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37th European Photovoltaic Solar Energy Conference and Exhibition; 409-413, High-intensity illumination treatments are a versatile method to reduce the performance loss of solar cells due to LeTID since they can be applied at any point of time between cell fabrication and module assembly. We evaluate the potential of these treatments using a true inline treatment tool and commercially available PERC solar cells. To test the stability of cell performance after the treatments, the cells were exposed to 0.15 suns and 75 °C at open circuit. These conditions are close to a recent testing standard suggestion and allow estimating the cell stability over the typical operating lifetime of solar modules. The results show that there is a window of process parameters which improves the stability of solar cell efficiency without compromising the efficiency immediately after the treatment, i.e. before the stability test. The treatments result in an estimated gain of ~ 3 % in the amount of energy produced by the cells during the operating lifetime of a solar module, corresponding to a reduction of LeTID-related energy yield losses by up to ~ 50 %. Importantly, this gain is achievable with belt speeds compatible with high throughput inline processing.

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35th European Photovoltaic Solar Energy Conference and Exhibition; 254-261, High-efficiency solar cells have a high internal capacitance that tends to distort I-V measurements during short voltage sweep times compatible with flash testing. Recently, it was shown that this distortion can be corrected with a weighted average of the measured output currents, using time derivatives of junction voltage as weighting factors. Although this procedure theoretically reproduces the steady-state I-V curve, errors from different sources exist. For example, time derivatives of measurement data are potentially sensitive to even low levels of noise in the original signal. In addition, the correction requires prior determination of the series resistance, which can be susceptible to an error. In this contribution, we investigate errors associated with the capacitance correction. We estimate the magnitude of additional noise that derives from using time derivatives of measurement data as weighting factors, as well as the significance of an error in the series resistance. Further, we provide indications that the physical lower limit for the voltage sweep length is dictated by minority carrier diffusivity. Additionally, we show that the effective minority carrier lifetime of the solar cell can be estimated based on output currents and time derivatives of the junction voltage during forward and reverse sweeps.

Copper contamination causes minority carrier lifetime degradation in p-type silicon bulk under illumination, leading to considerable efficiency losses in affected solar cells. Although the existence of this phenomenon has been known for almost two decades, ambiguity prevails about the underlying defect mechanism. In Paper I of this two-part contribution, we propose the first comprehensive mathematical model for Cu-related light-induced degradation in p-type silicon (Cu-LID). The model is based on the precipitation of interstitial Cu ions, which is assumed to be kinetically limited by electrostatic repulsion from the growing Cu precipitates. Hence, growth and dissolution rates of individual Cu precipitates are derived from the drift-diffusion equation of interstitial Cu and used in a kinetic precipitation model that is based on chemical rate equations. The kinetic model is interlinked to a Schottky junction model of metallic precipitates in silicon, enabling accurate calculation of the injection-dependent electric field enclosing the precipitates, as well as the precipitate-limited minority carrier lifetime. It is found that a transition from darkness to illuminated conditions can cause an increase in the kinetics of precipitation by five orders of magnitude. Since our approach enables a direct connection between the time evolution of precipitate size-density distribution and minority carrier lifetime degradation under illumination, a procedure for calculating the Cu-LID-related lifetime as a function of illumination time is included at the end of this article. The model verification with experiments is carried out in Paper II of this contribution along with a discussion of the kinetic and energetic aspects of Cu-LID.

The presence of copper impurities is known to deteriorate the bulk minority carrier lifetime of silicon. In p-type silicon, the degradation occurs only under carrier injection (e.g., illumination), but the reason for this phenomenon called copper-related light-induced degradation (Cu-LID) has long remained uncertain. To clarify the physics of this problem, a mathematical model of Cu-LID was introduced in Paper I of this article. Within the model, kinetic precipitation simulations are interlinked with a Schottky junction model for electric behavior of metallic precipitates. As this approach enables simulating precipitation directly at the minority carrier lifetime level, the model is verified in this second part with a direct comparison to the corresponding degradation experiments and literature data. Convincing agreement is found with different doping and Cu concentrations as well as at increased temperature, and in the dark, both simulated degradation and measured degradation are very slow. In addition, modeled final lifetimes after illumination are very close to experimental final lifetimes, and a correlation with the final precipitate size is found. However, the model underestimates experimentally observed differences in the degradation rate at different illumination intensities. Nevertheless, the results of this work support the theory of Cu-LID as a precipitate formation process. Part of the results also imply that heterogeneous nucleation sites play a role during precipitate nucleation. The model reveals fundamental aspects of the physics of Cu-LID including how doping and heterogeneous nucleation site concentrations can considerably influence the final recombination activity.

28th European Photovoltaic Solar Energy Conference and Exhibition; 2796-2798, Image process method is demonstrated to study the degradation at different counter electrodes (CE) of dye solar cells. The thermally platinized and Pt sputtered CE-CE cells were aged under extreme thermal stress of 80˚ C. The results show that visual appearance of the CE-CE change as a result of degradation, resulting in change in the transmittance of the cells. The gray scale value of the fresh and aged cells is recorded and correlated to the transmittance and electrical measurements of the cells. Interestingly, it was found that though the platinum catalyst is detaching at the counter electrode, the electrical performance of the cells is improved during 24 hours of ageing. In addition, image processing method is demonstrated to analyze the adhesion of Pt on the FTO coated glass using conventional tape test.