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.

Delocalized singlet biradical hydrocarbons hold promise as new semiconducting materials for high‐performance organic devices. However, to date biradical organic molecules have attracted little attention as a material for organic electronic devices. Here, this work shows that films of a crystallized diphenyl derivative of s‐indacenodiphenalene (Ph2‐IDPL) exhibit high ambipolar mobilities in organic field‐effect transistors (OFETs). Furthermore, OFETs fabricated using Ph2‐IDPL single crystals show high hole mobility (μh = 7.2 × 10−1 cm2 V−1 s−1) comparable to that of amorphous Si. Additionally, high on/off ratios are achieved for Ph2‐IDPL by inserting self‐assembled mono­layer of alkanethiol between the semiconducting layer and the Au electrodes. These findings open a door to the application of ambipolar OFETs to organic electronics such as complementary metal oxide semiconductor logic circuits.

We investigated the structural and electronic properties of vacuum sublimed 7,8,15,16-tetraazaterrylene (TAT) thin films on Au(111), Ag(111), and Cu(111) substrates using inverse photoemission spectroscopy, ultraviolet photoelectron spectroscopy (UPS), x-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED), and the x-ray standing wave (XSW) technique. The LEED reveals a flat adsorption geometry of the monolayer TAT on these three substrates, which is in accordance with the XSW results. The molecules are slightly distorted in monolayers on all three substrates with the nitrogen atoms having smaller averaged bonding distances than the carbon atoms. On Ag(111) and Cu(111), chemisorption with a net electron transfer from the substrate to the adsorbate takes place, as evidenced by UPS and XPS. Combining these results, we gain full insight into the correlation between electronic properties and interface geometry.

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.