On the influence of the sample properties on the measurement of the implied open-circuit voltage

The implied voltage iVOC is a popular parameter for the electronic quality of solar cell test samples. It is used to characterize properties like the passivation quality of surface coatings. While iVOC fundamentally depends on the sample properties besides the electronic quality of the interface, such influences have not been systematically quantified and are usually not stated, which questions the comparability of iVOC across multiple sample sets. This article is dedicated to study the influence of the wafer doping and thickness, surface passivation and reflection as well as light trapping on iVOC by device simulations using Quokka3, supported by experimental data. It is shown that, even moderate changes in these sample properties can result in a significant deviation in iVOC. This is emphasized if multiple influences are combined, as shown on two samples featuring an iVOC of 737 and 754 mV. This difference in iVOC can be broken down into individual contributions, demonstrating how the aforementioned influences can quickly add up to 10-15 mV if combined. From this perspective, it is difficult to compare their respective surface passivation performance, which only accounts for less than 10% of the total change in iVOC. Therefore, we recommend a precise description of the aforementioned sample properties when reporting iVOC values in publication. To quantify the surface recombination, we recommend the use of J0s instead of iVOC, since it specifically describes surface recombination and is usually independent from the discussed sample properties.