Ultra‐Thin Poly‐Si Layers: Passivation Quality, Utilization of Charge Carriers Generated in the Poly‐Si and Application on Screen‐Printed Double‐Side Contacted Polycrystalline Si on Oxide Cells
Yevgeniya Larionova, Henning Schulte‐Huxel, Byungsul Min, Sören Schäfer, T. Kluge, H. Mehlich, Rolf Brendel, Robby Peibst
Abstract
Herein, the various measures to improve the efficiency of large‐area screen‐printed double‐side contacted polycrystalline Si on oxide (POLO)‐cells are experimentally demonstrated. The short‐circuit current density J sc increases by 0.6 mA cm −2 upon reducing the thickness of poly‐Si from 25 to 10 nm due to the reduction of the parasitic absorption in the poly‐Si layer at the textured front side of the cell. Additionally, it is shown for the first time that the minority carriers generated by light absorbed in the poly‐Si layer can at least partially be transferred into the crystalline Si base. Remarkably high implied open‐circuit voltage V oc,impl values are achieved with n‐type cell precursors by introducing an hydrogenation step by Al x O y after reducing the poly‐Si thickness, and by an additional annealing step after sputtering of transparent conductive oxides (TCOs). All cell precursors show V oc,impl values of up to 740 mV independent of the poly‐Si thickness. A reduction in the open‐circuit voltage V oc is observed during back‐end processing to 728 mV as measured on the final cells. A certified cell energy conversion efficiency of 22.3% is reported.