REALISATION ET CARACTERISATION DE CELLULES PHOTOVOLTAIQUES PLASTIQUES

Organic materials are widely studied in sight of commercial applications, such as the photovoltaic devices, because of their easy processability and weak cost. The effeciency and stability of such devices are the main parameters to be improved.At first, we have fabricated and characterized a device based on a composite of poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene (MEH-PPV) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM). The insertion of the interfacial layers, the surface treatment and the improvement of the morphology of the active layer have significantly increased the photovoltaic performances of the structure compared to the previous performances. After, we studied a new organic materials in bulk heterojonction solar cells configuration. At last, we developed a new structure of solar cells to improve their stability.En raison de leur mise en forme facile et de leur faible coût, les matériaux organiques font l'objet de nombreuses études en vue d'applications industrielles. C'est le cas des dispositifs photovoltaïques plastiques. Le rendement de conversion et la stabilité de ces systèmes sont les points les plus importants à améliorer. La première partie de notre travail porte sur la réalisation et la caractérisation d'une cellule photovoltaïque à base du composite poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene (MEH-PPV) et [6,6]-phenyl C61 butyric acid methyl ester (PCBM). L'insertion des couches interfaciales, le traitement de surface et l'amélioration de la morphologie de la couche active nous ont permis d'accroître significativement les performances photovoltaïques de la structure par rapport aux performances antérieures.Les deuxième et troisième parties portent, respectivement, sur l'évaluation de nouveaux matériaux organiques dans les cellules à base de composite et sur le développement d'une nouvelle structure de cellules photovoltaïques améliorant leur stabilité

Réalisation et caractérisation des cellules photovoltaïques plastiques

En raison de leur mise en forme facile et de leur faible coût, les polymères font l'objet de nombreuses études en vue d'applications industrielles. C'est le cas des dispositifs photovoltaïques plastiques. Le rendement de conversion et la stabilité de ces systèmes sont les points les plus importants à améliorer. La première partie de notre travail porte sur la réalisation et la caractérisation d'une cellule photovoltaïque à base du composite MEH-PPV et PCBM. L'insertion des couches interfaciales, le traitement de surface et l'amélioration de la morphologie de la couche active nous ont permis d'accroître significativement les performances photovoltaïques de la structure par rapport aux performances antérieures (>2,5%). Les deuxième et troisième parties portent, respectivement, sur l'évaluation de nouveaux matériaux organiques dans les cellules à base de composite et sur le développement d'une nouvelle structure de cellules photovoltaïques améliorant la stabilité.Polymers are widely studied in view of commercial applications, such as the photovoltaic devices, because of their easy processability and relatively low cost. The efficiency and stability of such devices are the main parameters to be improved. At first, we have fabricated and characterized a device based on a composite of poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene (MEH-PPV) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM). The insertion of interfacial layers, the surface treatment and the improvement of the morphology of the active layer have significantly increased the photovoltaic performances of the structure compared to the previous performances (> 2.5%). After, we studied new organic materials in bulk heterojonction solar cell configurations. At last, we developed a new structure of solar cells to improve their stability.ANGERS-BU Lettres et Sciences (490072106) / SudocSudocFranceF

Planar polymer photovoltaic cells with millimeter interelectrode spacing

We present the photovoltaic measurements of planar photovoltaic cells with extremely large interelectrode spacing based on either pure polymers or polymer/fullerene blends. The planar configuration allows for both uniform and site-selective illuminations. As expected, cells with identical electrodes do not exhibit any photovoltaic action under uniform illumination. On the other hand, open-circuit voltage (V(OC)) greater than 1 V has been observed in pure polymer cells with dissimilar gold/calcium electrodes, which decreases when calcium is replaced with aluminum or when a fullerene derivative is added. In addition, all asymmetric cells exhibit photovoltaic action when the illumination is only applied to the anode half, the cathode, or the middle section of the cell. Our results provide unambiguous support to the metal/insulator/metal interpretation of polymer photovoltaic response. (c) 2008 American Institute of Physics. [DOI: 10.1063/1.3003082

Flexographic printing of polycarbazole-based inverted solar cells

The mass production of organic photovoltaics requires high throughput processes capable of producing a functional active layer which is homogenous, pinhole free and of a specified thickness. Common methods to achieve this are slot-die coating and gravure printing. We have demonstrated the fabrication of poly(N-9\u2032-heptadecanyl-2,7-carbazole-alt-5,5-(4\u2032,7\u2032-di-2-thienyl-2\u2032,1\u2032,3\u2032-benzothiadiazole (PCDTBT) based photovoltaic cells using the flexographic printing technique, which enables high throughput patterned active layers to be deposited on flexible substrates at lower cost. This was achieved by optimizing the flexographic plate pattern, print speed, the solvent and the drying process. By incorporating halftone patterning, a common process in the graphics printing industry, and optimizing the printing speed, the homogeneity of the active layer print was significantly improved. Further studies of suitable solvents and drying conditions led to reduced pinhole formation and improved uniformity. The functionality of the flexographically printed active layer was demonstrated by fabrication of 1 cm2 photovoltaic cells which showed an efficiency of up to 3.5%, which is comparable to alternative deposition techniques. These results demonstrate the suitability of flexography as a fabrication technique for bulk heterojunction organic photovoltaics.Peer reviewed: YesNRC publication: Ye

