Broadband Light Source Based Angular Resolved Measurement of Optical Properties of Materials and Solar Cells

Mekbib Wubishet Amdemeskel

Research output: Book/ReportPh.D. thesisResearch


High dimensional and accurate material characterization is becoming increasingly important in computer modelling and photo realistic rendering of scenes. This calls for measurements of angular and spectrally resolved light scattering properties. The same type of detailed characterization of solar cells and panels are important for simulation and optimization of the annual energy production of solar installations. This thesis deals with a measurement facility for the accurate measurement of the spectrally resolved bidirectional scattering distribution function (BSDF) which has been designed and installed. Using a high radiance broadband laser based white light source allows for a collimated white light illumination from UV over the visible to the NIR wavelength range and spectral reflection and/or transmission is measured using a broadband array spectrometer. The spectral power distribution of the light source is shown to be close to that of the standardized AM1.5 light used in solar characterization, and this makes the measurement facility very useful for laboratory investigation of solar cells and provides a new method for obtaining the angle of incidence characteristics. The developed facility has been used for measurements of spectrally resolved bidirectional reflection distribution function, BRDF, for a range of sample materials with different reflectance properties from diffusely scattering to specular. In order to be able to validate the results of physics based computer modelling and the applied BRDF data a comparison platform has been established. This platform builds a bridge between a physical mock-up of known and controllable properties and a 3D computer model of the same mock-up using physics based rendering engine. It is a demobox with spectrally controllable LED light in a chamber for illuminating materials/objects. Lambertian BRDF models have been used for the colour samples and have shown good agreement between calculations and measurements of photometric and colour differences parameters. The facility has been further developed for angle of incidence characterization of solar cells, and a number of different types of solar cells, with different surface structures, encapsulations and AR coatings, are characterised. There is a large interest from the solar cell research community and industry for this type of measurement, since it makes it possible to do controlled laboratory measurements. A round robin inter laboratory comparison has been designed and initiated involving eight European test laboratories, to determine the level of agreement in the measurement results including an uncertainty analysis. The sample cells have been selected and measurements been performed at DTU, and at PTB during an external research stay. Preliminary results are shown for these and a final publication is pending the completion of all the tests. This work will contribute to the validation of IEC-61853-2 standard and give better models of energy production of solar cells.
Original languageEnglish
PublisherTechnical University of Denmark
Number of pages109
Publication statusPublished - 2019


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