Resonant charge transfer during the backscattering of 3.0 keV Li+ from hydrogen- and iodine-covered Ni(100) is probed with time-of-flight spectroscopy. Hydrogen adsorption on Ni(100) induces only a small increase of the surface work function and the neutralization probabilities for backscattered Li are not significantly affected. Iodine adsorbs with some net negative charge, so that a dipole directed into the surface is expected. Such a dipole would increase the work function thereby decreasing the neutralization probability. iodine adsorption decreases the work function of Ni(100), however, and the neutralization probabilities for Li scattered from the iodine sites are always larger than for scattering from nickel sites. These results suggest that the local charge density associated with adsorbed iodine is not uniform. (C) 2003 American Vacuum Society.

Inorganic lead halide perovskite solar cells have emerged as a promising photovoltaic technology with their immense potential to consistently deliver high power output. This has been attributed to the unique electronic and optical properties of the perovskite and the carrier transport films. As a result, these devices possess power conversion efficiencies that vigorously compete with those of standard silicon solar cells. However, certain challenges prevent the commercialization of this technology. Existing methodologies for fabricating the carrier transport layers result in films with high defect densities that affect the device’s performance. In this work, we report the fabrication of the electron-selective layers for highly efficient perovskite solar cells via chemical bath deposition and sputter deposition. Improved process controls over the chemical bath deposition technique yielded highly efficient devices with a champion power conversion efficiency of 23.8%.

Time-of-flight spectra were collected for 2.5 keV Li-7(+) backscattered from Fe surfaces covered with submonolayers of iodine. Li singly scattered from the adatoms has a consistently larger neutral fraction than for scattering from the substrate, implying a region of positive charge atop the iodine. The neutral fraction decreases for off-normal exit angles, indicating a nonuniform charge distribution around the polarizable adsorbates. This demonstrates that ion scattering can image the internal electronic structure of an adatom and provides an explanation for anomalous work function changes.

The neutralization of 400-3000 eV Li-7(+) ions scattered from clean and adsorbate-covered Fe(110) and Fe(100) surfaces was measured with time-of-flight spectroscopy. Li singly scattered from bromine, iodine, and cesium adatoms has a consistently larger neutral fraction than that for scattered from substrate sites. This suggests that the local electrostatic potential directly above these adatoms is reduced from that of the clean substrate. The neutral fraction of Li scattered from halogen adatoms is surprising in that it decreases as the emission angle moves off-normal, yet increases in the usual manner for cesium and silver adatoms. This indicates that the charge distribution associated with a halogen adsorbate is nonuniform, most likely due to internal polarization. A semiquantitative theoretical analysis shows that a nonuniform internal electron density would give rise to the observed behavior. The polarization of halogen adatoms is likely responsible for anomalous work function changes observed previously. Alkali-ion scattering is shown to be an effective tool for detecting the internal electronic structure of an adatom.