Conventional wisdom is that the MAI and FAI are stable in the solution, but actually they are not. We demonstrated that the MAI first deprotonated to form methylamine (MA), and then MA reacted with FAI to form two condensation products N-methyl FAI and N, N 0 -dimethyl FAI. Moreover, triethyl borate was introduced to stabilize the perovskite precursor solution, which significantly reduced the impure phase in the perovskite film and enhanced the device performance and reproducibility.

Inorganic CsPbI 3 is promising to enhance the thermal stability of perovskite solar cells. The dimethylamine iodide (DMAI) derived method is currently the most efficient way to achieve high efficiency, but the effect of DMAI has not been fully explained. Herein, the chemical composition and phase evolution of the mixed DMAI/CsPbI 3 layer during thermal treatment has been studied. The results demonstrate that, with the common DMAI/CsI/PbI 2 recipe in DMSO solvent, a mixed perovskite DMA 0.15 Cs 0.85 PbI 3 is first formed through a solid reaction between DMAPbI 3 and Cs 4 PbI 6 . Further thermal treatment will transform the mixed perovskite phase directly to γ-CsPbI 3 and then spontaneously convert to δ-CsPbI 3 . It has been also demonstrated that the DMA 0.15 Cs 0.85 PbI 3 phase is thermodynamically stable and shows a bandgap of 1.67 eV, which is narrower than 1.73 eV of γ-CsPbI 3 . The device efficiency of the mixed DMA 0.15 Cs 0.85 PbI 3 perovskite is therefore highly improved in comparison with the pure inorganic γ-CsPbI 3 perovskite.

An easy and scalable methylamine (MA) gas healing method was realized for inorganic cesium-based perovskite (CsPbX 3 )l ayers by incorporating ac ertain amount of MAX (X = IorBr) initiators into the raw film. It was found that the excess MAX accelerated the absorption of the MA gas into the CsPbX 3 film and quickly turned it into al iquid intermediate phase.T hrough the healing process,ahighly uniform and highly crystalline CsPbX 3 film with enhanced photovoltaic performance was obtained. Moreover,t he chemical interactions between as eries of halides and MA gas molecules were studied, and the results could offer guidance in further optimizations of the healing strategy.Inthe past decade,organic-inorganic lead halide perovskite solar cells (PSCs) have witnessed rapid development. [1] The power conversion efficiency(PCE) of PSCs has been rapidly increased to up to 23.7 %. [2] Not only small-area laboratory devices,but also modules with up to 277 cm 2 in size have been reported with high PCEs of more than 17 %. [3] Currently,the stability of these organic-inorganic hybrid perovskite materials is considered to be the biggest challenge for their future commercial utilization. [4] One promising direction to address this issue is to replace the organic cations with inorganic cations such as Cs + to form all-inorganic perovskite materials. [5] All-inorganic perovskite materials CsPbX 3 (X = I, Br) have aband gap ranging from 1.72 eV for CsPbI 3 to 2.3 eV for CsPbBr 3 . [6] Among them, the cesium/lead mixed-halide perovskite CsPbI 2 Br has attracted greatest attention because it provides the best balance between band gap and phase stability. [7] Thes calable preparation of inorganic PSCs is undoubtedly another urgent issue.Although many methods have been developed for organic-inorganic perovskite films,barely any of them can be directly translated to the preparation of allinorganic perovskite layers. [8] Fori nstance,t he use of hydriodic acid (HI) additive in the precursor solution was confirmed to enable the formation of the hybrid mixed-cation perovskite phase Cs x DMA 1Àx PbI 3 but not that of the inorganic CsPbX 3 . [9] To obtain high-quality perovskite films,there are two general approaches:1 )Controlling the film crystallization and growth process during film deposition;a nd 2) introducing an additional post-treatment process to improve the film quality.Foro rganic-inorganic perovskite films,t he methylamine (MA) gas healing method has been widely studied in the past three years and has exhibited great compatibility with commercial film-making equipment. [10] Thef ormation of al iquid intermediate phase (normally MAPbI 3 ·x MA) plays acritical role in the MA gas healing process. [10a-c,11] We found that, quite differently,the previously used MA molecules can hardly break the ···Cs À X À Pb··· chemical bonds in the inorganic CsPbX 3 perovskite phase to form al iquid intermediate phase.T os olve this problem, herein, an excess of am ethylammonium halide (MAX) was introduced to the CsPbX 3 initial films to form mix...

