EU PVSEC Programme Online
EU PVSEC 2021, 6 - 10 September 2021
Presentation: 2DO.10.3 Influence of Intentional Alkali Metals and Alkaline Earth Metal Contamination on PID of Silicon Solar Cells
Type: Oral
Date: Thursday, 9th September 2021
17:00 - 18:30
Author(s): J. Hepp, C. Huse, B. Doll, V. Naumann, A. Linsenmeyer, J. Hauch, C.J. Brabec, I.M. Peters
Presenter / Speaker: J. Hepp, I-MEET, Erlangen, Germany
Event: Conference Conference
Session: 2DO.10 Defects in Silicon and their Characterisation
Topic: 2. 1 Feedstock, Crystallisation, Wafering, Defect Engineering
Summary / Abstract: Since PV module manufacturers need to guarantee high levels of device performance over the time span of multiple decades, degradation processes need to be understood and minimized as far as possible. One crucial mechanism potentially leading to a significant power loss is potential induced degradation (PID). According to current literature, PID is triggered in the presence of sodium (Na) on the solar cell surface, which subsequently migrates through the dielectric passivation layer under the influence of electric fields and thus into the junction [1]. Within this study, we investigate how other contaminants from the main groups of alkali metals and alkaline earth metals result in the development of PID, and compare this development to that induced by Na. The selected contaminants include lithium (Li), potassium (K), magnesium (Mg) and calcium (Ca). In our first approach, we used very high contaminant concentrations, to create a distinct effect. The contaminants were included into the modules in the form of dissolved salts that were dispersed on top of the solar cells. After drying, the cells were encapsulated with EVA and glass. This method has proven quite helpful for the detailed investigation of individual contaminants. PID is triggered and reversed using a commercial device. The device consists of a heating pad that covers the major part of a PV module and allows applying a potential of up to ±1500 V between the cells and the module surface at a temperature of 85 °C. Before and after degradation, multiple characterization steps are carried out: dark and illuminated IV curves, electroluminescence (EL) imaging and photoluminescence (PL) imaging. While our research shows that, of the evaluated elements, Na constitutes the greatest danger in respect to PID, other contaminants cannot be ignored completely. The second most problematic element of the investigated ones, appears to be Li. Moreover, we confirmed that we can record the characteristic PID pattern using not only EL but also completely contact free PL imaging. Since the incorporation of contaminants is technically possible at several fabrication steps, it is not unrealistic to encounter a variety of contaminants in the final device. For that reason, knowledge of their implications is very important to minimize degradation as well as for performance predictions. Future goals include the variation of concentrations, to set guidelines for the amount of each contaminant allowed within the device.