Front-floating Emitter Voltage Mapping of IBC Mercury Cells

Standard characterization techniques such as LBIC are difficult to apply to IBC solar cells with a front floating emitter (FFE). This is because the cells need to be under bias illumination, and this is often impossible in commercial LBIC measurement tools. To the best of our knowledge, LBIC measurements on FFE IBC cells have not been published so far. In this work we present a experimental method to spatially characterize the FFE of IBC cells and gain insights on electrical shading losses, without using LBIC. This method makes use of the commercially available CoreScan device, mapping the FFE voltage relative to the shorted back-contacts over the cell area. Using this technique we were able to resolve busbar, pads and finger features of both polarities with a scan of the front side. The scan shows that BSF features have higher voltage than emitter features, thus giving a direct evidence of the FFE pumping effect. If coupled to circuit simulation, FFE voltage maps can be the base for estimating electrical shading losses in IBC cells. The FFE voltage maps also give information on the homogeneity of the pumping effect across the wafer, e.g. affected by diffusion non-uniformity, and at least qualitatively its effect on the cell performance.