Recombination current measuring on solar cells by photoluminescence imaging

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Supervisor:
Dr. Mizsei János
Department of Electron Devices

This thesis provides an insight into the development of photoluminescence imaging equipments. The measurement methods were calibrated by QSS-μPCD technique of the PV-2000 equipment in the Semilab Zrt.

Firstly I present the current state of solar industry in general, including the issues of the passivation and one of the passivation parameter named the saturation current. I wrote about recombination mechanism and losses, more in the depths of the bulk and surface recombination processes. Secondly I panned out about the main recombination parameters: diffusion length, lifetime and emitter saturation current.

Two photoluminescence measurement structures are presented in the next topic, followed by a detailed description of the QSS-μPCD technique.

The first measurement structure is a stationary wafer configuration with whole wafer illumination and PL image acquisition with a 2D camera. The second measurement structure is a moving wafer configuration with a stripe like illumination and PL wafer image composed of line images consecutively captured with an infrared line camera.

The QSS-µPCD technique is used for recording an independent reference value for a direct J0 calibration. The linear correlation between the inverse of the emitted PL light intensity and J0 was observed experimentally. In the present work it is investigated theoretically in which range this linear relationship is valid. Our calculations led to the result that although in a large parameter range the linear relationship is proven as a good approximation, the correlation deviates from linearity if the neglecting of the bulk recombination process is not valid. We have introduced a mathematical model which makes the single PL image concept usable over an extended range of material parameters. The experimental results are in good agreement with predictions of the theoretical calculations.

Since both QSS-µPCD based J0 measurements and single PL image capturing can be completed at in-line production speed, this combination seems to be a promising approach for inline process control of surface passivation efficiency.

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