2022, Herguth, Axel, Kostrzewa, Fabian, Sperber, David

Bifacial metal-insulator-semiconductor (MIS) structures are used to intentionally manipulate field-effect passivation of dielectric layers on crystalline silicon substrates during lifetime measurements by external biasing. It is found that the impact of biasing on surface passivation depends on the quality of the substrate contact, in particular in asymmetric front/rear biasing conditions. A mathematical model is presented and used to demonstrate the problems arising from a high substrate contact resistance.

2018-10, Sperber, David, Herguth, Axel, Hahn, Giso

Different surface passivation approaches are applied on Cz-Si and FZ-Si samples and long-term stability is investigated during treatments at 60–80 °C and up to 1 sun equivalent illumination intensity. It is shown that SiN_x:H and AlO_x:H/SiN_x:H surface passivation show a much more stable passivation quality when deposited on P-diffused and B-diffused surfaces, respectively. Long-term measurements lead to the conclusion that Cz-Si samples fired at measured peak temperatures up to 750 °C are very stable after regeneration of bulk defects. Samples fired at 850 °C show much stronger bulk-related degradation potentially linked to light and elevated temperature induced degradation (LeTID). Furthermore, Cz-Si samples fired at 850 °C express an instable behavior after a regeneration treatment.

2018-09, Herguth, Axel, Derricks, Christian, Sperber, David

A light-induced degradation phenomenon of unknown origin in p-type Cz-Si passivated emitter and rear cell (PERC)-type solar cells is thoroughly investigated by collating results from different measurement techniques and predictions from various simulations. The observed degradation manifests in slight losses in j_sc, strong losses in V_oc, and devastating losses in FF, and thus massively impacts efficiency. It is found that the series resistance degrades significantly due to a degradation of front contact resistance. This, however, does not explain losses in V_oc and j_sc, which are attributed to the degradation of a different cell component. Neither a degradation by defect formation in the space charge region, nor the emitter, nor the bulk is found to consistently explain the observations. Only a rear surface-related degradation mechanism explains consistently all experimental findings.