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Rational modification of perovskite surfaces using organic ammonium salts can considerably improve the performance of perovskite solar cells (PSCs). However, the impact of the cation–anion bonding strength within organic ammonium salts on the resulting modified perovskite films is still quite unclear. Herein, a series of phenylethylammonium salts are systematically explored for surface passivation: iodide (PEAI), trifluoroacetate (PEATFA) and acetate (PEAAc), which show increasing cation–anion bonding strength. The bonding strength was found to govern the chemical and supramolecular interactions of phenylethylammonium salts with the perovskite components. While PEAI and PEATFA show weak interactions with FAI and PbI2, PEAAc reveals surprisingly high reactivity and forms chemical species through unprecedented pathways. NMR spectroscopy and advanced infrared near-field optical microscopy (IR s-SNOM) unravel that PEAI and PEATFA are passivators mainly targeting the perovskite grain boundaries. By contrast, the reactive PEAAc-modification achieves simultaneous defect passivation through the formation of a lead acetate shell on the grain surface and accumulation of PEAI at the grain boundaries. Increasing the cation–anion bonding strength is also found to reduce the reactivity of phenylethylammonium salts to form two-dimensional perovskites. While PEAI-modification leads to little gain in power conversion efficiency (PCE) of PSCs, PEATFA-modification obviously improves the PCE and stability of PSCs. In particular, PEAAc-modification effectively chelates the undercoordinated Pb2+ and enables the most favorable energy band alignment to enhance the hole extraction at the perovskite/hole transport layer heterointerface. The photovoltaic performance and stability of corresponding PSCs with n–i–p architecture are improved considerably and a champion PCE of 24.9% is achieved. The presented "smart passivation" strategy using reactive modifiers also provides principally new opportunities in the development of efficient and stable PSCs. [ABSTRACT FROM AUTHOR]

Tin-based perovskites have become the most promising non-lead perovskites due to their ideal band gap and low toxicity. Although the open circuit voltage of tin-based perovskite solar cells (TPSCs) continues to approach the theoretical value, the short-circuit current is still far from the theoretical value. Here, we describe an interface modification method by regulating the property of hole transport layer, PEDOT:PSS, which improves the surface molecular morphology and the energy level alignment of PEDOT:PSS/perovskite interface. Advanced GIWAXS and IR s-SNOM characterization are conducted to achieve multi-dimensional characterization of nanoscale surface morphology and chemical distribution of PEDOT:PSS. With the multi-attribute optimization, charge carrier extraction and non-radiative recombination are also improved. The resultant TPSCs exhibit a higher power conversion efficiency of 13.32% in compared with the control device of 10.50%, accompanied with an increase in the short-circuit current from 18.10 to 20.50 mA cm-2 and FF from 68.23% to 76.43%. This work demonstrates a reliable strategy for improving charge carrier extraction and device performance for lead-free TPSCs. [ABSTRACT FROM AUTHOR]

[Display omitted] The impact of different electron transport layers (ETLs) based on fullerene derivatives, such as the well-known PC 61 BM and promising 3-pyridyl-substituted pyrrolidino[60]fullerene (PYF-30), on the electric field-induced degradation of inverted perovskite solar cells has been demonstrated. Devices assembled using PYF-30 and PC 61 BM deposited from deuterated chloroform exhibit significantly higher stability compared to PC 61 BM films deposited from chlorobenzene. The main reason for the decrease in the efficiency of the device during aging is the formation of pinhole-type defects in the ETL caused by the agglomeration of molecules of fullerene derivatives. [ABSTRACT FROM AUTHOR]

