Effect of physisorption of inert organic molecules on Au(111) surface electronic states.

The modification of the Au(111) Shockley surface state (SS) by an n-alkane molecule (n-tetratetracontane) monolayer was observed by angle-resolved ultraviolet photoemission spectroscopy. Although there is little chance of chemical interaction in this ideal physisorption system, the volume of the Fermi surface of the SS was significantly reduced accompanied by the formation of large interface electric dipoles. Moreover, Rashba splitting of the SS by spin-orbit interactions was slightly increased upon n-tetratetracontane adsorption, which arose from the decrease in the symmetry of the wave function around the Au nuclei at the surface. The detailed information about the simple physisorption system presented in this paper provides basic knowledge for understanding the electronic structure at the interface between other organic molecules and metal substrates.

Halide-Substituted Electronic Properties of Organometal Halide Perovskite Films: Direct and Inverse Photoemission Studies.

Solution-processed perovskite solar cells are attracting increasing interest due to their potential in next-generation hybrid photovoltaic devices. Despite the morphological control over the perovskite films, quantitative information on electronic structures and interface energetics is of paramount importance to the optimal photovoltaic performance. Here, direct and inverse photoemission spectroscopies are used to determine the electronic structures and chemical compositions of various methylammonium lead halide perovskite films (MAPbX3, X = Cl, Br, and I), revealing the strong influence of halide substitution on the electronic properties of perovskite films. Precise control over halide compositions in MAPbX3 films causes the manipulation of the electronic properties, with a qualitatively blue shift along the I → Br → Cl series and showing the increase in ionization potentials from 5.96 to 7.04 eV and the change of transport band gaps in the range from 1.70 to 3.09 eV. The resulting light absorption of MAPbX3 films can cover the entire visible region from 420 to 800 nm. The results presented here provide a quantitative guide for the analysis of perovskite-based solar cell performance and the selection of optimal carrier-extraction materials for photogenerated electrons and holes.