An innovative design for a monolithic perovskite/silicon tandem solar cell, featuring a mesoscopic perovskite top subcell and a high-temperature tolerant homojunction c-Si bottom subcell.

improving the performance of this technology. For example, materials such as metal oxides, nitrides, and fluorides have been demonstrated to form electron and hole selective interfaces when applied to c-Si. [1][2][3][4][5][6][7] Such an approach has potential benefits over conventional heavily doped direct-metallization approaches, including lower processing temperatures, simpler contact formation, and the removal of fundamental limitations, such as Auger recombination and free carrier absorption. [8,9] In addition, the unique interface properties of some metal compound/c-Si interfaces have even enabled novel solar cell architectures, for example, n-type c-Si cells with undoped partial rear contacts (PRCs). [10,11] This specific architecture utilizes a near-ideal surface passivation layer, such as hydrogenated silicon nitride SiN x , [12] to cover the vast majority of the rear surface which can greatly reduce the average surface recombination factor J 0 and increase the rear reflection. Only a small percentage of the area is contacted, typically < 5%, where electrons flow to be collected. An n-type undoped PRC cell structure was not previously attainable due to the tendency of n-type c-Si to form an interface potential barrier under direct metallization, which resulted in prohibitively high contact resistivity ρ c . The first successful demonstration of this cell came after a breakthrough in low resistance interfaces to n-type c-Si with a low work function LiF x /Al electrode. This contact was used to fabricate an undoped PRC cell attaining an efficiency of 20.6% with a PRC covering only ≈1% of the rear surface. [11] The next evolutionary step in this cell structure was the integration of a passivation layer at the PRC interface. This came with the introduction of a TiO x /Ca/Al contact, [10] which was found to provide both reduced surface recombination and low contact resistivity, enabling an efficiency of 21.8%. Following on from these early developments, there exist three major avenues to easily improve the electron PRC: i) reduction in the PRC interface recombination and resistivity; ii) increase in the PRC material's stability to thermal stressors; and iii) increasing the rear surface reflectivity via appropriate choice of PRC materials.This article introduces the next in this family of carrier selective interfaces, which targets the abovementioned three issues. To address this a TiO x /LiF x /Al heterocontact is developed and integrated into a PRC cell shown in Figure 1a. The

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This paper presents a direct quantitative comparison of the effectiveness of boron diffusion, phosphorus diffusion, and aluminum alloying in removing interstitial iron in crystalline silicon in the context of silicon solar cells. Phosphorus diffusion gettering was effective in removing more than 90% of the interstitial iron across a range of diffusion temperatures, sheet resistances, and iron doses. Even relatively light phosphorus diffusions (145 X/h) were found to give very effective gettering, especially when combined with extended low temperature annealing. Aluminum alloying was extremely effective and removed more than 99% of the implanted iron for a range of alloying temperatures and aluminum film thicknesses. In contrast, our experimental results showed that boron diffusion gettering is very sensitive to the deposition conditions and can change from less than 5% of the Fe being gettered to more than 99.9% gettered by changing only the gas flow ratios and the post-oxidation step. V

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