Energetics of Solvent-Based Deposition of Fullerene Derivative on the Inorganic-Organic Hybrid Lead Halide Perovskite Surface
MFN Taufique and S Choudhury and S Banerjee, JOURNAL OF PHYSICAL CHEMISTRY C, 123, 22368-22376 (2019).
The elementary processes that govern particle deposition on substrates during solution processing of thin films are not well understood due to the complex interactions between solute-solvent, solute-substrate, and solvent-substrate. This study presents a fundamental step-by-step systematic analysis of the deposition of a rather complex molecule, the 6,6-phenyl-C61-butyric acid methyl ester (PCBM), with seemingly infinite orientational configurations, on the (110) surface of methylammonium lead iodide (CH3NH3PbI3) perovskite in a solvated environment. We employed the adaptive biasing force (ABF) method in conjunction with classical molecular dynamics (MD) simulations to determine the potential of mean force (PMF) and corresponding configurations of deposited PCBM in the presence of chlorobenzene (CB) and vacuum. Our calculations underscore the impact of solvent on the energetics of deposition and the resulting configurations of deposited PCBM. In the presence of solvent, the most energetically favorable configuration occurs when the carbonyl oxygen (CO) of PCBM is attached with a Pb atom of perovskite surface with the fullerene (C60) pointing away from the surface. The corresponding binding energy between PCBM and perovskite is 12.9 kcal/mol at 325 K and increases with increasing temperature. In contrast, in a vacuum, the most energetically favorable configuration occurs when both C60 moiety and the CO atom of PCBM are associated with the perovskite surface resulting in a stronger binding energy of 23.6 kcal/mol due to the absence of solvent screening. We investigated the different energetic contributions that govern the overall deposition process. In solvated systems, the deposited configurations are stabilized primarily by entropic contribution due to loss of solvent structure around both perovskite surface and PCBM during deposition.
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