Energy level evolution of air and oxygen exposed molybdenum trioxide films

Abstract

The evolution of electronic energy levels of controlled air and oxygen exposed molybdenum trioxide (MoO3) films has been investigated with ultraviolet photoemission spectroscopy, inverse photoemission spectroscopy, and x-ray photoemission spectroscopy. We found that while most of the electronic levels of as deposited MoO3 films remained largely intact, the reduction in the work function (WF) was substantial. The gradual surface WF change from 6.8 to 5.3 eV was observed for air exposed film, while oxygen exposed film the surface WF saturated at ∼5.7 eV. Two distinct stages of exposure are observed, the first dominated by oxygen adsorption for <1013 Langmuir (L) exposure and at the final step moisture absorption >1013 L.

Processing and charge state engineering of MoOx

“…1 and the evolution of the gap states is preserved, hence we attribute the enhancement of the gap state density to the presence of MoO x reduced states, in accordance with previous reports by other authors. 12,37,50,51 Moreover, we can state that not only surface states are affected, but also deeper layers within the material, as deduced from the ARXPS measurements in Fig. 1.…”

“…52,53 The reduction effect, not confined only to the surface layers, is correlated with the development of gap states -likely due to chemisorbed species -which lead to an electron transfer to the transition metal oxide system. 12,37 Independently of the processing protocol, reduction and gap state intensities are stable after four days of air exposure. We have found by means of XRR measurements that fully metallic and fully oxidized phases have the highest stability…”

“…[33][34][35] MoO x surface and, consequently, on the device efficiency and lifetime. 12,[36][37][38][39][40][41][42][43] Surface hydration or hydroxylation are suggested as possible mechanisms for reduction of cations in the MoO x system and, thus, for electronic structure changes. In particular, the hydroxylation mechanism is supported by recent density functional theory (DFT) calculations.…”

Carbon nanotubes for organic/inorganic hybrid solar cells

“…First, especially exposure into the atmosphere is known to substantially degrade the work function of the evaporated films of MoO x [88]. However, the measurements show the change of sheet resistance to less than 10 % over 20 days in ambient and less than 2% with overnight heating to 300 °C in air.…”

Surface Analytical Investigation on Organometal Triiodide Perovskite

“…The VB edges are obtained using linear extrapolation as illustrated in our previous works. 24,25 With Au deposition, a finite density of valence states are observed within the gap of CH 3 NH 3 PbI 3 . We observed clear Fermi surface when Au coverage reaches 8 Å and a true metallic Fermi edge develops completely with the Au deposition of up to 64 Å .…”