Importance of Low Humidity and Selection of Halide Ions of Octylammonium Halide in 2D–3D Perovskite Solar Cells Fabricated in Air

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.

Improving the performance and stability of perovskite solar cells via surface passivation of phthalimide N-alkylammonium iodides

“…We calculated the internal quantum efficiency (IQE) of both the control and the target devices based on the measured reflectance and EQE data. 54 The reduced J SC of the control device as compared with the target device can primarily be attributed to the reduced IQEs shown in Fig. S9 (ESI†), which indicate inefficient charge transport in the control device.…”

Sn-Doped Zinc Oxide as an Electron Transporting Layer for Enhanced Performance in PbS Quantum Dot Solar Cells

“…Interestingly, Table also reveals that the relative portion of the hydroxyl group increases with Sn doping. The hydroxyl group on the surface of an ETL is typically known to be detrimental in the research field of hybrid perovskite solar cells, because the hydroxyl group act as Bro̷nsted base and induces the deprotonation reaction of organic ammonium cations such as methylammonium (MA + ), and hence leads to defects formation in the perovskite films. − However, the surface hydroyl group on the ZnO ETL in PbS QDSCs does not harm the photovoltaic performance. This is supported by the recent study of H. T. Dastjerdi et al for PbS QDSCs with H-plasma-treated ZnO nanowires .…”

An efficient approach for controlling the crystallization, strain, and defects of the perovskite film in hybrid perovskite solar cells through antisolvent engineering

“…The article by S. Y. Kwon et al describes the application of OABr, OAI, and OACl on the perovskite surface under regulated humidity conditions. 36 The authors found that the application of octylammonium salts had a small positive effect on the device performance, and at high humidity, the Cl − ions can cause serious damage to the device. It is noteworthy that all these studies feature the application of alkylammonium halide salts as a surface treatment of perovskite surface only in normal PSCs.…”