A Scalable Methylamine Gas Healing Strategy for High‐Efficiency Inorganic Perovskite Solar Cells

Abstract

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...

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