aMonolithic perovskite/silicon tandem solar cells show great promise for further efficiency enhancement for current silicon photovoltaic technology. In general, an interface (tunnelling or recombination) layer is usually required for electrical contact between the top and the bottom cells, which incurs higher fabrication costs and parasitic absorption. Most of the monolithic perovskite/Si tandem cells demonstrated use a hetero-junction silicon (Si) solar cell as the bottom cell, on small areas only. This work is the first to successfully integrate a low temperature processed (r150 1C) planar CH 3 NH 3 PbI 3 perovskite solar cell on a homo-junction silicon solar cell to achieve a monolithic tandem without the use of an additional interface layer on large areas (4 and 16 cm 2 ).Solution processed SnO 2 has been effective in providing dual functions in the monolithic tandem, serving as an ETL for the perovskite cell and as a recombination contact with the n-type silicon homo-junction solar cell that has a boron doped p-type (p++) front emitter. The SnO 2 /p++ Si interface is characterised in this work and the dominant transport mechanism is simulated using Sentaurus technology computer-aided design (TCAD) modelling. The champion device on 4 cm 2 achieves a power conversion efficiency (PCE) of 21.0% under reverse-scanning with a V OC of 1.68 V, a J SC of 16.1 mA cm À2 and a high FF of 78% yielding a steady-state efficiency of 20.5%. As our monolithic tandem device does not rely on the SnO 2 for lateral conduction, which is managed by the p++ emitter, up scaling to large areas becomes relatively straightforward. On a large area of 16 cm 2 , a reverse scan PCE of 17.6% and a steady-state PCE of 17.1% are achieved. To our knowledge, these are the most efficient perovskite/homo-junction-silicon tandem solar cells that are larger than 1 cm 2 . Most importantly, our results demonstrate for the first time that monolithic perovskite/silicon tandem solar cells can be achieved with excellent performance without the need for an additional interface layer. This work is relevant to the commercialisation of efficient large-area perovskite/homo-junction silicon tandem solar cells. Broader contextA simple approach for integrating a perovskite solar cell monolithically onto a Si solar cell is reported here. The first advantage of this approach is that it does not require additional fabrication of an additional interface layer between the perovskite and Si cell. The second advantage of this approach is that it is compatible with a homo-junction p-n Si solar cell, which is a common Si solar cell structure for commercial cells. The third advantage is that the entire sequence for the planar perovskite cell fabrication is done at low temperatures, minimising damage to the bottom Si solar cell. The fourth advantage is that the SnO 2 electron transport layer of the perovskite top cell also serves as a recombination contact with the silicon bottom cell. Finally, this monolithic tandem approach does not rely on the SnO 2 for lateral conducti...

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Stability of the passivation quality of poly-Si on oxide junctions against the conventional mainstream high-temperature screen-print firing processes is highly desirable and also expected since the poly-Si on oxide preparation occurs at higher temperatures and for longer durations than firing. We measure recombination current densities (J 0 ) and interface state densities (D it ) of symmetrical samples with n-type poly-Si contacts before and after firing. Samples without a capping dielectric layer show a significant deterioration of the passivation quality during firing. The D it values are (3 ± 0.2) Â 10 11 and (8 ± 2) Â 10 11 eV/cm 2 when fired at 620 C and 900 C, respectively. The activation energy in an Arrhenius fit of D it versus the firing temperature is 0.30 ± 0.03 eV. This indicates that thermally induced desorption of hydrogen from Si H bonds at the poly-Si/SiO x interface is not the root cause of depassivation. Postfiring annealing at 425 C can improve the passivation again. Samples with SiN x capping layers show an increase in J 0 up to about 100 fA/cm 2 by firing, which can be attributed to blistering and is not reversed by annealing at 425 C. On the other hand, blistering does not occur in poly-Si samples capped with AlO x layers or AlO x /SiN y stacks, and J 0 values of 2-5 fA/cm 2 can be achieved after firing. Those findings suggest that a combination of two effects might be the root cause of the increase in J 0 and D it : thermal stress at the SiO z interface during firing and blistering. Blistering is presumed to occur when the hydrogen concentration in the capping layers exceeds a certain level.