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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 937 records · Page 52
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

Electronic structure of molybdenum-oxide films and associated charge injection mechanisms in organic devices

We report on the electronic structure of freshly evaporated and air-exposed Molybdenum tri-oxide (MoO 3 ) and the energy-level alignment between this compound and a hole-transport material [e.g., N,N'-diphenyl-N,N'-bis (1-naphthyl)-1,1'-biphenyl-4,4'-diamine (α-NPD)]. Ultraviolet and inverse photoelectron spectroscopy show that freshly evaporated MoO 3 exhibits deep-lying electronic states with an electron affinity (EA) of 6.7 eV and ionization energy (IE) of 9.7 eV. Air exposure reduces EA and IE by ~1 eV, to 5.5 and 8.6 eV, respectively, but does not affect the hole-injection efficiency, which is confirmed by device studies. Thus, MoO 3 can be applied in low-vacuum environment, which is particularly important for low-cost manufacturing processes. Our findings of the energy-level alignment between MoO 3 and α-NPD also leads to a revised interpretation of the charge-injection mechanism, whereby the hole-injection corresponds to an electron extraction from the organic highest-occupied molecular orbital (HOMO) level via the MoO 3 conduction band.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2011

Novel Approach for Correlating Capacitance Data with Performance During Thin-Film Device Stress Studies: Preprint

A new data mining algorithm was developed to identify the strongest correlations between capacitance data (measured between -1.5 V and +0.49 V) and 1st and 2nd level performance metrics (efficiency, open-circuit voltage (VOC), short-circuit current density (JSC), and fill-factor (FF)) during the stress testing of voltage-stabilized CdS/CdTe devices. When considering only correlations between 1stand 2nd level metrics, 96.5% of the observed variation in efficiency was attributed to FF. The overall decrease in VOC after 1000 hours of open-circuit, light-soak stress at 60 degrees C was about 1.5%. As determined by our algorithm, the most consistent correlation existing between FF and 3rd level metric capacitance data at all stages during stress testing was between FF and the apparent CdTeacceptor density (Na) calculated at a voltage of +0.49 V during forward voltage scans. Since the contribution of back contact capacitance to total capacitance increases with increasing positive voltage, this result suggests that FF degradation is associated with decreases in Na near the CdTe/back contact interface. Also of interest, it appears that capacitance data at these higher voltagesappears to more accurately fit the one-sided abrupt junction model.

14 SOLAR ENERGY↗