First-principles study of the polar O-terminated ZnO surface in thermodynamic equilibrium with oxygen and hydrogen

Using density-functional theory in combination with a thermodynamic formalism we calculate the relative stability of various structural models of the polar O-terminated (000-1)-O surface of ZnO. Model surfaces with different concentrations of oxygen vacancies and hydrogen adatoms are considered. Assuming that the surfaces are in thermodynamic equilibrium with an O2 and H2 gas phase we determine a phase diagram of the lowest-energy surface structures. For a wide range of temperatures and pressures we find that hydrogen will be adsorbed at the surface, preferentially with a coverage of 1/2 monolayer. At high temperatures and low pressures the hydrogen can be removed and a structure with 1/4 of the surface oxygen atoms missing becomes the most stable one. The clean, defect-free surface can only exist in an oxygen-rich environment with a very low hydrogen partial pressure. However, since we find that the dissociative adsorption of molecular hydrogen and water (if also the Zn-terminated surface is present) is energetically very preferable, it is very unlikely that a clean, defect-free (000-1)-O surface can be observed in experiment.Comment: 10 pages, 4 postscript figures. Uses REVTEX and epsf macro

OVPD

The precise control of organic thin film processing by organic vapor phase deposition (OVPD®) is presented and analyzed on device level. OVPD® offers accurate and individual control of deposition layer properties like mixing of several materials (co-deposition) and the control of various morphologies by a wide process parameter space given by, e.g. substrate temperature, deposition rate and pressure. The benefit of precise co-deposition is demonstrated by an OLED with a sensitive twofold-doped emissive layer and revealed a doping level of 0.26% for the red dopant with a std. dev. of 0.38%. The effect of the various morphologies is investigated by optimizing the efficiency of molecular organic solar cells consisting of copper phthalocyanine (CuPc) and C60. With defined process parameters efficiencies of up to 3.0% were demonstrated

OVPD circledR technology

The precise control of organic thin film processing by organic vapor phase deposition OVPD is presented and analyzed on device level. OVPD offers accurate and individual control of deposition layer properties like mixing of several materials co deposition and the control of various morphologies by a wide process parameter space given by, e.g. substrate temperature, deposition rate and pressure. The benefit of precise co deposition is demonstrated by an OLED with a sensitive twofold doped emissive layer and revealed a doping level of 0.26 for the red dopant with a std. dev. of 0.38 . The effect of the various morphologies is investigated by optimizing the efficiency of molecular organic solar cells consisting of copper phthalocyanine CuPc and C60. With defined process parameters efficiencies of up to 3.0 were demonstrate