# Installation

Do I require admin rights on my PC to install and use Quokka3?

No. The Quokka3-client software runs fully standalone within a single folder. Installation barely requires extracting the downloaded zip-archive into a new folder.

Can I install the full version on my own servers instead of using the cloud-service?

Currently not. But please feel free to flag your interest, things might change in future.

Is Quokka3 available also for Linux or OSX?

Other OS than windows are currently not supported. But please get in contact to discuss you needs. For example simple command-line versions are reasonable low effort to provide.

# GUI troubleshooting

The GUI hangs when trying to plot a large geometry

Very large meshes (millions of elements) require a significant amount of memory when displaying the geometry, which may exceed your PC's free memory. Furthermore, a "bug" prevents the memory from being cleared when closing a geometry plot. That means that in particular for repeatedly plotting a large geometry you might run out of memory. Frequent restarting of the GUI is then required, which is the current workaround until the issue is fixed at a future release.

The GUI hangs for no obvious reason, what to do?

Restart. Unless a local (free version) simulation is running, restarting the GUI is very safe to do, i.e. there will be no accidental loss of cloud simulation results or similar. Please contact support if you observe crashes in a reproducible manner.

ASCII, encoding, or similar problems, e.g. Chinese character problem

The GUI is based on python 2 which has problems handling special characters, including e.g. Chinese or Japanese characters. Omit such characters in pathnames both to the Quokka3 folder and to your settingsfiles, as well as for filenames for settingsfiles and additional input files.

# General modeling questions

Can Quokka3 model tunnel-oxide passivating contacts (e.g. TOPCon)?

Yes, Quokka3 can account for passivating contacts either with the lumped skin approach, or within a detailed skin approach using MIS theory. The lumped skin approach is mostly straightforward: one needs to define the sheet resistance of the passivating contact system (which could be the TCO sheet resistance), the effective recombination ($$J_{0,skin}$$), and the contact resistivity, same as with classical diffused contacts. Additional to classical contacts a vertical skin resistivity can play a role, which represents the tunneling-resistance, which is separate to the contact resistivity to the metal. Such a vertical skin resistivity can be defined in Quokka3 (different to Quokka2). Note that those two resistivities are not trivial to separately measure by the common TLM technique. Quokka3 can support the characterization by simulating dedicated contact resistance structures, see e.g. (Koekbudak et al. 2017). the lumped skin model assumes the contact resistivity and / or the vertical skin resistivity to be constant, i.e. ohmic, which can be quite inaccurate. For this Quokka3 offers a more detailed modeling of passivating contact physics using MIS theory within a detailed skin approach: here the input parameters are an effective Schottky barrier, surface SRH recombination parameters, and tunneling layer properties (essentially thickness and tunneling barrier). This approach resolves the band-bending within the near-surface of the silicon absorber, it's interplay with surface SRH, and the non-ohmic tunneling transport by simple analytical direct tunneling model. Note that Quokka3 does not (yet) provide a fully detailed approach to model passivating contacts, that is simulating semiconductor transport within the involved material layers other than the silicon absorber. However, the applicability of such a fully detailed approach generally suffers from the many more required input parameters with substantial uncertainty, and it has not (yet) shown to have more predictive power than the simpler MIS approach. A journal paper describing the MIS approach used in Quokka3 is currently in review process. Example settingsfiles will be available soon.

# References

Koekbudak, G., R. Müller, F. Feldmann, A. Fell, R. Turan, and S.W. Glunz. 2017. “On the Determination of the Contact Resistivity for Passivating Contacts Using 3d Simulations.” In 34th European Photovoltaic Solar Energy Conference and Exhibition. https://www.ise.fraunhofer.de/content/dam/ise/de/documents/publications/conference-paper/33-eupvsec-2017/Koekbudak_2AO43.pdf.