Towards anode with low indium content as effective anode in organic solar cells

In2O3 thin films (100 nm thick) have been deposited by reactive evaporation of indium, in an oxygen partial atmosphere. Conductive (σ = 3.5×103 S/cm) and transparent films are obtained using the following experimental conditions: oxygen partial pressure = 1×10−1 Pa, substrate temperature = 300 ◦C and deposition rate = 0.02 nm/s. Layers of this In2O3 thick of 5 nm have been introduced in AZO/In2O3 and FTO/In2O3 multilayer anode structures. The performances of organic photovoltaic cells, based on the couple CuPc/C60, are studied using the anode as parameter. In addition to these bilayers, other structures have been used as anode: AZO, FTO, AZO/In2O3/MoO3, FTO/In2O3/MoO3 and FTO/MoO3. It is shown that the use of the In2O3 film in the bilayer structures improves significantly the cell performances. However the open circuit voltage is quite small while better efficiencies are achieved when MoO3 is present. These results are discussed in the light of surface roughness and surface work function of the different anodes

Order-of-magnitude speedup for steady states and traveling waves via Stokes preconditioning in Channelflow and Openpipeflow

Steady states and traveling waves play a fundamental role in understanding hydrodynamic problems. Even when unstable, these states provide the bifurcation-theoretic explanation for the origin of the observed states. In turbulent wall-bounded shear flows, these states have been hypothesized to be saddle points organizing the trajectories within a chaotic attractor. These states must be computed with Newton's method or one of its generalizations, since time-integration cannot converge to unstable equilibria. The bottleneck is the solution of linear systems involving the Jacobian of the Navier-Stokes or Boussinesq equations. Originally such computations were carried out by constructing and directly inverting the Jacobian, but this is unfeasible for the matrices arising from three-dimensional hydrodynamic configurations in large domains. A popular method is to seek states that are invariant under numerical time integration. Surprisingly, equilibria may also be found by seeking flows that are invariant under a single very large Backwards-Euler Forwards-Euler timestep. We show that this method, called Stokes preconditioning, is 10 to 50 times faster at computing steady states in plane Couette flow and traveling waves in pipe flow. Moreover, it can be carried out using Channelflow (by Gibson) and Openpipeflow (by Willis) without any changes to these popular spectral codes. We explain the convergence rate as a function of the integration period and Reynolds number by computing the full spectra of the operators corresponding to the Jacobians of both methods.Comment: in Computational Modelling of Bifurcations and Instabilities in Fluid Dynamics, ed. Alexander Gelfgat (Springer, 2018

Adapting Algebraic Recursive Multilevel Solvers (ARMS) for Solving CFD Problems

This paper presents results using preconditioners that are based on a number of variations of the Algebraic Recursive Multilevel Solver (ARMS). ARMS is a recursive block ILU factorization based on a multilevel approach. Variations presented in this paper include approaches which incorporate inner iterations, and methods based on standard reordering techniques. Numerical tests are presented for three-dimensional incompressible, compressible and magneto-hydrodynamic (MHD) problems

Tailored ZnS/Ag/TiO

Organic photovoltaic cells (OPVCs) attract high interest for solar energy harvesting. They are based on organic thin films sandwiched between two electrodes, one of them being transparent and conductive. Nowadays, ITO remains the most widely used transparent conductive electrode (TCE) because of its excellent optical and electrical properties compared to other TCEs. However, it has some drawbacks such as scarcity of indium, high fabrication cost, and mechanical properties poorly adapted to use as flexible substrates. To keep these performances without indium, several materials can replace ITO such as MoO3, ZnO, ZnS, TiO2,… as dielectric and Ag, Cu,... as metal inside a dielectric/metal/dielectric three-layer structure. A Transfer Matrix Method (TMM) based numerical model is used to predict the optical behavior of the considered electrodes. ZnS/Ag/TiOx electrodes are manufactured by a vacuum electron beam evaporator on glass substrates, then characterized by UV-Visible spectrophotometer for obtaining transmittance and reflectance and by a four-point method for the measurement of sheet resistance. It is found that the simulation and experimental curves are quite similar. The transmittance is measured to be higher than 80% on a wide spectral band that can be tailored by the thickness of the upper dielectric material. The optical window Δλ, for T > 80%, can be tuned in the 400–800 nm spectral band, according to the thickness of TiOx in the 25–50 nm range. This variation allows us to adapt our electrode to organic materials in order to optimize the performance of organic solar cells. The sheet resistance obtained is around to 7 Ω/sq, which gives our electrodes the transparent and conductive character simultaneously. A typical parameter to compare the electrodes is the merit figure, which questions the average optical transmission T av in the visible range and the sheet resistance R sq. By applying this figure to many manufactured electrodes, the obtained optimal structure of our TCEs is demonstrated to be ZnS (40 nm)/Ag (10 nm)/TiOx (30 nm)

N-Annulation of the BTI Rylene Imide Organic Building Block: Impact on the Optoelectronic Properties of π-Extended Molecular Structures

Benzothioxanthene imide (BTI) has recently emerged as an interesting and promising block for organic electronics. In this contribution, we report on the impact of the N-annulation of the latter dye on the optoelectronic of π-extended molecular structures. To do so, the thiophene-diketopyrrolopyrrole was selected, as central π-conjugated core, and either end-capped with two BTIs or its N-annulated version, namely the TCI. While almost similar band gaps were measured for individual rylene imide dyes, significant differences were highlighted, and rationalized, on their π-extended counterparts

Stabilisation Attempts of the Electrical and Optical Properties of Oxide/Cu/Oxide Structures Through the Use of Different Cu:M Alloys

International audienc

Stabilisation Attempts of the Electrical and Optical Properties of Oxide/Cu/Oxide Structures Through the Use of Different Cu:M Alloys

International audienc

Stabilisation Attempts of the Electrical and Optical Properties of Oxide/Cu/Oxide Structures Through the Use of Different Cu:M Alloys

International audienc