Thermographic measurements on solar cells

The primary part of this work is the localisation of short circuits in solar cells with the help of an infrared camera. Short circuits in solar cells worse their efficiency so its detection maybe useful to improve cell concepts as well as processing parameters.Thermal resolutions of suitable infrared cameras are about 20 to 100 mK. For detection of weaker heat losses in the range of 10 to 20 µK the sensivity is improved by using the lock-in technique.The established lock-in thermography induces the current flow at the short circuits by applying an external current source via the existing electrical connectors of the solar cell. The metallization of the solar cells is one of the last steps in its fabrication. Therefore this measuring method is restricted to readily processed solar cells.In this work this method was improved by the new developed LimoLIT (Light modulated Lock-In Thermography). Here the p/n-junction of the semiconductor is used to seperate electron/hole-pairs generated by incident light. Metal connectors are no longer neccesary. This gives the option to do measurements in early processing stages cause the definition of the p/n-junction is one of the first steps in processing solar cells.Studies of both measurement techniques on selected solar cells are presented especially a process monitoring enabled by LimoLIT. Although both techniques are compared with each other