Ambipolar organic field-effect transistor fabricated by co-evaporation of pentacene and N,N '-ditridecylperylene-3,4,9,10-tetracarboxylic diimide

Organic field-effect transistors were fabricated where the active semiconductor layer consisted of a co-evaporated film of pentacene and a perylene derivative, N,N′-ditridecylperylene-3,4,9,10-tetracarboxylic diimide. The device characteristics were evaluated in an oxygen-free environment. The field-effect transistor showed excellent ambipolar operation with field-effect hole mobility of 0.09 cm2 V-1 s-1 and field-effect electron mobility of 9.3 × 10-3 cm2 V-1 s-1. The threshold voltage for p-channel operation was -18 V and the same for n-channel operation was 15 V. This ambipolar device could be a building block to form flexible integrated circuits with low-power consumption and ease of design

Degradation mechanism of benzodithiophene-based conjugated polymers when exposed to light in air

We report the investigation of the air photostability of benzo[1,2-b:4,5-b\u2032]dithiophene (BDT) based conjugated polymers using UV\u2013visible spectroscopy, X-ray photoelectron spectroscopy, gel permeation chromatography, and nuclear magnetic resonance spectroscopy. Three low band gap alternating D\u2013A copolymers consisting of 3-fluoro-2-heptylcarbonylthieno[3,4-b]thiophene and alkyl-substituted BDT, alkoxy-substituted BDT, or dithienosilole, respectively, were prepared for investigating their photovoltaic performance and photostability. After only two hours of simultaneous exposure to light and air, the main absorption peak of the polymer films containing BDT units blue-shifted and its intensity dramatically decreased. We demonstrated that the BDT unit underwent dramatic structural change under illumination in air by reacting with the oxygen molecules at the excited state, leading to the disruption of the main-chain conjugation of the polymer. As a result, the color of the alkyl-BDT based polymer film permanently changed from deep blue to light yellow. In contrast, the dithienosilole based polymer was quite stable when treated under the same condition with negligible change in the absorption spectrum.Peer reviewed: YesNRC publication: Ye

Flexo printed sol-gel derived vanadium oxide films as an interfacial hole-transporting layer for organic solar cells

In this paper we report on the synthesis and development of vanadium oxide precursor flexographic ink for the printing of hole-transporting layers in organic solar cells. For the synthesis of vanadium oxide inks, a sol-gel methodology was utilized. By modifying the vanadium alkoxide precursor with a right type of coordinating ligands a stable and flexoprintable ink has been successfully developed. Flexo-printing afforded smooth and uniform vanadium oxide sol-gel films on top of PCDTBT:PC<inf>70</inf>BM films. The conversion of the synthesized sol-gel film into a corresponding vanadium oxide layer was followed by DSC/TGA and XPS analyses. The inks were used for the fabrication of inverted organic solar cells by flexo-printing. Power conversion efficiencies ranging between 3.5 % and 4.5 % were achieved, which are slightly lower than the reference cells using vacuum-deposited MoO<inf>3</inf> as the hole-transporting layers.Peer reviewed: YesNRC publication: Ye

Synthesis of oligofluorene modified C60 derivatives for organic solar cell applications

Peer reviewed: YesNRC publication: Ye

Germafluorenes : New Heterocycles for Plastic Electronics

The synthesis and characterization of new heterofluorene derivatives based on germanium are described. These germafluorene monomers have been polymerized with different aromatic comonomers. The resulting homopolymers and alternating copolymers have been characterized by size exclusion chromatography, thermal analyses (TGA and DSC), UV-vis-NIR absorption spectroscopy, X-ray diffraction, and cyclic voltammetry. These homopolymers and copolymers are air-stable and present bandgaps ranging from 3.0 to 1.6 eV. Some copolymers were tested in field-effect transistors (FETs) and bulk heterojunction photovoltaic cells (PCs). Best results in FETs were obtained with poly[2,7-(9,9-di-n-butylgermafluorene)-alt 3,6-bis(thiophen-5-yl)-2,5-dioctylpyrrolo[3,4-]pyrrole-1,4-dione], which shows a hole mobility up to 0.04 cm2 (V 3 s)-1 with an Ion/Ioff ratio of 1.0_106. For photovoltaic applications, the best results were obtained with poly[2,7-(9,9-di-n-octylgermafluorene)-alt-5,5-(40,70-di-2-thienyl-20,10,30-benzothiadiazole)] with a power conversion efficiency (PCE) of 2.8%.Peer reviewed: YesNRC publication: Ye