Organic–inorganic hybrid perovskites (OIHPs) are one of the hottest fields on account of their immense potential for photovoltaics. As one of the most promising OIHPs, formamidinium (FA)‐based perovskites have been developed very fast in the past few years. The power conversion efficiency (PCE) has reached certified 24.2%, which is comparable with that of monocrystalline silicon solar cells. However, the easy formation of nonperovskite δ‐phase formamidinium lead triiodide (FAPbI3) at a low temperature needs to be solved when fabricating a high‐quality light absorber layer. Several strategies have been used to avoid the formation of δ‐phase FAPbI3 and improve phase stability in recent years such as tolerance factor adjustment, dimensional engineering, addictive processing, interfacial modification, defects passivation, and in situ growth. These approaches can enhance the phase stability to some extent; however, their contribution to long‐term stability and especially their real mechanism is still unknown. Herein, the relationships among the tolerance factors, the structure of FAPbI3, and the phase transition phenomenon are summarized. In addition, various methodologies and potential mechanisms for stabilizing α‐phase FAPbI3 at room temperature (RT) are discussed. In conclusion, a series of challenges in the popular processings of perovskite solar cells and their corresponding solutions that help achieve commercialization faster are summarized.

Interface engineering is of great concern in photovoltaic devices. For the solution‐processed perovskite solar cells, the modification of the bottom surface of the perovskite layer is a challenge due to solvent incompatibility. Herein, a Cl‐containing tin‐based electron transport layer; SnOx‐Cl, is designed to realize an in situ, spontaneous ion‐exchange reaction at the interface of SnOx‐Cl/MAPbI3. The interfacial ion rearrangement not only effectively passivates the physical contact defects, but, at the same time, the diffusion of Cl ions in the perovskite film also causes longitudinal grain growth and further reduces the grain boundary density. As a result, an efficiency of 20.32% is achieved with an extremely high open‐circuit voltage of 1.19 V. This versatile design of the underlying carrier transport layer provides a new way to improve the performance of perovskite solar cells and other optoelectronic devices.

We report the new measurement of initial current pulses in rocket‐triggered lightning with a broadband magnetic sensor at 78 m distance. The high sensitivity of our sensor makes it possible to detect weak ripple deflections (as low as 0.4 A) that are not readily resolved in the typical measurements of channel‐base current in rocket‐triggered lightning experiments. The discernible magnetic pulses within 1 ms after the inception of a sustained upward positive leader from the triggering wire can be classified into impulsive pulses and ripple pulses according to the discernibility of separation between individual pulses. The time scale (usually >20 µs) of ripple pulses is substantially longer than the leading impulsive pulses (with time scales typically <10 µs), and the amplitude is significantly reduced, whereas there is no considerable difference in the interpulse pulse. Along with our previous finding on the burst of magnetic pulses during the initial continuous current in rocket‐triggered lightning, the new measurements suggest that the stepwise propagation might be a persistent feature for the upward positive leader in rocket‐triggered lightning, and the stepping of positive leader early in triggered lightning could be characterized with the observation of ripple pulses. The precedence of impulsive magnetic pulse measured at 78 m range relative to the arrival of corresponding current pulse at the channel base indicates that the ionization wave launched by individual stepping of positive leader propagates downward along the triggering wire at a mean velocity of 1.23 × 108 m/s to 2.25 × 108 m/s.

With the measurements in SHandong Triggering Lightning Experiment and GuangdongComprehensive Observation Experiment on Lightning Discharge in China, we examine the electromagnetic signals associated with the upward positive leaders during the initial stage of negative triggered lightning. The magnetic field (B field) signals measured at close range (<100 m) for both sites can be divided into two categories (i.e., impulsive and ripple pulses) according to the discernibility of separation between individual pulses. The impulsive pulses are well simulated by using the transmission line model, which suggests that these pulses are generated by leader current pulses propagating downward along the steel wire. Because the length of extended leader channel ahead of the wire is not negligible during the stage of ripple pulses, the waveform of impulsive current pulses is changed after traveling through the high impedance leader channel. Taking the filtered current pulse as the input variable, the waveform of ripple pulse can be simulated properly, which indicates that ripple pulses are caused by the attenuation of impulsive current along prolonging leader channel. In addition, the paper analyzes the fast electric field (E field) changes measured at 60-m range from the launching site during the initial stage by using the transmission line model and shows that the polarity of E field change at a given range is determined by the inception height of upward leader, namely the surface E field change caused by the individual charge transfer of initial upward leader also involves the problem of reverse distance as present for a vertical dipole. Plain Language SummaryLightning can occur at a predictable time and place by using the technique of rocket-triggered lightning, which launches a small rocket trailing a grounded steel wire toward the charged thundercloud overhead. Therefore, the technique facilitates the research of lightning discharges and their electromagnetic effects. At the beginning of triggered lightning, a sustained train of current pulses can be measured at the base of discharge path, and the synchronous electromagnetic field signals can also be recorded by the electric and magnetic sensors deployed around the rocket launching site. The paper focuses on the characteristics of electromagnetic signals measured at close range (<100 m) during the SHandong Triggering Lightning Experiment and Guangdong Comprehensive Observation Experiment on Lightning Discharge (two experimental sites of triggered lightning in China) campaign. The main contributions of this article include two aspects: first, we clarify the relationship between the electromagnetic signals and current pulses during the initial stage of triggered lightning; second, we demonstrate the influences of the triggering height on the polarity of electric field waveform.

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