We present a p+/n+ poly-Si tunneling junction (TJ) based on a tunnel oxide passivated contact (TOPCon) that enables both low contact resistivity ρc and high implied open-circuit voltages iVoc. It will be shown that the charge carrier profile of the TJ and the junction resistance are strongly affected by the applied thermal budget, consisting of a furnace anneal and/or a rapid thermal processing treatment, and the deposition parameters of the a-Si layers. A minimum combined junction resistance of the p+/n+ poly-Si/SiOx stack of less than 10 mΩ cm2 and iVoc of up to 726 mV at 1 sun illumination is reported. This work aims for incorporation of our p+/n+ poly-Si TJ into an industrially feasible tandem solar cell featuring a Si bottom cell with a TOPCon front emitter and the industrial standard technology of a passivated emitter and rear cell rear structure.

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Improving the activity of catalysts for the oxygen evolution reaction (OER) requires a detailed understanding of the surface chemistry and structure to deduce structure-function relationships (descriptors) for fundamental insight. We chose epitaxial (100)-oriented La 0.6 Sr 0.4 Mn 1−δ O 3 (LSMO) thin films as a model system with high electrochemical activity comparable to (110)-oriented IrO 2 to investigate the effect of Mn off-stoichiometry on both catalytic activity and stability. Extensive structural characterization was performed by microscopic and spectroscopic methods before and after electrochemical characterization using rotating ring-disk studies. Stoichiometric LSMO had the highest activity, while both Mn deficiency and excess reduced the catalytic activity. Furthermore, all samples preserved the crystal structure up to the very surface. Mn excess improved the long-term activity, and we hypothesize that excess Mn stabilizes the surface chemistry during catalysis. Our data show that the defect chemistry should be considered when designing catalysts with enhanced activity and rugged stability.

Passivating contacts based on poly-Si/SiO x structures also known as TOPCon (tunnel oxide passivated contacts) have a great potential to improve the efficiency of crystalline silicon solar cells, resulting in more than 26% and 24% for laboratory and industrial cells, respectively. This publication gives an overview of the historical development of such contact structures which have started already in the 1980s and describes the current state-of-the-art in laboratory and industry. In order to demonstrate the great variety of scientific and technological research, four different research topics are addressed in more detail: (i) the superior passivation quality of TOPCon structures made it necessary to re-parametrize intrinsic recombination in silicon, (ii) the control of diffusion of dopants through the intermediate SiO x layer is essential to optimize passivation and transport properties, (iii) single-sided deposition of the poly-Si layer would reduce process complexity for industrial TOPCon cells, and (iv) silicon-based tunnel junctions for perovskite-silicon tandem cells can be fabricated using the TOPCon technology.

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