The stability of CH3NH3PbI3 was investigated by observing the degradation in a coevaporated film irradiated by a blue laser in ultrahigh vacuum. X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were employed to investigate the effects of irradiation on the surface. The core levels of CH3NH3PbI3 were observed to shift toward a higher binding energy (BE) during the irradiation, suggesting that the surface became more n-type. A new metallic Pb component in the XPS spectrum appeared after 120 min of irradiation, indicating that the film had started to decompose. The decomposition saturated after about 480 min of irradiation when the ratio of metallic Pb to total Pb was about 33%. Furthermore, the film was no longer continuous after irradiation, as the elements gold and oxygen from the substrate were detected by XPS. SEM images also show a roughened surface after irradiation. The results strongly indicate that CH3NH3PbI3 is sensitive to the laser irradiation and that the light induced decomposition is a self-limiting process.

We demonstrate the ability of the highly fluorinated, chemically inert copolymer poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) to significantly increase the work function of a variety of common electrode materials. The work function change is hypothesized to occur via physisorption of the polymer layer and formation of a surface dipole at the polymer/conductor interface. When incorporated into organic solar cells, an interlayer of PVDF-HFP at an Ag anode increases the open circuit voltage by 0.4 eV and improves device power conversion efficiency by approximately an order of magnitude relative to Ag alone. Solution-processable in air, PVDF-HFP thin films provide one possible route toward achieving low cost, nonreactive, high work function electrodes.

Angle-resolved photoemission spectroscopy (ARPES) is a vital technique, collecting data from both the energy and momentum of photoemitted electrons, and is indispensable for investigating the electronic band structure of solids. This article provides a review on ARPES studies of the electronic band structure of organic single crystals, including organic charge transfer conductors; organic semiconductors; and organo-metallic perovskites. In organic conductors and semiconductors, band dispersions are observed that are highly anisotropic. The Van der Waals crystal nature, the weak electron wavefunction overlap, as well as the strong electron-phonon coupling result in many organic crystals having indiscernible dispersion. In comparison, organo-metallic perovskite halides are characterized by strong s-p orbitals from the metal and halide at the top of the valence bands, with dispersions similar to those in inorganic materials.

No abstract

No abstract