Evaluation of the Impact of the UV Excitation Intensity on the Ultraviolet Fluorescence Measurement System for Photovoltaics

Ultraviolet fluorescence (UVF) is an optical non-destructive inspection method that is used to evaluate Photovoltaics (PV) modules. By detecting the fluorescence intensity of UV fluorescence images, the degradation of PV module encapsulation can be characterized and visually assessed qualitatively. It would be beneficial to evaluate more quantitatively as there is further information on the state of the module in determining the magnitude and the spectrum of the fluorescence. Quantitative analysis requires an understanding of the correlation of the linearity of the detector, the response (=Fluorescence response) to the signal (=UV excitation), as well as the settings of the camera. Nowadays, the selection of the light intensity of the light source of the UVF measurement device is typically specified to be within a certain range, but the correlation to the fluorescence response as well as the camera settings is normally not given. The camera sensor might saturate to a level where there are pixels bleeding into each other, or it may be below sensitivity. Ideally, the signal (and thus excitation) should be in the linear range of the camera sensor. This paper gives a workflow to link the response of the DUT (device under test), camera sensor and excitation intensity and to arrive at higher quality measurements; the metrological framework will be evaluated in this paper, as well as the importance of sample temperature.