Hydrophilicity and Water Contact Angle on Methylammonium Lead Iodide

Abstract

and by relating its value to the liquidsurface adhesion: the larger the adhesion, the smaller the contact angle. [1] Contact angle measurements have become accordingly a powerful yet cheap technique to quantify the water interaction with solid surfaces, a problem of huge technological importance in fluid dynamics, [2] aerospace engineering, [3] biology, [4] surface chemistry, [5] textile, [6] and materials science. [7] In photovoltaics, the interaction of water with surfaces is of great importance for example for organic and hybrid solar cells that are sensitive to humid conditions. This is the case of methylammonium lead iodide (CH 3 NH 3 PbI 3 or MAPI) which is at the core of the nowadays most efficient hybrid-based solar technology (with 23% maximum power conversion efficiencies [8][9][10][11] ) and which has potential applications also in the fields of optoelectronics, [12,13] lasing, [14][15][16][17][18] photocatalysis, [19] and thermoelectricity. [20][21][22] The interaction of MAPI with water is a major concern for such technology as it drives degradation in humid air and full decomposition in liquid water. [23][24][25] Accordingly, there is an increasing number of research items focusing on increasing the hydrophobicity of MAPI via, e.g., surface functionalization. In this context, contact angle measurements have been performed on pristine and hydrophobized films to assess their wettability. [26][27][28] Measurements of the contact angle of water on hybrid perovskites and, more in general, on soluble or transforming surfaces is challenging. If the substrate degrades, several nonequilibrium phenomena must be taken into account such as the solubilization and phase transformations of the solid. This led to ambiguous results on MAPI, with a contact angle that strongly depends on the time of measurement, [26][27][28] calling for a detailed microscopic investigation at the origin of the variability of the measured CA.Here, we combine molecular dynamics (MD) simulations with millisecond contact angle-measurements. We show that finite temperature MD simulations can reproduce experimental contact angles of water in a good agreement with the Young-Dupré (YD) continuum relation between liquid-solid adhesion and contact angle, and we explain the high CA value measured for water on MAPI as the result of the interaction of water with degraded superficial layers at the water/perovskite interface.Surface properties are often assessed with measurements of the contact angle of a water drop. The process is however flawed for the very important class of hybrid perovskite materials, extensively employed in solar cells and optoelectronics research, because they are water soluble and their surface degrades during contact angle measurements. While hybrid perovskites are considered to be highly hydrophilic, a contact angle with water of 83° can be measured, as if they were almost hydrophobic. By combining experiments and simulations, the actual value is explained as the result of the interaction of water with degraded superficial...

Defect Dynamics in MAPbI3 Polycrystalline Films: The Trapping Effect of Grain Boundaries

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N‐methyl‐2‐pyrrolidone Iodide as Functional Precursor Additive for Record Efficiency 2D Ruddlesden‐Popper (PEA)2(Cs)n−1PbnI3n+1 Solar Cells

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Morphology and surface analyses for CH3NH3PbI3perovskite thin films treated with versatile solvent–antisolvent vapors

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