Prevention of electron field emission from molybdenum substrates for photocathodes by the native oxide layer

Comprehensive investigations of the electron field emission (FE) properties of annealed single crystal and polycrystalline molybdenum plugs, which are used as substrates for actual alkali-based photocathodes were performed with a FE scanning microscope. Well-polished and dry-ice cleaned Mo samples with native oxide did not show parasitic FE up to a field level of 50 MV/m required for photoinjector cavities. In situ heat treatments (HT) above 400°C, which are usual before photocathode deposition, activated field emission at lower field strength. Oxygen loading into the Mo surface, however, partially weakened these emitters. X-ray photoelectron spectroscopy of comparable Mo samples showed the dissolution of the native oxide during such heat treatments. These results reveal the suppression of field emission by native Mo oxides. Possible improvements for the photocathode preparation will be discussed

Prevention of electron field emission from molybdenum substrates for photocathodes by the native oxide layer

Comprehensive investigations of the electron field emission (FE) properties of annealed single crystal and polycrystalline molybdenum plugs, which are used as substrates for actual alkali-based photocathodes were performed with a FE scanning microscope. Well-polished and dry-ice cleaned Mo samples with native oxide did not show parasitic FE up to a field level of 50 MV/m required for photoinjector cavities. In situ heat treatments (HT) above 400 °C, which are usual before photocathode deposition, activated field emission at lower field strength. Oxygen loading into the Mo surface, however, partially weakened these emitters. X-ray photoelectron spectroscopy of comparable Mo samples showed the dissolution of the native oxide during such heat treatments. These results reveal the suppression of field emission by native Mo oxides. Possible improvements for the photocathode preparation will be discussed

PTB7 as an Ink-Additive for Spin-Coated Versus Inkjet-Printed Perovskite Solar Cells

We report on the fabrication and optimization of Cs0.05FA0.79MA0.16Pb(Br0.17I0.83)3 perovskite solar cells from inks containing the polymer PTB7 as an additive, comparing spin-coating and inkjet printing as deposition methods. Spin-coated devices exhibited a maximum power conversion efficiency of 17.75% but showed little difference between samples with and without the polymer ink additive. For inkjet-printed devices, the combined optimization of printing parameters and the amount of the polymer additive in the precursor ink enabled a perovskite layer with increased quality. In comparison, devices with added PTB7 improved the power conversion efficiency to 10.35% as compared to 8.0% for cells prepared without the polymer additive. The effect is attributed to the modified crystallization dynamics of the perovskite layer by the PTB7 addition after inkjet printing and improved quality of the resulting perovskite layers. We found that the effect of the polymer additive on film formation in spin-coated samples was obscured when using an antisolvent drip, but the incorporation of PTB7 has a positive effect on the opto-electronic quality of thin films, indicated by the increased grain size and the photoluminescence quantum yield. Our results emphasize the technological potential of polymer additives in perovskite precursor inks when using scalable manufacturing processes, such as inkjet printing, where the control and induction of controlled crystallization are more difficult to implement by additional quenching steps