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Hydrazine derivatives have been extensively studied as some of the earliest reductants for Sn–Pb mixed perovskite precursors. However, phenyl hydrazine (BH) as a strong reductant for Sn-based perovskite solutions has not been reported yet, and Sn2+ is unusually oxidized in the precursor solution with BH additives in our experiment. Thus, not all organic reductants are suitable as additives, and therefore selecting a suitable reductant should be paid special attention to. Herein, it is found that BH as a Brønsted base deprotonates MA+ to produce HI, which further catalyzes the oxidation of Sn2+ by DMSO. As an alternative, hydrochloride phenyl hydrazine with a sulfonic amide group (–SO2–NH2) is added to the precursor as a reductant and passivator. As a result, a power conversion efficiency of 22.01% is achieved, and prolonged shelf stability is realized. [ABSTRACT FROM AUTHOR]

Understanding the degradation kinetics of perovskite materials in operating perovskite solar cells (PSCs) is critical for developing methods to further enhance their device stability. However, it remains a challenge to capture the details and characteristics of the perovskite degradation process inside operating PSCs under different environmental conditions in real‐time at the microscopic scale. Herein, a novel, nondestructive real‐time in situ monitoring method based on a tapered seven‐core fiber optic sensor is demonstrated. The fiber‐optic sensor can be facilely inserted near the surface of the perovskite layer of a working PSCs to monitor its degradation kinetics without interfering with the performance of the device. Stable and reproducible correlations between real‐time material degradation and optical wavelength response under different humidity and temperature conditions are observed and quantified. This new measurement tool allows real‐time access to the detailed degradation evolution of PSCs, which not only guides the design of more stable devices but also offers the possibility to monitor the health status of PSCs in field applications. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: Formamidinium (FA)‐based Sn‐Pb perovskite solar cells (FAPb0.5Sn0.5I3 PSCs) with ideal bandgap and impressive thermal stability have caught enormous attention recently. However, it still suffers from the challenge of realizing high efficiency due to the surface imperfections of the transport materials and the energy‐level mismatch between functional contacts. Herein, it is demonstrated that the modification on buried interface with alkali metal salts is a viable strategy to alleviate these issues. We systematically investigate the role of three alkali metal bromide salts (NaBr, KBr, CsBr) by burying them between the NiOx hole transport layer (HTL) and the perovskite light‐absorbing layer, which can effectively passivate interface defects, improve energy‐level matching and release the internal residual strain in perovskite layers. The device with CsBr buffer layer exhibits the best power conversion efficiency (PCE) approaching 20%, which is one of the highest efficiencies for FA‐based Sn‐Pb PSCs employing NiOx HTLs. Impressively, the long‐term storage stability of the unencapsulated device is also greatly boosted. Our work provides an efficient strategy to prepare desired FA‐based ideal‐bandgap Sn‐Pb PSCs which could be applied in tandem solar cells. [ABSTRACT FROM AUTHOR]

Organic–inorganic hybrid perovskite solar cells (PSCs) are regarded as a promising next‐generation photovoltaic technology. However, poor device stability limits their commercialization. Carbon‐based inorganic PSCs (C‐IPSCs) can meet stability challenge owing to the absence of organic components. Meanwhile, the hydrophobic carbon materials as hole transport layers and back electrodes simplify fabrication process, decrease costs, and protect devices from moisture erosion. Since the first attempt for C‐IPSCs in 2016, a series of strategies have been proposed to improve device performance, including the fabrication technique optimization, solvent engineering, composition engineering, interface engineering, charge transport layer optimization, and so on, and the power conversion efficiency of C‐IPSCs are rapidly increased from initial 5% to exceeding 15%. In this review, the recent progress of C‐IPSCs is summarized, the existing challenges in this field are discussed, followed by a prospect for future development. [ABSTRACT FROM AUTHOR]

We report a solution-processing method to prepare an inorganic LaNiO3 (LNO) hole-transport layer (HTL) under low temperature (<150 °C) for the first time. The inverted PSCs prepared with LNO exhibit high UV-stability and promising efficiency (17.15%). Our preliminary results show great potential for LNO HTL in the fabrication of efficient and photostable inverted perovskite solar cells (PSCs). [ABSTRACT FROM AUTHOR]

