Mechanistic Insights from Functional Group Exchange Surface Passivation: A Combined Theoretical and Experimental Study

Four different functional groups including amino (−NH2), phosphine (−PH2), hydroxyl (−OH), and thiol (−SH) were combined with POSS (polyhedral oligomeric silsesquioxane) molecules to investigate how functional groups affect the surface passivation of POSS systems. Results from density-functional theory (DFT) calculations indicate that functional group amino (−NH2) with adsorption energy 86 (56) kJ mol–1 is consistently better than that of thiol (−SH) with adsorption energy 68 (43) kJ mol–1 for different passivation mechanisms. Theoretical studies on the analogous POSS–OH and POSS–PH2 systems show similar adsorption energies. Two of the systems were also investigated experimentally; aminopropyl isobutyl POSS (POSS–NH2) and mercaptopropyl isobutyl POSS (POSS–SH) were applied as passivation materials for MAPbI3 (MA = methylammonium) perovskite and (FA)0.85(MA)0.15Pb­(I3)0.85(Br3)0.15 (FA = formamidinium) perovskite films. The same conclusion was drawn based on the results from contact angle studies, X-ray diffraction (XRD), and the stability of solar cells in ambient atmosphere, indicating the vital importance of choice of functional groups for passivation of the perovskite materials