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.

The implementation of efficient hole blocking layers (BLs) is of vital importance to achieve high efficiency in solar cells using organolead trihalide materials as the solar light absorber. BLs permit electronic charge separation and avoid the recombination of charges by blocking the hole transfer to the anode. In this study, BLs have been prepared by aerosol spray pyrolysis and spin-coating using various solution compositions. The morphological, optical, microstructural and crystalline properties as well as the phase composition of these layers have been characterized by scanning electron microscopy, Raman spectroscopy, and optical measurements. Their blocking ability has been evaluated by cyclic voltammetry. A strong relationship has been found between these properties and the solar cell J–V characteristics and performances. Overall, we figured out that the sprayed BLs were thin, highly compact, covering, and conformal. No cracks or pinholes were found because the precursor underwent degradation and condensation directly at high temperature. They were made of the pure anatase phase and were perfectly blocking. They produced high-efficiency perovskite solar cells. The BL has also an influence on the impedance spectroscopy response of the cells over the whole frequency range from several hundreds of Hz to some tens of mHz. We have found that the inductive loop if present for all the cells was more pronounced and observed over a larger potential range in the case of the most poorly working devices with inaccurate BLs. An equivalent electrical circuit is proposed to fit the full spectra. The various electrical parameters of the circuit have been compared for the various BLs and thoroughly analyzed. Influences of the BL on the internal resistance, recombinations, interfacial traps, and the inductive response are detailed.

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...

To develop novel hole-transporting materials (HTMs) is an important issue of perovskite solar cells (PSCs), especially favoring the stability improvement and the cost reduction. Herein, we use ternary quantum dots (QDs) as HTM in mesoporous TiO2/CH3NH3PbI3/HTM/Au solar cell, and modify the surface of CuInS2 QDs by cation exchange to improve the carrier transport. The device efficiency using CuInS2 QDs with a ZnS shell layer as HTM is 8.38% under AM 1.5, 100 mW cm(-2). The electrochemical impedance spectroscopy suggested that the significantly enhanced performance is mainly attributed to the reduced charge recombination between TiO2 and HTM. It paves a new pathway for the future development of cheap inorganic HTMs for the high efficiency PSCs.

One of the limitations of TiO2 based perovskite solar cells is the poor electron mobility of TiO2. Here, perovskite oxide BaSnO3 is used as a replacement. It has a higher electron mobility and the same perovskite structure as the light harvesting materials. After optimization, devices based on BaSnO3 showed the best performance of 12.3% vs. 11.1% for TiO2.

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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.