e-beam system and normal of substrate or so called deposition angle.n our work, a specific holder is designed for oblique-angle deposition. It can produce nanoporous thin films with different deposition angle at the same time. Indium tin oxide (ITO) is chosen as deposition source for oblique-angle deposition for the transparency and conductivity. And different thermal annealing parameters are applied after oblique-angle deposition for increasing transparency of ITO thin film. Optical properties like transmittance and refractive index of nanoporous ITO thin films with different deposition angle and different thermal annealing parameters are measured and discussed. The sheet resistance of ITO nanoporous thin films with different deposition angle and thermal annealing parameters is also measured in this thesis. multi-layer gradient-index AR coating on silicon is designed. This AR coating has 3 layers of ITO nanoporous thin films by oblique-angle deposition and 1 layer of amorphous silicon. Reflection < 5% for our multi-layer gradient-index AR coating is from about 520 nm to 960 nm. The lowest reflection of our AR coating is at 800 nm and reflection reduces from 33% for bare silicon to 1.5%. For oblique incident light, the reflection is still smaller than 10% at 60o of oblique incident light. Degradation for oxidation in amorphous silicon layer in our AR coating is also discussed. Finally, different between morphology of single layer and multi-layer of nanoporous thin film by oblique-angle deposition is observed and discussed.
Subjects
oblique-angle deposition
Anti-Reflection (AR) coating
nanoporous thin film
oxidation
Type
thesis
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