Vertically integrated modeling of light-induced defects: Process modeling, degradation kinetics and device impact

As photovoltaic (PV) device architectures advance, they turn more sensitive to bulk minority charge carrier lifetime. The conflicting needs to develop ever advancing cell architectures on ever cheapening silicon substrates ensure that various impurity-related light-induced degradation (LID) mechanisms will remain an active research area in the silicon PV community. Here, we propose vertically integrated defect modeling as a framework to accelerate the identification and mitigation of different light induced defects. More specifically, we propose using modeled LID-kinetics to identify the dominant LID mechanism or mechanisms within complete PV devices. Coupling the LID-kinetics model into a process model allows development of process guidelines to mitigate the identified LID-mechanism within the same vertically integrated simulation tool. We use copper as an example of a well-characterized light-induced defect: we model the evolution of copper during solar cell processing and light soaking, and then map the deleterious lifetime effect of Cu-LID onto device performance. We validate our model using intentionally Cu-contaminated material processed on an industrial PERC-line and find that our model reproduces the LID-behavior of the manufactured solar cells. We further show via simulations that Cu-LID can be mitigated by reducing the contact co-firing peak temperature, or the cooling rate after the firing process.