Perovskite solar cells have already demonstrated high radiation hardness substantially exceeding that of crystalline silicon and GaAs based solar panels commonly used in space. However, aerospace applications of PSCs require a number of other important prerequisites, among which the stability towards a combination of multiple stress factors characteristic of the outer space environment is of particular importance. Herein, we present an in-depth investigation of the influence of the Eu2+/Eu3+ redox pair on the intrinsic photostability of PbI2 and complex lead halides. We confirm that the incorporation of europium effectively suppresses the photochemical production of metallic lead and other aging products. Furthermore, the Eu-modified methylammonium-free double cation perovskite formulation Cs0.12FA0.88Pb0.99Eu0.01I3 demonstrated excellent radiation hardness under exposure to ultrahigh doses of gamma rays (5.5 MGy) and 8.5 MeV electron beams (fluences up to 3 × 1016 e per cm²) owing to the mitigated aging pathways such as radiochemical Pb0 formation and segregation of CsPbI3 and/or FAPbI3 Ζ-phases. Thus, the stabilizing effect of the Eu2+/Eu3+ redox shuttle was exploited here for the first time to substantially increase the stability of perovskite absorber materials with respect to three different stress factors simultaneously: light, gamma-rays and high-energy electrons. Further development of this research direction might facilitate commercialization of PSCs for aerospace applications. [ABSTRACT FROM AUTHOR]

The high power-conversion efficiencies of hybrid perovskite solar cells encourage many researchers. However, their limited photostability represents a serious obstacle to the commercialization of this promising technology. Herein, we present an efficient method for improving the intrinsic photostability of a series of commonly used perovskite material formulations such as MAPbI3, FAPbI3, Cs0.12FA0.88PbI3, and Cs0.10MA0.15FA0.75PbI3 through modification with octenidine dihydroiodide (OctI2), which is a widely used antibacterial drug with two substituted pyridyl groups and two cationic centers in its molecular framework. The most impressive stabilizing effects were observed in the case of FAPbI3 and Cs0.12FA0.88PbI3 absorbers that were manifested in significant suppression or even blocking of the undesirable perovskite films' recrystallization and other decomposition pathways upon continuous 110 mW/cm2 light exposure. The achieved material photostability—within 9000 h for the Oct(FA)n−1PbnI3n+1 (n = 40–400) and 20,000 h for Oct(Cs0.12FA0.88)n−1PbnI3n+1 (where n = 40–400) formulations—matches the highest values ever reported for complex lead halides. It is important to note that the stabilizing effect is maintained when OctI2 is used only as a perovskite surface-modifying agent. Using a two-cation perovskite composition as an example, we showed that the performances of the solar cells based on the developed Oct(Cs0.12FA0.88)399Pb400I1201 absorber material are comparable to that of the reference devices based on the unmodified perovskite composition. These findings indicate a great potential of the proposed approach in the design of new highly photostable and efficient light absorbers. We believe that the results of this study will also help to establish important guidelines for the rational material design to improve the operational stability of perovskite solar cells. [ABSTRACT FROM AUTHOR]

Perovskite solar cells represent the most attractive emerging photovoltaic technology, but their practical implementation is limited by solar cell devices' low levels of operational stability. The electric field represents one of the key stress factors leading to the fast degradation of perovskite solar cells. To mitigate this issue, one must gain a deep mechanistic understanding of the perovskite aging pathways associated with the action of the electric field. Since degradation processes are spatially heterogeneous, the behaviors of perovskite films under an applied electric field should be visualized with nanoscale resolution. Herein, we report a direct nanoscale visualization of methylammonium (MA+) cation dynamics in methylammonium lead iodide (MAPbI3) films during field-induced degradation, using infrared scattering-type scanning near-field microscopy (IR s-SNOM). The obtained data reveal that the major aging pathways are related to the anodic oxidation of I− and the cathodic reduction of MA+, which finally result in the depletion of organic species in the channel of the device and the formation of Pb. This conclusion was supported by a set of complementary techniques such as time-of-flight secondary ion mass spectrometry (ToF-SIMS), photoluminescence (PL) microscopy, scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) microanalysis. The obtained results demonstrate that IR s-SNOM represents a powerful technique for studying the spatially resolved field-induced degradation dynamics of hybrid perovskite absorbers and the identification of more promising materials resistant to the electric field. [ABSTRACT FROM AUTHOR]