No abstract

No abstract

efficiency enhancement is achieved by the compositional engineering of perovskite crystal of ABX 3 , where A, B, and X indicate the monovalent cation such as foramidinium (FA + ) and methylammonium (MA + ), the divalent cation such as Pb 2+ , and halide ion, respectively. [5][6][7][8] Saliba and co-workers have discovered that quadruple (Rb/Cs/MA/FA) cation-based perovskite materials with the "cation cascade" formulated by embedding the small and oxidation-stable rubidium cation (Rb + ) can have excellent material properties.Solution-processed 3D perovskite films typically contain defects such as grain boundaries, undercoordinated Pb 2+ , or halide vacancies. [9][10][11][12][13][14] These defect sites can facilitate the nonradiative carrier recombination at the interface and bulk. [15][16][17][18][19] Among the many defect passivation techniques, dimensional engineering of perovskite films has drawn significant interest. [20][21][22][23][24][25][26][27] The introduction of large organic cations such as alkylammonium into the A-site of the ABX 3 perovskite can convert a 3D perovskite crystal structure into a 2D or quasi-2D layer. A number of studies have reported beneficial effects of interfacial treatment with alkylammonium halide (OAX) on 3D perovskite surface, which can form 2D-3D-layered structure. Seok and co-workers investigated different chain lengths of alkylammonium with perovskite [composition: (FAPbI 3 ) 0.95 (MAPbBr 3 ) 0.05 ] Air fabrication of efficient and stable perovskite solar cells with substantial reproducibility is of importance for commercialization of perovskite solar cells.There has been little consensus on which halide is the best selection for thin 2D perovskite layer on 3D perovskite when processing in ambient air. In this work, the influence of humidity and halide ions in alkylammonium halide (OAX)-treated perovskite layer on photovoltaic performance is investigated. The authors find that a combination of high humidity and the presence of chloride ions can induce the deprotonation of methylammonium (MA + ) ions. With X-ray diffraction, cross-sectional scanning electron microscope, Fourier-transform infrared spectroscopy, the authors elucidate that the deprotonation reaction in the octylammonium chloride (OACl)-treated perovskite layer makes MA + ions (CH 3 NH 3 +) volatile MA (CH 3 NH 2 ), which results in void volumes and defects in the bulk of perovskite layer as well as at the interface. The defective perovskite solar cells induced by the deprotonation reaction have the suppressed hole transfer at the interface between the perovskite layer and the hole transport layer, yielding the reduced internal quantum efficiency and J SC . Space chargelimited current analysis reveals that the reduced V OC is caused by the high trap density estimated from V TFL of hole-only devices.