Youzhen Li

Degradation by Exposure of Coevaporated CH3NH3PbI3 Thin Films

Degradation of co-evaporated CH3NH3PbI3 thin films was investigated with x-ray photoelectron spectroscopy (XPS) and x-ray diffraction (XRD) as the films were subjected to exposure of oxygen, dry air, ambient, or H2O. The co-evaporated thin films have consistent stoichiometry and crystallinity suitable for detailed surface analysis. The results indicate that CH3NH3PbI3 is not sensitive to oxygen. Even after 10^13 Langmuire (L, one L equals 10^-6 torr sec) oxygen exposure, no O atoms could be found on the surface. The film is not sensitive to dry air as well. A reaction threshold of about 2*10^10 L is found for H2O exposure, below which no CH3NH3PbI3 degradation takes place and the H2O acts as an n-dopant. Above the threshold, the film begins to decompose, and the amount of N and I decrease quickly, leaving the surface with PbI2, amorphous C and O contamination.

Molecular orientation of copper phthalocyanine thin films on different monolayers of fullerene on SiO2 or highly oriented pyrolytic graphite

The interface electronic structures of copper phthalocyanine (CuPc) have been studied using ultraviolet photoemission spectroscopy as different monolayers of C60 were inserted between CuPc and a SiO2 or highly ordered pyrolytic graphite (HOPG) substrate. The results show that CuPc has standing up configuration with one monolayer of C60 insertion on SiO2 while lying down on HOPG, indicating that the insertion layer propagates the CuPc-substrate interaction. Meanwhile, CuPc on more than one monolayers of C60 on different substrates show that the substrate orientation effect quickly vanished. Our study elucidates intriguing molecular interactions that manipulate molecular orientation and donor-acceptor energy level alignment.

Investigation on thermal evaporated CH{sub 3}NH{sub 3}PbI{sub 3} thin films

CH3NH3I, PbI2 and CH3NH3PbI3 films were fabricated by evaporation and characterized with X-ray Photoelectron Spectroscopy (XPS) and X-ray diffraction (XRD). The XPS results indicate that the PbI2 and CH3NH3PbI3 films are more uniform and stable than the CH3NH3I film. The atomic ratio of the CH3NH3I, PbI2 and CH3NH3PbI3 films are C:N:I=1.00:1.01:0.70, Pb:I= 1.00:1.91 and C: N: Pb: I = 1.29:1.07:1.00:2.94, respectively. The atomic ratio of CH3NH3PbI3 is very close to that of the ideal perovskite. Small angle x-ray diffraction results demonstrate that the as evaporated CH3NH3PbI3 film is crystalline. The valence band maximum (VBM) and work function (WF) of the CH3NH3PbI3 film are about 0.85eV and 4.86eV, respectively.

Investigation on thermal evaporated CH 3 NH 3 PbI 3 thin films

CH3NH3I, PbI2 and CH3NH3PbI3 films were fabricated by evaporation and characterized with X-ray Photoelectron Spectroscopy (XPS) and X-ray diffraction (XRD). The XPS results indicate that the PbI2 and CH3NH3PbI3 films are more uniform and stable than the CH3NH3I film. The atomic ratio of the CH3NH3I, PbI2 and CH3NH3PbI3 films are C:N:I=1.00:1.01:0.70, Pb:I= 1.00:1.91 and C: N: Pb: I = 1.29:1.07:1.00:2.94, respectively. The atomic ratio of CH3NH3PbI3 is very close to that of the ideal perovskite. Small angle x-ray diffraction results demonstrate that the as evaporated CH3NH3PbI3 film is crystalline. The valence band maximum (VBM) and work function (WF) of the CH3NH3PbI3 film are about 0.85eV and 4.86eV, respectively.