Characterization and Solar Cell Processing

Silicon ribbons are grown directly out of the silicon melt in the required size and thickness. Therefore, they have the potential to significantly reduce the costs of a crystalline silicon solar cell module, as cost intensive wafering steps are completely avoidable. However, more crystal defects can be found in these materials than in conventionally cast silicon. Consequently, the solar cell process has to be adapted specifically to the needs of ribbon materials in order to reach high conversion efficiencies, so that the lower crystallisation costs can be turned into profit.For that reason, the material properties of vertically grown, multicrystalline Edge-defined Film-fed Growth (EFG) and String Ribbon silicon are investigated in this work with the help of Hall- and minority charge carrier lifetime measurements first. Afterwards lifetime enhancements that can be achieved by gettering or hydrogenation steps are discussed. Combinations of both types of processing steps are also investigated. With the help of the obtained results a solar cell process is developed which is well adapted to the needs of the mentioned ribbon materials, so that finally new record efficiencies of 16.7 for EFG and 17.7 for String Ribbon silicon have been reached