About MoO3 as buffer layer in organic optoelectronic devices, Technology Letters

MoO3 is well known as efficient anode buffer layer in optoelectronic devices. Actually, MoO3 can be easily deposited under vacuum, by sublimation for instance, and also by wet process. So it is known from a long time that the films deposited by sublimation are amorphous and slightly oxygen deficient, which induces a light blue coloration due to oxygen vacancies. These oxygen vacancies imply the presence of Mo4+ and Mo5+ in the films. The presence of oxygen vacancies increases the conductivity from 10-12 to 10-6 (Ωcm)-1, while stoichiometric films are insulating and MoO2 has a metallic like behaviour with s = 2 102 (Ωcm)-1. About the efficiency of MoO3 as buffer layer, recent studies questioned the MoO3 band structure generally admitted. Under ultra high vacuum, the measured ionisation energy, IE, and electron affinity are found to be 9.7 eV and 6.7 eV respectively, while the films are strongly n-type. Its means that the very large IE energy of the MoO3 excludes any hole transport via the valence band, while the energy alignment between the band conduction minimum, CB, of MoO3 and the Highest Occupied Molecular Orbital (HOMO) of the organic material is favourable for electron transfer between the two materials. In the case of organic photovoltaic cells, the photogenerated hole recombines with an electron at the interface between MoO3 and the organic layer. Indeed, the work function, WF, of the molybdenum oxide films depends strongly of its composition, WF decreases when the oxygen deficiency increases, and on the exposition, or not, of its surface to air contamination. This makes that WF varies from 6.9 eV for a layer studied under ultra high vacuum to 5.2 eV for a layer exposed to the air a few hours. However, since the initial value of WF is very high, MoO3 remains effective if the Highest Occupied Molecular Orbital of the organic material is lower than 6 eV. The band structure of MoO3 and the large possible variations of WF make that, for specific conditions of preparation and conditioning, MoO3 can also be used as CBL

Copper:molybdenum sub-oxide blend as transparent conductive electrode (TCE) indium free

Oxide/metal/oxide structures have been shown to be promising alternatives to ITO. In such structures, in order to decrease the high light reflection of the metal film it is embedded between two metal oxides dielectric. MoO3-x is often used as oxide due to its capacity to be a performing anode buffer layer in organic solar cells, while silver is the metal the most often used [1]. Some attempts to use cheaper metal such as copper have been done. However it was shown that Cu diffuses strongly into MoO3-x [2]. Here we used this property to grow simple new transparent conductive oxide (TCE), i.e., Cu: MoO3-x blend. After the deposition of a thin Cu layer, a film of MoO3-x is deposited by sublimation. An XPS study shows more than 50% of Cu is present at the surface of the structure. In order to limit the Cu diffusion an ultra-thin Al layer is deposited onto MoO3-x. Then, in order to obtain a good hole collecting contact with the electron donor of the organic solar cells, a second MoO3-x layer is deposited. After optimization of the thickness of the different layers, the optimum structure is as follow:       Cu (12 nm) : MoO3-x (20 nm)/Al (0.5 nm)/ MoO3-x (10 nm). The sheet resistance of this structure is Rsq = 5.2 Ω/sq. and its transmittance is Tmax = 65%. The factor of merit ϕM = T10/Rsq. = 2.41 × 10-3 Ω-1, which made this new TCE promising as anode in organic solar cells

A giant occipital encephalocele: A case report

Occipital encephalocele is a rare congenital anomaly that is characterized by herniation of brain tissue through a defect in the skull. Because of their enormous size, they pose a surgical challenge. Occipital encephalocele is the commonest of all encephalocele; the management of encephalocele defects requires immediate surgical closure. The author reports a case of a five months old female baby who presented a progressively increasing swelling over the occipital region. This swelling was present since birth. Surgery was planned to reduce the size of the swelling as well as its contents. The sac was excised and reduced sufficiently enough to accommodate the healthy-looking brain tissue. This infant did well postoperatively

