C. Bergeret

Tuning the Raman resonance behavior of single-walled carbon nanotubes via covalent functionalization.

We present a systematic Raman study over a range of excitation energies of arc discharge single-walled carbon nanotubes (SWCNTs) covalently functionalized according to two processes, esterification and reductive alkylation. The SWCNTs are characterized by resonance Raman spectroscopy at each step of the functionalization process, showing changes in radial breathing mode frequencies and transition energies for both semiconducting and metallic tubes. Particular attention is given to a family of tubes clearly identified in the Kataura plot for which we continuously tune the excitation energy from 704 to 752 nm. This allows us to quantify the energy shift occurring in the spacing of the van Hove singularities. We demonstrate that, independently of the functionalization technique, the type of chain covalently bound to the tubes plays an important role, notably when oxygen atoms lie close to the tubes, inducing a larger shift in transition energy as compared to that of other carbonaceous chains. The study shows the complexity of interpreting Raman data and suggests many interpretations in the literature may need to be revisited.

New fullerene derivatives for the photovoltaic application

Cyclopropano[70]fullerenes have been synthesized in the aim of being used as acceptors in blends based on regioregular poly (3,5-Hexylthiophene) RR -P3HT for photovoltaic (PV) plastic cells. These molecules used with RR -P3HT in bulk heterojunction (BHJ) configuration provided interesting characteristics: 1.5% solar conversion efficiency, 9.29 mA/cm 2 current density, 0.51 V open circuit voltage, and 0.34 fill factor. The IPCE spectrum for P3HT: cyclopropano[70]fullerene cells shows a peak around 430 nm with 71% external quantum efficiency. This result justifies the increased current density.

Functionalized single wall carbon nanotubes improve the properties of polymer solar cells

The optical and electrical properties of bulk polymer RR-P3HT (Regio-Regular Poly(3-hexylthiophène-2,5- diyl):PCBM (Methanofullerene Phenyl-C61-Butyric-Acid-Methyl-Ester) heterojunction incorporating single wall carbon nanotubes (SWCNTs) have been already reported by a number of research groups. We investigated a new approach to functionalize CarboLex single wall carbon nanotubes (SWCNTs-e) for increasing their dispersion in various solvents. The addition of SWCNTs-e in the matrix of P3HT:PCBM improves the photovoltaic (PV) characteristics. Results show that the photovoltaic parameters depend on the concentration of SWCNTs-e. The incorporation of low concentrations of SWCNTs-e in the photoactive layer increases the current density Jsc before annealing. We attribute the improved performance to partial crystallisation of the RR-P3HT. As revealed by XRD studies and confirmed by the absorbance spectra which exhibit the characteristic 600 nm shoulder. Interestingly, we observed also that doping the P3HT:PCBM system with the functionalized SWCNTs increases Voc from 0.583 to 0.744 V.

Increase of open circuit voltage of polymer bulk heterojunction solar cell by functionalized single walled carbon nanotubes

Abstract We report on an improvement of the open circuit voltage over 0.8 V, together with decent fill factor and large short circuit current, through the incorporation of ester-functionalized single wall carbon nanotubes in a poly(3-hexylthiophene): 1-(3-methoxycarbonyl) propyl-1-phenyl[6,6]C61 bulk heterojunction solar cell. The technique may open new margins for an extra efficiency enhancement through increase of the open circuit voltage using state of the art highly crystalline low band gap bulk heterojunction polymer solar cells.

New cyclopropano[70]fullerene derivatives for the photovoltaic application

New cyclopropano[70]fullerenes derivatives were synthesised for photovoltaic (PV) application. The organic PV cells realized with these molecules blended with RR-P3HT polymer provided improved characteristics: 1.5% conversion efficiency (η%), 9.29 mA/cm2 current density, 0.51 V open circuit voltage and 0.34 fill factor. The IPCE spectrum for P3HT: cyclopropano[70]fullerene cells shows a new peak around 430 nm with 71% external quantum efficiency. This explains the increased current density.

Improving the efficiency of polymer solar cells by incorporation of functionalized SWCNTs in organic photovoltaic cells based on P3HT:PCBM photoactive layer

The optical and electrical properties of bulk polymer RR-P3HT (Regio-Regular Poly(3-hexylthiophène-2,5-diyl): PCBM (Methanofullerene Phenyl-C61-Butyric-Acid-Methyl-Ester) incorporated single walled carbon nanotubes (SWCNTs) have been already reported by a number of research groups. We investigated new approach to functionalize CarboLex single wall carbon nanotubes (SWCNTs-e) for increasing their dispersion on different solvent. The addition of SWCNTs-e in the matrix of P3HT:PCBM improve the photovoltaic (PV) characteristics. The results show that the photovoltaic parameters depend on the concentration of SWCNTs-e. The incorporation of low concentrations of SWCNTs-e in the photoactive layer increases the current density Jsc before annealing. We attribute the improved performance to partial crystallisation of the RR-P3HT. As revealed by XRD studies and confirmed by the absorbance spectra which exhibit the characteristic 600 nm shoulder. Interestingly, we observed also that doping the P3HT:PCBM system with the functionalized SWCNTs increases Voc from 0.583 to 0.744 V.

Realisation and characterisation organic plastic solar cells based on different derivatives of fullerene-C 60

Photovoltaic electricity is considered as an alternative to the actual ways of producing electricity for its different advantages. Its friendly impact on the environment and projected low cost makes it an attractive substitute. The plastic photovoltaic technology has been developing in recent years with a need to improve yield efficiency to end-up taking an important place in the world market. Different plastic photovoltaic solar cells have been fabricated recently using a variety of designs including small molecules, polymers or hybrid (organic /inorganic) materials. Record photovoltaic conversion efficiency was reported for interpenetrated based on the P3HT: PCBM system with 4~5% yield. The PCBM molecule presents some drawbacks such as low visible absorption, relatively high cost and multi-step synthesis. Due to the above, some new synthetic approaches around the fullerene C60 unit were proposed. In this study, we investigate the photovoltaic properties of different fullerene C60 derivatives blended into poly(3-hexylthiophene). An attempt to explain our photovoltaic characteristics in correlation with FTIR, fluorescence and UV/Vis absorption spectra was carried out. A study of the morphology was also achieved.