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Wide-bandgap perovskite solar cells (PSCs) with optimal bandgap (E g ) and high power conversion efficiency (PCE) are key to high-performance perovskite-based tandem photovoltaics. A 2D/3D perovskite heterostructure passivation is employed for double-cation wide-bandgap PSCs with engineered bandgap (1.65 eV ≤ E g ≤ 1.85 eV), which results in improved stabilized PCEs and a strong enhancement in open-circuit voltages of around 45 mV compared to reference devices for all investigated bandgaps. Making use of this strategy, semitransparent PSCs with engineered bandgap are developed, which show stabilized PCEs of up to 25.7% and 25.0% in fourterminal perovskite/c-Si and perovskite/CIGS tandem solar cells, respectively. Moreover, comparable tandem PCEs are observed for a broad range of perovskite bandgaps. For the first time, the robustness of the four-terminal tandem configuration with respect to variations in the perovskite bandgap for two state-of-the-art bottom solar cells is experimentally validated.

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We study ion implantation for patterned doping of back-junction back-contacted solar cells with polycrystallinemonocrystalline Si junctions. In particular, we investigate the concept of counterdoping, that is, a process of first implanting a blanket emitter and afterward locally overcompensating the emitter by applying masked ion implantation for the back surface field (BSF) species. On planar test structures with blanket implants, we measure saturation current densities J 0 ,p oly of down to 1.0 ± 1.1 fA/cm 2 for wafers passivated with phosphorusimplanted poly-Si layers and 4.4 ± 1.1 fA/cm 2 for wafers passivated with boron-implanted poly-Si layers. The corresponding implied pseudofill factors pF F im p l . are 87.3% and 84.6%, respectively. Test structures fabricated with the counterdoping process applied on a full area also exhibit excellent recombination behavior (J 0 ,p oly = 0.9 ± 1.1 fA/cm 2 , pF F im p l. = 84.7%). By contrast, the samples with patterned counterdoped regions exhibit a far worse recombination behavior dominated by a recombination mechanism with an ideality factor n > 1. A comparison with the blanket-implanted test structures points to recombination in the space charge region inside the highly defective poly-Si layer. Consequently, we suggest introducing an undoped region between emitter and BSF in order to avoid the formation of p + /n + junctions in poly-Si.

We investigate the passivation quality of hole‐collecting junctions consisting of thermally or wet‐chemically grown interfacial oxides, sandwiched between a monocrystalline‐Si substrate and a p‐type polycrystalline‐silicon (Si) layer. The three different approaches for polycrystalline‐Si preparation are compared: the plasma‐enhanced chemical vapor deposition (PECVD) of in situ p+‐type boron‐doped amorphous Si layers, the low pressure chemical vapor deposition (LPCVD) of in situ p+‐type B‐doped polycrystalline Si layers, and the LPCVD of intrinsic amorphous Si, subsequently ion‐implanted with boron. We observe the lowest J0e values of 3.8 fA cm−2 on thermally grown interfacial oxide on planar surfaces for the case of intrinsic amorphous Si deposited by LPCVD and subsequently implanted with boron. Also, we obtain a similar high passivation of p+‐type poly‐Si junctions on wet‐chemically grown oxides as well as for all the investigated polycrystalline‐Si deposition approaches. Conversely, on alkaline‐textured surfaces, J0e is at least 4 times higher compared to planar surfaces. This finding holds for all the junction preparation methods investigated. We show that the higher J0e on textured surfaces can be attributed to a poorer passivation of the p+ poly/c‐Si stacks on (111) when compared to (100) surfaces.