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Outstanding optoelectronic properties of mixed tin‐lead perovskites are the cornerstone for the development of high‐efficiency all‐perovskite tandems. However, recombination losses in Sn‐Pb perovskites still limit the performance of these perovskites, necessitating more fundamental research. Here, rubidium iodide is employed as an additive for methylammonium‐free Sn‐Pb perovskites. It is first investigated the effect of the RbI additive on the perovskite composition, crystal structure, and element distribution. Quasi‐Fermi level splitting and transient photoluminescence measurements reveal that the RbI additive reduces recombination losses and increases carrier lifetime of the perovskite films. This finding is attributed to an approximately ten‐fold reduction in the defect density following RbI treatment, as probed using constant final state yield photoelectron spectroscopy. Additionally, the concentration of Sn vacancies is also reduced, and the perovskite film becomes less p‐type both in the bulk and at the interface towards the electron contact. Thus, the conductivity for electrons increases, improving carrier extraction. As a result, the open‐circuit voltage of RbI‐containing solar cells improves by 61 mV on average, with the best efficiency >20%. This comprehensive study demonstrates that RbI is effective at reducing recombination losses and carrier trapping, paving way for a new approach to Sn‐Pb perovskite solar cell research. [ABSTRACT FROM AUTHOR]

Inorganic perovskite solar cells show excellent thermal stability, but the reported power conversion efficiencies are still lower than for organic–inorganic perovskites. This is mainly caused by lower open‐circuit voltages (VOCs). Herein, the reasons for the low VOC in inorganic CsPbI2Br perovskite solar cells are investigated. Intensity‐dependent photoluminescence measurements for different layer stacks reveal that n–i–p and p–i–n CsPbI2Br solar cells exhibit a strong mismatch between quasi‐Fermi level splitting (QFLS) and VOC. Specifically, the CsPbI2Br p–i–n perovskite solar cell has a QFLS–e ·VOC mismatch of 179 meV, compared with 11 meV for a reference cell with an organic–inorganic perovskite of similar bandgap. On the other hand, this study shows that the CsPbI2Br films with a bandgap of 1.9 eV have a very low defect density, resulting in an efficiency potential of 20.3% with a MeO–2PACz hole‐transporting layer and 20.8% on compact TiO2. Using ultraviolet photoelectron spectroscopy measurements, energy level misalignment is identified as a possible reason for the QFLS–e ·VOC mismatch and strategies for overcoming this VOC limitation are discussed. This work highlights the need to control the interfacial energetics in inorganic perovskite solar cells, but also gives promise for high efficiencies once this issue is resolved. [ABSTRACT FROM AUTHOR]

The fullerene C60 is commonly applied as the electron transport layer in high‐efficiency metal halide perovskite solar cells and has been found to limit their open circuit voltage. Through ultra‐sensitive near‐UV photoelectron spectroscopy in constant final state mode (CFSYS), with an unusually high probing depth of 5–10 nm, the perovskite/C60 interface energetics and defect formation is investigated. It is demonstrated how to consistently determine the energy level alignment by CFSYS and avoid misinterpretations by accounting for the measurement‐induced surface photovoltage in photoactive layer stacks. The energetic offset between the perovskite valence band maximum and the C60 HOMO‐edge is directly determined to be 0.55 eV. Furthermore, the voltage enhancement upon the incorporation of a LiF interlayer at the interface can be attributed to originate from a mild dipole effect and probably the presence of fixed charges, both reducing the hole concentration in the vicinity of the perovskite/C60 interface. This yields a field effect passivation, which overcompensates the observed enhanced defect density in the first monolayers of C60. [ABSTRACT FROM AUTHOR]

Optical, structural and electrical properties of thermally co‐evaporated indium tungsten oxide (IWOx) thin films with varied stoichiometry, from pure tungsten oxide to pure indium oxide (InOx) are investigated upon stepwise annealing, up to 700 °C. The thin films are candidate materials for carrier selective contacts in different types of solar cells, such as silicon hetero junction and perovskite solar cells. Three different phases for the thin films with different stoichiometry and crystallization temperatures of Tc > 500 °C for tungsten‐rich layers and Tc ≈ 200 °C for indium‐rich layers are found. The pronounced optical absorption of the as‐deposited InOx‐rich layers is strongly decreased after crystallization. Tungsten oxide rich layers show low optical absorption in the as‐deposited state as well as for all applied annealing temperatures. The lateral conductivity of the pure indium oxide can be increased from 1.24 × 10−2 up to 0.83 S cm−1 after 700 °C annealing. The conductivity of the pure tungsten oxide increases slightly after crystallization from 2.55 × 10−5 to 8.25 × 10−5 S cm−1 after annealing at 700 °C. However, for mixed oxide layers with ≈25% InOx‐fraction in the mixture, the highest conductivity of 4.0 × 10−6 S cm−1 cannot be increased by the applied annealing process. [ABSTRACT FROM AUTHOR]

Perovskite solar cells (PSCs) are promising for high‐efficiency tandem applications, but their long‐term stability, particularly due to ion migration, remains a challenge. Despite progress in stabilizing PSCs, they still fall short compared to mature technologies like silicon. This study explores how different piperazinium salt treatments using iodide, chloride, tosylate, and bistriflimide anions affect the energetics, carrier dynamics, and stability of 1.68 eV bandgap PSCs. Chloride‐based treatments achieved the highest power conversion efficiency (21.5%) and open‐circuit voltage (1.28 V), correlating with stronger band bending and n‐type character at the surface. At the same time, they showed reduced long‐term stability due to increased ionic losses. Tosylate‐treated devices offered the best balance, retaining 96.4% efficiency after 1000 h (ISOS‐LC‐1I). These findings suggest that targeted surface treatments can enhance both efficiency and stability in PSCs. [ABSTRACT FROM AUTHOR]