Light‐ and elevated temperature‐induced degradation (LeTID) can have significant and long‐lasting effects on silicon photovoltaic modules. Its behaviour is complex, showing highly variable degradation under different conditions or due to minor changes in device fabrication. Here, we show the large difference in LeTID kinetics and extents in multi‐crystalline passivated emitter and rear cell (multi‐PERC) modules from four different manufacturers. Varied accelerated testing conditions are found to impact the maximum extent of degradation in different ways for different manufacturers complicating the ability to develop a universal predictive model for field degradation. Relative changes in the open‐circuit voltage (VOC) have previously been used to assess extents of LeTID; however, due to the greater impact of the defect at lower injection, the VOC is shown to degrade less than half as much as the voltage at maximum power point (VMPP). The MPP current (IMPP) and fill factor (FF) also degrade significantly, having an even larger overall impact on the power output. These observations imply that currently employed methodologies for testing LeTID are inadequate, which limits the reliability of future predictive models. In light of this, the field must develop a more holistic approach to analysing LeTID‐impacted modules, which incorporates information about changes under MPP conditions. This will allow for a much clearer understanding of LeTID in the field, which will assist the performance of future PV systems.

Performance monitoring of crystalline silicon solar cells often requires terminal voltage measurements, which are strongly influenced by the sample temperature via the large temperature dependence of the intrinsic carrier density. The impact of sample temperature variations can be corrected for by using the temperature coefficient of the terminal voltage, however this relies on having both accurate values for the temperature coefficient and accurate measurements of the sample temperature. This paper demonstrates that in situations where the sample temperature cannot be accurately measured, for example in some high volume production facilities or during module degradation experiments, implied voltages determined from either electroluminescence or photoluminescence provide a more accurate measure of sample performance than the terminal voltage. The results presented here show that implied voltages exhibit a temperature sensitivity that is one order of magnitude lower than that of the terminal voltage. This is largely due to the fact that luminescence intensity is not strongly temperature dependent around room temperature. This is confirmed by experimental temperature dependent measurements on four different crystalline silicon solar cell types. The benefit of using implied voltage measurements over temperature corrected terminal voltage measurements for the monitoring of light and elevated temperature induced degradation in silicon solar modules is demonstrated.

Luminescence inspection of modules is currently being adopted as a standard practice in the photovoltaic industry. This paper presents a comparison of electroluminescence and photoluminescence imaging on industrial crystalline silicon modules, employed with a line scan system. We find that specific defects appear differently in the two techniques due to the difference in excitation method. Line scan photoluminescence images enable differentiation of series resistance defects from recombination defects and can identify the presence of encapsulant discolouration. Line scan electroluminescence images allow defects that prevent majority carrier transport to be evaluated. The use of both techniques enables robust defect characterisation.

Cast-mono crystalline silicon wafers contain crystallographic defects, which can severely impact the electrical performance of solar cells. This paper demonstrates that applying hydrogenation processes at moderate temperatures to finished screen print cells can passivate dislocation clusters within the cast-mono crystalline silicon wafers far better than the hydrogenation received during standard commercial firing conditions. Efficiency enhancements of up to 2% absolute are demonstrated on wafers with high dislocation densities. The impact of illumination to manipulate the charge state of hydrogen during annealing is investigated and found to not be significant on the wafers used in this study. This finding is contrary to a previous study on similar wafers that concluded increased H− or H0 from laser illumination was responsible for the further passivation of positively charged dangling bonds within the dislocation clusters.

Finger interruptions or finger breaks are a common occurrence in screen printed solar cell manufacturing and may result in decreased performance due to an increase in effective series resistance. Identification of finger interruptions is typically accomplished using electroluminescence imaging. This paper demonstrates contactless detection of finger interruptions using line scan photoluminescence imaging. Modeling is used to highlight the difference between line scan photoluminescence images and conventional luminescence imaging methods. Significant benefits of using line scan photoluminescence imaging over electroluminescence imaging to identify finger interruptions are presented: in line scan photoluminescence images, finger interruptions cause an increase in luminescence intensity, while high recombination regions cause a decrease in intensity. This contrast inversion allows for a more unambiguous identification of defect types. Detailed modeling is performed to determine the impact of finger interruptions on line scan photoluminescence images, as a function of the location of the finger interruption and of illumination intensity. The increase in luminescence intensity from a finger interruption is found to correlate linearly with the corresponding power loss. Finally, experimental line scan photoluminescence images of industrial cells and full sized modules are presented and found to agree well with the modeling results.