A minimalist approach to integration yields tandem solar cells with high efficiency.

Crude oil and hydrocarbon fuel spills are a perennial threat to aquatic environments. Inexpensive and sustainable sorbents are needed to mitigate the ecological harm of this pollution. To address this need, this study features a low‐density polysulfide polymer that is prepared by the direct reaction of sulfur and used cooking oils. Because both sulfur and cooking oils are hydrophobic, the polymer has an affinity for hydrocarbons such as crude oil and diesel fuel and can rapidly remove them from seawater. Through simple mechanical compression, the oil can be recovered and the polymer can be reused in oil spill remediation. The polysulfide is unique because it is prepared entirely from repurposed waste: sulfur is a by‐product of the petroleum industry and used cooking oil can be used as a comonomer. In this way, sulfur waste from the oil industry is used to make an effective sorbent for combatting pollution from that same sector.

Defect‐mediated carrier recombination at the interfaces between perovskite and neighboring charge transport layers limits the efficiency of most state‐of‐the‐art perovskite solar cells. Passivation of interfacial defects is thus essential for attaining cell efficiencies close to the theoretical limit. In this work, a novel double‐sided passivation of 3D perovskite films is demonstrated with thin surface layers of bulky organic cation–based halide compound forming 2D layered perovskite. Highly efficient (22.77%) mixed‐dimensional perovskite devices with a remarkable open‐circuit voltage of 1.2 V are reported for a perovskite film having an optical bandgap of ≈1.6 eV. Using a combination of experimental and numerical analyses, it is shown that the double‐sided surface layers provide effective defect passivation at both the electron and hole transport layer interfaces, suppressing surface recombination on both sides of the active layer. Despite the semi‐insulating nature of the passivation layers, an increase in the fill factor of optimized cells is observed. The efficient carrier extraction is explained by incomplete surface coverage of the 2D perovskite layer, allowing charge transport through localized unpassivated regions, similar to tunnel‐oxide passivation layers used in silicon photovoltaics. Optimization of the defect passivation properties of these films has the potential to further increase cell efficiencies.

Mixed‐dimensional perovskite solar cells combining 3D and 2D perovskites have recently attracted wide interest owing to improved device efficiency and stability. Yet, it remains unclear which method of combining 3D and 2D perovskites works best to obtain a mixed‐dimensional system with the advantages of both types. To address this, different strategies of combining 2D perovskites with a 3D perovskite are investigated, namely surface coating and bulk incorporation. It is found that through surface coating with different aliphatic alkylammonium bulky cations, a Ruddlesden–Popper “quasi‐2D” perovskite phase is formed on the surface of the 3D perovskite that passivates the surface defects and significantly improves the device performance. In contrast, incorporating those bulky cations into the bulk induces the formation of the pure 2D perovskite phase throughout the bulk of the 3D perovskite, which negatively affects the crystallinity and electronic structure of the 3D perovskite framework and reduces the device performance. Using the surface‐coating strategy with n‐butylammonium bromide to fabricate semitransparent perovskite cells and combining with silicon cells in four‐terminal tandem configuration, 27.7% tandem efficiency with interdigitated back contact silicon bottom cells (size‐unmatched) and 26.2% with passivated emitter with rear locally diffused silicon bottom cells is achieved in a 1 cm2 size‐matched tandem.

MoO 3 is known as high work function (WF) transparent metal oxides. It is used as anode buffer layer in organic based solar cells because of its capability to extract electrons and inject holes from the active layer due to its high WF. Here a broad range of techniques is used to determine the energy levels of the bulk heterojunction (BHJ) and MoO 3 to determine that the minimum deposition thickness to achieve a closed layer is 1 nm due to penetration of the evaporated MoO 3 into the BHJ. The investigation shows that upon evaporation of the MoO 3 , a strong dipole is formed at the extended interface between the active layer and the MoO 3 and that the strength of the dipole increases with increasing thickness of the MoO 3 layer and saturates at 2.2 eV at a thickness around 3 nm.