International audienceWhile they have different electronic properties n-type MoO3 and p-type NiO are very efficient as buffer layers between the ITO anode and the organic electron donor in organic photovoltaic cells. While it is admitted that MoO3 is n-type, its band structure is still under study. Here, the band alignment at the interface of an ITO/MoO3 heterojunction is studied by X-ray photoelectron spectroscopy (XPS). The same study is realized on the structure ITO/NiO, NiO being a p-type semiconductor. The measurements have been performed on samples obtained under the same experimental conditions as those used to achieve organic photovoltaic cells. The MoO3 (NiO) upper layer was 3 nm thick. The semidirect XPS technique used to measure the band offsets allows us to estimate the band discontinuities at the interface ITO/MoO3: ΔEv = 0.50 eV and ΔEc = 0.90 eV, while at the interface ITO/NiO we have ΔEv = −2.10 eV and ΔEc = −1.90 eV. Therefore, n-type MoO3 and p-type NiO, which are both very efficient anode buffer layers (ABLs), exhibit different band structure at the contact with ITO. However, the measurement, by means of a Kelvin probe, of the work functions of the structures ITO/NiO and ITO/MoO3, shows that they are close and significantly higher than that of ITO alone
The effect of fillers on the mechanical properties such as stress— strain behavior, tensile strength, percentage strain at-break, Young's modulus and tear strength have been investigated. Different filled crosslinked thermoplastic elastomers of styrene butadiene rubber (SBR)/high density polyethylene blends (HDPE) blends were prepared using silica, HAF-carbon black, china clay and TiO2. The extent of polymer-filler interaction has been analyzed by Kraus as well as Cunneen—Russell equation. The reinforcement ability of the filler was increased in the order of silica>HAF-black>clay>TiO 2. The nature of the filler and filler loading has a dramatic effect on the mechanical properties of SBR/ HDPE blends. Filled blends showed improved mechanical properties such as enhanced of strain at-break, when fillers are incorporated. The initial trend of properties for all filled system is the enhancement of properties. When HAF-black is used as the filler, at higher loading strain at- break is found to decrease due to the stiffness of the matrix. In the case of clay, there is a deterioration of properties occurs on higher loading, which is attributed to dilution effect and all TiO 2 filled system have lower elongation at break than the base polymer. Theoretical models namely Guith's and Kerner's model have been compared with the experimental values of Young's modulus of filled system. The experimental values of modulus are found to be higher than the theoretical values indicating strong interaction between the filler and the matrix. SEM studies of the tensile and tear fractured surfaces of the filled blends have been carried out. The variation in properties was correlated with the morphology of the system.
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