Ionic Liquid as an Additive for Two-Step Sequential Deposition for Air-Processed Efficient and Stable Carbon-Based CsPbI2Br All-Inorganic Perovskite Solar Cells

All-inorganic lead halide perovskite CsPbI2Br is a promising candidate in the photovoltaic field due to its improved thermal stability and suitable band gap. However, the perovskite phase of CsPbI2Br is not stable under an ambient atmosphere because of its water vapor-induced phase transition. Most of the CsPbI2Br perovskite solar cells are manufactured in gloveboxes to avoid the negative effect of water vapor, which would considerably increase the cost of large-scale manufacturing. Herein, we describe a methylamine acetate (MAAc) additive strategy for two-step sequential deposition, which allows for air-processed formation of the CsPbI2Br film. MAAc is used to improve the crystallization of CsPbI2Br in the two-step deposition process. X-ray diffraction patterns reveal the formation of the intermediate phase of MA2Pb3X8 (X = I and Br) during the preparation. In addition, ethylene glycol is added to the cesium halide solution to further increase the uniformity of the CsPbI2Br film. The carbon-based CsPbI2Br planar perovskite solar cells prepared under an ambient atmosphere with a relative humidity of 15% could achieve a champion efficiency of 11.2% and retain 79.3% of their initial efficiency value after aging in an ambient atmosphere with 15% relative humidity at room temperature for 360 h.