Stabilisation thermique de la couche photo-active d une cellule solaire organique par réticulation

Dans une configuration optimale, la couche photo-active d une cellule solaire organique forme une hétérojonction volumique entre un matériau donneur et un matériau accepteur d électrons. Cette morphologie optimale se trouve dans un état thermodynamique métastable. En cours de fonctionnement, l absorption incidente provoque une élévation de la tempéra- ture des dispositifs. L apport d énergie thermique au système le fait évoluer vers un état thermodynamique stable correspondant à une micro-séparation de phase entre les deux matériaux nuisible aux performances photovoltaïques du dispositif. La solution à cette problématique envisagée dans cette thèse est de figer la morphologie optimale de la couche photo-active par réticulation chimique. Dans le but de prévenir la diffusion et la cristallisation des dérivés du fullerène, plusieurs approches ont été étudiées : la formation d une maille de polymères réticulés, l accroche des dérivés du fullerène aux chaînes du polymères ou la liaison entre plusieurs dérivés du fullerène. Les différentes fonctions réticulantes utilisées dans ces approches sont l allyle, le cinnamate, l anthracène et l azoture. Au cours de ces travaux, des résultats satisfaisants ont été obtenus avec la fonction azoture. Basé sur cette fonction, nous avons développé un additif qui permet d augmenter notablement la stabilité thermique des cellules solaires réticulées. Cette approche a été validée sur plusieurs couples de matériaux polymères/dérivés du fullerène à l état de l art.Efficient bulk-heterojunction solar cells require an interpenetrating network of electron donating and electron accepting materials. Indeed, the optimum nano-sized phase segregation is a thermodynamically metastable system. Under operating conditions, especially under solar illumination, the temperature of the solar cell increases significantly. Adding thermal energy to the system leads to further micro-phase separation that is harmful for photovoltaic device performances. In order to freeze the optimal morphology, several approaches based on chemical cross-linking have been studied : formation of cross-linked polymer network, binding fullerene derivatives to polymer side chains or cross-linking between fullerene derivatives. Different cross-linkable functions have been used : allyl, cinamate, anthracene and azide. A versatile stabilization strategy of bulk heterojunctions morphology has been found by mean of incorporating a cross-linkable additive in low amounts with different polymer :fullerene blends. This approach is validated on multiple materials at the state-of-the-art.BORDEAUX1-Bib.electronique (335229901) / SudocSudocFranceF

Control of carrier mobilities for performance enhancement of anthracene-based polymer solar cells

International audienceHigh performance organic solar cells were realized using an anthracene-based polymer. Charge carrier mobilities of both electrons and holes in solvent annealed polymer and fullerene derivative mixtures were studied using organic field-effect transistors. Fine tuning of donor to acceptor ratios revealed optimum conditions for balanced mobilities, which led to a high power conversion efficiency (PCE) of 4.02% in the organic solar cells. A methanol wash approach further enhanced the PCE to 4.65%. This work demonstrates the importance of carrier transport control in optimizing the performance of polymer solar cells

2,5-Thiophene Substituted Spirobisiloles - Synthesis, Characterization, Electrochemical Properties and Performance in Bulk Heterojunction Solar Cells

International audienceNew spirobisilole molecules containing thienyl (DTSBS) and bis-thienyl (BBTSBS) electron donor groups have been synthesized for use as the donor material in bulk-heterojunction solar cells together with PCBM. The spectroscopic, electrochemical and thermal properties of DTSBS and BBTSBS have been investigated. All these new spirobisiloles exhibit excellent thermal stability. Cyclic voltammetry measurements revealed reversible and irreversible oxidation and irreversible reduction processes. The highest occupied and lowest unoccupied molecular orbital (HOMO/LUMO) energy levels were determined from electrochemical measurements and DFT calculations. The HOMO/LUMO energy levels were estimated to lie in the range -5.2 to -2.3 eV for DTSBS and -4.9 to -2.6 eV for BBTSBS. For both compounds, electropolymerization processes occur at potentials higher than 1.5 V leading to low band gap electrogenerated polymers. Spin-coating-deposited bulk-heterojunction solar cells fabricated with the novel spirobisiloles as donor and PCBM as acceptor displayed open-circuit voltages up to 0.4 V, short-circuit currents around 0.5 mA.cm-2, and power conversion efficiencies approaching 0.1 %

Topological aspects of geometrical signatures of phase transitions

Certain geometric properties of submanifolds of configuration space are numerically investigated for classical lattice phi^4 models in one and two dimensions. Peculiar behaviors of the computed geometric quantities are found only in the two-dimensional case, when a phase transition is present. The observed phenomenology strongly supports, though in an indirect way, a recently proposed topological conjecture about a topology change of the configuration space submanifolds as counterpart of a phase transition.Comment: REVTEX file, 4 pages, 5 figure

Narcissistic self-sorting of n-acene nano-ribbons yielding energy-transfer and electroluminescence at p-n junctions