Treatment of chronic pain by spinal cord stimulation

Failed back surgery syndrome (FBSS) is often used to describe the condition of patients who have experienced continued pain after surgery. It is of multifactorial genesis and may be the consequence of various lumbar spinal diseases; lumbar disc herniation surgery or spinal canal stenosis laminectomy. The presented series included 13 patients affected with chronic pain related to FBSS who underwent implantation of spinal cord stimulation. The mean percentage of pain relief was 90 % for all patients. 60% of the patients were in a better psychological status and the intake of analgesic medications has been reduced of more than 70%. More than 50% of the patients could resume professional activities. Analysis of the risks and benefits comes in favour of spinal cord stimulation

Toward indium-free optoelectronic devices: Dielectric/metal/dielectric alternative transparent conductive electrode in organic photovoltaic cells

Depending on their resistivity and their transmittance, the thin films of transparent conductive oxide (TCO) are widely used in optoelectronic devices. In2O3:Sn (ITO) is the most widely used TCO in optoelectronic devices. As indium is scarce and ITO is limited in flexibility due to its ceramic structure, many studies have been dedicated to new transparent conductive electrodes. This review article presents the state-of-the-art concerning the dielectric/metal/dielectric structures and their application as transparent electrodes in organic photovoltaic cells (OPVCs). First, TCO/Ag/TCO structures were created to achieve higher conductivity than ITO films. Then others dielectrics have been used such as transition-metal oxides (WO3, MoO3, V2O5, etc.), ZnS, etc. Such structures exhibit excellent flexibility, high conductivity, and good transparency. They can be deposited onto substrates at room temperature by simple evaporation under vacuum. Moreover, it is possible to manage the anode work function through the choice of the dielectric, which can allow them to be used as cathodes or anodes and as intermediate electrodes in tandem solar cells. The properties of the dielectric/metal/dielectric (D/M/D) structures depend on the thickness of the different layers. The threshold thickness value of the metal film is usually around 10 nm, where the structures change from an insulating state to a highly conductive state. This is attributed to the percolation of conducting metal paths. The transmittance of the films increases when the metal thickness increases up to the percolation thickness, while further increase induces a decrease in transmittance. Finally, the nature and the thickness of the dielectric layers can be chosen as a function of the device properties requested, which is illustrated through different examples of OPVCs

Study of CuI thin films properties for application as anode buffer layer in organic solar cells

After chemico-physical characterization of CuI thin films, the structures indium tin oxide (ITO) /CuI are systematically studied. We show that the morphology of the 3 nm thick CuI film depends on its deposition rate. To obtain smooth homogeneous CuI film, it is necessary to depose it at 0.005 nm/s. After optimization of the deposition conditions of CuI, it is shown that it behaves like a template for the organic layer. For instance, when the organic film is copper-phthalocyanine, the molecules which are usually perpendicular to the plane of the substrate lie parallel to it when deposited onto CuI. In a same way, when the electron donor is a prophyrin derivative, CuI allows to double the power conversion efficiency of the cells based on the heterojunction porphyrin/C-60. When CuI is used as anode buffer layer, it increases systematically the short circuit current, the open circuit voltage, thus the efficiency of the organic solar cell. These effects are related, not only to the improvement of the band matching between the ITO and the electron donor, but also to the templating effect of the CuI. Moreover, we show that the beneficial effect of CuI. is effective, not only with ITO, but also with fluorine doped tin oxide

Communicating spinal epidural thoracic arachnoid cyst en-bloc resection: A case report

Background: Spinal extradural arachnoid cyst is an uncommon, expanding lesion which may communicate with the subarachnoid space, The etiology still remains unclear, but the most accepted explanation is the existence of areas of weakness in the spinal dura , Spinal arachnoid cysts are usually in the thoracic spine, and they may cause symptoms due to spinal cord compression. Case Presentation: Patient is a 54-years-old female who presented with progressive back pain and motor deficit, Magnetic resonance imaging (MRI) study revealed an extradural cyst extending from T2 to T4 isointense with the cerebrospinal fluid (CSF) on all sequences and did not enhance on T1-weighted post-contrast MRI. Patient underwent T2-T4 laminectomy, en-bloc resection of the lesion was achieved and the histopathological examination objectified an arachnoid cyst. Conclusion: Spinal extradural arachnoid cyst can cause neurologic deficit and the mainstay of treatment in patients with neurological symptoms is surgical removal of the cyst together with ligation of the communicating pedicle and closure of the dural defect