Effect of the deposition conditions of NiO anode buffer layers inorganic solar cells, on the properties of these cells

tNiO thin films deposited by DC reactive sputtering were used as anode buffer layer in organic photovoltaiccells (OPVs) based on CuPc/C60planar heterojunctions. Firstly we show that the properties of the NiOfilms depend on the O2 partial pressure during deposition. The films are first conductive between 0 and2% partial oxygen pressure, then they are semiconductor and p-type between 2 and 6% partial oxygenpressure, between 6 and 9% partial oxygen pressure the conduction is very low and the films seem to be n-type and finally, for a partial oxygen pressure higher than 9%, the conduction is p-type. The morphology ofthese films depends also on the O2 partial pressure. When the NiO films is thick of 4 nm, its peak to valleyroughness is 6 nm, when it is sputtered with a gas containing 7.4% of oxygen, while it is more than double,13.5 nm, when the partial pressure of oxygen is 16.67%. This roughness implies that a forming process,i.e. a decrease of the leakage current, is necessary for the OPVs. The forming process is not necessary ifthe NiO ABL is thick of 20 nm. In that case it is shown that optimum conversion efficiency is achievedwith NiO ABL annealed 10 min at 400◦C

XPS study of the band alignment at ITO/oxide (n-type MoO3 or p-type NiO) interface

While 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

Growth of piezoelectric thin films by sputtering

Lead titanate thin films have been deposited on different substrates by radio frequency magnetron sputtering from pressed powders targets. The films have been deposited without substrate heating. The amorphous films were then annealed in order to obtain the perovskite structure. Two types of post-annealing were study : conventional annealing and rapid thermal annealing (R.T.A.). The main advantage of the RTA process is to avoid (or to limit) the problem of interdiffusion or of interfacial disturbance between the substrate (in particular Silicium substrate) and the lead titanate thin film. The composition, structure and microstructure of PT films were evaluated as a function of the annealing parameters for conventional and rapid annealing

CIGSe absorber layers deposition by single target magnetron sputtering

In the last decades, the deposition of CIGSe thin films by sputtering has seldom been investigated. Besides, the sputtering of a single quaternary CIGSe target would be a real advantage for industrial development. Indeed, sputtering technique exhibits a good compatibility with industrial up-scaling and limits selenium use with respect to toxicity issues. In 1992, Hernandez et al.1 early published on CIGSe layers deposited by sputtering of a single quaternary CIGSe target. More recently, Frantz et al2 using such so called "one step sputtering" succeeded to obtain a CIGSe solar cell with an efficiency of 8.9%. At IMN laboratory, a dedicated chamber has been home-designed for CIGSe thin films deposition using one step sputtering. CIGSe thin films were deposited on SLG/Mo substrates by radio-frequency magnetron sputtering and then annealed under controlled atmosphere. The evolution of chemical composition, electrical and structural properties versus deposition parameters will be presented. 1. Hernández Rojas, J. L. et al.. Appl. Phys. Lett. 60, 1875-1877 (1992). 2. Frantz, J. A. et al. Thin Solid Films 519, 7763-7765 (2011)

CIGSe absorber layers deposition by single target magnetron sputtering

In the last decades, the deposition of CIGSe thin films by sputtering has seldom been investigated. Besides, the sputtering of a single quaternary CIGSe target would be a real advantage for industrial development. Indeed, sputtering technique exhibits a good compatibility with industrial up-scaling and limits selenium use with respect to toxicity issues. In 1992, Hernandez et al.1 early published on CIGSe layers deposited by sputtering of a single quaternary CIGSe target. More recently, Frantz et al2 using such so called "one step sputtering" succeeded to obtain a CIGSe solar cell with an efficiency of 8.9%. At IMN laboratory, a dedicated chamber has been home-designed for CIGSe thin films deposition using one step sputtering. CIGSe thin films were deposited on SLG/Mo substrates by radio-frequency magnetron sputtering and then annealed under controlled atmosphere. The evolution of chemical composition, electrical and structural properties versus deposition parameters will be presented. 1. Hernández Rojas, J. L. et al.. Appl. Phys. Lett. 60, 1875-1877 (1992). 2. Frantz, J. A. et al. Thin Solid Films 519, 7763-7765 (2011)

Incidence, predictors and clinical impact of electrical storm in patients with left ventricular assist devices: new insights from the ASSIST-ICD study

International audienceBackground - Ventricular arrhythmias (VAs) can occur after continuous flow left ventricular assist device (LVAD) implantation as a single arrhythmic event or as electrical storm (ES) with multiple repetitive VA episodes. Objective - We aimed at analyzing the incidence, predictors, and clinical impact of ES in LVAD recipients. Methods - Patients analyzed were those included in the multicenter ASSIST-ICD observational study. ES was consensually defined as occurrence of ≥3 separate episodes of sustained VAs within a 24-hour interval. Results - Of 652 patients with an LVAD, 61 (9%) presented ES during a median follow-up period of 9.1 (interquartile range [IQR] 2.5-22.1) months. The first ES occurred after 17 (IQR 4.0-56.2) days post LVAD implantation, most of them during the first month after the device implantation (63%). The incidence then tended to decrease during the initial years of follow-up and increased again after the third year post LVAD implantation. History of VAs before LVAD implantation and heart failure duration > 84 months were independent predictors of ES. The occurrence of ES was associated with an increased early mortality since 20 patients (33%) died within the first 2 weeks of ES. Twenty-two patients (36.1%) presented at least 1 recurrence of ES, occurring 43.0 (IQR 8.0-69.0) days after the initial ES. Patients experiencing ES had a significantly lower 1-year survival rate than did those free from ES (log-rank, P = .039). Conclusion - There is a significant incidence of ES in patients with an LVAD. The short-term mortality after ES is high, and one-third of patients will die within 15 days. Whether radiofrequency ablation of arrhythmias improves outcomes would require further studies