The 2,3-didecyloxy derivative of an n-type anthracene (n-BG) and a p-type tetracene (p-R) have been synthesized and their self-assembly into nano-ribbons studied. Hyperspectral fluorescence imaging revealed their narcissistic self-sorting, leading to separated nanoribbons emitting with very different colors (blue or green for n-BG, depending on the growth solvent, and red for p-R). It is unique that the usual origins of self-sorting, such as specific H-bonding, different growth kinetics, or incompatible steric hindrance can be ruled out. Hence, the narcissistic behaviour is herein proposed to originate from a sofar unconsidered cause: the discrepancy between the quadrupolar character of n-BG and dipolar character of p-R. At the p-n junctions of these nanoribbons, inter-ribbon FRET and electro-luminescence switch-on were observed by fluorescence/luminescence microscopy.The authors acknowledge the financial support of the European Research Council Marie Curie Actions (FP7-PEOPLE-2012-ITN SMARTNET Grant agreement Nr 316656); the CNRS; the French Ministry of Education and Research; the Region Aquitaine; the ANR-06-JCJC-0030; the Department of Education, Science and Universities of the Basque Country Government (postdoctoral grant and project IT1639-22); the "Arina" informatic cluster of UPV/EHU; the facilities ELORGA of UB; and the ANR-17-CE24-0033-01 RESOLVE. The authors thank Dr A. Mendez-Ardoy for the CV measurements and CESAMO for structural analyses (ISM, Univ. Bordeaux)

Diketo-Pyrrolo Pyrrole-Based Acceptor-Acceptor Copolymers with Deep HOMO and LUMO Levels Absorbing in the Near Infrared

A series of acceptor-acceptor (A-A') alternated copolymers based on dithienodiketopyrrolo pyrrole were synthesized by copolymerizing it with itself and other different electron-poor monomers. The experimental and computed optoelectronic properties of four DPP-based copolymers, P(DPP-DPP) (with linear and branched chains), copolymer with diazapentalene P(DPP-DAP) and also with dioxothienopyrrolebenzodifurandione P(DPP-BTPBF), as well as thermal characterizations were described. UV-visible spectrophotometry and cyclic voltammetry were used to estimate the optical and electrochemical bandgaps, and were found as very small: 1.3, 1.0, and 0.9 eV for P(DPP-DPP), P(DPP-DAP), and P(DPP-BTPBF), respectively. The BTPBF unit allowed a strong reduction of the bandgap, leading to a broad absorption in the visible and near infra-red regions from 650 to 1450 nm. These results were compared to analogous donor-acceptor (D-A) copolymers previously reported, in which DPP is replaced by DTS, P(DTS-DPP), P(DTS-DAP), and P(DTS-BTPBF). The same trend was observed. By comparing A-A' to D-A' copolymers analogues, it was shown that the bandgap remained the same while both HOMO and LUMO levels were lowered by roughly 0.2 eV.Technologie alternative pour les photodétecteurs infrarougeE2

Narcissistic Self-Sorting of n-Acene Nano-Ribbons yielding Energy-Transfer and Electroluminescence at p-n Junctions

The 2,3-didecyloxy-derivative of an n-type anthracene (n-BG) and a p-type tetracene (p-R) have been synthesized and their self-assembly into nano-ribbons studied. Hyperspectral fluorescence imaging revealed their narcissistic self-sorting, leading to separated nanoribbons emitting with very different colors (blue or green for n-BG, depending on the growth solvent, and red for p-R). It is unique that the usual origins of self-sorting, such as specific H-bonding, different growth kinetics, or incompatible steric hindrance can be ruled out. Hence, the narcissistic behaviour is herein proposed to originate from a sofar unconsidered cause: the discrepancy between the quadrupolar character of n-BG and dipolar character of p-R. At the pn-junctions of these nanoribbons, inter-ribbon FRET and electro-luminescence switch-on were observed by fluorescence microscopy.Modulation of Organic Optic Information InterfacesFabrication Supramoléculaire de Dispositifs OLED Haute Résolution par voie ImprimableSoft Materials Advanced Research Training Networ

Narcissistic self-sorting of n-acene nano-ribbons yielding energy-transfer and electroluminescence at p–n junctions

The 2,3-didecyloxy derivative of an n-type anthracene (n-BG) and a p-type tetracene (p-R) have been synthesized and their self-assembly into nano-ribbons studied. Hyperspectral fluorescence imaging revealed their narcissistic self-sorting, leading to separated nanoribbons emitting with very different colors (blue or green for n-BG, depending on the growth solvent, and red for p-R). It is unique that the usual origins of self-sorting, such as specific H-bonding, different growth kinetics, or incompatible steric hindrance can be ruled out. Hence, the narcissistic behaviour is herein proposed to originate from a so-far unconsidered cause: the discrepancy between the quadrupolar character of n-BG and dipolar character of p-R. At the p–n junctions of these nanoribbons, inter-ribbon FRET and electro-luminescence switch-on were observed by fluorescence/luminescence microscopy.Fabrication Supramoléculaire de Dispositifs OLED Haute Résolution par voie ImprimableModulation of Organic Optic Information Interface