This work reports on the application of the differential junction photovoltage (diff-JPV) technique to characterize conducting layers at the emitter side of silicon heterojunction (HJT) cells structures by measuring their sheet resistance (Rsh). The diff-JPV measuring principle developed for homojunction emitters can be directly adopted for HJT cell structures to accurately determine Rsh of the transparent conductive oxide (TCO) layer at the emitter side. This is the first application of diff-JPV for non-silicon layers and heterojunctions.

Furthermore, the result of this simple and rapid measurement is not influenced by the resistivity of the substrate wafer, and exhibits excellent correlation to optimized four-point-probe measurement. The unique feature of the diff-JPV technique is its capability to characterize emitter type layers even with very large sheet resistance, which is hardy accessible by other contactless techniques. It was found that performing the diff- JPV measurement on wafers after the PE-CVD process to deposit the hydrogenated amorphous Si layer stack, the resulted Rsh values lie in the 80 – 240 kΩ/sq. range. The dependence of the sheet resistance on the substrate doping indicates that the measurement is related to the inversion layer formed under the emitter amorphous silicon layer stack.

Since such sensitive detection and characterization of the inversion layers cannot be accomplished by other techniques, diff-JPV can be an important method for the further optimization of heterojunction interfaces.

If you want to know more about our research with ENEL, follow the link and read the full work at AIP Conference Proceedings: https://aip.scitation.org/doi/abs/10.1063/5.0089290