Pentaerythritol based push–pull tetramers for organic photovoltaics

The synthesis and characterization of two tetramers based on the functionalization of a central pentaerythritol σ-linker with push–pull chromophores is reported herein. Prepared in only few steps, these original molecules exhibit interesting optical and electrochemical properties. Moreover, once evaluated as donor materials, promising power conversion efficiencies of 4.5% were reached when blended with the [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) in bulk heterojunction solar cells

Effect of side chains on the electronic and photovoltaic properties of diketopyrrolopyrrole-based molecular acceptors

Four molecular electron acceptors based on a common phthalimide end-capped diketopyrrolopyrrole pconjugated backbone, solubilized by different alkyl groups, have been synthesized. The influence of the nature and position of the solubilizing alkyl chains attached at the three constitutive blocks has been investigated. Results collected from UV-Vis absorption spectroscopy, cyclic voltammetry, solar cells fabrication and testing as well as atomic force microscopy show that the mode of substitution has negligible effect at the molecular level but strongly affects the material self-assembling properties, charge carrier transport and in turn, devices performances

Darboux polynomials for Lotka-Volterra systems in three dimensions

We consider Lotka-Volterra systems in three dimensions depending on three real parameters. By using elementary algebraic methods we classify the Darboux polynomials (also known as second integrals) for such systems for various values of the parameters, and give the explicit form of the corresponding cofactors. More precisely, we show that a Darboux polynomial of degree greater than one is reducible. In fact, it is a product of linear Darboux polynomials and first integrals.Comment: 16 page

Triphenylamine-Based Push–Pull σ–C60 Dyad As Photoactive Molecular Material for Single-Component Organic Solar Cells: Synthesis, Characterizations, and Photophysical Properties

A push–pull σ–C60 molecular dyad was synthesized via Huisgen-type click chemistry and used as photoactive material for single-component organic solar cells. Steady-state photoluminescence (PL) experiments of the dyad in solution show a significant quenching of the emission of the push–pull moiety. Spin-casting of a solution of the dyad results in homogeneous and smooth thin films, which exhibit complete PL quenching in line with ultrafast photoinduced electron-transfer in the solid state. Spectroelectrochemistry reveals the optical signatures of radical cations and radical anions. Evaluation of the charge carrier mobility by space-charge limited current measurements gives an electron-mobility of μe = 4.3 × 10–4 cm2 V–1 s–1, ca. 50 times higher than the hole-mobility. Single-component organic solar cells yield an open-circuit voltage Voc of 0.73 V and a short-circuit current density of 2.1 mA cm–2; however, a poor fill factor FF (29%) is obtained, resulting in low power conversion efficiency of only 0.4%. Combined transient absorption (TA) and time-delayed collection field (TDCF) experiments show mostly ultrafast photon-to-charge conversion and a small component of diffusion-limited exciton dissociation, revealing the presence of pure fullerene domains. Furthermore, a strong field dependence of charge generation is observed, governing the device fill factor, which is further reduced by a competition between extraction and fast recombination of separated charges

The Fourier Singular Complement Method for the Poisson problem. Part III: Implementation Issues

This paper is the last part of a three-fold article aimed at some efficient numerical methods for solving the Poisson problem in threedimensional prismatic and axisymmetric domains. In the first and second parts [7][8], the Fourier singular complement method (FSCM) was introduced and analysed for prismatic and axisymmetric domains with reentrant edges, as well as for the axisymmetric domains with sharp conical vertices. In this paper we shall mainly conduct numerical experiments to check and compare the accuracies and efficiencies of FSCM and some other related numerical methods for solving the Poisson problem in the aforementioned domains. In the case of prismatic domains with a reentrant edge, we shall compare the convergence rates of three numerical methods: 3D finite element method using prismatic elements, FSCM, and the 3D finite element method combined with the FSCM. For axisymmetric domains with a non-convex edge or a sharp conical vertex we investigate the convergence rates of the Fourier finite element method (FFEM) and the FSCM, where the FFEM will be implemented on both quasi-uniform meshes and locally graded meshes. The complexities of the considered algorithms are also analysed