Zinc oxide (ZnO) is an appealing electron transport layer for inorganic perovskite solar cells (IPSCs). However, attempts to achieve high device performance have been undermined by the imperfections at the ZnO/perovskite interface, including the intrinsic defects of ZnO and the nonideal contact between ZnO and perovskite films, which can cause severe interfacial recombination losses. With the purpose of resolving these problems, cesium salts with functional anions of acetate (Ac−), fluoride (F−) and trifluoroacetate (TFA−) are explored to modulate the deposition of ZnO films. It is evidenced that these functional anions can coordinate with both Zn2+ and Pb2+ ions, causing defect passivation of the ZnO and the top perovskite films to different extents. Meanwhile, the Cs+ ions can reduce the hydroxyl defects and form an interfacial dipole on the surface of ZnO via Zn–O–Cs bonds. Therefore, more stable and efficient interfacial electron transport can be established. Accordingly, we obtained a maximum power conversion efficiency (PCE) of 14.25% in low-temperature carbon-based IPSCs (C-IPSCs) using a CsPbI2Br light absorber. This PCE is the highest value among all the ZnO-based C-IPSCs reported to date. Moreover, the corresponding devices without encapsulation demonstrate improved long-term stability in ambient air. [ABSTRACT FROM AUTHOR]

Low band gap tin‐lead perovskite solar cells (Sn−Pb PSCs) are expected to achieve higher efficiencies than Pb‐PSCs and regarded as key components of tandem PSCs. However, the realization of high efficiency is challenged by the instability of Sn2+ and the imperfections at the charge transfer interfaces. Here, we demonstrate an efficient ideal band gap formamidinium (FA)‐based Sn−Pb (FAPb0.5Sn0.5I3) PSC, by manipulating the buried NiOx/perovskite interface with 4‐hydroxyphenethyl ammonium halide (OH‐PEAX, X=Cl−, Br−, or I−) interlayer, which exhibits fascinating functions of reducing the surface defects of the NiOx hole transport layer (HTL), enhancing the perovskite film quality, and improving both the energy level matching and physical contact at the interface. The effects of different halide anions have been elaborated and a 20.53 % efficiency is obtained with OH‐PEABr, which is the highest one for FA‐based Sn−Pb PSCs using NiOx HTLs. Moreover, the device stability is also boosted. [ABSTRACT FROM AUTHOR]

Carbon-based CsPbI2Br perovskite solar cells (PSCs) have attracted widespread attention due to their low cost and superior thermal stability. Unfortunately, the bulk defects and interfacial energy level mismatch limit the improvement of device performance. To solve the above issues, we introduce aromatic phenylethylammonium halides (PEAI and PEABr) and their fluorinated derivatives of 4-fluorophenylethylammonium halides (P-F-PEAI and P-F-PEABr) as a passivation layer to post-treat low-temperature CsPbI2Br films. Benefiting from reduced perovskite defects and better energy level alignments, the charge non-radiative recombination is effectively suppressed, and the hole extraction is promoted. Compared with the reference PSCs, the optimized devices achieve a maximum power conversion efficiency (PCE) of 13.97%. To the best of our knowledge, it should be one of the highest PCEs reported among those of low-temperature carbon-based CsPbI2Br PSCs. In addition, nonencapsulated devices exhibit improved moisture and thermal stability in ambient air. [ABSTRACT FROM AUTHOR]

With the advantages of narrow bandgap and excellent thermal stability, fomamidinium lead triiodide (FAPbI3) perovskite holds the promise to boost the power conversion efficiency (PCE) of perovskite solar cells (PSCs) to over 25%. However, such a promise is blurred by the poor structural stability of the black α‐phase FAPbI3, as it can spontaneously transform into photoinactive δ‐phase at room temperature and this process can be accelerated by the ambient moisture. The incorporation of small ions such as cesium (Cs+), methylammonium (MA), and bromide (Br−) into the perovskite lattice is proven to be successful in stabilizing the α‐phase FAPbI3; however, the resultant mixed perovskites suffer the phase segregation problem, which inevitably undermines the long‐term stability of the corresponding PSCs. Therefore, continuous efforts are made to realize stable and pure‐phase α‐FAPbI3 perovskites. Herein, the recent progress on the development of efficient and stable FAPbI3 PSCs is summarized with a focus on the different phase stabilization strategies. In addition, the challenges and possible directions for future study are proposed. [ABSTRACT FROM AUTHOR]