Spectroscopic ellipsometry characterization of thin film photovoltaic materials and devices

One of the biggest challenges in the photovoltaic industry is creating a high efficiency device with low manufacturing and material costs. This challenge can be overcome by accurately characterizing thin film materials and photovoltaic device structures to determine properties such as thickness, absorption coefficient, composition, crystallinity, blend morphology, and phase separation, all of which may be modified to result in a more efficient photovoltaic device. One way to characterize thin film materials and photovoltaic device structures is to use spectroscopic ellipsometry, a non-invasive, non-destructive, and non-contact optical technique which can provide all of the above thin film properties, as well as other information, such as optical properties and band gap values. Spectroscopic ellipsometry works on the basis that linearly polarized light, when reflected off of a sample, becomes elliptically polarized. The resultant elliptical polarization state can be modeled in order to provide information about the sample. Because of the information it can provide, spectroscopic ellipsometry is a very powerful technique for the study of thin film photovoltaic materials and devices. In particular, spectroscopic ellipsometry can be applied to anti-reflection coatings, TCO layers, amorphous and micro-crystalline silicon thin films, and organic solar cell devices, as will be demonstrated here.